Nitrogen-doped graphene nanosheets supported assembled Pd nanoflowers for efficient ethanol electrooxidation

Journal Pre-proof Nitrogen-doped graphene nanosheets supported assembled Pd nanoflowers for efficient ethanol electrooxidation Ying Wang, Liujun Jin, Caiqin Wang, Yukou Du

PII:

S0927-7757(19)31252-X

DOI:

https://doi.org/10.1016/j.colsurfa.2019.124257

Reference:

COLSUA 124257

To appear in:

Colloids and Surfaces A: Physicochemical and Engineering Aspects

Received Date:

31 May 2019

Revised Date:

6 August 2019

Accepted Date:

19 November 2019

Please cite this article as: Wang Y, Jin L, Wang C, Du Y, Nitrogen-doped graphene nanosheets supported assembled Pd nanoflowers for efficient ethanol electrooxidation, Colloids and Surfaces A: Physicochemical and Engineering Aspects (2019), doi: https://doi.org/10.1016/j.colsurfa.2019.124257

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Nitrogen-doped graphene nanosheets supported assembled Pd nanoflowers for efficient ethanol electrooxidation Ying Wang a, Liujun Jin c, Caiqin Wang b*, Yukou Du c*

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Department of Pharmacy, Jiangsu Agri-animal Husbandry Vocational College,

Taizhou, 225300, China b

College of Science & Institute of Materials Physics and Chemistry, Nanjing Forestry

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University, Nanjing 210037, P. R. China.

College of Chemistry, Chemical Engineering and Materials Science, Soochow

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University, Suzhou 215123, PR China

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E-mail: [email protected] (C. Wang), [email protected] (Y. Du).

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Graphical Abstract

Abstract The electrooxidation of ethanol to convert chemical energy into electrical energy is significant for alleviating the energy crisis and environmental pollution but still challenging because of the lack of highly efficient and low-cost catalysts. Herein, we report the design and fabrication of an advanced nanocatalyst constructed by uniformly distributing 3D palladium nanoflowers (NFs) on the surface of

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nitrogen-doped graphene (NG) support surface. Impressively, taking advantages of the morphological and structural advantages, the as-obtained Pd NFs/NG with high surface areas can display greatly improved electrocatalytic activity for ethanol

oxidation reaction (EOR) in alkaline media. More importantly, the introduction of NG

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support renders this composite high conductivity and fast electron transport, resulting in the large promotion of electrocatalytic activity and stability. This work provides

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facile synthetic concept to build multi-dimensional composite catalysts with

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synergetic enhancement effects for wide electrocatalytic reactions.

Keywords：Nitrogen-doped graphene; Pd nanoflowers; Nanosheets; Ethanol

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electrooxidation

1. Introduction

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The extensive consumption of exhausted fossil fuels and increasingly serious environmental pollution problems motivated a large number of researchers to explore

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renewable energy [1-3]. Direct fuel cells, especially direct ethanol fuel cells (DEFCs), have attracted scientific and industrial attention as the green and sustainable energy conversion devices [4]. This is due to their tremendous advantages, such as convenient storage, high energy density, and low pollution emissions [5-7]. Despite all these, to realize the wide practical application of DEFCs still face lots of obstacles, and one of the biggest challenges is the lack of highly efficient catalysts for boost the liquid fuel electrooxidation reaction [8, 9]. As the central part of fuel cells,

electrocatalyst played a critical role in determining their properties [10-11]. Pt and Pt-based nanpcatalysts have been widely used as the anode electrode materials in DEFCs because of their high electrocatalytic activity [12]. Unfortunately, the relatively high cost and natural scarcity greatly limited their wide application, thus impeding the commercial application of DEFCs [13]. Therefore, it is crucial to design and develop appropriate electrode materials with low cost to replace Pt as efficient electrocatalysts toward EOR. Recently, Pd is regarded as a promising catalyst system for EOR given its

