- Email: [email protected]
Auto-combustion synthesis, structural analysis, and electrochemical solid-state hydrogen storage performance of strontium cobalt oxide nanostructures
international journal of hydrogen energy xxx (xxxx) xxx
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/he
Review Article
Auto-combustion synthesis, structural analysis, and electrochemical solid-state hydrogen storage performance of strontium cobalt oxide nanostructures Fatemeh Sadat Razavi a, Maryam Sadat Morassaei a, Ali Salehabadi b, Masoud Salavati-Niasari a,*, Hossein Moayedi c,** a
Institute of Nanoscience and Nanotechnology, University of Kashan, Kashan, P.O. Box 87317-51167, Iran Environmental Technology Division, School of Industrial Technology, Universiti Sains Malaysia, 11800, Minden, Penang, Malaysia c Institute of Research and Development, Duy Tan University, Da Nang, 550000, Viet Nam b
highlights Auto-combustion utilize for production of Sr2Co9O14 nanostructures. Variation of reducing agents foster particles formation. Polycrystalline Sr2Co9O14 nanostructures well growth in glucose. A mixed conductive matrix, and crystalline texture support hydrogen storage ability. Presence of redox species in structure enhance hydrogen discharge properties.
article info
abstract
Article history:
Hydrogen storage in transition mixed metal oxides (MMOs) are predicted from their ten-
Received 1 August 2019
dency for adsorption-desorption hydrogen. Hydrogen itself requires initial forces pressure
Received in revised form
for initiation of condensation. MMOs, based on their effective immobilization matrices, are
30 September 2019
potential nanocatalysts for energy storage. Even various materials are highlighted for
Accepted 3 October 2019
hydrogen storage; however, their adsorption capacities are insufficient for real applica-
Available online xxx
tions. Here we report, for the first time, a novel hydrogen storage MMOs (Sr2Co9O14 nanoparticles) potential for physical hydrogen sorption, containing a redox species. This
Keywords:
polycrystalline nanoparticle is prepared via a combustion method in the presence of
Sr2Co9O14
various fuels like glucose, fructose, sucrose, lactose, and maltose. The glucose supports the
Nanostructures
pure and homogenous formation of Sr2Co9O14 nanoparticles consisting the particles less
Energy
than 100 nm. Interestingly, a maximum discharge capacity of around 950 mA h/g at room
Hydrogen storage
temperature has recorded; emphasizing Sr2Co9O14 nanoparticles is a potential substrate for
Mixed metal oxides
hydrogen storage. © 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (M. Salavati-Niasari), [email protected] (H. Moayedi). https://doi.org/10.1016/j.ijhydene.2019.10.012 0360-3199/© 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article as: Razavi FS et al., Auto-combustion synthesis, structural analysis, and electrochemical solid-state hydrogen storage performance of strontium cobalt oxide nanostructures, International Journal of Hydrogen Energy, https://doi.org/10.1016/ j.ijhydene.2019.10.012
2
international journal of hydrogen energy xxx (xxxx) xxx
Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Experimental study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Synthesis of blank sample and strontium cobalt oxide nanostructures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Structural analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electrochemical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Introduction Owing to the rapid urbanization, consumerism and depletion of fossil fuel resources, there is an urgently need for stablishing technologies based on renewable energy sources [1]. Solid-state energy storage materials are a key solution in integrating and managing the renewable energy [2]. The tendency of the materials in hydrogen storage is one of the recent strategies for developing the practical applications renewable energy. Carbon materials [3], metal-organic frameworks (MOFs) [4], hydrides (metal-, complex-, boro-) [5], polymers [6], and (mixed)metal oxides (MOs) [7] are the most important materials in hydrogen storage systems. Among them, CNTs, hydrides, and MOFs are assigned as promising targets for future hydrogen sorption by the US department of energy (DOE). Hydrogen storage can be occurred either physically (physisorption) or chemically (Chemisorption) [8]. Since the majority of hydrogen storage take place based on adsorption, the specific surface area plays an important role. With the advent of metal hydride (MH) batteries, solidstate hydrogen storage materials have been achieved a great interest [9]. MH can store hydrogen up to an atomic ratio of hydrogen: metal/1:1. Poor cycle-ability of hydride families and irreversible structural change during the process of hydrogen storages are the main deficiencies of this class of materials. Mixed-metal hydrides (which known as alloy hydride) are another recently developed target for electrochemical hydrogen storage in portable rechargeable batteries. In hydride-based materials the hydrogen can be stored into two regions, either on the surface adsorption or/and solid-state diffusion in bulk. MOFs belong to the organic-inorganic hybrid porous materials with multi-dimensional structure [10]. Structural performance correlations in MOFs can be classified as; heterocyclic azolate-based frameworks, mixed-ligand/ functionality systems, carboxylate-based frameworks, metal-cyanide frameworks, covalent organic frameworks [11]. This class of material is composed of organic ligands and almost one transition metal ions. MOFs possess high specific surface area, high crystallinity, and high porosity. The mechanism of hydrogen storage in MOFs are mainly physical
00 00 00 00 00 00 00 00 00 00 00
adsorption [12]. The pore size in MOFs can adjust by changing the organic ligands, which can further reflect in specific surface area, and ultimately enhancing hydrogen sorption performances. Mixed metal oxides (MMOs) recently utilize as a host for physical hydrogen sorption. Unique structure, morphology, and stability of MMOs are three main factors seems to be effective in boosting their hydrogen sorption [13]. In molecular level, based on electrons and ions interactions with each other, the electronic structures of MMOs can be proposed, which is important to understand the electric conductivity, magnetism, and many optical effects [7]. The electronic activities of MMOs can be further reflected into hydrogen storage performances [14]. In addition, the redox properties of some metals enhanced more the hydrogen storage performances of the target. Various molecular structures of MMOs are reported for solid-state hydrogen storage [15e18] nanostructures. Since MMOs have not been evaluated as a promising host for solidstate hydrogen storage materials by the US department of energy (DOE), consecutive and continuous works are required in order to fill up the gaps in this field. Cobalt oxides (CoO) are impressive materials, which utilized widely for designing and synthesis of novel MMO materials [19,20]. CoO impart fascinating properties to the final product like conductivity. The term “Triple CoII, III, IV” charge ordering have been reported by David and his coworkers [21] in a study on the modular cobaltite. They observed a systematic evolution of the electronic and magnetic states of different packing modes of CoO containing compound with general formula BanCo2þnO3nþ2. They theoretically proposed a series of ordered CoII/CoIII versus mixed CoIII/IV charge segregation. This versatility of coordination, valence and spin states which offered by cobalt ions can be impart additional performances to the host MMOs structure [22]. Various phase diagrams of CoO in MMOs containing strontium (Sr) and their respective properties have been rarely investigated/reported such as Sr4Co3O9 [23], Sr5Co4O11 [24], Sr6Co5O15 [25], and Sr14Co11O33 [26]. The structure and properties of SreCoeO complex materials, these class of materials are appropriate as a host for energy storage systems. Polycrystalline MMOs attract great interest as carrier in energy storage systems due to their complex structure and
Please cite this article as: Razavi FS et al., Auto-combustion synthesis, structural analysis, and electrochemical solid-state hydrogen storage performance of strontium cobalt oxide nanostructures, International Journal of Hydrogen Energy, https://doi.org/10.1016/ j.ijhydene.2019.10.012
3
international journal of hydrogen energy xxx (xxxx) xxx
Fig. 1 e Schematic pathway of the Sr2Co9O14 fabrication. defects. MMOs compose of crystalline phases, which can create oxygen vacancies. Mnþ1ConO3nþ3 - Co8O8 (M ¼ Sr, Ba) is a type of polycrystalline MMO with perovskite blocks of Mnþ1ConO3nþ3. Polycrystalline Ba2Co9O14 nanostructures have
an inorganic backbone, where magnetically ordered generally in a comples conductivity [27,28]. Though various structures of SreCoeO have been reported, polycrystalline Sr2Co9O14 has not been investigated elsewhere. In the current study, the Sr2Co9O14 nanoparticles were synthesized via a combustion method. The unique structure, morphology, and properties of polycrystalline Sr2Co9O14 nanoparticles were served as effective strategies to investigate its respective hydrogen sorption in a typical hydrogen storage setup.
Experimental study Materials In this study, all reagents for the production of Sr2Co9O14 nanostructures including strontium nitrate (Sr(NO3)2, Purity 99.99%, Mw 211.63 g mol1), Cobalt (II) nitrate hexahydrate (Co(NO3)2$6H2O, Purity 99%, Mw 291.03 g mol1), glucose (C6H12O6, Purity 99.5%, Mw 180.16 g mol1), fructose (C6H12O6, Mw 180.16 g mol1), sucrose (C12H22O11, Purity 99.5%, Mw 342.30 g mol1), lactose (C12H22O11, Purity 99%, Mw 342.30 g mol1) and maltose monohydrate (C12H22O11$H2O,
Table 1 e CV results of Sr2Co9O14 nanoparticles synthesized in various reducing agents. Electrode
Fig. 2 e XRD patterns of Sr2Co9O14 fabricated at 900 C utilizing various fuels.
Glassy carbon Sr2Co9O14-Glucose Sr2Co9O14-Fructose Sr2Co9O14-Lactose Sr2Co9O14-Sucrose Sr2Co9O14-Maltose
Ipa
Ipc
Epa
Epc
*D (nm)
45.10 50.61 41.61 47.86 47.38 46.43
46.37 50.38 42.18 46.23 45.17 44.19
0.376 0.348 0.422 0.390 0.377 0.395
0.011 0.029 0.057 0.029 0.017 0.021
e 32 32 29 30 23
*Average crystallite sizes calculated from Scherrer equation.
