Cobalt-nickel silicate hydroxide on amorphous carbon derived from bamboo leaves for hybrid supercapacitors

Chemical Engineering Journal 375 (2019) 121938

Contents lists available at ScienceDirect

Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej

Cobalt-nickel silicate hydroxide on amorphous carbon derived from bamboo leaves for hybrid supercapacitors

T

⁎

Yifu Zhang , Chen Wang, Hanmei Jiang, Qiushi Wang, Jiqi Zheng, Changgong Meng School of Chemical Engineering, Dalian University of Technology, Dalian 116024, PR China

H I GH L IG H T S

G R A P H I C A L A B S T R A C T

hierarchical petal-like CoNiSi/C • 3D composites are derived from bamboo leaves.

shows the performance with • CoNiSi/C 226 F g (316 C g ) at 0.5 A g . exhibits the excellent reten• CoNiSi/C tion of 99% after 10,000 cycles. HSC device achieves • The at 2 mA cm , 254 mF cm −1

−1

−2

•

−1

3D hierarchical petal-like CoxNi3−xSi2O5(OH)4/C composites are derived from bamboo leaves and explored to electrode materials for supercapacitor. The CoNiSi/C electrode shows remarkable electrochemical performance with 226 F g−1 (316 C g−1) at 0.5 A g−1 in the voltage window of −0.8 ~ 0.6 V and the retention of 99% after 10,000 cycles. The CoNiSi/C//Ni(OH)2 HSC device achieves the excellent electrochemical performance with the capacitance of 254 mF cm−2 (64 F g−1) at 2 mA cm−2, energy density of 1.3 Wh m−2 (20.6 Wh kg−1) at power density of 4 W m−2 (63.3 W kg−1) and cycle stability with 82% after 10,000 cycles.

−2

0.793 Wh m−2 at 3.75 W m−2. The HSC device exhibits high cycle stability with 82% after 10,000 cycles.

A R T I C LE I N FO

A B S T R A C T

Keywords: Cobalt-nickel silicate Biomass-derived carbon Hierarchical porous structure Electrode materials Electrochemical performance Hybrid supercapacitor

3D hierarchical cobalt-nickel silicate hydroxide/C (CoxNi3−xSi2O5(OH)4, denoted as CoNiSi) composites are derived from bamboo leaves and explored as electrode materials for supercapacitor. The CoNiSi architectures with hierarchical petal-like shapes are in-situ generated on 3D amorphous carbon derived from bamboo leaves using the biomass-inherent SiO2 species as the silicon source. The CoNiSi/C electrode shows a 3D hierarchical porous structure, high specific surface area and remarkable electrochemical performance with 226 F g−1 at 0.5 A g−1 in the voltage window of −0.8 ~ 0.6 V, which is superior to the specific capacitances of SiO2/C, CoSi/ C, NiSi/C and even the reported values of silicates-based materials. It also achieves excellent cycling performance with 99% after 10,000 cycles. Moreover, a high-performance solid-state hybrid supercapacitor (HSC) device is fabricated by CoNiSi/C and Ni(OH)2. This HSC device achieves an outstanding electrochemical performance with the capacitance up to 254 mF cm−2 (64 F g−1) at 2 mA cm−2, and the energy density up to 0.793 Wh m−2 (20.0 Wh kg−1) at 3.75 W m−2 (94.5 W kg−1), which are higher than a majority of former SCs based on silicates. Besides, the HSC device shows good cycle stability with 82% after 10,000 cycles and can light the red LED lasting for more than 2 min. These features demonstrate that the 3D CoNiSi/C architectures can be considered as a promising and efficient material for SCs with high performance.

⁎

Corresponding author. E-mail address: [email protected] (Y. Zhang).

https://doi.org/10.1016/j.cej.2019.121938 Received 16 April 2019; Received in revised form 1 June 2019; Accepted 9 June 2019 Available online 10 June 2019 1385-8947/ © 2019 Elsevier B.V. All rights reserved.

Chemical Engineering Journal 375 (2019) 121938

Y. Zhang, et al.

1. Introduction

imbedding and exhaling in the electrochemical reaction, as long as the metal ions can take place Faraday redox reaction which has the advantage for high capacitance [9]. Furthermore, the above investigations are mainly based on Co3Si2O5(OH)4 or Ni3Si2O5(OH)4, however, the study on cobalt-nickel binary silicate hydroxide CoxNi3−xSi2O5(OH)4 (0 < x < 3), denoted as CoNiSi, is deemed insufficient. Therefore, the focus of this work is on the exploration of the synthesis of CoNiSi with novel architectures applied to high-performance SCs. Previous studies on the synthesis of CoNiSi are based on SiO2 synthesized by a traditional Stöber method using ammonia and TEOS [40–44]. Thus, the development of new methods to synthesize CoNiSi with novel structures is urgent and meaningful. Besides, the previous studies reported that the poor conductivity of TMSs greatly restricts their application in the field of electrode materials [22–24]. The combination of the materials with high conductivity with CoNiSi becomes the preferred solution [32]. In this work, we sought a novel method to fabricate the 3D CoxNi3−xSi2O5(OH)4/C composite (denoted as CoNiSi/C). Hierarchical CoNiSi with petal-like shapes was in-situ grown on the 3D biomassderived carbon. The biomass-derived SiO2/C acquired by pyrolysis of bamboo leaves keeps the natural layered porous structure and the carbon is heteroatoms doped [36,37,45]. And the petal-like CoNiSi was generated using the highly dispersed SiO2 species inherited from bamboo leaves derived SiO2/C as the silicon source by a facile hydrothermal route. The hierarchically porous 3D CoNiSi/C with petal-like shapes and large surface area can facilitate electronic transfer and promote the electrolyte ion diffusion. As expected, 3D CoNiSi/C composite exhibits remarkable electrochemical performance as an electrode and applied to a solid-state hybrid supercapacitor (HSC) device.

Nowadays, as the acceleration of the globalization, energy crisis has been an essential problem attributed to the rapid population increase, environmental pollution and resource waste. Low-cost and reproducible energy sources are in extremely urgent needs and strategically significant for humanity [1–3]. To address the energy crisis, it should be explored advanced electrical technologies for high-performance energy storage systems, which can store and deliver huge quantities of energy. Among different kinds of energy storage devices, supercapacitors (SCs) are deemed to be a sensible choice due to their prominent advantages including rapid charge-discharge rates, long cycle life, high power density and excellent stability [3–8]. With regard to the charge storage mechanisms, SCs are mainly classified into two types: electrochemical double-layer capacitor (EDLC) and pseudo-capacitor [9–11]. The energy density (E) of the SC device is decided by the specific capacitance (C) and potential window (V) according to the equation E = 1/2CV2. Increasing C value and enlarging V value are essential to achieve highperformance SCs and these parameters are depended on the intrinsic properties of the electrode materials and electrolytes [12]. Therefore, designing novel electrode materials for high-performance SCs is vitally significant and full of huge challenges [13–18]. Recently, increasing attention has been paid on transition metal silicates (TMSs) applied to the field of energy storage because of their abundant, low cost and high capacity [19–26]. For example, Liqiang Mai’s group synthesized a sandwich-like structure with copper silicate nanotubes grown on both sides of rGO) and it exhibited high reversible capacity and excellent cycling stability [20]. As the family of TMSs, cobalt silicate hydroxide Co3Si2O5(OH)4 (CoSi) and nickel silicate hydroxide Ni3Si2O5(OH)4 (NiSi) show the phyllosilicate structures formed by tetrahedral silicon (SiO4) and octahedral metal cations (CoO6 or NiO6) [27]. As shown in Scheme 1, Co3Si2O5(OH)4 or Ni3Si2O5(OH)4 has a two-dimensional infinite extension silicate composed of Si-O tetrahedrons. The oxygen on top of the unshared siloxane tetrahedron has a residual negative charge, which combine with the Co2+ or Ni2+ to form Co-O or Ni-O octahedron sheets in the layer [27,28]. Co3Si2O5(OH)4 and Ni3Si2O5(OH)4 have received more and more attention owing to their potential application to batteries [29–35]. However, little literature has been studied their electrochemical performance applied to high-performance SCs [36–39] although their unique structure is according with the design principle of SC: their layer structure and channels can transfer mass fleetly and benefic for ion

2. Results and discussion 2.1. Morphology, composition and structure of 3D CoNiSi/C The synthetic strategy for 3D CoNiSi/C is illuminated in Scheme 1 and the detail experiments is represented in Supporting Information. In the first step, 3D SiO2/C is derived from bamboo leaves using the carbonization process under N2 atmosphere. Both FE-SEM and TEM images (Fig. S1) demonstrate that the SiO2/C frameworks compose of 3D porous structures with the amorphous phase of both SiO2 and C and smooth surface, which facilitates the formation of metal silicates [32,45]. In the second step, the hydrothermal reaction between 3D

Scheme 1. Schematic illustration of the synthetic strategy of 3D CoNiSi/C and layered structure of CoNiSi. 2

Chemical Engineering Journal 375 (2019) 121938

Y. Zhang, et al.

Fig. 1. FE-SEM images of 3D CoNiSi/C-2, inserting a picture of flowers in (d).