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potential to substitute Pt due to its high electrocatalytic activity [14]. However, monometallic Pd with unmodified electronic structure is difficult to engineer with high electrocatalytic performance, which also can’t meet the high requirement for

practical applications [15, 16]. Currently, rationally designing the surface structure of

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catalysts provides new opportunity for preparing desirable electrocatalysts since the

electrocatalytic reaction is a surface-sensing reaction [17-19]. Generally speaking, a

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catalyst with high surface active areas, abundant defects and steps used to display relatively higher catalytic activity. This is due to the sufficient contact between

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surface active sites and small liquid fuel during the electrooxidation reaction [20]. More recently, a variety of catalysts with unique morphologies have been designed for

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enhance the electrocatalytic performance of catalysts. The 3D nanofower structure that assembled by 2D nanosheets has attracted tremendous attention, which not only facilitates the mass/electron transport, but also maximizes the utilization efficiency

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[21-23]. Although some 3D flower-like Pd nanostructures have been developed as catalysts for electrooxidation reaction, their unsatisfactory electrocatalytic

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performance also can’t meet the practical application of fuel cells due to their limited electrical conductivity and serious aggregation. In addition to the rational morphology design, introducing appropriate catalyst

support is also another efficient route to enhance their electrocatalytic performance. This is because the introduced catalyst supports can not only enhance the electrical conductivity, but also provide more anchoring sites for metal nanoparticles to improve the electrochemical surface areas, leading to the excellent electrocatalytic

performance [24, 25]. In recent years, owing to the high surface area and electrical conductivity, carbon black (Vulcan XC-72R) has been widely used as the catalyst support [26]. However, it is unstable at high potentials, leading to the sintering and agglomeration of metal nanoparticles. Apart from the carbon black, nitrogen-doped graphene (NG) was deemed as promising catalyst support for fuel cell reactions due to high surface area and electron mobility [27]. Moreover, the strengthened combination between metal nanoparticles and NG also contributed to the greatly enhanced long-term stability of catalysts [28].

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Based on the above considerations, we herein reported the design and preparation of an advanced catalyst by dispersing 3D Pd NFs on the surface of NG support. The Pd NFs/NG catalyst with high surface areas, high mechanical stability, and good electrical conductivity displayed large promotion in electrocatalytic activity and

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stability for EOR, showing bright promise for practical application in fuel cells and

2. Experimental section 2.1 Synthesis of 3D Pd NFs catalysts

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beyond.

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First, 10.0 mg of Na2PdCl4, 30.0 mg of W(CO)6, 2.0 mL of acetic acid, and 8.0 mL of N, N-Dimethylformamide (DMF) were added into a vial (volume: 35 mL). After that,

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the mixture was ultrasonicated for around 5 min and then heated at 140 °C for 2 h in an oil bath. The products were washed with water and ethanol and dired at 70 °C overnight.

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2.2 Synthesis of Pd NFs/NG composite 2 mg of previously prepared Pd NFs were added to a vial containing 10 mL of NG

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solution (8 mg/mL). Then, the mixture was then sonicated for another 1 h to disperse uniformly the 3D Pd NFs on the surface of NG. 2.3 Synthesis of Pd NFs/C composite For comparison, we have also prepared the Pd NFs/C composite. The synthetic procedure is similar to that of Pd NFs/NG composite just changing the 8 mg of NG into 8 mg of carbon black (Vulcan XC-72R) while keeping other reaction conditions unchanged.