Please cite this article as: Razavi FS et al., Auto-combustion synthesis, structural analysis, and electrochemical solid-state hydrogen storage performance of strontium cobalt oxide nanostructures, International Journal of Hydrogen Energy, https://doi.org/10.1016/ j.ijhydene.2019.10.012
4
international journal of hydrogen energy xxx (xxxx) xxx
Purity 99%, Mw 360.32 g mol1) were supplied from MerckGermany and used as received.
Synthesis of blank sample and strontium cobalt oxide nanostructures In the current study, in order to have an evidence for pure formation of Sr2Co9O14 nanostructures, a blank sample was prepared. In this sample, stoichiometric amount of starting materials (Sr(NO3)2 and Co(NO3)2$6H2O) were dissolved in water without any fuels, evaporated and calcined at 900 C for 4 h. This sample was used as an evidence for further investigation. Utilizing auto-combustion method, the Sr2Co9O14 nanostructures were purely synthesized. Primarily, 1 mmol Sr(NO3)2 was dissolved in distilled water to create a clear solution. An aqueous solution containing reducing agent (glucose, fructose, sucrose, lactose, or maltose) was added drop-wise into the strontium nitrate solution under the strong magnetic stirring at room temperature. The molar ratio of reducing agent to Sr was selected to be 11: 1. This solution was heated up by continuous stirring at 60 C for 30 min. In the second container, an aqueous solution containing 4.5 mmol Co(NO3)2$6H2O was added to above admixture (i.e. Sr(NO3)2 and reducing agent) and stirred at 120 C for 60 min. Evaporation of the reaction solution caused formation of a viscose gel. Finally, the Sr2Co9O14 nanostructures was formed from the gel after drying at 70 C for 24 h and calcination at 900 C
for 4 h in normal atmosphere. Fig. 1 represents the schematic of the preparation pathway of the strontium cobaltite nanostructures. After annealing at 900 C, the structural formation and morphology of the samples were analyzed based on the reducing agents.
Characterization The composition and the bulk morphology of the samples were measured using an X-ray diffractometer (Philips X’Pert Promonochromatized Cu Ka radiation (l ¼ 1.54 A) in the range of 2q ¼ 10e80 ), and a TESCAN MIRA3 Field Emission Scanning Electron Microscopy (FE-SEM), respectively. The best sample from all above samples was selected for detailed structural and elemental analysis using a Shimadzu Varian 4300 spectrophotometer in KBr pellets ranging from 4000 to 400 cm1, and an Energy Dispersive X-ray Spectroscope (EDX Hitachi S4300), respectively. In addition, the physical properties of the selected sample i.e. band gap energy and magnetic properties were measured using a Ultra-Violet diffuse reflectance spectra (UV-DRS), and a vibrating sample magnetometer 60 (VSM, Meghnatis Kavir Kashan co., Kashan, Iran). The specific surface area of the sample was measured by a nitrogen gas adsorption-desorption BELsorp mini II, Japan) utilizing BarretteEmmetteTeller (BET). The electrochemical properties of the sample were analyzed in three electrode setups, primarily by a voltammeter, and finally using a chronopotentiometer. The former was run in a probe solution of K3(Fe(CN)6)/
Fig. 3 e FESEM micrographs of Sr2Co9O14 particles fabricated at 900 C utilizing various fuels; (a) blank (without fuel), (b) glucose, (c) fructose, (d) lactose, (e) sucrose, and (f) maltose. Please cite this article as: Razavi FS et al., Auto-combustion synthesis, structural analysis, and electrochemical solid-state hydrogen storage performance of strontium cobalt oxide nanostructures, International Journal of Hydrogen Energy, https://doi.org/10.1016/ j.ijhydene.2019.10.012
international journal of hydrogen energy xxx (xxxx) xxx
K4(Fe(CN)6) in the 0.1 M phosphate buffer solution (pH 7.0) in a scan rate of 0.1 V-1, while the later was utilized in 1 mA at ambient temperature, in 6 M KOH electrolyte. In this study, the working electrode is composed of a porous copper sheet, solid-state hydrogen absorber (Sr2Co9O14) having a surface area of ~1 1 cm2.
Results and discussion Structural analysis The crystal structure of the Sr2Co9O14, prepared in glucose, fructose, sucrose, lactose, and maltose, were identified by their respective XRD patterns (Fig. 2). The diffractograms of the samples show a series of intense peaks in the range of 10>2q > 70. Since no similar structural data is reported for Sr2Co9O14, therefore, no JCPDS data is available. In Ba2Co9O14, it is reported a rhombohedral R-3m space group [29]. Approximately similar diffraction peaks can be observed in the media of various fuels. The most intense peaks grow at 28.73 , 32.78 , 37.00 , 44.06 , 47.07 , 55.84 , 59.51 , and 65.39 . The results are in good agreement with previous computational study on crystallographic and magnetic structure of SrCoO2.5 brownmillerite [30]. As mentioned before,
5
Mnþ1ConO3nþ3 - Co8O8 (M ¼ Sr, Ba) is a polycrystalline MMOs with perovskite blocks (Mnþ1ConO3nþ3). In this study, the XRD pattern is proposed to be indexed in an orthorhombic unit cell. Scherrer equation (Eq. 1); D ¼ k l/b cosq (1) is used in order to calculate the average crystallite size, where, D, q, k, and l are average crystallite size, diffraction angle, Scherrer constant (~0.9), and wavelength, respectively [31]. In this equation (Eq.1) b is a factor of full width at half-maximum (FWHM). The calculated D factors are summarized in Table 1. The surface morphology and particle size of the samples were observed on their respective FESEM micrographs (Fig. 3). The blank sample consists of agglomerated cube like particles with the particle size larger than 100 nm (Fig. 3a). The surface morphology of the sample synthesized in glucose, the particles are highly dense with narrow distributions, and uniform shapes almost less than 100 nm (Fig. 3b). The morphology of the particles, which combusted in fructose (Fig. 3c), lactose (Fig. 3d), sucrose (Fig. 3e), and maltose (Fig. 3f) consist of a series of irregular and inhomogeneous particles. Especially in the Sr2Co9O14 samples were combusted in fructose, lactose, and sucrose some very large particles can be observed. Since a homogenous, nanosized, and crystalline Sr2Co9O14 sample is formed in the presence of glucose, according to FESEM micrographs and XRD patterns, this sample is selected for further investigation.
Fig. 4 e (a) TEM micrographs, and (b) particle diameters histogram of Sr2Co9O14 nanostructures annealed at 900 C. Please cite this article as: Razavi FS et al., Auto-combustion synthesis, structural analysis, and electrochemical solid-state hydrogen storage performance of strontium cobalt oxide nanostructures, International Journal of Hydrogen Energy, https://doi.org/10.1016/ j.ijhydene.2019.10.012
6
international journal of hydrogen energy xxx (xxxx) xxx
Complementary morphological observation of the Sr2Co9O14 nanoparticles which synthesized in glucose was captured using TEM. The respective micrographs (Fig. 4a) affirm the spherical and highly crystalline formation of the particles, in the range of 40e100 nm. In the particle diameter histogram of the sample, the most of the particles are in the range of 80e100 nm (Fig. 4b). The particle diameters are obtained from its respective TEM images using Digimizer analyzer. Potent contrast in the Sr2Co9O14 sample demonstrate a dense and crystalline host phase. Elemental analysis of the selected sample was confirmed the purity of the sample (Fig. 5a). The EDX spectrum of Sr2Co9O14 nanoparticles contains only strontium (Sr), cobalt (Co) and oxygen (O). In addition, the composition of the sample was investigated using an X-ray florescence (XRF). The XRF result was also affirmed that the sample composed of SrO and CoO (major phase), and very minor (less than 1%) amounts of CaO (0.086%), SiO2 (0.100%), Cl (0.074%), and Na2O (0.160%). The structural formation of the sample was also identified using FTIR analyzer (Fig. 5b). Here, four intense peaks are assigned at around 3432 cm1, 663 cm1 and 566 cm1 correspond to the stretching vibration of eOH, bending and symmetrical stretching vibration of M-O-M and O-M-O. In addition, a sharp peak at 414 cm1 and a small peak at 485 cm1 can be assigned to stretching vibration of SreO
species. Generally, in mixed metal oxides, the areas below 1000 cm1 are emanated from the stretching vibration frequencies of the M-O motions. In this spectrum a doublet at around 566 cm1 can be observed in association with yCo-O. This doublet is due to the valence states of cobalt ions; JahnTeller and supplementary polarization. Optical property of Sr2Co9O14 nanoparticles was recorded by UV-DRS (Fig. 5c). A strong absorption in the visible region can be observed at around 365 nm, most probably formed by pure and unoccupied Sr 5s and 5d states and impurity of CoO charge transfer interaction [16]. The band gap energy were calculated using Tauc plot (Eq. 2), (ahy)n¼ A(hy - Eg) (2), indicating a direct transition allowance. In this equation, hy is the photon energy, a is the absorption coefficient, A is a constant relative to the material and n is 2 for a direct transition. The direct band gap of the sample was obtained to be around 3.12 eV. This Eg from Tauc equation were further confirmed by a theoretical calculation using Eq. 3, Eg ¼ 1240/l (3), where l is the maximum wavelength. The Eg from this equation was obtained to be around 3.26 eV. Finally, the magnetism of the Sr2Co9O14 nanoparticles was identified from the vibrating sample magnetometer (VSM) (Fig. 5d) at ambient temperature with the field sweeping from 8.0 to þ8.0 kOe. Nearly narrow hypothesis loop can observe in its VSM profile with a saturation magnetization around 0.28 emu/g (Fig. 5d: inset). There are two types of ferromagnets,
Fig. 5 e Physico-chemical characterization of the Sr2Co9O14 nanostructures synthesized at 900 C in glucose; (a) EDX spectrum, (b) FTIR spectrum, (c) UV-DR spectrum, and (d) VSM curve. Please cite this article as: Razavi FS et al., Auto-combustion synthesis, structural analysis, and electrochemical solid-state hydrogen storage performance of strontium cobalt oxide nanostructures, International Journal of Hydrogen Energy, https://doi.org/10.1016/ j.ijhydene.2019.10.012
international journal of hydrogen energy xxx (xxxx) xxx
7
ferromagnetic. In addition, Jeen and his coworkers [33] reported the magnetism of the SrCoO2.5 and SrCoO3 phases. They expressed a large ferromagnetic signal in the SrCoO3 phase and an antiferromagnetic signal in the SrCoO2.5 phase. Fig. 6 illustrates the BET analysis of the Sr2Co9O14 nanoparticles well matched to type III isotherm having a H3 hysteresis loop (according to the IUPAC classification). In H3 hysteresis loop, the aggregated particles form slit-shaped pores with non-uniform sizes and/or shapes. The total pore volume, mean pore radii and average pore size of the sample were calculated to be around 1.11 (cm3 g1), 2.38 nm and 26.79 nm, respectively. The BJH mean pore radii (rp) between 1 nm and 25 nm are aggregates of nanosized particles.