SiO2/C and various concentrations of Co2+ and Ni2+ solution is conducted to synthesize 3D CoNiSi/C. In this step, Co2+ and Ni2+ can react with the amorphous SiO2 species in 3D SiO2/C composite to form CoNiSi. As the reaction goes on, the constant consumption of SiO2 species leads to an in-situ grown CoNiSi architectures on the 3D amorphous carbon, as confirmed by FE-SEM images. During the experiments (details in Supporting Information), considering to get the highest capacitance, the influence of the quantity of Co on the electrochemical properties of CoSi/C was first studied and the quantity of Co(OAc)2·4H2O was fixed to 0.0275 g, 0.055 g, 0.0825 g and 0.11 g, and these samples were named as CoSi/C-1, CoSi/C-2, CoSi/C-3 and CoSi/ C-4, respectively. The sample CoSi/C-2 in the recipe showed the best electrochemical performance. Then, to study the influence of Ni on the electrochemical properties of CoNiSi/C, the quantity of Ni(OAc)2·4H2O was fixed to 0.0077 g, 0.0232 g, 0.0385 g and 0.0540 g, and these samples were named as CoNiSi/C-1, CoNiSi/C-2, CoNiSi/C-3 and CoNiSi/C-4, respectively. For comparison, NiSi/C with 0.0232 g of Ni (OAc)2·4H2O was also synthesized. Figs. 1, S2 and S3 respectively show FE-SEM images of the 3D CoNiSi/C-2, CoSi/C-2 and NiSi/C, proving that all samples remain the 3D hierarchical porous structure of SiO2/C. It can be observed from Fig. 1 that CoNiSi architectures with petal-like shapes grow on the 3D amorphous carbon with heterogeneous porosity compared with smooth surface of SiO2/C (Fig. S1). These CoNiSi nanosheets are interconnected with each other to form a 3D flower-like structure (Fig. 1d). As for CoSi/C-2 (Fig. S2) and NiSi/C (Fig. S3), the petal-like CoSi nad NiSi nanosheets also grow on the 3D amorphous carbon as the same as CoNiSi nanosheets. The petal-like structures of CoNiSi is dense than the structures of CoSi and NiSi as the amount of CoSi and NiSi in CoSi/C-2 and NiSi/C is less than that of CoNiSi in CoNiSi/C-2. Fig. S4 shows FESEM images of the 3D CoNiSi/C obtained with various reaction times (3, 6 and 12 h), revealing that all of them inherit the hierarchical porous structure of 3D SiO2/C. When the reaction time is 3 h, only some

sheets or particles on the 3D amorphous carbon (Fig. S4a-b). With the reaction time increasing, more and more sheets are observed and these sheets are interconnected with each other to form a 3D flower-like structure (Figs. S4c-f and 1). After 12 h, the 3D CoNiSi architectures with petal-like shapes on the amorphous carbon are formed. TEM images in Fig. 2 further confirm that the main structure of 3D CoNiSi/C2 inherits the 3D structure of SiO2/C (Fig. S1). CoNiSi nanoparticles are dispersive on the surface of 3D carbon frameworks in agreement with FE-SEM images of 3D CoNiSi/C-2 (Fig. 1). Although the CoNiSi nanosheets can be seen in TEM images (Fig. 2a and b), some irregular CoNiSi nanoparticles also appear owing to the ultrasonication before TEM test. A complete flower-like CoNiSi consisting of nanosheets is occasionally seen (Fig. 2d), in line with the FE-SEM observations. Both large magnification TEM image (Fig. 2c) and HRTEM image (Fig. 2e) reveal the layered structures of CoNiSi, which corresponds with the structure of CoxNi3-xSi2O5(OH)4 as shown in Scheme 1. The CoNiSi possesses a phyllosilicate structure constructed by sheets of tetrahedral silicon (SiO4) and octahedral CoⅡ (NiⅡ) cations (CoO6 or NiO6). This structure provides a clear multichannel for rapid ion transportation [43]. The layered structure of CoNiSi is similar with Co3Si2O5(OH)4 and Ni3Si2O5(OH)4 reported previously [30,31]. The HRTEM image also shows that the carbon in CoNiSi/C-2 is amorphous structure. The interplanar spacing of CoNiSi in the HRTEM image is approximately 0.732 nm, which is in accordance with the (0 0 1) plane (0.726 nm) of Co3Si2O5(OH)4 (JCPDS, No. 21-0872) and the (0 0 2) plane (0.743 nm) of Ni3Si2O5(OH)4 (JCPDS, No. 22-0754) respectively, in agreement with XRD observation (Fig. 3a). The SAED image reveals that the diffraction patterns of the CoNiSi is a little weak. The low crystalline CoNiSi observed from the HRTEM image (Fig. 2e) and SAED image (Fig. 2f) of 3D CoNiSi/C-2 matches the XRD patterns (Fig. 3a) well. The interplanar spacings of CoNiSi in the SAED image are approximately 0.265 nm and 0.154 nm, respectively. These values are assigned to the (2 0 0) and (0 6 0) planes of Co3Si2O5(OH)4 and the (2 0 0) and ( −2 0 8) planes of 3

Chemical Engineering Journal 375 (2019) 121938

Y. Zhang, et al.

Fig. 2. TEM images of 3D CoNiSi/C-2: (a-d) Images with different magnifications, inserting a flower in (d); (e) a HRTEM image; (f) a SAED image.

Fig. 3. XRD patterns (a), FTIR spectra (b) and Raman spectra (c) of SiO2/C and CoNiSi/C-2; (d) Survey XPS spectrum of CoNiSi/C-2. 4