2.4 Characterizations The morphologies of the samples were analyzed by transmission electron microscope (TEM, Hitachi, HT7700) at 120 kV. X-ray photoelectron spectroscopy spectra (XPS) spectra of samples were obtained through a Thermo Scientific ESCALAB 250 XI X-ray photoelectron spectrometer. The structures of the samples were determined by high-resolution TEM (HRTEM, FEI Tecnai F20 microscope). 2.5 Electrochemical measurements The EOR electrochemical measurements for the catalysts were conducted in a

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CHI760e electrochemical workstation equipped with a three-electrode system. The Pt wire and the Ag/AgCl electrode were employed as counter and reference electrode, respectively. The glass carbon electrode (GCE) that loaded with catalyst inks (Pd

loading: 4 µg) was selected as the working electrode. The cyclic voltammetry (CV)

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chronoamperometry (CA) were conducted in alkaline media. The electrochemical impedance spectroscopy (EIS) was also performed to evaluate the charge transfer

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capability of catalysts.

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3. Results and discussion

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Fig.1 Scheme for the preparation of Pd NFs/NG composites. As illustrated by Fig.1, the NG supported 3D Pd NFs composites were prepared

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according to a robust two-step method, where the 3D Pd NFs were first prepared via a facile wet-chemical method and then deposited on the surface of NG support by ultrasound. In order to analyze the morphologies of the as-obtained Pd nanomaterials, the HAADF-STEM images were obtained. From Fig.2a and b, the newly generated Pd nanomaterials showed the unique 3D NF structure, which was assembled by many ultrathin 2D nanosheets, confirming the successful fabrication of 3D flower-like Pd nanocatalysts. The detailed morphological information of 3D Pd NFs was also

thoroughly investigated by TEM. Fig.2c also showed the 2D Pd nanosheet-constructed 3D flower-like structure. A detailed observation of Fig.2d showed that the surface of ultrathin 2D nanosheets was rough, which was conducive to providing more active sites for reactants. The crystalline nature of this 3D Pd NFs was unveiled by HRTEM (Fig.2e), where a clear d-spacing of 0.22 nm was

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well-matched to the (111) facet of face-centered cubic (fcc) Pd [29].

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The composites were synthesized by depositing the 3D Pd NFs on the surface of NG support by ultrasound, and the composites were also investigated by TEM. As shown in Fig.3a and b, the resulting 3D Pd NFs dispersed uniformly on the surface of NG, demonstrating the formation of Pd NFs/NG. The NG with large support areas can improve conductivity and mass-transfer efficiency during electrocatalytic reactions. For comparison, the TEM images of the carbon black supported Pd NFs composite

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were also obtained in Fig.3c and d.

Fig.3 TEM images of (a and b) Pd NFs/NG and (c and d) Pd NFs/C. To explore the surface composition and chemical valences of the Pd, C, and N presented in the Pd NFs/NG composite, the XPS analysis was also conducted. As depicted in Fig. 4a, the peaks that presented at the binding energies around 284 eV, 340 eV, 400 eV, and 530 eV are ascribed to the C 1s, Pd 3d, N 1s, and O 1s peaks,

respectively. Notably, the appearance of O 1s and N 1s peaks confirmed the existence of oxygen-containing functional groups and nitrogen on the surface of composite. From Fig.4b, the Pd 3d spectrum consists of two strong peaks present at around 335.1 and 340.4 eV, corresponding to 3d5/2 and 3d3/2 states of Pd(0), whereas the other two week peaks are ascribed to the Pd (II) species [30]. Fig. 4c shows the XPS spectrum of C 1s, where the peak at 284.0 eV is associated with the sp2 C-C/C=C bonds, whereas the other peaks aroused at 285.4 eV and 288.0 eV can be attributed to the C-N and C-O [31], respectively. Fig. 4d showed deconvoluted N 1s spectrum, where

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and graphitic-N species were evidently observed [32].