Electrochemical properties Fig. 6 e N2 absorption-desorption and BJH (inset) of the Sr2Co9O14 nanostructures.
hard and soft. In a hard ferromagnet, the hysteresis loop is broad, while in a soft ferromagnet, this loop is narrow, therefore much more responsive to the applied field [32]. In addition, narrow hysteresis loop is due to a small-dissipated energy. In conclusion, at room temperature, the sample is
As mentioned before, benefiting from the MMOs electrochemical properties in energy storage will play significant roles for low-cost and environmentally friendly energy storage systems. To touch the aim of this work, the electrochemical performances of the Sr2Co9O14 nanoparticles were recorded by a cyclic voltammogram (CV) (Fig. 7a and b). The obtaining results from CV analysis were further served to peruse hydrogen storage capacity (Fig. 7c). As we mentioned before, owing the structural analysis of the samples (Section
Fig. 7 e (a) Cyclic voltammograms of the Sr2Co9O14 particles synthesized in various fuels, (b) Cyclic voltammogram of the Sr2Co9O14 nanoparticles synthesized in glucose, and (c) fifteen succeeded discharge sequences of the Sr2Co9O14 nanoparticles synthesized in glucose. Please cite this article as: Razavi FS et al., Auto-combustion synthesis, structural analysis, and electrochemical solid-state hydrogen storage performance of strontium cobalt oxide nanostructures, International Journal of Hydrogen Energy, https://doi.org/10.1016/ j.ijhydene.2019.10.012
8
international journal of hydrogen energy xxx (xxxx) xxx
Structural analysis), the best sample was obtained in glucose. Similar to that, the CV analysis of the samples were synthesized in various fuels, clearly confirmed a superior electrochemical performance. The electrode responses are tabulated in Table 1. The anodic and cathodic peak currents (Ipa and Ipc) of the glassy carbon electrode (GCE) are lower than that of the polycrystalline Sr2Co9O14 nanoparticles, synthesized in Glucose. Therefore, this sample was selected for electrochemical hydrogen storage properties. As the major aim of the current study, the hydrogen storage properties of the Sr2Co9O14 nanoparticles were investigated using a chronopotentiometer via charge and discharge cycles (Fig. 7c). In the current study, in order to follow up the hydrogen sorption ability of the sample, the system was adjusted for continuous 15 charge-discharge sequences. However, the discharge sequences can be continued as far as all hydrogen sites on the sample occupied. Hydrogen physisorption shows a maximum discharge capacity of around 950 mA h/g after 15 cycles of discharging. The hydrogen content of the sample was calculated to be around 3.4 wt%. According to US-DOE, for commercialization of hydrogen-fueled vehicle, the target should meet a 1.5 kWh/kg system (4.5 wt% hydrogen) or 1.0 kWh/L system (0.030 kg hydrogen/L) with $10/ kWh ($333/kg stored hydrogen capacity) [34]. Despite of lower hydrogen capacity of Sr2Co9O14 nanoparticles as compared to the US-DOE assumption, this class of material (i.e. MMO) must be improved to match the key-values targeting. Owing to the complexity of the polycrystalline samples, various sites for hydrogen sorption exist, which can further reflect in stability and hydrogen storage performance of the solid substrate [16,16,35,35]. Nanosystems (nanoparticles, nanotubes, nanolayers, etc) have either single or multiple wall structure and pores, therefore, multiple adsorption sites are present which result in higher capacity. Practically, this phenomenon can be observed in the multistate, long and flat potential plateaus of the electrochemical plots [36,37]. Van der Waals interaction, which is known as resonant fluctuations in charge distributions are the origin of the hydrogen sorption mechanism of solid species. This phenomenon is the major reaction (which is called as physisorption) of hydrogen onto the surface of a solid host. The physisorption mechanism can be proposed as Eq. 4; Sr2Co9O14 þ xH2O þ xe 4 Sr2Co9O14-Hx þ xOH (4). In addition, the rich redox reactions involving cobalt ion can be contributed to hydrogen storage performance of the sample beyond those of conventional physisorption as Eq. 5; Sr2Conþ9O14 þ xH2O þ xe 4 Sr2Conþ9-y Comþy O14 - Hx þ xOH (5). Therefore, Co-based polycrystalline MMO nanomaterials like Sr2Co9O14 are anticipated to be appealing working electrode (WE) for hydrogen storage system. Compared with other reported MMOs in the hydrogen storage systems [38e40], this composition, even with lower discharge capacity, can be preferably served as a superior matrix for energy storage.
Conclusion In conclusion, primarily, a pure phase Sr2Co9O14 nanoparticles were synthesized via combustion method in glucose after annealing at 900 C. The structural analyses were confirmed
the crystalline nanosized formation of the proposed product composed of only Sr, Co, and Oxygen. In addition, the physical properties were confirmed ferromagnetism of the sample with a band gap of 3.12 eV. As a major significant of this work, the reversible physisorption and redox activities were proposed in a series of electrochemical discharging processes, which could be accomplished at significantly appropriate hydrogen storage of 950 mA h/g. It can be now finalized that the nanosized Sr2Co9O14 is a new material we reported here, for hydrogen sorption. Despite of its lower hydrogen capacity (~3.4 wt%), for fifteen discharge sequences, as compared to the key-values targeting reported by US-DOE, in explanation for future industrial application, this nanosystem can provide a pathway to the future design of new solid materials with pivotal role in energy storage system.
Acknowledgement Authors are grateful to the council of Iran National Science Foundation; INSF (97017837) and University of Kashan for supporting this work by Grant No (159271/33).