Chemical Engineering Journal 375 (2019) 121938

Y. Zhang, et al.

These structured characteristics are advantageous to better electronic conductivity [20]. XPS was conducted to explore the surface chemical composition of CoNiSi/C-2, as displayed in Fig. 3d and 4. From the survey spectrum (Fig. 3d), the elements C, N, O, Si, Co and Ni can be observed. The C1s spectrum (Fig. 4a) can be resolved into four different bands: CeNeC (287.3 eV), CeSeC (285.3 eV), CeC (284.8 eV) and C]C (284.2 eV) [36]. The N1s peak at around 400 eV (Fig. 4c) can be divided into three peaks: graphitic N (401.5 eV), pyrrolic N (400.4 eV) and pyridinic N (398.3 eV). Both XPS and elemental analysis show the existence of N from biomass and the N atoms replaced with the C atoms can enhance the electronic conductivity of carbon-based materials, resulting in a high conductivity of CoNiSi/C-2, which is desperately needed for electrode materials [48]. Fig. 3c shows the O1s peak (about 532.7 eV) and the signal of O can be ascribed to the O-containing functional groups in CoNiSi and the carbon basement in CoNiSi/C-2. It splits into four peaks, OeH (533.6 eV), O-N (532.8 eV), OeC (532.0 eV) and OeSi (531.0 eV) [36]. From Si2p spectrum (Fig. 4d), it consists of four peaks corresponding to CoeO3Si (104.5 eV), NieO3Si (102.4 eV), CeO3Si (103.3 eV) and OeSieO (104.0 eV), which gives an evidence for the formation of CoNiSi [30]. The appearance of at CeO3Si is related to the strong combination between the amorphous carbon component and CoNiSi, ensuring the structural integrity during the cycling process of charge/discharge, leading to improve the cycle performance of CoNiSi/ C. Furthermore, the presence of an oxygen bridge between the 3D carbon matrix and layered CoNiSi can enhance the charge overlapping at the interface and form a channel for electron transfer during chargedischarge process [37]. Compared with the reported SiO2/C [45], the OeSieO bond decreases while the CoeO3Si and NieO3Si bonds appear in CoNiSi/C-2, suggesting the conversion of SiO2 to CoNiSi. Fig. 4e exhibits the core-level XPS spectrum of Co2p. The peak at 782.3 eV is related to Co2p3/2, and the peak at 798.1 eV is corresponding with Co2p1/2. Besides, two peaks (around 786.5 eV and 804.1 eV) are indexed to two shake-up type peaks of the Co2p3/2 and Co2p1/2 edge. From the XPS spectrum of Ni2p in Fig. 4f, two peak at 874.8 eV and 857.1 eV can be related to Ni2p1/2 and Ni2p3/2. And each peak accompanies with a satellite signal at 880.8 eV and 862.2 eV [38]. The binding energy values of Co2p and Ni2p prove that both Co and Ni elements are in +2 oxidation state in CoNiSi/C. Based on the above characterizations, it is a sure conclusion that 3D CoNiSi/C is successfully synthesized from 3D SiO2/C by an in-situ hydrothermal reaction. The porous structures of SiO2/C and CoNiSi/C-2 were determined by nitrogen adsorption-desorption isotherms, as summarized in Fig. 5 and Table S1. The nitrogen adsorption-desorption isotherms (Fig. 5a) show the combined characteristics of type I and type IV isotherms with H4 hysteresis loops according to IUPAC, which are related to the coexistence of micropores and mesopores. The isothermal of CoNiSi/C-2 exhibits a significant increase in the low pressure, suggesting a remarkable increase of nitrogen uptake and the presence of lots of mesopores. Fig. 5b depicts the pore size distributions of SiO2/C and CoNiSi/C-2 calculated by the BJH method. Their pore size is predominantly between 1.2 nm and 6 nm. CoNiSi/C-2 not only inherits the pores of SiO2/C located on 2.39 nm, but also forms the main pores centered on 3.94 nm. As expected, CoNiSi/C-2 has a higher specific surface area of 377 m2 g−1 and a larger total pore volume of 0.467 cm3 g−1 than those of SiO2/C (325 m2 g−1 and 0.396 cm3 g−1) based on the BET method because of the distribution of 3D flower-like CoNiSi nanosheets on the surface of carbon basement. To sum up, combined with previous FE-SEM images, CoNiSi/C-2 possesses micropores, mesopores and macropores, and these structures can release the stress and strain caused by the volume expansion during the chargedischarge process, which is particularly crucial for materials used as electrodes [20,23,36].

Ni3Si2O5(OH)4, respectively, in agreement with XRD observation (Fig. 3a). The results from the HRTEM and SAED images further prove the successful synthesis of CoNiSi on 3D carbon. XRD patterns of SiO2/C, CoSi/C-1 ~ 4, CoNiSi/C-1 ~ 4 and NiSi/C are shown in Figs. 3a and S4. Amorphous SiO2/C is first derived from bamboo leaves, and the broad peak ranging from 15° to 25° is ascribed to amorphous phase of SiO2 and C in SiO2/C [45]. After the in-situ hydrothermal growth of metal silicates inheriting from SiO2/C, the asobtained CoSi, CoNiSi or NiSi represent similar XRD patterns (Fig. S4). Compared with XRD pattern of SiO2/C, these new XRD peaks are attributed to Co3Si2O5(OH)4 (JCPDS, No. 21-0872) and Ni3Si2O5(OH)4 (JCPDS, No. 22-0754), which matches well with Co3Si2O5(OH)4-, Ni3Si2O5(OH)4- and CoxNi3−xSi2O5(OH)4-based materials reported previously [32,36,37,40,43]. The broad and weak XRD peaks of CoSi, CoNiSi and NiSi as well as some peaks which are not observed from XRD patterns suggest their low crystallinity in the CoSi/C-1 ~ 4, CoNiSi/C-1 ~ 4 and NiSi/C. The above results suggest that metal silicates are successfully generated on the 3D amorphous carbon frameworks. Figs. S5 and S6 depict the EDS spectrum and elemental mapping images of CoNiSi/C-2, respectively. The elements including C, O, Si, Co and Ni are observed and homogeneously dispersed. The ratio of Co/Ni by ICP-AES is 2:1, revealing that the formula of the as-synthesized CoNiSi can be expressed as Co2NiSi2O5(OH)4. The ratio of (Co + Ni)/Si is less than 3/2 (the theoretical ratio in Co2NiSi2O5(OH)4), suggesting that the in-situ formation of CoNiSi mainly uses the SiO2 species on the surface of 3D SiO2/C in line with FE-SEM observations (Figs. 1, S1–S3). The elemental analysis shows 51.62 wt% of C, 2.320 wt% of N and 1.444 wt% of H in the CoNiSi/C. The large amount of C and other elements demonstrate the 3D framework carbon with heteroatom-enriched components [37]. Fig. 3b displays FTIR spectra of SiO2/C and CoNiSi/C-2. The differences between SiO2/C and CoNiSi/C-2 demonstrate the successful formation of (Co, Ni)3Si2O5(OH)4 on 3D carbon. To be specific, the wavenumbers at 3740 and 3632 cm−1 are ascribed to the stretching mode of –OH of (Co, Ni)3Si2O5(OH)4 in CoNiSi/C [30]. In SiO2/C, the wavenumber at 1081 cm−1 corresponds to the asymmetric stretching vibration of Si-O-Si bond, and the wavenumbers at 801 cm−1 and 470 cm−1 are indexed to the symmetrical stretching vibration of Si-O-Si bond and symmetrical stretching vibration of Si-O bond, respectively [37]. After the CoNiSi in-situ growth on SiO2/C, the wavenumbers at 801 and 470 cm−1 disappear, which indicates SiO2 is consumed to form CoNiSi architectures. The strong wavenumber of Si–O–Si at 1081 cm−1 transfers to 1047 cm−1, which is ascribed to the formation of Si–O–Co and Si–O–Ni bonds. The new peaks at 669 and 456 cm−1 are respectively related to the lattice vibration of the Ni–O and Co–O bonds in CoNiSi [36,37]. Besides, the broad wavenumber at 3427 cm−1 is related to the stretching vibration of OH groups of physically adsorbed water molecules. Some small wavenumbers ranging from 1700 to 1300 cm−1 are attributed to the stretching vibration of C–S, C–H, C–N, C–O in the biomass carbon [36]. The Raman spectra of SiO2/C and CoNiSi/C-2 are presented in Fig. 3c. It is obvious that there are two typical peaks, respectively called the D band and G band. The former is situated at 1345 cm−1, which is attributed to the disorder-induced defects of graphitic carbon. The latter is centered at 1594 cm−1, which results from the vibration of sp2–hybridized carbon atoms in rings and chains. These observations verify the existence and amorphous property of carbon in SiO2/C and CoNiSi/C-2 in agreement with XRD result (Fig. 3a). The intensity ratio of D band (ID) and G band (IG) shows the extent of the disorder and the graphitization in the carbon-based materials [46,47]. The ratio value of ID/IG is 0.81 in SiO2/C, while it equals to 0.93 in CoNiSi/C-2. The result indicates there is a large amount of structural disorder in the nickel-cobalt silicate. It is also suggested that the carbon material here is partially graphitized. Moreover, the intensities of peaks of the CoNiSi/C-2 have a sharp decrease, proving that the generation of CoNiSi covers a fraction of the structural defects. 5

Chemical Engineering Journal 375 (2019) 121938

Y. Zhang, et al.

Fig. 4. Core-level XPS spectra of C1s, N1s, O1s, Si2p, Co2p, and Ni2p of CoNiSi/C-2.