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the three different bonding configurations corresponded to pyridinic-N, pyrrolic-N,

Fig.4 The (a) XPS survey scan, (b) Pd 3d, (c) C 1s, and (d) N 1s XPS spectra of Pd NFs/NG. Prior to evaluating the electrocatalytic properties of the as-obtained Pd NFs/NG and Pd NFs/C catalysts toward EOR, CVs of different catalysts were firstly performed in 1 M KOH solution to activate the catalysts (Fig.5a). For comparison, the

commercial Pd/C was selected as benchmarked catalyst. And the electrochemically surface areas (ECSAs) of these electrocatalysts can be estimated by integrating the reduction peaks of Pd oxides through the equation [33]. From Fig.5b, the ECSA value of Pd NFs/NG was 33.0 m2 g-1, which was much larger than Pd NFs/C (24.4 m2 g-1), suggesting that the NG support was better for dispersing the 3D Pd NFs than carbon black. After the activation process, the electrocatalytic activities of these catalysts toward EOR were evaluated with CV in 1.0 M CH3CH2OH + 1 M KOH solution. As shown in Fig.5c, the CV curves of these three electrocatalysts displayed similar

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features, all of which contained two well-defined peaks: forward and backward peaks. The forward peak current density normalized with the mass of Pd loading on the GCE and ECSA were mass activity and specific activity, respectively, both of which were commonly utilized to evaluate the electrocatalytic activity of catalyst. As shown in

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Fig.5d, the Pd NFs/C catalyst showed the mass (specific) activity of 1187.3 mA mg-1 (4.8 mA cm-2), which was 2.2 (3.7) times higher than commercial Pd/C (528.3 mA

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mg-1; 1.3 mA cm-2), indicating the 3D flower-like nanostructure was favorable for the improvement of electrocatalytic activity. More importantly, Pd NFs/NG catalysts

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displayed the highest electrocatalytic activity (2070 mA mg-1 for mass activity; 6.3 mA cm-2 for specific activity) among these electrocatalysts investigated (Table S1).

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This result manifested the significant role of NG in promoting the electrocatalytic

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activity of catalysts.

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Fig.5 CV curves of Pd NFs/NG, Pd NFs/C, and Pd/C catalysts in (a) 1 M KOH solution and (c) 1 M KOH + 1 M CH3CH2OH solution. Histograms for the (b) ECSA values and (d) electrocatalytic activities of different catalysts.

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Besides the electrocatalytic activity, the durability is also a key factor of catalyst for practical application. To evaluate the durability of Pd NFs/NG, Pd NFs/C, and Pd/C catalysts, the long-term CV tests were performed in 1 M KOH + 1 M CH3CH2OH

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solution. As illustrated in Fig.6a, the rapid decay of current densities for Pd NFs/NG and Pd NFs/C was clearly observed at the beginning of the tests, which was ascribed

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to the accumulation of poisonous intermediates or the active site inactivation [34, 35]. Notably, regardless of rapid current density decay of Pd NFs/NG and Pd NFs/C in the

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initial stage, the normalized current density percentages of Pd NFs/NG and Pd NFs/C were much higher than Pd/C catalysts over cycle number, suggesting the higher durability of Pd NFs/NG and Pd NFs/C than Pd/C, which was due to the robust structure stability of 3D Pd nanoflowers [36]. Moreover, for detailed comparison, the normalized current density percentage and retained mass activities of these catalysts after continuous CV of 300 cycles were also recorded in Fig.6d. As observed, the retained mass activity of Pd NFs/NG was (1064.6 mA mg-1), which was 7.1 and 1.9

times higher than Pd/C (149.8 mA mg-1) and Pd NFs/C (559.2 mA mg-1), further confirming the superior durability of Pd NFs/NG toward EOR. This is because the introduced NG support can strengthen the combination of graphene and Pd NFs, enhancing the structure stability of composite and resulting in the great enhancement

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in long-term electrochemical stability [37, 38].

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Fig.6 (a) Durability comparison of Pd NFs/NG, Pd NFs/C, and Pd/C for 300 cycles. (b) The histogram for the normalized current density percentage and retained mass activities of Pd NFs/NG, Pd NFs/C, and Pd/C after 300 cycles.