references
[1] Schlapbach L, Zu¨ttel A. Hydrogen-storage materials for mobile applications. Nature 2001;414:353e8. https://doi.org/ 10.1038/35104634. [2] Suib SL, Kojima Y, Miyaoka H, Ichikawa T. Hydrogen storage materials. New Futur Dev Catal 2013:99e136. https://doi.org/ 10.1016/B978-0-444-53880-2.00006-5. Elsevier. [3] Froudakis GE. Hydrogen storage in nanotubes & nanostructures. Mater Today 2011;14:324e8. https://doi.org/ 10.1016/S1369-7021(11)70162-6. [4] Salehabadi A, Morad N, Ahmad MI. A study on electrochemical hydrogen storage performance of b-copper phthalocyanine rectangular nanocuboids. Renew Energy 2020;146:497e503. https://doi.org/10.1016/ J.RENENE.2019.06.176. [5] Ley MB, Jepsen LH, Lee YS, Cho YW, Bellosta Von Colbe JM, Dornheim M, et al. Complex hydrides for hydrogen storage new perspectives. Mater Today 2014;17:122e8. https:// doi.org/10.1016/j.mattod.2014.02.013. chet JMJ, Svec F. Nanoporous polymers for [6] Germain J, Fre hydrogen storage. Small 2009;5:1098e111. https://doi.org/ 10.1002/smll.200801762. [7] Wang F, Zhang Y, Yu N, Fu L, Zhu Y, van Ree T. Metal oxides in batteries. Met Oxides Energy Technol 2018:127e67. https:// doi.org/10.1016/B978-0-12-811167-3.00006-7. Elsevier. [8] Hirscher M. Handbook of hydrogen storage: new materials for future energy storage. Wiley-VCH Verlag & Co; 2010. [9] Sakintuna B, Lamaridarkrim F, Hirscher M. Metal hydride materials for solid hydrogen storage: a review. Int J Hydrogen Energy 2007;32:1121e40. https://doi.org/10.1016/ j.ijhydene.2006.11.022. [10] Langmi HW, Ren J, Musyoka NM. Metal-organic frameworks for hydrogen storage. Compend Hydrogen Energy 2016:163e88. https://doi.org/10.1016/B978-1-78242-3621.00007-9. [11] Wjihi S, Yang J, Sellaoui L, Knani S, Ben Lamine A. Interpreting the hydrogen adsorption on organic groups functionalized MOF-5s by statistical physics model. Int J
Please cite this article as: Razavi FS et al., Auto-combustion synthesis, structural analysis, and electrochemical solid-state hydrogen storage performance of strontium cobalt oxide nanostructures, International Journal of Hydrogen Energy, https://doi.org/10.1016/ j.ijhydene.2019.10.012
international journal of hydrogen energy xxx (xxxx) xxx
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
[21]
[22]
[23]
[24]
[25]
Hydrogen Energy 2017;42:10023e37. https://doi.org/10.1016/ j.ijhydene.2017.01.149. Rahali S, Belhocine Y, Seydou M, Maurel F, Tangour B. Multiscale study of the structure and hydrogen storage capacity of an aluminum metal-organic framework. Int J Hydrogen Energy 2017;42:15271e82. https://doi.org/10.1016/ j.ijhydene.2017.04.258. Chen B, Liu Z, Li C, Zhu Y, Fu L, van Ree T. Metal oxides for hydrogen storage. Met Oxides Energy Technol 2018:251e74. https://doi.org/10.1016/B978-0-12-811167-3.00009-2. Elsevier. Zhang J, Yan S, Yu LP, Zhou XJ, Zhou T, Peng P. Enhanced hydrogen storage properties and mechanisms of magnesium hydride modified by transition metal dissolved magnesium oxides. Int J Hydrogen Energy 2018;43:21864e73. https:// doi.org/10.1016/J.IJHYDENE.2018.10.017. Salehabadi A, Salavati-Niasari M, Sarrami F, Karton A. SolGel auto-combustion synthesis and physicochemical properties of BaAl2O4 nanoparticles; electrochemical hydrogen storage performance and density functional theory. Renew Energy 2017;114:1419e26. https://doi.org/ 10.1016/j.renene.2017.07.119. Salehabadi A, Salavati-Niasari M, Gholami T. Green and facial combustion synthesis of Sr3Al2O6 nanostructures; a potential electrochemical hydrogen storage material. J Clean Prod 2018;171:1e9. https://doi.org/10.1016/J.JCLEPRO.2017.09.250. Salehabadi A, Sarrami F, Salavati-Niasari M, Gholami T, Spagnoli D, Karton A. Dy3Al2(AlO4)3 ceramic nanogarnets: sol-gel auto-combustion synthesis, characterization and joint experimental and computational structural analysis for electrochemical hydrogen storage performances. J Alloy Comp 2018;744:574e82. https://doi.org/10.1016/ j.jallcom.2018.02.117. Salehabadi A, Salavati-Niasari M, Gholami T, Khoobi A. Dy3Fe5O12 and DyFeO3 nanostructures: green and facial auto-combustion synthesis, characterization and comparative study on electrochemical hydrogen storage. Int J Hydrogen Energy 2018;43:9713e21. https://doi.org/10.1016/ J.IJHYDENE.2018.04.018. Li M, Zhao K, Zhao Z, Li H, He F, Lv P. Enhanced hydrogenrich syngas generation in chemical looping methane reforming using an interstitial doped La1.6Sr0.4FeCoO6. Int J Hydrogen Energy 2019;44:10250e64. https://doi.org/10.1016/ J.IJHYDENE.2019.03.012. Umeshbabu E, Rajeshkhanna G, Rao GR. Urchin and sheaflike NiCo2O4 nanostructures: synthesis and electrochemical energy storage application. Int J Hydrogen Energy 2014;39:15627e38. https://doi.org/10.1016/ J.IJHYDENE.2014.07.168. David R, Kabbour H, Bordet P, Pelloquin D, Leynaud O, Trentesaux M, et al. Triple CoII, III, IV charge ordering and spin states in modular cobaltites: a systematization through experimental and virtual compounds. J Mater Chem C 2014;2:9457e66. https://doi.org/10.1039/c4tc01486c. Cheng JG, Zhou JS, Hu Z, Suchomel MR, Chin YY, Kuo CY, et al. Spin-state transition in Ba2Co9O14. Phys Rev B Condens Matter Mater Phys 2012;85:1e6. https://doi.org/ 10.1103/PhysRevB.85.094424. Chupakhina TI, Melkozerova MA, Bazuev GV. Phase formation features and magnetic properties of complex oxides in the systems Sr-Co-M-O (M ¼ Zn, Cu). Russ J Inorg Chem 2013;58:253e8. https://doi.org/10.1134/ S0036023613030054. Wong-Ng W, Liu G, Martin J, Thomas EL, Lowhorn N, Kaduk JA. Phase compatibility and thermoelectric properties of compounds in the Sr-Ca-Co-O system. J Appl Phys 2010;107. https://doi.org/10.1063/1.3276158. 0335081e6. Iwasaki K, Shimada M, Yamane H, Takahashi J, Kubota S, Nagasaki T, et al. Electrical resistivity and Seebeck coefficient
[26]
[27]
[28]
[29]
[30]
[31]
[32]
[33]
[34]
[35]
[36]
[37]
[38]
[39]
[40]
9
of Sr6Co5O15. J Alloy Comp 2004;377:272e6. https://doi.org/ 10.1016/J.JALLCOM.2004.01.060. Jankovsky´ O, Sedmidubsky´ D, Vı´tek J, Simek P, Sofer Z. Phase diagram of the SreCoeO system. J Eur Ceram Soc 2015;35:935e40. https://doi.org/10.1016/ J.JEURCERAMSOC.2014.09.040. G, Mentre O. Ehora G, Daviero-Minaud S, Colmont M, Andre Ba2Co9O14: new inorganic building blocks with magnetic ordering through super-super exchanges only. Chem Lett 2007;19:2180e8. https://doi.org/10.1021/CM062897Q. Delorme F, Chen C, Pignon B, Schoenstein F, Perriere L, Giovannelli F. Promising high temperature thermoelectric properties of dense Ba2Co9O14ceramics. J Eur Ceram Soc 2017;37:2615e20. https://doi.org/10.1016/ j.jeurceramsoc.2017.01.034. Takami T, Saiki S, Cheng J, Goodenough JB. Magnetic and transport properties of Ba2Co9O 14 and Ba1.9A0.1Co9O14 (A ¼ La or Na). J Phys Soc Japan 2010;79:1e5. https://doi.org/ 10.1143/JPSJ.79.114713. ~ oz A, Calle C, Alonso JA, Botta PM, Pardo V, Baldomir D, Mun et al. Crystallographic and magnetic structure of SrCoO2.5 brownmillerite: neutron study coupled with band-structure calculations. Phys Rev B 2008;78. 0544041e8. Salehabadi A, Salavati-Niasari M, Ghiyasiyan-Arani M. Selfassembly of hydrogen storage materials badsed multi-walled carbon nanotubes (MWCNTs) and Dy3Fe5O12 (DFO) nanoparticles. J Alloy Comp 2018;745:789e97. https://doi.org/ 10.1016/J.JALLCOM.2018.02.242. Khan MA, Riaz S, Ali I, Akhtar MN, Murtaza G, Ahmad M, et al. Structural and magnetic behavior evaluation of Mg-Tb ferrite/ polypyrrole nanocomposites. Ceram Int 2014;41:651e6. https://doi.org/10.1016/j.ceramint.2014.08.117. Jeen H, Choi WS, Biegalski MD, Folkman CM, Tung I-C, Fong DD, et al. Reversible redox reactions in an epitaxially stabilized SrCoO x oxygen sponge. Nat Mater 2013;12:1057e63. https://doi.org/10.1038/nmat3736. US Department of Energy. Target explanation document: onboard hydrogen storage for light-duty fuel cell vehicles. 2015. Salehabadi A, Ahmad MI, Morad N, Salavati-Niasari M, Enhessari M. Electrochemical hydrogen storage properties of Ce0.75Zr0.25O2 nanopowders synthesized by sol-gel method. J Alloy Comp 2019;790:884e90. https://doi.org/ 10.1016/J.JALLCOM.2019.03.160. Niaz S, Manzoor T, Pandith AH. Hydrogen storage: materials, methods and perspectives. Renew Sustain Energy Rev 2015;50:457e69. https://doi.org/10.1016/j.rser.2015.05.011. Deng G, Chen Y, Tao M, Wu C, Shen X, Yang H, et al. Study of the electrochemical hydrogen storage properties of the proton-conductive perovskite-type oxide LaCrO3 as negative electrode for Ni/MH batteries. Electrochim Acta 2010;55:884e6. https://doi.org/10.1016/j.electacta.2009.06.071. Liu E, Wang J, Li J, Shi C, He C, Du X, et al. Enhanced electrochemical hydrogen storage capacity of multi-walled carbon nanotubes by TiO2 decoration. Int J Hydrogen Energy 2011;36:6739e43. https://doi.org/10.1016/ j.ijhydene.2011.02.128. Gholami T, Salavati-Niasari M. Effects of copper:aluminum ratio in CuO/Al2O3nanocomposite: electrochemical hydrogen storage capacity, band gap and morphology. Int J Hydrogen Energy 2016;41:15141e8. https://doi.org/10.1016/ j.ijhydene.2016.06.191. Gholami T, Salavati-Niasari M, Salehabadi A, Amiri M, Sabani M, Rezaei M. Electrochemical hydrogen storage properties of NiAl2O4/NiO nanostructures using TiO2, SiO2 and graphene by auto-combustion method using green tea extract. Renew Energy 2018;115:199e207. https://doi.org/ 10.1016/J.RENENE.2017.08.037.