2.2. Electrochemical properties of 3D CoNiSi/C electrode The electrochemical performance of 3D CoNiSi/C electrode was studied by CV, GCD and EIS tests using a conventional three-electrode system in 3.0 M KOH electrolyte solution at room temperature. The voltage window of −0.8 ~ 0.6 V was chosen owing to the best electrochemical performance of CoNiSi/C electrode (Fig. S8). Fig. S9 displays the GCD curves of CoSi/C-1 ~ 4, and CoSi/C-2 exhibits the longest charge/discharge time indicating that it shows the best electrochemical performance. Thus, CoNiSi/C-1 ~ 4 were synthesized according to CoSi/C-2. The electrochemical properties of CoNiSi/C-1 ~ 4 were studied by CV and GCD curves, as shown in Figs. 6a, b, S10 and S11. The CV curves of CoNiSi/C-1 ~ 4 at the scan rates from 5 to 100 mV s−1 (Figs. 6a and S10a-c) maintain a similar shape, indicating their outstanding reversibility and rate performance. The good rate capability is ascribed to the hierarchical porosity of CoNiSi/C, which demonstrates fast transport of electrolyte ions in the channels. These CV curves are close to the rectangular shape from −0.8 ~ 0.2 V with a pair of redox peaks from 0.2 to 0.6 V, which is different from pure EDLCs or pure redox capacitors. The electrochemical storage mechanism here is attributed to electric double-layer capacitance of amorphous carbon and redox capacitance of CoNiSi [36,40]. The possible redox reactions are represented as follows:

(Co x Ni3 −x ) IISi2 O5 (OH)4 + 3OH− ↔ (Co x Ni3 − x ) IIISi2 O5 (OH)7 + 3e− The above equation is supported by the XPS spectra of Co2p and Ni2p (Fig. S12), which reveal that both Co and Ni elements are in +3 oxidation state at the full charged state. Fig. S11a summarizes the CV curves of CoNiSi/C-1 ~ 4 at 10 mV s−1 and CoNiSi/C-2 exhibits the best electrochemical performance owing to its largest integral area. The GCD curves of CoNiSi/C-1 ~ 4 at different current densities from 0.5 A g−1 to 10 A g−1 (Figs. 6b and S10d-e) show similar triangular profiles with slight platforms, which are in accordance with the CV curves. These GCD curves are nearly linear without any distinct chargedischarge platforms, suggesting a small internal resistance of the CoNiSi/C electrode system. The good symmetry of GCD curves at different current densities indicates high columbic efficiency. From the GCD curves, CoNiSi/C-2 also displays the best electrochemical

Fig. 5. (a) Nitrogen adsorption-desorption isotherms of SiO2/C and CoNiSi/C-2; (b) Pore size-distribution curves calculated by the BJH method.

6

Chemical Engineering Journal 375 (2019) 121938

Y. Zhang, et al.

Fig. 6. (a) CV curves of CoNiSi/C-2 at different scan rates from 5 mV s−1 to 100 mV s−1; (b) GCD curves of CoNiSi/C-2 at different current densities from 0.5 A g−1 to 10 A g−1; (c) CV curves of SiO2/C, CoSi/C-2, NiSi/C and CoNiSi/C-2 at 10 mV s−1; (d) GCD curves of SiO2/C, CoSi/C-2, NiSi/C and CoNiSi/C-2 at 0.5 A g−1; (e) The relationship between specific capacitance and current density; (f) Cycling performance and coulombic efficiency of CoNiSi/C-2.

and 316 C g−1), respectively. All about results reveal CoNiSi/C-2 has the best electrochemical performance. The specific capacitances of CoNiSi/C-2 reach 226, 165, 87, 50 and 42 F g−1 (316, 231, 120, 70 and 59 C g−1) at the current densities of 0.5, 1, 3, 5 and 10 A g−1, respectively, which is corresponding with the theoretical capacitance (Supporting Information, Fig. S10). As the current densities increase, the capacitances gradually decrease. This phenomenon can be explained by the fact that the internal active sites cannot completely maintain the adsorbed/desorbed charges and redox transitions at rapid scan rates [41]. The high capacitance of CoNiSi/C-2 is owing to its larger surface area and more abundant hierarchical pores (Figs. 1, 2 and 5), which can provide an effective electron percolation path and easy access for electrolyte ion diffuse to the inner of the electrochemically active materials without restricting charge transport [49]. The electrochemical performance of CoNiSi/C-2 achieved in this work is preferable to most of electrode materials based on silicates reported previously (Table 1). Cycling stability is a quite prominent factor for evaluating practicality of electrode materials. Fig. 6f describes the cycling performance and coulombic efficiency of CoNiSi/C-2 by the continuous charge–discharge cycles at 1 A g−1 for 10,000 cycles. The capacitance retention of CoNiSi/C-2 slightly increases with the increasing of cycle numbers and reaches up to about 105% after about 500 cycles. The rise of the capacitance retention with cycles results from the electro-activation process or improved wettability of the CoNiSi/C-2 electrode during the circulating process in agreement with the reported carbonaceous materials [47]. Remarkably, 99% of the capacitance can be retained after 10,000 cycles, and the coulombic efficiency of CoNiSi/C-2 is around 100% at every cycle, suggesting the as-prepared 3D CoNiSi/C can work steadily and safely as a type of supercapacitor material. The light decrease of the capacitance retention of CoNiSi/C-2 electrode is possibly caused by the slight structural collapse during the process of the ions intercalation/deintercalation [38]. The cycle performance is superior to most silicates-based electrodes reported previously (Table 1). To further investigate the kinetics of the as-obtained electrodes, EIS measurements of SiO2/C, CoSi/C-2 and CoNiSi/C-2 were conducted in the frequency ranging from 100 kHz to 0.01 Hz, and the corresponding Nyquist plots are depicted in Fig. S12. These three samples display

performance as depicted in Fig. S11b-c. For instance, the specific capacitance of CoNiSi/C-1 ~ 4 is estimated as 162, 226, 186 and 149 F g−1 at 0.5 A g−1, respectively (Fig. S11b). It is significant to explore the electrochemical mechanism of the electrode, which is a key factor for evaluating its resulting performance. The CV is regarded as a powerful technique to achieve the goal. Taking CoNiSi/C-2 as an example (Fig. 6a), these CV curves exhibit the rectangular shape from −0.8 to 0.2 V with a pair of redox peaks from 0.2 to 0.6 V, which is attributed to electric double-layer capacitance of amorphous carbon and redox capacitance of CoNiSi. In general, the relationship between the measured current (i) of the redox peak and the potential sweep rate (v) follows the power law:

i = av b The b-value can be found from the slope of the log(v)-log(i) plots. When the b = 0.5, the material is battery behavior which is controlled by diffusion. Whereas b is equal or closed to 1, which is the key characteristic of intercalation pseudocapacitive materials [8,18]. Fig. S13 shows the plots of log (i) versus log (v) from 5 to 100 mV s−1 for the redox current peaks of CoNiSi/C-2. The b-values of peak 1 and peak 2 equal to 0.79 and 0.74, respectively, suggesting a fast K+ intercalation process with a surface-controlled pseudocapacitive behavior [8,18]. To further exhibit the electrochemical performance of CoNiSi/C, the electrochemical properties of SiO2/C, CoSi/C-2 and NiSi/C were systematically investigated to draw a comparison with CoNiSi/C-2, as depicted in Figs. 6a and b and S14. The shapes of CV curves at various scan rates from 5 to 100 mV s−1 (Fig. S14a-c) and GCD curves at different current densities from 0.5 A g−1 to 10 A g−1 (Fig. S14d-f) of CoSi/C-2 and NiSi/C are similar with the CV (Fig. 6a) and GCD (Fig. 6b) curves of CoNiSi/C-2 except SiO2/C, suggesting that these samples have the same storage mechanism. The electrochemical storage mechanism of SiO2/C is mainly attributed to electric double-layer capacitance of amorphous carbon. Fig. 6c and d compare the CV curves at 10 mV s−1 and GCD curves at 0.5 A g−1 of SiO2/C, CoSi/C-2, NiSi/C and CoNiSi/C2, respectively, and Fig. 6e summarizes the connection between current density and specific capacities of SiO2/C, CoSi/C-2, NiSi/C and CoNiSi/ C-2. At 0.5 A g−1, the specific capacitances of SiO2/C, CoSi/C-2, NiSi/C and CoNiSi/C-2 measure 106, 131, 123 and 226 F g−1 (148, 183, 172 7