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To further evaluate the durability of Pd NFs/NG, Pd NFs/C, and Pd/C catalysts, i-t tests were also performed in 1 M KOH + 1 M CH3CH2OH solution at potential of -0.2

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V for 3600 s. As seen in Fig.7a, the Pd NFs/NG displayed the highest retained mass activity after 3600 s among these electrocatalysts, confirming its high excellent durability, which was also consistent with the analysis of long-term CV tests.

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Moreover, the EIS test was also conducted to assess the charge transfer properties of these catalysts [39]. Fig.7b showed the Nyquist plots of Pd NFs/NG, Pd NFs/C, and

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Pd/C catalysts in 1.0 M CH3CH2OH + 1.0 M KOH solution at 0.7 V. The diameter of impedance arc (DIA) of electrocatalysts from the minimum to maximum are: Pd

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NFs/NG < Pd NFs/C < Pd/C. Notably, the Pd NFs/NG had the smallest DIA among all catalysts [40], suggesting the introduction of NG accelerate the charge transfer rate during EOR, which was due to the enhancement of conductivity of composite after the introduction of NG.

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Fig.7 (a) i-t curves of Pd NFs/NG, Pd NFs/C, and Pd/C at -0.2 V for 3600 s. (b) Nyquist plots of Pd NFs/NG, Pd NFs/C, and Pd/C at 0.7 V. 4. Conclusions

To summarize, we have demonstrated a facile and robust strategy to construct the

hybrid catalysts by growing 3D Pd NFs that assembled by NG nanosheets uniformly

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supported on the surface of NG. The doped nitrogen element improved the dispersion of 3D Pd NFs, enhancing the mobility of electrons and the conductivity of the

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composite catalysts as well. These favorable terms resulted in the large promotion of electrocatalytic activity of Pd NFs/NG towards EOR with the mass (specific) activity

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of 2070 mA mg-1 (6.3 mA cm-2), being 1.7 (1.3) and 4.8 (3.9) times higher than those of Pd NFs/C and commercial Pd/C catalysts, respectively. More importantly, the introduced NG support also strengthened the combination of graphene and Pd NFs,

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leading to the large promotion in long-term electrochemical stability. We believe this work will provide guidance for the rational design and construction of desirable

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electrocatalysts for fuel cells reactions and beyond. Acknowledgement

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We thank the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), the National Natural Science Foundation of China (Grant No. 51873136).

References [1] M. Shao, Q. Chang, J.-P. Dodelet, R. Chenitz, Recent advances in electrocatalysts for oxygen reduction reaction, Chem. Rev, 116 (2016) 3594-3657. [2] Y. Jiao, Y. Zheng, M. Jaroniec, S.Z. Qiao, Design of electrocatalysts for oxygenand hydrogen-involving energy conversion reactions, Chem. Soc. Rev., 44 (2015) 2060-2086. [3] C.C.L. McCrory, S. Jung, I.M. Ferrer, S.M. Chatman, J.C. Peters, T.F. Jaramillo,

ro of

Benchmarking hydrogen evolving reaction and oxygen evolving reaction electrocatalysts for solar water splitting devices, J. Am. Chem. Soc. 137 (2015) 4347-4357.

[4] S. Lu, K. Eid, Y. Deng, J. Guo, L. Wang, H. Wang, H. Gu, One-pot synthesis of

reaction, J. Mater. Chem. A, 5 (2017) 9107-9112.

-p

PtIr tripods with a dendritic surface as an efficient catalyst for the oxygen reduction

re

[5] D.R. Dekel, Review of cell performance in anion exchange membrane fuel cells, ACS Appl. Mater. Interfaces, 375 (2018) 158-169.

lP

[6] K. Eid, Yahia H. Ahmad, H. Yu, Y. Li, X. Li, S. Y. AlQaradawi, H. Wang, L. Wang, Rational one-step synthesis of porous PtPdRu nanodendrites for ethanol oxidation

18881-18889.

na

reaction with a superior tolerance for CO-poisoning, Nanoscale, 9 (2017)