Please cite this article as: Razavi FS et al., Auto-combustion synthesis, structural analysis, and electrochemical solid-state hydrogen storage performance of strontium cobalt oxide nanostructures, International Journal of Hydrogen Energy, https://doi.org/10.1016/ j.ijhydene.2019.10.012
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/he
Review Article
Auto-combustion synthesis, structural analysis, and electrochemical solid-state hydrogen storage performance of strontium cobalt oxide nanostructures Fatemeh Sadat Razavi a, Maryam Sadat Morassaei a, Ali Salehabadi b, Masoud Salavati-Niasari a,*, Hossein Moayedi c,** a
Institute of Nanoscience and Nanotechnology, University of Kashan, Kashan, P.O. Box 87317-51167, Iran Environmental Technology Division, School of Industrial Technology, Universiti Sains Malaysia, 11800, Minden, Penang, Malaysia c Institute of Research and Development, Duy Tan University, Da Nang, 550000, Viet Nam b
highlights Auto-combustion utilize for production of Sr2Co9O14 nanostructures. Variation of reducing agents foster particles formation. Polycrystalline Sr2Co9O14 nanostructures well growth in glucose. A mixed conductive matrix, and crystalline texture support hydrogen storage ability. Presence of redox species in structure enhance hydrogen discharge properties.
article info
abstract
Article history:
Hydrogen storage in transition mixed metal oxides (MMOs) are predicted from their ten-
Received 1 August 2019
dency for adsorption-desorption hydrogen. Hydrogen itself requires initial forces pressure
Received in revised form
for initiation of condensation. MMOs, based on their effective immobilization matrices, are
30 September 2019
potential nanocatalysts for energy storage. Even various materials are highlighted for
Accepted 3 October 2019
hydrogen storage; however, their adsorption capacities are insufficient for real applica-
Available online xxx
tions. Here we report, for the first time, a novel hydrogen storage MMOs (Sr2Co9O14 nanoparticles) potential for physical hydrogen sorption, containing a redox species. This
Keywords:
polycrystalline nanoparticle is prepared via a combustion method in the presence of
Sr2Co9O14
various fuels like glucose, fructose, sucrose, lactose, and maltose. The glucose supports the
Nanostructures
pure and homogenous formation of Sr2Co9O14 nanoparticles consisting the particles less
Energy
than 100 nm. Interestingly, a maximum discharge capacity of around 950 mA h/g at room
Hydrogen storage
temperature has recorded; emphasizing Sr2Co9O14 nanoparticles is a potential substrate for
Mixed metal oxides
hydrogen storage. © 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (M. Salavati-Niasari), [email protected] (H. Moayedi). https://doi.org/10.1016/j.ijhydene.2019.10.012 0360-3199/© 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article as: Razavi FS et al., Auto-combustion synthesis, structural analysis, and electrochemical solid-state hydrogen storage performance of strontium cobalt oxide nanostructures, International Journal of Hydrogen Energy, https://doi.org/10.1016/ j.ijhydene.2019.10.012
2
international journal of hydrogen energy xxx (xxxx) xxx
Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Experimental study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Synthesis of blank sample and strontium cobalt oxide nanostructures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Structural analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electrochemical properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Introduction Owing to the rapid urbanization, consumerism and depletion of fossil fuel resources, there is an urgently need for stablishing technologies based on renewable energy sources [1]. Solid-state energy storage materials are a key solution in integrating and managing the renewable energy [2]. The tendency of the materials in hydrogen storage is one of the recent strategies for developing the practical applications renewable energy. Carbon materials [3], metal-organic frameworks (MOFs) [4], hydrides (metal-, complex-, boro-) [5], polymers [6], and (mixed)metal oxides (MOs) [7] are the most important materials in hydrogen storage systems. Among them, CNTs, hydrides, and MOFs are assigned as promising targets for future hydrogen sorption by the US department of energy (DOE). Hydrogen storage can be occurred either physically (physisorption) or chemically (Chemisorption) [8]. Since the majority of hydrogen storage take place based on adsorption, the specific surface area plays an important role. With the advent of metal hydride (MH) batteries, solidstate hydrogen storage materials have been achieved a great interest [9]. MH can store hydrogen up to an atomic ratio of hydrogen: metal/1:1. Poor cycle-ability of hydride families and irreversible structural change during the process of hydrogen storages are the main deficiencies of this class of materials. Mixed-metal hydrides (which known as alloy hydride) are another recently developed target for electrochemical hydrogen storage in portable rechargeable batteries. In hydride-based materials the hydrogen can be stored into two regions, either on the surface adsorption or/and solid-state diffusion in bulk. MOFs belong to the organic-inorganic hybrid porous materials with multi-dimensional structure [10]. Structural performance correlations in MOFs can be classified as; heterocyclic azolate-based frameworks, mixed-ligand/ functionality systems, carboxylate-based frameworks, metal-cyanide frameworks, covalent organic frameworks [11]. This class of material is composed of organic ligands and almost one transition metal ions. MOFs possess high specific surface area, high crystallinity, and high porosity. The mechanism of hydrogen storage in MOFs are mainly physical
00 00 00 00 00 00 00 00 00 00 00
adsorption [12]. The pore size in MOFs can adjust by changing the organic ligands, which can further reflect in specific surface area, and ultimately enhancing hydrogen sorption performances. Mixed metal oxides (MMOs) recently utilize as a host for physical hydrogen sorption. Unique structure, morphology, and stability of MMOs are three main factors seems to be effective in boosting their hydrogen sorption [13]. In molecular level, based on electrons and ions interactions with each other, the electronic structures of MMOs can be proposed, which is important to understand the electric conductivity, magnetism, and many optical effects [7]. The electronic activities of MMOs can be further reflected into hydrogen storage performances [14]. In addition, the redox properties of some metals enhanced more the hydrogen storage performances of the target. Various molecular structures of MMOs are reported for solid-state hydrogen storage [15e18] nanostructures. Since MMOs have not been evaluated as a promising host for solidstate hydrogen storage materials by the US department of energy (DOE), consecutive and continuous works are required in order to fill up the gaps in this field. Cobalt oxides (CoO) are impressive materials, which utilized widely for designing and synthesis of novel MMO materials [19,20]. CoO impart fascinating properties to the final product like conductivity. The term “Triple CoII, III, IV” charge ordering have been reported by David and his coworkers [21] in a study on the modular cobaltite. They observed a systematic evolution of the electronic and magnetic states of different packing modes of CoO containing compound with general formula BanCo2þnO3nþ2. They theoretically proposed a series of ordered CoII/CoIII versus mixed CoIII/IV charge segregation. This versatility of coordination, valence and spin states which offered by cobalt ions can be impart additional performances to the host MMOs structure [22]. Various phase diagrams of CoO in MMOs containing strontium (Sr) and their respective properties have been rarely investigated/reported such as Sr4Co3O9 [23], Sr5Co4O11 [24], Sr6Co5O15 [25], and Sr14Co11O33 [26]. The structure and properties of SreCoeO complex materials, these class of materials are appropriate as a host for energy storage systems. Polycrystalline MMOs attract great interest as carrier in energy storage systems due to their complex structure and
Please cite this article as: Razavi FS et al., Auto-combustion synthesis, structural analysis, and electrochemical solid-state hydrogen storage performance of strontium cobalt oxide nanostructures, International Journal of Hydrogen Energy, https://doi.org/10.1016/ j.ijhydene.2019.10.012
3
international journal of hydrogen energy xxx (xxxx) xxx
Fig. 1 e Schematic pathway of the Sr2Co9O14 fabrication. defects. MMOs compose of crystalline phases, which can create oxygen vacancies. Mnþ1ConO3nþ3 - Co8O8 (M ¼ Sr, Ba) is a type of polycrystalline MMO with perovskite blocks of Mnþ1ConO3nþ3. Polycrystalline Ba2Co9O14 nanostructures have
an inorganic backbone, where magnetically ordered generally in a comples conductivity [27,28]. Though various structures of SreCoeO have been reported, polycrystalline Sr2Co9O14 has not been investigated elsewhere. In the current study, the Sr2Co9O14 nanoparticles were synthesized via a combustion method. The unique structure, morphology, and properties of polycrystalline Sr2Co9O14 nanoparticles were served as effective strategies to investigate its respective hydrogen sorption in a typical hydrogen storage setup.
Experimental study Materials In this study, all reagents for the production of Sr2Co9O14 nanostructures including strontium nitrate (Sr(NO3)2, Purity 99.99%, Mw 211.63 g mol1), Cobalt (II) nitrate hexahydrate (Co(NO3)2$6H2O, Purity 99%, Mw 291.03 g mol1), glucose (C6H12O6, Purity 99.5%, Mw 180.16 g mol1), fructose (C6H12O6, Mw 180.16 g mol1), sucrose (C12H22O11, Purity 99.5%, Mw 342.30 g mol1), lactose (C12H22O11, Purity 99%, Mw 342.30 g mol1) and maltose monohydrate (C12H22O11$H2O,
Table 1 e CV results of Sr2Co9O14 nanoparticles synthesized in various reducing agents. Electrode
Fig. 2 e XRD patterns of Sr2Co9O14 fabricated at 900 C utilizing various fuels.
Glassy carbon Sr2Co9O14-Glucose Sr2Co9O14-Fructose Sr2Co9O14-Lactose Sr2Co9O14-Sucrose Sr2Co9O14-Maltose
Ipa
Ipc
Epa
Epc
*D (nm)
45.10 50.61 41.61 47.86 47.38 46.43
46.37 50.38 42.18 46.23 45.17 44.19
0.376 0.348 0.422 0.390 0.377 0.395
0.011 0.029 0.057 0.029 0.017 0.021
e 32 32 29 30 23
*Average crystallite sizes calculated from Scherrer equation.