Chemical Engineering Journal 375 (2019) 121938

Y. Zhang, et al.

Table 1 Comparison of the electrochemical performance of CoNiSi/C with the reported silicate-based materials. Silicate-based materials Co3(Si2O5)2(OH)2 (Ni, Co)3Si2O5(OH)4 Co3Si2O5(OH)4 Ni3Si2O5(OH)4 Mesoporous-Li2MnSiO4 Co2.18Ni0.82Si2O5(OH)4 in situ CNT/nanoclay/PANI ex situ CNT/nanoclay/PANI Manganese silicate drapes C/Co3Si2O5(OH)4 Ni3Si2O5(OH)4/RGO Ni3Si2O5(OH)4 spheres MnSiO3 C/Ni3Si2O5(OH)4 C/MnSiOx MnSiO3/MWCNTs MnSiO3/GO C-zinc silicate MnSi hollow sphere CoSi hollow sphere NiSi hollow sphere 3D CoNiS/C

Electrolyte 6M 1M 6M 6M 2M 3M 1M 1M 1M 3M 2M 2M 6M 3M 3M 1M 1M 6M 3M 3M 3M 3M

KOH KOH KOH KOH KOH KOH KCl KCl KOH KOH KOH KOH KOH KOH KOH Na2SO4 Na2SO4 KOH KOH KOH KOH KOH

Potential/V 0.1–0.55 0 ~ 0.5 0 ~ 0.5 0 ~ 0.5 0 ~ 0.55 0 ~ 0.5 0 ~ 0.8 0 ~ 0.8 −0.5 ~ 0.4 −0.05 ~ 0.4 0.2 ~ 0.6 0.2 ~ 0.6 0.2 ~ 0.6 −1 ~ −0.3 −1 ~ −0.3 −0.2 ~ 0.8 −0.2 to 1 −1.0 ~ −0.3 −0.5 ~ 0.2 0 ~ 0.5 0 ~ 0.6 −0.8 to 0.6

Capacitance −1

Capacity −2

237 F g , 5.7 mA cm 144 F g−1, 1 A g−1 570 F g−1, 0.7 A g−1 887 F g−1, 0.7 A g−1 150 F g−1, 0.5 A g−1 981 F g−1, 0.7 A g−1 331 F g−1, 10 mV·s−1 202 F g−1, 10 mV·s−1 283F g−1, 0.5 A g−1 1600 F g−1, 1 A g−1 178.9 F g−1, 1 A g−1 138.4 F·g−1, 1 A·g−1 251 F·g−1, 0.6 A·g−1 132.4 F·g−1, 0.5 A·g−1 162.2 F·g−1, 0.5 A·g−1 236 F g−1, 0.5 A g−1 262.5 F g−1, 0.5 A g−1 450 mF cm−2, 5 mV·s−1 517F g−1, 0.5 A g−1 452.8 F g−1, 0.5 A g−1 66.7 F g−1, 0.5 A g−1 226 F·g−1, 0.5 A·g−1

a

−1

107 C g 72 C g−1 285 C g−1 444 C g−1 83 C g−1 491 C g−1 265 C g−1 162 C g−1 255C g−1 720 C g−1 72 C g−1 55 C g−1 100 C g−1 93 C g−1 114 C g−1 236 C g−1 315 C g−1 315 mC cm−2 362 C g−1 226 C g−1 40 C g−1 316 C g−1

Cycle

Ref.

95%, 150 cycles 99.3%, 10,000 cycles — 96.8%, 2000 cycles 85.7%, 500 cycles 98.9%, 6000 cycles 92%, 2000 cycles 92%, 2000 cycles 74.7%, 1000 cycles 90.9%, 6000 cycles 97.6%, 5000 cycles — — 100%, 10,000 cycles 85%, 10,000 cycles 41%, 1000 cycles 53%, 5000 cycles 83%, 10,000 cycles 34%, 3600 cycles 89%, 10,000 cycles 44%, 5000 cycles 99%, 10,000 cycles

[50] [41] [38] [38] [51] [40] [52] [52] [53] [36] [54] [54] [55] [37] [56] [57] [58] [45] [39] [39] [39] This work

a The capacity (Q) equals to capacitance multiply potential window, for example, as for 3D CoNiS/C in this work, the capacity (Q) = capacitance * potential window = 226 F·g−1 * 1.4 V = 316 C g−1.

electrochemically active sites and a large contact area between electrolyte and electrode for electrochemical reaction [40]. Thus, the CoNiSi/C-2 shows the best electrochemical performance.

similar curves with a straight line in the low-frequency region and a depressed semicircle in the high-frequency region. It is obvious that the growth of silicates on 3D carbon can greatly improve ion diffusion and migration as CoSi/C-2 and CoNiSi/C-2 show the larger slope in the low frequency region [47]. The semicircle diameter represents the chargetransfer resistance at the interface of the electrode/electrolyte [53] and the charge-transfer resistances of CoSi/C-2 (0.60 Ω) and CoNiSi/C-2 (0.56 Ω) are smaller than that of SiO2/C (1.05 Ω), suggesting the enhanced electrical conductivity of the in-situ generated silicates on bamboo leaves derived 3D amorphous carbon. The improved electrical conductivity is owing to that the petal-like metal silicates nanosheets can increase the porous structures and specific area to provide adequate

2.3. Electrochemical performance of 3D CoNiSi/C as HSC device To further explore CoNiSi/C-2 in practical application for SCs, the flexible solid-state CoNiSi/C//Ni(OH)2 HSC device was fabricated, as inserted in Fig. 7c. The synthesis and electrochemical properties of Ni (OH)2 are shown in Supporting Information (Fig. S16). The appropriate operating voltage of the CoNiSi/C//Ni(OH)2 HSC device was selected to be 0 ~ 1.5 V (Fig. 7a). Fig. 7b shows the CV curves at the scan rates

Fig. 7. Electrochemical performance of the CoNiSi/C//Ni(OH)2 HSC device: (a) CV curves at different voltage windows at 10 mV s−1; (b) CV curves at different scan rates; (c) Cycling performance, inserting a schematic configuring of the HSC device; (d) GCD curves at various current densities and (e) the corresponding areal and specific capacitances; (f) Nyquist plots in the frequency ranging from 100 kHz to 0.01 Hz. 8