[7] S.-H. Han, H.-M. Liu, P. Chen, J.-X. Jiang, Y. Chen, Porous trimetallic PtRhCu

ur

cubic nanoboxes for ethanol electrooxidation, Adv. Energy Mater., 8 (2017) 1801326. [8] Z. Gu, H. Xu, D. Bin, B. Yan, S. Li, Z. Xiong, K. Zhang, Y. Du, Preparation of

Jo

PdNi nanospheres with enhanced catalytic performance for methanol electrooxidation in alkaline medium, Colloids Surf. A, 529 (2017) 651-658. [9] D. Xu, Y. Liu, S. Zhao, Y. Lu, M. Han, J. Bao, Novel surfactant-directed synthesis of ultra-thin palladium nanosheets as efficient electrocatalysts for glycerol oxidation, Chem. Commun., 53 (2017) 1642-1645. [10] S. Fu, C. Zhu, D. Du, Y. Lin, Facile one-step synthesis of three-dimensional Pd-Ag bimetallic alloy networks and their electrocatalytic activity toward ethanol

oxidation, ACS Appl. Mater. Interfaces, 7 (2015) 13842-13848. [11] Y. Lu, Y. Jiang, X. Gao, X. Wang, W. Chen, Strongly coupled Pd nanotetrahedron/tungsten oxide nanosheet hybrids with enhanced catalytic activity and stability as oxygen reduction electrocatalysts, J. Am. Chem. Soc., 136 (2014) 11687-11697. [12] K. Eid, Yahia H. Ahmad, S. Y. Al-Qaradawi, N.K. Allam, Rational design of porous binary Pt-based nanodendrites as efficient catalysts for direct glucose fuel cells over a wide pH range, Catal. Sci. Technol., 7 (2017) 2819-2827.

ro of

[13] S.S. Chen, Z.Z. Yang, A.J. Wang, K.M. Fang, J.J. Feng, Facile synthesis of bimetallic gold-palladium nanocrystals as effective and durable advanced catalysts for improved electrocatalytic performances of ethylene glycol and glycerol oxidation, J. Colloid Interface Sci., 509 (2018) 10-17.

-p

[14] L. Chen, L. Lu, H. Zhu, Y. Chen, Y. Huang, Y. Li, L. Wang, Improved ethanol

electrooxidation performance by shortening Pd–Ni active site distance in Pd–Ni–P

re

nanocatalysts, Nat. Commun., 8 (2017) 14136.

[15] S.-H. Ye, J.-X. Feng, G.-R. Li, Pd nanoparticle/CoP nanosheet hybrids: highly

lP

electroactive and durable catalysts for ethanol electrooxidation, ACS Catal., 6 (2016) 7962-7969.

na

[16] S. Lu, K. Eid, D. Ge, J. Guo, L. Wang, H. Wang, H. Gu, One-pot synthesis of PtRu nanodendrites as efficient catalysts for methanol oxidation reaction, Nanoscale, 9 (2017) 1033-1039.

ur

[17] L. Jin, H. Xu, C. Chen, T. Song, C. Wang, Y. Wang, H. Shang, Y. Du, Uniform PdCu coated Te nanowires as efficient catalysts for electrooxidation of ethylene

Jo

glycol, J. Colloid Interface Sci. 540 (2019) 265-271. [18] H. Xu, P. Song, C. Fernandez, J. Wang, M. Zhu, Y. Shiraishi, Y. Du, Sophisticated construction of binary PdPb alloy nanocubes as robust electrocatalysts toward ethylene glycol and glycerol oxidation, ACS Appl. Mater. Interfaces, 10 (2018) 12659-12665. [19] Z. Gu, Z. Xiong, F. Ren, S. Li, H. Xu, B. Yan, Y. Du, Flower-like PdCu catalyst with high electrocatalytic properties for ethylene glycol oxidation, J. Taiwan Inst. of