Please cite this article as: Razavi FS et al., Auto-combustion synthesis, structural analysis, and electrochemical solid-state hydrogen storage performance of strontium cobalt oxide nanostructures, International Journal of Hydrogen Energy, https://doi.org/10.1016/ j.ijhydene.2019.10.012
4
international journal of hydrogen energy xxx (xxxx) xxx
Purity 99%, Mw 360.32 g mol1) were supplied from MerckGermany and used as received.
Synthesis of blank sample and strontium cobalt oxide nanostructures In the current study, in order to have an evidence for pure formation of Sr2Co9O14 nanostructures, a blank sample was prepared. In this sample, stoichiometric amount of starting materials (Sr(NO3)2 and Co(NO3)2$6H2O) were dissolved in water without any fuels, evaporated and calcined at 900 C for 4 h. This sample was used as an evidence for further investigation. Utilizing auto-combustion method, the Sr2Co9O14 nanostructures were purely synthesized. Primarily, 1 mmol Sr(NO3)2 was dissolved in distilled water to create a clear solution. An aqueous solution containing reducing agent (glucose, fructose, sucrose, lactose, or maltose) was added drop-wise into the strontium nitrate solution under the strong magnetic stirring at room temperature. The molar ratio of reducing agent to Sr was selected to be 11: 1. This solution was heated up by continuous stirring at 60 C for 30 min. In the second container, an aqueous solution containing 4.5 mmol Co(NO3)2$6H2O was added to above admixture (i.e. Sr(NO3)2 and reducing agent) and stirred at 120 C for 60 min. Evaporation of the reaction solution caused formation of a viscose gel. Finally, the Sr2Co9O14 nanostructures was formed from the gel after drying at 70 C for 24 h and calcination at 900 C
for 4 h in normal atmosphere. Fig. 1 represents the schematic of the preparation pathway of the strontium cobaltite nanostructures. After annealing at 900 C, the structural formation and morphology of the samples were analyzed based on the reducing agents.
Characterization The composition and the bulk morphology of the samples were measured using an X-ray diffractometer (Philips X’Pert Promonochromatized Cu Ka radiation (l ¼ 1.54 A) in the range of 2q ¼ 10e80 ), and a TESCAN MIRA3 Field Emission Scanning Electron Microscopy (FE-SEM), respectively. The best sample from all above samples was selected for detailed structural and elemental analysis using a Shimadzu Varian 4300 spectrophotometer in KBr pellets ranging from 4000 to 400 cm1, and an Energy Dispersive X-ray Spectroscope (EDX Hitachi S4300), respectively. In addition, the physical properties of the selected sample i.e. band gap energy and magnetic properties were measured using a Ultra-Violet diffuse reflectance spectra (UV-DRS), and a vibrating sample magnetometer 60 (VSM, Meghnatis Kavir Kashan co., Kashan, Iran). The specific surface area of the sample was measured by a nitrogen gas adsorption-desorption BELsorp mini II, Japan) utilizing BarretteEmmetteTeller (BET). The electrochemical properties of the sample were analyzed in three electrode setups, primarily by a voltammeter, and finally using a chronopotentiometer. The former was run in a probe solution of K3(Fe(CN)6)/
Fig. 3 e FESEM micrographs of Sr2Co9O14 particles fabricated at 900 C utilizing various fuels; (a) blank (without fuel), (b) glucose, (c) fructose, (d) lactose, (e) sucrose, and (f) maltose. Please cite this article as: Razavi FS et al., Auto-combustion synthesis, structural analysis, and electrochemical solid-state hydrogen storage performance of strontium cobalt oxide nanostructures, International Journal of Hydrogen Energy, https://doi.org/10.1016/ j.ijhydene.2019.10.012
international journal of hydrogen energy xxx (xxxx) xxx
K4(Fe(CN)6) in the 0.1 M phosphate buffer solution (pH 7.0) in a scan rate of 0.1 V-1, while the later was utilized in 1 mA at ambient temperature, in 6 M KOH electrolyte. In this study, the working electrode is composed of a porous copper sheet, solid-state hydrogen absorber (Sr2Co9O14) having a surface area of ~1 1 cm2.
Results and discussion Structural analysis The crystal structure of the Sr2Co9O14, prepared in glucose, fructose, sucrose, lactose, and maltose, were identified by their respective XRD patterns (Fig. 2). The diffractograms of the samples show a series of intense peaks in the range of 10>2q > 70. Since no similar structural data is reported for Sr2Co9O14, therefore, no JCPDS data is available. In Ba2Co9O14, it is reported a rhombohedral R-3m space group [29]. Approximately similar diffraction peaks can be observed in the media of various fuels. The most intense peaks grow at 28.73 , 32.78 , 37.00 , 44.06 , 47.07 , 55.84 , 59.51 , and 65.39 . The results are in good agreement with previous computational study on crystallographic and magnetic structure of SrCoO2.5 brownmillerite [30]. As mentioned before,
5
Mnþ1ConO3nþ3 - Co8O8 (M ¼ Sr, Ba) is a polycrystalline MMOs with perovskite blocks (Mnþ1ConO3nþ3). In this study, the XRD pattern is proposed to be indexed in an orthorhombic unit cell. Scherrer equation (Eq. 1); D ¼ k l/b cosq (1) is used in order to calculate the average crystallite size, where, D, q, k, and l are average crystallite size, diffraction angle, Scherrer constant (~0.9), and wavelength, respectively [31]. In this equation (Eq.1) b is a factor of full width at half-maximum (FWHM). The calculated D factors are summarized in Table 1. The surface morphology and particle size of the samples were observed on their respective FESEM micrographs (Fig. 3). The blank sample consists of agglomerated cube like particles with the particle size larger than 100 nm (Fig. 3a). The surface morphology of the sample synthesized in glucose, the particles are highly dense with narrow distributions, and uniform shapes almost less than 100 nm (Fig. 3b). The morphology of the particles, which combusted in fructose (Fig. 3c), lactose (Fig. 3d), sucrose (Fig. 3e), and maltose (Fig. 3f) consist of a series of irregular and inhomogeneous particles. Especially in the Sr2Co9O14 samples were combusted in fructose, lactose, and sucrose some very large particles can be observed. Since a homogenous, nanosized, and crystalline Sr2Co9O14 sample is formed in the presence of glucose, according to FESEM micrographs and XRD patterns, this sample is selected for further investigation.
Fig. 4 e (a) TEM micrographs, and (b) particle diameters histogram of Sr2Co9O14 nanostructures annealed at 900 C. Please cite this article as: Razavi FS et al., Auto-combustion synthesis, structural analysis, and electrochemical solid-state hydrogen storage performance of strontium cobalt oxide nanostructures, International Journal of Hydrogen Energy, https://doi.org/10.1016/ j.ijhydene.2019.10.012
6
international journal of hydrogen energy xxx (xxxx) xxx
Complementary morphological observation of the Sr2Co9O14 nanoparticles which synthesized in glucose was captured using TEM. The respective micrographs (Fig. 4a) affirm the spherical and highly crystalline formation of the particles, in the range of 40e100 nm. In the particle diameter histogram of the sample, the most of the particles are in the range of 80e100 nm (Fig. 4b). The particle diameters are obtained from its respective TEM images using Digimizer analyzer. Potent contrast in the Sr2Co9O14 sample demonstrate a dense and crystalline host phase. Elemental analysis of the selected sample was confirmed the purity of the sample (Fig. 5a). The EDX spectrum of Sr2Co9O14 nanoparticles contains only strontium (Sr), cobalt (Co) and oxygen (O). In addition, the composition of the sample was investigated using an X-ray florescence (XRF). The XRF result was also affirmed that the sample composed of SrO and CoO (major phase), and very minor (less than 1%) amounts of CaO (0.086%), SiO2 (0.100%), Cl (0.074%), and Na2O (0.160%). The structural formation of the sample was also identified using FTIR analyzer (Fig. 5b). Here, four intense peaks are assigned at around 3432 cm1, 663 cm1 and 566 cm1 correspond to the stretching vibration of eOH, bending and symmetrical stretching vibration of M-O-M and O-M-O. In addition, a sharp peak at 414 cm1 and a small peak at 485 cm1 can be assigned to stretching vibration of SreO
species. Generally, in mixed metal oxides, the areas below 1000 cm1 are emanated from the stretching vibration frequencies of the M-O motions. In this spectrum a doublet at around 566 cm1 can be observed in association with yCo-O. This doublet is due to the valence states of cobalt ions; JahnTeller and supplementary polarization. Optical property of Sr2Co9O14 nanoparticles was recorded by UV-DRS (Fig. 5c). A strong absorption in the visible region can be observed at around 365 nm, most probably formed by pure and unoccupied Sr 5s and 5d states and impurity of CoO charge transfer interaction [16]. The band gap energy were calculated using Tauc plot (Eq. 2), (ahy)n¼ A(hy - Eg) (2), indicating a direct transition allowance. In this equation, hy is the photon energy, a is the absorption coefficient, A is a constant relative to the material and n is 2 for a direct transition. The direct band gap of the sample was obtained to be around 3.12 eV. This Eg from Tauc equation were further confirmed by a theoretical calculation using Eq. 3, Eg ¼ 1240/l (3), where l is the maximum wavelength. The Eg from this equation was obtained to be around 3.26 eV. Finally, the magnetism of the Sr2Co9O14 nanoparticles was identified from the vibrating sample magnetometer (VSM) (Fig. 5d) at ambient temperature with the field sweeping from 8.0 to þ8.0 kOe. Nearly narrow hypothesis loop can observe in its VSM profile with a saturation magnetization around 0.28 emu/g (Fig. 5d: inset). There are two types of ferromagnets,
Fig. 5 e Physico-chemical characterization of the Sr2Co9O14 nanostructures synthesized at 900 C in glucose; (a) EDX spectrum, (b) FTIR spectrum, (c) UV-DR spectrum, and (d) VSM curve. Please cite this article as: Razavi FS et al., Auto-combustion synthesis, structural analysis, and electrochemical solid-state hydrogen storage performance of strontium cobalt oxide nanostructures, International Journal of Hydrogen Energy, https://doi.org/10.1016/ j.ijhydene.2019.10.012
international journal of hydrogen energy xxx (xxxx) xxx
7
ferromagnetic. In addition, Jeen and his coworkers [33] reported the magnetism of the SrCoO2.5 and SrCoO3 phases. They expressed a large ferromagnetic signal in the SrCoO3 phase and an antiferromagnetic signal in the SrCoO2.5 phase. Fig. 6 illustrates the BET analysis of the Sr2Co9O14 nanoparticles well matched to type III isotherm having a H3 hysteresis loop (according to the IUPAC classification). In H3 hysteresis loop, the aggregated particles form slit-shaped pores with non-uniform sizes and/or shapes. The total pore volume, mean pore radii and average pore size of the sample were calculated to be around 1.11 (cm3 g1), 2.38 nm and 26.79 nm, respectively. The BJH mean pore radii (rp) between 1 nm and 25 nm are aggregates of nanosized particles.