Chemical Engineering Journal 375 (2019) 121938

Y. Zhang, et al.

from 5 to 100 mV s−1 and all CV curves present the cap-like shape, suggesting the mixed behavior (EDLC and redox mechanism of CoNiSi/ C and battery-type of Ni(OH)2) of the device. As the scan rate gradually increases, shape of curves without much change and the current responses of the HSC device increase correspondingly, indicating a good capacitive behavior with outstanding rate performance. Fig. 7d describes the GCD curves of the CoNiSi/C//Ni(OH)2 HSC device at various current densities from 2 to 10 mA cm−2, and the corresponding areal and mass capacitances are painted in Fig. 7e. At the current densities of 2, 4, 6, 8 and 10 mA cm−2, the areal capacitances of the CoNiSi/C//Ni (OH)2 HSC device reach 254, 235, 209, 192 and 176 mF cm−2 (381, 353, 313, 288 and 264 mC cm−2), respectively, and the corresponding mass capacitances according to the total mass of the active materials on the two electrodes measure 64, 59, 53, 48 and 44 F g−1, respectively. The maximum capacitance of the CoNiSi/C//Ni(OH)2 HSC device achieved in this work is superior to most of SC devices based on silicatebased materials or some vanadium-based materials, as listed in Table S2, for example, Co2.18Ni0.82Si2O5(OH)4//Graphene (194.3 mF cm−2, 0.5 mA cm−2) [40], C/Co3Si2O5(OH)4//AC (352 mF cm−2, 1 mA cm−2) [36], C-zinc silicate//AC (194 mF cm−2, 2 mA cm−2) [45], VO2(B) hollow spheres SSC (246 mF cm−2, 1 mA cm−2) [59], VN@C SSC (65 mF cm−2, 5 mV·s−1) [60], etc. The kinetics of the CoNiSi/C//Ni (OH)2 HSC device are investigated by EIS tests. As shown in Fig. 7f, obviously, it exhibits minor displacement of the Nyquist plot on the X axis (~4.1 Ω) illustrates the low resistance due to the 3D biomass-inherited carbon and petal-like CoNiSi nanosheets, which facilitate the fast charge propagation and help to shorten the pathway for ion and electron transfer [61]. Excellent long cycle life is a significant index for storage energy in actual applications. The cycling stability of the CoNiSi/C//Ni(OH)2 HSC device tested at 1 A g−1 is shown in Fig. 7c. Remarkably, it presents excellent cycling stability with high capacitance retention of 82% after 10,000 cycles. Power density and energy density are equally vital to evaluate

electrical performance of SCs. Fig. 8a and b and Table S2 compare the value of the CoNiSi/C//Ni(OH)2 HSC device with the typical data of silicate-based SC devices or some other SC devices reported in the previous literatures [17,45,47,59,60]. Energy densities decrease but power densities increase also suggesting that CoNiSi/C-2 is a hopeful electrode material for high-efficiency SCs [62]. The energy densities of the CoNiSi/C//Ni(OH)2 HSC device can reach 0.793 Wh m−2 (0.696 mWh cm−3, 20.0 Wh kg−1) at the power density of 3.75 W m−2 (3.29 mW cm−3, 94.5 W kg−1) and 0.55 Wh m−2 (0.482 mWh cm−3, 13.9 Wh kg−1) at the power density of 18.75 W m−2 (16.45 mW cm−3, 472.3 W kg−1) with an increasing current density from 2 to 10 mA cm−2. These performance values are higher or comparable than the reported SC devices based on silicate-based materials or some vanadium-based materials (Fig. 8b and Table S2), for instance, NiSi//AC (0.93 mWh cm−3, 3.78 Wh kg−1) [39], Co2.18Ni0.82Si2O5(OH)4 architectures//Graphene (0.496 mWh cm−3) [40], C/CoNi3O4//AC −1 (19.2 Wh kg ) [63], NiO//carbon (11 Wh kg−1) [64], AC//VO2(A)@C (0.714 Wh·m−2 at 3.75 W·m−2) [47], VO2(B) hollow spheres SSC device (669 mWh·m−2 at 3.5 W·m−2) [59], VO2(B) solid spheres SSC device (333 mWh·m−2 at 3.5 W·m−2) [59], etc. Fig. 8c shows the CV curves at 20 mV s−1 under three bending states to evaluate the flexibility and mechanical stability of the CoNiSi/C//Ni(OH)2 HSC device. There is little evident change in these CV curves, demonstrating the super flexibility and stability of the CoNiSi/C//Ni(OH)2 HSC device. Fig. S17 shows the cycling stability of flexibility by bending the CoNiSi/C//Ni (OH)2 HSC device for 10, 50, 100 and 500 cycles. And these CV curves are similar, suggesting that the cycling stability of flexibility of the device is good. On account of the above electrochemical performance, three concatenated devices were used to light a red LED (Fig. 8d and Movie S1). It can last for more than 2 min. Thus, it is possible to apply CoNiSi/C-2 in energy supply and it is supposed that the fabricated HSC device using CoNiSi/C-2 and Ni(OH)2 can be an excellent SC.

Fig. 8. Electrochemical performance of the CoNiSi/C//Ni(OH)2 HSC device: (a, b) Ragone plots of the assembled device and comparison with previous values; (c) The flexible properties of the HSC device; (d) Photograph of lighting a red LED powered by two HSC devices in series. 9