Electrochemical properties Fig. 6 e N2 absorption-desorption and BJH (inset) of the Sr2Co9O14 nanostructures.
hard and soft. In a hard ferromagnet, the hysteresis loop is broad, while in a soft ferromagnet, this loop is narrow, therefore much more responsive to the applied field [32]. In addition, narrow hysteresis loop is due to a small-dissipated energy. In conclusion, at room temperature, the sample is
As mentioned before, benefiting from the MMOs electrochemical properties in energy storage will play significant roles for low-cost and environmentally friendly energy storage systems. To touch the aim of this work, the electrochemical performances of the Sr2Co9O14 nanoparticles were recorded by a cyclic voltammogram (CV) (Fig. 7a and b). The obtaining results from CV analysis were further served to peruse hydrogen storage capacity (Fig. 7c). As we mentioned before, owing the structural analysis of the samples (Section
Fig. 7 e (a) Cyclic voltammograms of the Sr2Co9O14 particles synthesized in various fuels, (b) Cyclic voltammogram of the Sr2Co9O14 nanoparticles synthesized in glucose, and (c) fifteen succeeded discharge sequences of the Sr2Co9O14 nanoparticles synthesized in glucose. Please cite this article as: Razavi FS et al., Auto-combustion synthesis, structural analysis, and electrochemical solid-state hydrogen storage performance of strontium cobalt oxide nanostructures, International Journal of Hydrogen Energy, https://doi.org/10.1016/ j.ijhydene.2019.10.012
8
international journal of hydrogen energy xxx (xxxx) xxx
Structural analysis), the best sample was obtained in glucose. Similar to that, the CV analysis of the samples were synthesized in various fuels, clearly confirmed a superior electrochemical performance. The electrode responses are tabulated in Table 1. The anodic and cathodic peak currents (Ipa and Ipc) of the glassy carbon electrode (GCE) are lower than that of the polycrystalline Sr2Co9O14 nanoparticles, synthesized in Glucose. Therefore, this sample was selected for electrochemical hydrogen storage properties. As the major aim of the current study, the hydrogen storage properties of the Sr2Co9O14 nanoparticles were investigated using a chronopotentiometer via charge and discharge cycles (Fig. 7c). In the current study, in order to follow up the hydrogen sorption ability of the sample, the system was adjusted for continuous 15 charge-discharge sequences. However, the discharge sequences can be continued as far as all hydrogen sites on the sample occupied. Hydrogen physisorption shows a maximum discharge capacity of around 950 mA h/g after 15 cycles of discharging. The hydrogen content of the sample was calculated to be around 3.4 wt%. According to US-DOE, for commercialization of hydrogen-fueled vehicle, the target should meet a 1.5 kWh/kg system (4.5 wt% hydrogen) or 1.0 kWh/L system (0.030 kg hydrogen/L) with $10/ kWh ($333/kg stored hydrogen capacity) [34]. Despite of lower hydrogen capacity of Sr2Co9O14 nanoparticles as compared to the US-DOE assumption, this class of material (i.e. MMO) must be improved to match the key-values targeting. Owing to the complexity of the polycrystalline samples, various sites for hydrogen sorption exist, which can further reflect in stability and hydrogen storage performance of the solid substrate [16,16,35,35]. Nanosystems (nanoparticles, nanotubes, nanolayers, etc) have either single or multiple wall structure and pores, therefore, multiple adsorption sites are present which result in higher capacity. Practically, this phenomenon can be observed in the multistate, long and flat potential plateaus of the electrochemical plots [36,37]. Van der Waals interaction, which is known as resonant fluctuations in charge distributions are the origin of the hydrogen sorption mechanism of solid species. This phenomenon is the major reaction (which is called as physisorption) of hydrogen onto the surface of a solid host. The physisorption mechanism can be proposed as Eq. 4; Sr2Co9O14 þ xH2O þ xe 4 Sr2Co9O14-Hx þ xOH (4). In addition, the rich redox reactions involving cobalt ion can be contributed to hydrogen storage performance of the sample beyond those of conventional physisorption as Eq. 5; Sr2Conþ9O14 þ xH2O þ xe 4 Sr2Conþ9-y Comþy O14 - Hx þ xOH (5). Therefore, Co-based polycrystalline MMO nanomaterials like Sr2Co9O14 are anticipated to be appealing working electrode (WE) for hydrogen storage system. Compared with other reported MMOs in the hydrogen storage systems [38e40], this composition, even with lower discharge capacity, can be preferably served as a superior matrix for energy storage.
Conclusion In conclusion, primarily, a pure phase Sr2Co9O14 nanoparticles were synthesized via combustion method in glucose after annealing at 900 C. The structural analyses were confirmed
the crystalline nanosized formation of the proposed product composed of only Sr, Co, and Oxygen. In addition, the physical properties were confirmed ferromagnetism of the sample with a band gap of 3.12 eV. As a major significant of this work, the reversible physisorption and redox activities were proposed in a series of electrochemical discharging processes, which could be accomplished at significantly appropriate hydrogen storage of 950 mA h/g. It can be now finalized that the nanosized Sr2Co9O14 is a new material we reported here, for hydrogen sorption. Despite of its lower hydrogen capacity (~3.4 wt%), for fifteen discharge sequences, as compared to the key-values targeting reported by US-DOE, in explanation for future industrial application, this nanosystem can provide a pathway to the future design of new solid materials with pivotal role in energy storage system.
Acknowledgement Authors are grateful to the council of Iran National Science Foundation; INSF (97017837) and University of Kashan for supporting this work by Grant No (159271/33).