Chemical Engineering Journal 375 (2019) 121938

Y. Zhang, et al.

3. Conclusion

[12] C. Zhong, Y. Deng, W. Hu, J. Qiao, L. Zhang, J. Zhang, A review of electrolyte materials and compositions for electrochemical supercapacitors, Chem. Soc. Rev. 44 (2015) 7484–7539. [13] Q. Wei, F. Xiong, S. Tan, L. Huang, E.H. Lan, B. Dunn, L. Mai, Porous one-dimensional nanomaterials: design, fabrication and applications in electrochemical energy storage, Adv. Mater. 29 (2017) 1602300. [14] M. Chen, Y. Zhang, Y. Liu, Q. Wang, J. Zheng, C. Meng, Three-dimensional network of vanadium oxyhydroxide nanowires hybridize with carbonaceous materials with enhanced electrochemical performance for supercapacitor, ACS Appl. Energy Mater. 1 (2018) 5527–5538. [15] L. Zhou, Z. Zhuang, H. Zhao, M. Lin, D. Zhao, L. Mai, Intricate hollow structures: controlled synthesis and applications in energy storage and conversion, Adv. Mater. 29 (2017). [16] J. Zheng, Y. Zhang, T. Hu, T. Lv, C. Meng, New strategy for the morphology-controlled synthesis of V2O5 microcrystals with enhanced capacitance as battery-type supercapacitor electrodes, Cryst. Growth Des. 18 (2018) 5365–5376. [17] Y. Zhang, X. Jing, Q. Wang, J. Zheng, H. Jiang, C. Meng, Three-dimensional porous V2O5 hierarchical spheres as a battery-type electrode for a hybrid supercapacitor with excellent charge storage performance, Dalton Trans. 46 (2017) 15048–15058. [18] T. Hu, Y. Liu, Y. Zhang, M. Chen, J. Zheng, C. Meng, Self-assembled HVxOy nanobelts/rGO nanocomposite with an ultrahigh specific capacitance: synthesis and promising applications in supercapacitors, Appl. Surf. Sci. 481 (2019) 59–68. [19] F. Liu, Q. Xiao, H.B. Wu, L. Shen, D. Xu, M. Cai, Y. Lu, Fabrication of hybrid silicate coatings by a simple vapor deposition method for lithium metal anodes, Adv. Energy Mater. 8 (2018) 1701744. [20] C. Tang, J. Zhu, X. Wei, L. He, K. Zhao, C. Xu, L. Zhou, B. Wang, J. Sheng, L. Mai, Copper silicate nanotubes anchored on reduced graphene oxide for long-life lithium-ion battery, Energy Storage Mater. 7 (2017) 152–156. [21] S.-H. Yu, B. Quan, A. Jin, K.-S. Lee, S.H. Kang, K. Kang, Y. Piao, Y.-E. Sung, Hollow nanostructured metal silicates with tunable properties for lithium ion battery anodes, ACS Appl. Mater. Interfaces 7 (2015) 25725–25732. [22] X. Wei, C. Tang, X. Wang, L. Zhou, Q. Wei, M. Yan, J. Sheng, P. Hu, B. Wang, L. Mai, Copper silicate hydrate hollow spheres constructed by nanotubes encapsulated in reduced graphene oxide as long-life lithium-ion battery anode, ACS Appl. Mater. Interfaces 7 (2015) 26572–26578. [23] J. Zhu, C. Tang, Z. Zhuang, C. Shi, N. Li, L. Zhou, L. Mai, Porous and low-crystalline manganese silicate hollow spheres wired by graphene oxide for high-performance lithium and sodium storage, ACS Appl. Mater. Interfaces 9 (2017) 24584–24590. [24] J. Qu, Y. Yan, Y.-X. Yin, Y.-G. Guo, W.-G. Song, Improving the Li-ion storage performance of layered zinc silicate through the interlayer carbon and reduced graphene oxide networks, ACS Appl. Mater. Interfaces 5 (2013) 5777–5782. [25] Q. Dong, J. Yang, M. Wu, X. Zhou, Y. Zhang, W. Wang, W. Si, W. Huang, X. Dong, Template-free synthesis of cobalt silicate nanoparticles decorated nanosheets for high performance lithium ion batteries, ACS Sustain. Chem. Eng. 6 (2018) 15591–15597. [26] Y. Cheng, Y. Zhang, C. Meng, Template fabrication of amorphous Co2SiO4 nanobelts/graphene oxide composites with enhanced electrochemical performances for hybrid supercapacitors, ACS Appl. Energy Mater. (2019). [27] F. Alvarez-Ramírez, J.A. Toledo-Antonio, C. Angeles-Chavez, J.H. Guerrero-Abreo, E. López-Salinas, Complete structural characterization of Ni3Si2O5(OH)4 nanotubes: theoretical and experimental comparison, J. Phys. Chem. C 115 (2011) 11442–11446. [28] R.D. White, D.V. Bavykin, F.C. Walsh, Morphological control of synthetic Ni3Si2O5(OH)4 nanotubes in an alkaline hydrothermal environment, J. Mater. Chem. A 1 (2013) 548–556. [29] Y. Yang, Q. Liang, J. Li, Y. Zhuang, Y. He, B. Bai, X. Wang, Ni3Si2O5(OH)4 multiwalled nanotubes with tunable magnetic properties and their application as anode materials for lithium batteries, Nano Res. 4 (2011) 882–890. [30] C.-X. Gui, S.-M. Hao, Y. Liu, J. Qu, C. Yang, Y. Yu, Q.-Q. Wang, Z.-Z. Yu, Carbon nanotube@ layered nickel silicate coaxial nanocables as excellent anode materials for lithium and sodium storage, J. Mater. Chem. A 3 (2015) 16551–16559. [31] R. Jin, Y. Yang, Y. Li, X. Liu, Y. Xing, S. Song, Z. Shi, Sandwich-structured graphenenickel silicate–nickel ternary composites as superior anode materials for lithium-ion batteries, Chem.-Eur. J. 21 (2015) 9014–9017. [32] C. Tang, J. Sheng, C. Xu, S.M.B. Khajehbashi, X. Wang, P. Hu, X. Wei, Q. Wei, L. Zhou, L. Mai, Facile synthesis of reduced graphene oxide wrapped nickel silicate hierarchical hollow spheres for long-life lithium-ion batteries, J. Mater. Chem. A 3 (2015) 19427–19432. [33] Q.-Q. Wang, J. Qu, Y. Liu, C.-X. Gui, S.-M. Hao, Y. Yu, Z.-Z. Yu, Growth of nickel silicate nanoplates on reduced graphene oxide as layered nanocomposites for highly reversible lithium storage, Nanoscale 7 (2015) 16805–16811. [34] X. Chen, Y. Huang, K. Zhang, Cobalt nanofibers coated with layered nickel silicate coaxial core-shell composites as excellent anode materials for lithium ion batteries, J. Colloid Interface Sci. 513 (2018) 788–796. [35] X.-Q. Zhang, W.-C. Li, B. He, D. Yan, S. Xu, Y. Cao, A.-H. Lu, Ultrathin phyllosilicate nanosheets as anode materials with superior rate performance for lithium ion batteries, J. Mater. Chem. A 6 (2018) 1397–1402. [36] X. Li, S. Ding, X. Xiao, J. Shao, J. Wei, H. Pang, Y. Yu, N, S co-doped 3D mesoporous carbon-Co3Si2O5(OH)4 architectures for high-performance flexible pseudo-solidstate supercapacitors, J. Mater. Chem. A 5 (2017) 12774–12781. [37] Q. Wang, Y. Zhang, H. Jiang, T. Hu, C. Meng, In situ generated Ni3Si2O5(OH)4 on mesoporous heteroatom-enriched carbon derived from natural bamboo leaves for high-performance supercapacitors, ACS Appl. Energy Mater. 1 (2018) 3396–3409. [38] J. Zhao, Y. Zhang, T. Wang, P. Li, C. Wei, H. Pang, Reed leaves as a sustainable silica source for 3D mesoporous nickel (Cobalt) silicate architectures assembled into ultrathin nanoflakes for high-performance supercapacitors, Adv. Mater. Interfaces 2

In summary, bamboo leaves-derived 3D hierarchical CoNiSi/C architectures have been prepared by an in-situ hydrothermal route, which is convenient and environment-friendly in terms of raw materials and preparation method. The as-prepared CoNiSi/C shows abundant hierarchical pores, high specific surface area and remarkable electrochemical performance. The CoNiSi/C single electrode exhibits a promising capacitance of 226 F g−1 (316 C g−1) at 0.5 A g−1 in the voltage window of −0.8 ~ 0.6 V, which is superior to the specific capacitances of SiO2/C (106 F g−1), CoSi/C (131 F g−1), NiSi/C (123 F g−1) and even the reported values of silicates-based materials, and excellent capacitance retention with 99% after 10,000 cycles. The CoNiSi/C//Ni(OH)2 HSC device achieves the excellent electrochemical performance with the capacitance of 254 mF cm−2 (64 F g−1) at 2 mA cm−2, energy density of 0.793 Wh m−2 (20.0 Wh kg−1) at 3.75 W m−2 (94.5 W kg−1), high cycle stability with 82% after 10,000 cycles. This work not only demonstrates that the 3D CoNiSi/C architectures can be regarded as a hopeful and remarkable material for SCs with high performance, but also provides a feasible strategy to prepare binary metal silicate/biomass-inherited carbon composites for recycling biomass rich in carbon and silicon to be applied in energy storages. Acknowledgements This work was partially supported by the National Natural Science Foundation of China (Grant Nos. 21601026, 21771030), Fundamental Research Funds for the Central Universities (DUT18RC(6)008) and the China Sponsorship Council (201806065025). Declaration of Competing Interest There are no conflicts of interest to declare. Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.cej.2019.121938. References [1] P. Yu, Y. Zeng, H. Zhang, M. Yu, Y. Tong, X. Lu, Flexible Zn-ion batteries: recent progresses and challenges, Small 15 (2019) 1804760. [2] M.-S. Balogun, Y. Huang, W. Qiu, H. Yang, H. Ji, Y. Tong, Updates on the development of nanostructured transition metal nitrides for electrochemical energy storage and water splitting, Mater. Today 20 (2017) 425–451. [3] H. Yalan, Z. Yinxiang, Y. Minghao, L. Peng, T. Yexiang, C. Faliang, L. Xihong, Recent smart methods for achieving high-energy asymmetric supercapacitors, Small Methods 2 (2018) 1700230. [4] Z.-H. Huang, Y. Song, X.-X. Liu, Boosting operating voltage of vanadium oxidebased symmetric aqueous supercapacitor to 2 V, Chem. Eng. J. 358 (2019) 1529–1538. [5] P. Simon, Y. Gogotsi, Materials for electrochemical capacitors, Nat. Mater. 7 (2008) 845. [6] S. Zheng, X. Li, B. Yan, Q. Hu, Y. Xu, X. Xiao, H. Xue, H. Pang, Transition-metal (Fe Co, Ni) based metal-organic frameworks for electrochemical energy storage, Adv. Energy Mater. 7 (2017) 1602733. [7] B. Li, P. Gu, Y. Feng, G. Zhang, K. Huang, H. Xue, H. Pang, Ultrathin nickel-cobalt phosphate 2D nanosheets for electrochemical energy storage under aqueous/solidstate electrolyte, Adv. Funct. Mater. 27 (2017) 1605784. [8] Y. Zhang, M. Chen, T. Hu, C. Meng, 3D interlaced networks of VO(OH)2 nanoflakes wrapped with graphene oxide nanosheets as electrodes for energy storage devices, ACS Appl. Nano Mater. 2 (2019) 2934–2945. [9] Y. Wang, Y. Song, Y. Xia, Electrochemical capacitors: mechanism, materials, systems, characterization and applications, Chem. Soc. Rev. 45 (2016) 5925–5950. [10] Y. Zhang, J. Zheng, Q. Wang, S. Zhang, T. Hu, C. Meng, One-step hydrothermal preparation of (NH4)2V3O8/carbon composites and conversion to porous V2O5 nanoparticles as supercapacitor electrode with excellent pseudocapacitive capability, Appl. Surf. Sci. 423 (2017) 728–742. [11] T. Hu, Y. Liu, Y. Zhang, M. Chen, J. Zheng, J. Tang, C. Meng, 3D hierarchical porous V3O7·H2O nanobelts/CNT/reduced graphene oxide integrated composite with synergistic effect for supercapacitors with high capacitance and long cycling life, J. Colloid Interface Sci. 531 (2018) 382–393.