references
[1] Schlapbach L, Zu¨ttel A. Hydrogen-storage materials for mobile applications. Nature 2001;414:353e8. https://doi.org/ 10.1038/35104634. [2] Suib SL, Kojima Y, Miyaoka H, Ichikawa T. Hydrogen storage materials. New Futur Dev Catal 2013:99e136. https://doi.org/ 10.1016/B978-0-444-53880-2.00006-5. Elsevier. [3] Froudakis GE. Hydrogen storage in nanotubes & nanostructures. Mater Today 2011;14:324e8. https://doi.org/ 10.1016/S1369-7021(11)70162-6. [4] Salehabadi A, Morad N, Ahmad MI. A study on electrochemical hydrogen storage performance of b-copper phthalocyanine rectangular nanocuboids. Renew Energy 2020;146:497e503. https://doi.org/10.1016/ J.RENENE.2019.06.176. [5] Ley MB, Jepsen LH, Lee YS, Cho YW, Bellosta Von Colbe JM, Dornheim M, et al. Complex hydrides for hydrogen storage new perspectives. Mater Today 2014;17:122e8. https:// doi.org/10.1016/j.mattod.2014.02.013. chet JMJ, Svec F. Nanoporous polymers for [6] Germain J, Fre hydrogen storage. Small 2009;5:1098e111. https://doi.org/ 10.1002/smll.200801762. [7] Wang F, Zhang Y, Yu N, Fu L, Zhu Y, van Ree T. Metal oxides in batteries. Met Oxides Energy Technol 2018:127e67. https:// doi.org/10.1016/B978-0-12-811167-3.00006-7. Elsevier. [8] Hirscher M. Handbook of hydrogen storage: new materials for future energy storage. Wiley-VCH Verlag & Co; 2010. [9] Sakintuna B, Lamaridarkrim F, Hirscher M. Metal hydride materials for solid hydrogen storage: a review. Int J Hydrogen Energy 2007;32:1121e40. https://doi.org/10.1016/ j.ijhydene.2006.11.022. [10] Langmi HW, Ren J, Musyoka NM. Metal-organic frameworks for hydrogen storage. Compend Hydrogen Energy 2016:163e88. https://doi.org/10.1016/B978-1-78242-3621.00007-9. [11] Wjihi S, Yang J, Sellaoui L, Knani S, Ben Lamine A. Interpreting the hydrogen adsorption on organic groups functionalized MOF-5s by statistical physics model. Int J
Please cite this article as: Razavi FS et al., Auto-combustion synthesis, structural analysis, and electrochemical solid-state hydrogen storage performance of strontium cobalt oxide nanostructures, International Journal of Hydrogen Energy, https://doi.org/10.1016/ j.ijhydene.2019.10.012
international journal of hydrogen energy xxx (xxxx) xxx
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
[21]
[22]
[23]
[24]
[25]
Hydrogen Energy 2017;42:10023e37. https://doi.org/10.1016/ j.ijhydene.2017.01.149. Rahali S, Belhocine Y, Seydou M, Maurel F, Tangour B. Multiscale study of the structure and hydrogen storage capacity of an aluminum metal-organic framework. Int J Hydrogen Energy 2017;42:15271e82. https://doi.org/10.1016/ j.ijhydene.2017.04.258. Chen B, Liu Z, Li C, Zhu Y, Fu L, van Ree T. Metal oxides for hydrogen storage. Met Oxides Energy Technol 2018:251e74. https://doi.org/10.1016/B978-0-12-811167-3.00009-2. Elsevier. Zhang J, Yan S, Yu LP, Zhou XJ, Zhou T, Peng P. Enhanced hydrogen storage properties and mechanisms of magnesium hydride modified by transition metal dissolved magnesium oxides. Int J Hydrogen Energy 2018;43:21864e73. https:// doi.org/10.1016/J.IJHYDENE.2018.10.017. Salehabadi A, Salavati-Niasari M, Sarrami F, Karton A. SolGel auto-combustion synthesis and physicochemical properties of BaAl2O4 nanoparticles; electrochemical hydrogen storage performance and density functional theory. Renew Energy 2017;114:1419e26. https://doi.org/ 10.1016/j.renene.2017.07.119. Salehabadi A, Salavati-Niasari M, Gholami T. Green and facial combustion synthesis of Sr3Al2O6 nanostructures; a potential electrochemical hydrogen storage material. J Clean Prod 2018;171:1e9. https://doi.org/10.1016/J.JCLEPRO.2017.09.250. Salehabadi A, Sarrami F, Salavati-Niasari M, Gholami T, Spagnoli D, Karton A. Dy3Al2(AlO4)3 ceramic nanogarnets: sol-gel auto-combustion synthesis, characterization and joint experimental and computational structural analysis for electrochemical hydrogen storage performances. J Alloy Comp 2018;744:574e82. https://doi.org/10.1016/ j.jallcom.2018.02.117. Salehabadi A, Salavati-Niasari M, Gholami T, Khoobi A. Dy3Fe5O12 and DyFeO3 nanostructures: green and facial auto-combustion synthesis, characterization and comparative study on electrochemical hydrogen storage. Int J Hydrogen Energy 2018;43:9713e21. https://doi.org/10.1016/ J.IJHYDENE.2018.04.018. Li M, Zhao K, Zhao Z, Li H, He F, Lv P. Enhanced hydrogenrich syngas generation in chemical looping methane reforming using an interstitial doped La1.6Sr0.4FeCoO6. Int J Hydrogen Energy 2019;44:10250e64. https://doi.org/10.1016/ J.IJHYDENE.2019.03.012. Umeshbabu E, Rajeshkhanna G, Rao GR. Urchin and sheaflike NiCo2O4 nanostructures: synthesis and electrochemical energy storage application. Int J Hydrogen Energy 2014;39:15627e38. https://doi.org/10.1016/ J.IJHYDENE.2014.07.168. David R, Kabbour H, Bordet P, Pelloquin D, Leynaud O, Trentesaux M, et al. Triple CoII, III, IV charge ordering and spin states in modular cobaltites: a systematization through experimental and virtual compounds. J Mater Chem C 2014;2:9457e66. https://doi.org/10.1039/c4tc01486c. Cheng JG, Zhou JS, Hu Z, Suchomel MR, Chin YY, Kuo CY, et al. Spin-state transition in Ba2Co9O14. Phys Rev B Condens Matter Mater Phys 2012;85:1e6. https://doi.org/ 10.1103/PhysRevB.85.094424. Chupakhina TI, Melkozerova MA, Bazuev GV. Phase formation features and magnetic properties of complex oxides in the systems Sr-Co-M-O (M ¼ Zn, Cu). Russ J Inorg Chem 2013;58:253e8. https://doi.org/10.1134/ S0036023613030054. Wong-Ng W, Liu G, Martin J, Thomas EL, Lowhorn N, Kaduk JA. Phase compatibility and thermoelectric properties of compounds in the Sr-Ca-Co-O system. J Appl Phys 2010;107. https://doi.org/10.1063/1.3276158. 0335081e6. Iwasaki K, Shimada M, Yamane H, Takahashi J, Kubota S, Nagasaki T, et al. Electrical resistivity and Seebeck coefficient
[26]
[27]
[28]
[29]
[30]
[31]
[32]
[33]
[34]
[35]
[36]
[37]
[38]
[39]
[40]
9
of Sr6Co5O15. J Alloy Comp 2004;377:272e6. https://doi.org/ 10.1016/J.JALLCOM.2004.01.060. Jankovsky´ O, Sedmidubsky´ D, Vı´tek J, Simek P, Sofer Z. Phase diagram of the SreCoeO system. J Eur Ceram Soc 2015;35:935e40. https://doi.org/10.1016/ J.JEURCERAMSOC.2014.09.040. G, Mentre O. Ehora G, Daviero-Minaud S, Colmont M, Andre Ba2Co9O14: new inorganic building blocks with magnetic ordering through super-super exchanges only. Chem Lett 2007;19:2180e8. https://doi.org/10.1021/CM062897Q. Delorme F, Chen C, Pignon B, Schoenstein F, Perriere L, Giovannelli F. Promising high temperature thermoelectric properties of dense Ba2Co9O14ceramics. J Eur Ceram Soc 2017;37:2615e20. https://doi.org/10.1016/ j.jeurceramsoc.2017.01.034. Takami T, Saiki S, Cheng J, Goodenough JB. Magnetic and transport properties of Ba2Co9O 14 and Ba1.9A0.1Co9O14 (A ¼ La or Na). J Phys Soc Japan 2010;79:1e5. https://doi.org/ 10.1143/JPSJ.79.114713. ~ oz A, Calle C, Alonso JA, Botta PM, Pardo V, Baldomir D, Mun et al. Crystallographic and magnetic structure of SrCoO2.5 brownmillerite: neutron study coupled with band-structure calculations. Phys Rev B 2008;78. 0544041e8. Salehabadi A, Salavati-Niasari M, Ghiyasiyan-Arani M. Selfassembly of hydrogen storage materials badsed multi-walled carbon nanotubes (MWCNTs) and Dy3Fe5O12 (DFO) nanoparticles. J Alloy Comp 2018;745:789e97. https://doi.org/ 10.1016/J.JALLCOM.2018.02.242. Khan MA, Riaz S, Ali I, Akhtar MN, Murtaza G, Ahmad M, et al. Structural and magnetic behavior evaluation of Mg-Tb ferrite/ polypyrrole nanocomposites. Ceram Int 2014;41:651e6. https://doi.org/10.1016/j.ceramint.2014.08.117. Jeen H, Choi WS, Biegalski MD, Folkman CM, Tung I-C, Fong DD, et al. Reversible redox reactions in an epitaxially stabilized SrCoO x oxygen sponge. Nat Mater 2013;12:1057e63. https://doi.org/10.1038/nmat3736. US Department of Energy. Target explanation document: onboard hydrogen storage for light-duty fuel cell vehicles. 2015. Salehabadi A, Ahmad MI, Morad N, Salavati-Niasari M, Enhessari M. Electrochemical hydrogen storage properties of Ce0.75Zr0.25O2 nanopowders synthesized by sol-gel method. J Alloy Comp 2019;790:884e90. https://doi.org/ 10.1016/J.JALLCOM.2019.03.160. Niaz S, Manzoor T, Pandith AH. Hydrogen storage: materials, methods and perspectives. Renew Sustain Energy Rev 2015;50:457e69. https://doi.org/10.1016/j.rser.2015.05.011. Deng G, Chen Y, Tao M, Wu C, Shen X, Yang H, et al. Study of the electrochemical hydrogen storage properties of the proton-conductive perovskite-type oxide LaCrO3 as negative electrode for Ni/MH batteries. Electrochim Acta 2010;55:884e6. https://doi.org/10.1016/j.electacta.2009.06.071. Liu E, Wang J, Li J, Shi C, He C, Du X, et al. Enhanced electrochemical hydrogen storage capacity of multi-walled carbon nanotubes by TiO2 decoration. Int J Hydrogen Energy 2011;36:6739e43. https://doi.org/10.1016/ j.ijhydene.2011.02.128. Gholami T, Salavati-Niasari M. Effects of copper:aluminum ratio in CuO/Al2O3nanocomposite: electrochemical hydrogen storage capacity, band gap and morphology. Int J Hydrogen Energy 2016;41:15141e8. https://doi.org/10.1016/ j.ijhydene.2016.06.191. Gholami T, Salavati-Niasari M, Salehabadi A, Amiri M, Sabani M, Rezaei M. Electrochemical hydrogen storage properties of NiAl2O4/NiO nanostructures using TiO2, SiO2 and graphene by auto-combustion method using green tea extract. Renew Energy 2018;115:199e207. https://doi.org/ 10.1016/J.RENENE.2017.08.037.
Please cite this article as: Razavi FS et al., Auto-combustion synthesis, structural analysis, and electrochemical solid-state hydrogen storage performance of strontium cobalt oxide nanostructures, International Journal of Hydrogen Energy, https://doi.org/10.1016/ j.ijhydene.2019.10.012