10

Chemical Engineering Journal 375 (2019) 121938

Y. Zhang, et al.

25156–25163. [52] R. Oraon, A. De Adhikari, S.K. Tiwari, G.C. Nayak, Enhanced specific capacitance of self-assembled three-dimensional carbon nanotube/layered silicate/polyaniline hybrid sandwiched nanocomposite for supercapacitor applications, ACS Sustain. Chem. Eng. 4 (2016) 1392–1403. [53] H.-Y. Wang, Y.-Y. Wang, X. Bai, H. Yang, J.-P. Han, N. Lun, Y.-X. Qi, Y.-J. Bai, Manganese silicate drapes as a novel electrode material for supercapacitors, RSC Adv. 6 (2016) 105771–105779. [54] Y. Zhang, W. Zhou, H. Yu, T. Feng, Y. Pu, H. Liu, W. Xiao, L. Tian, Self-templated synthesis of nickel silicate hydroxide/reduced graphene oxide composite hollow microspheres as highly stable supercapacitor electrode material, Nanoscale Res. Lett. 12 (2017) 325. [55] C. Tian, S. Zhao, Q. Lu, Self-templated synthesis of mesoporous manganese silicates as an electrode material for supercapacitor, Ceram. Inter. 44 (2018) 17007–17012. [56] Q. Wang, Y. Zhang, H. Jiang, C. Meng, In-situ grown manganese silicate from biomass-derived heteroatom-doped porous carbon for supercapacitors with high performance, J. Colloids Interface Sci. 534 (2019) 142–155. [57] Q. Wang, Y. Zhang, S. Jia, Y. Han, J. Xu, F. Li, C. Meng, Amorphous manganese silicate anchored on multiwalled carbon nanotubes with enhanced electrochemical properties for high performance supercapacitors, Colloids Surf. A-Physicochem. Eng. Asp. 548 (2018) 158–171. [58] Y. Cheng, Y. Zhang, Q. Wang, C. Meng, Synthesis of amorphous MnSiO3/graphene oxide with excellent electrochemical performance as supercapacitor electrode, Colloids Surf. A-Physicochem. Eng. Asp. 562 (2019) 93–100. [59] Y. Zhang, X. Jing, Y. Cheng, T. Hu, M. Changgong, Controlled synthesis of 3D porous VO2(B) hierarchical spheres with different interiors for energy storage, Inorg. Chem. Front. 5 (2018) 2798–2810. [60] Y. Zhang, J. Zheng, X. Jing, C. Meng, A strategy for the synthesis of VN@C and VC@C core-shell composites with hierarchically porous structures and large specific surface area for high performance symmetric supercapacitors, Dalton Trans. 47 (2018) 8052–8062. [61] X. Zhang, H. Zhang, Z. Lin, M. Yu, X. Lu, Y. Tong, Recent advances and challenges of stretchable supercapacitors based on carbon materials, Sci. China Mater. 59 (2016) 475–494. [62] Y. Liu, Z. Shi, Y. Gao, W. An, Z. Cao, J. Liu, Biomass-swelling assisted synthesis of hierarchical porous carbon fibers for supercapacitor electrodes, ACS Appl. Mater. Interfaces 8 (2016) 28283–28290. [63] J. Zhu, J. Jiang, Z. Sun, J. Luo, Z. Fan, X. Huang, H. Zhang, T. Yu, 3D carbon/cobaltnickel mixed-oxide hybrid nanostructured arrays for asymmetric supercapacitors, Small 10 (2014) 2937–2945. [64] D.-W. Wang, F. Li, H.-M. Cheng, Hierarchical porous nickel oxide and carbon as electrode materials for asymmetric supercapacitor, J. Power Sources 185 (2008) 1563–1568.

(2015) 1400377. [39] Q. Wang, Y. Zhang, H. Jiang, X. Li, Y. Cheng, C. Meng, Designed mesoporous hollow sphere architecture metal (Mn Co, Ni) silicate: a potential electrode material for flexible all solid-state asymmetric supercapacitor, Chem. Eng. J. 362 (2019) 818–829. [40] J. Zhao, M. Zheng, Z. Run, J. Xia, M. Sun, H. Pang, 1D Co2.18Ni0.82Si2O5(OH)4 architectures assembled by ultrathin nanoflakes for high-performance flexible solidstate asymmetric supercapacitors, J. Power Sources 285 (2015) 385–392. [41] Q. Rong, L.-L. Long, X. Zhang, Y.-X. Huang, H.-Q. Yu, Layered cobalt nickel silicate hollow spheres as a highly-stable supercapacitor material, Appl. Energy 153 (2015) 63–69. [42] C. Qiu, L. Ai, J. Jiang, Layered phosphate-incorporated nickel-cobalt hydrosilicates for highly efficient oxygen evolution electrocatalysis, ACS Sustain. Chem. Eng. 6 (2018) 4492–4498. [43] C. Qiu, J. Jiang, L. Ai, When layered nickel-cobalt silicate hydroxide nanosheets meet carbon nanotubes: a synergetic coaxial nanocable structure for enhanced electrocatalytic water oxidation, ACS Appl. Mater. Interfaces 8 (2016) 945–951. [44] Z. Li, J. Yang, D.A. Agyeman, M. Park, W. Tamakloe, Y. Yamauchi, Y.-M. Kang, CNT@Ni@Ni–Co silicate core–shell nanocomposite: a synergistic triple-coaxial catalyst for enhancing catalytic activity and controlling side products for Li–O2 batteries, J. Mater. Chem. A 6 (2018) 10447–10455. [45] Y. Zhang, H. Jiang, Q. Wang, C. Meng, In-situ hydrothermal growth of Zn4Si2O7(OH)2·H2O anchored on 3D N, S-enriched carbon derived from plant biomass for flexible solid-state asymmetrical supercapacitors, Chem. Eng. J. 352 (2018) 519–529. [46] Y. Zhang, M. Fan, X. Liu, C. Huang, H. Li, Beltlike V2O3@C core–shell-structured composite: design, preparation, characterization, phase transition, and improvement of electrochemical properties of V2O3, Eur. J. Inorg. Chem. 2012 (2012) 1650–1659. [47] J. Zheng, Y. Zhang, Q. Wang, H. Jiang, Y. Liu, T. Lv, C. Meng, Hydrothermal encapsulation of VO2(A) nanorods in amorphous carbon by carbonization of glucose for energy storage devices, Dalton Trans. 47 (2018) 452–464. [48] Y. Zhang, H. Jiang, Q. Wang, J. Zheng, C. Meng, Kelp-derived three-dimensional hierarchical porous N, O-doped carbon for flexible solid-state symmetrical supercapacitors with excellent performance, Appl. Surf. Sci. 447 (2018) 876–885. [49] F. Wang, Y. Zheng, J. Qiu, S. Liu, Y. Tong, F. Zhu, G. Ouyang, Graphene-based metal and nitrogen-doped carbon composites as adsorbents for highly sensitive solid phase microextraction of polycyclic aromatic hydrocarbons, Nanoscale 10 (2018) 10073–10078. [50] G.-Q. Zhang, Y.-Q. Zhao, F. Tao, H.-L. Li, Electrochemical characteristics and impedance spectroscopy studies of nano-cobalt silicate hydroxide for supercapacitor, J. Power Sources 161 (2006) 723–729. [51] P. Chaturvedi, A. Kumar, A. Sil, Y. Sharma, Cost effective urea combustion derived mesoporous-Li2MnSiO4 as a novel material for supercapacitors, RSC Adv. 5 (2015)

11