Chem. Eng., 83 (2018) 32-39. [20] L. Sun, H. Wang, K. Eid, L. Wang, Shape-controlled synthesis of porous AuPt nanoparticles and their superior electrocatalytic activity for oxygen reduction reaction, Sci. Tech. Adv. Mater.17 (2016) 58-62. [21] K. Eid, H. Wang, Z.A. Alothman, Y. Yamauchi, L. Wang, Facile synthesis of porous dendritic bimetallic platinum–nickel nanocrystals as efficient catalysts for the oxygen reduction reaction, Chem. Asian. J., 11 (2016) 1388-1393. [22] K. Eid, H. Wang, H. Pei, S.M. Alshehri, Y. Yamauchi, L. Wang, One-step

ro of

synthesis of porous bimetallic PtCu nanocrystals with high electrocatalytic activity for methanol oxidation reaction, Nanoscale, 7 (2015) 16860-16866.

[23] X. Huang, S. Tang, X. Mu, Y. Dai, G. Chen, Z. Zhou, F. Ruan, Z. Yang, N. Zheng, Freestanding palladium nanosheets with plasmonic and catalytic properties, Nat.

-p

Nanotec., 6 (2011) 28-32.

[24] R. Kiyani, S. Rowshanzamir, M.J. Parnian, Nitrogen doped graphene supported

re

palladium-cobalt as a promising catalyst for methanol oxidation reaction: Synthesis, characterization and electrocatalytic performance, Energy, 113 (2016) 1162-1173.

lP

[25] L. Shang, B. Zeng, F. Zhao, Fabrication of novel nitrogen-doped graphene-hollow AuPd nanoparticle hybrid films for the highly efficient

na

electrocatalytic reduction of H2O2, ACS Appl. Mater. Interfaces 7(2015) 122-128. [26] D.-X. Yu, A.-J. Wang, L.-L. He, J. Yuan, L. Wu, J.-R. Chen, J.-J. Feng, Facile synthesis of uniform AuPd@Pd nanocrystals supported on three-dimensional porous

ur

N-doped reduced graphene oxide hydrogels as highly active catalyst for methanol oxidation reaction, Electrochim. Acta 213(2016) 565-573.

Jo

[27] H. Huang, G. Ye, S. Yang, H. Fei, C.S. Tiwary, Y. Gong, R. Vajtai, J. M. Tour, X. Wang, P.M. Ajayan, Nanosized Pt anchored onto 3D nitrogen-doped graphene nanoribbons towards efficient methanol electrooxidation, J. Mater. Chem. A, 3 (2015) 19696-19701. [28] X. Xu, Y. Zhou, J. Lu, X. Tian, H. Zhu, J. Liu, Single-step synthesis of PtRu/N-doped graphene for methanol electrocatalytic oxidation, Electrochim. Acta, 120 (2014) 439-451.

[29] B. Yan, H. Xu, K. Zhang, S. Li, J. Wang, Y. Shi, Y. Du, Cu assisted synthesis of self-supported PdCu alloy nanowires with enhanced performances toward ethylene glycol electrooxidation, Appl. Surf. Sci., 434 (2018) 701-710. [30] M. Wang, Z. Ma, R. Li, B. Tang, X.-Q. Bao, Z. Zhang, X. Wang, Novel Flower-like PdAu(Cu) Anchoring on a 3D rGO-CNT Sandwich-stacked Framework for Highly Efficient Methanol and Ethanol Electro-oxidation, Electrochim. Acta, 227 (2017) 330-344. [31] J. Lu, Y. Zhou, X. Tian, X. Xu, H. Zhu, S. Zhang, T. Yuan, Synthesis of boron

electrooxidation, Appl. Surf. Sci., 317 (2014) 284-293.

ro of

and nitrogen doped graphene supporting PtRu nanoparticles as catalysts for methanol

[32] J.-J. Lv, J.-X. Feng, S.-S. Li, Y.-Y. Wang, A.-J. Wang, Q.-L. Zhang, J.-R. Chen, J.-J. Feng, Ionic liquid crystal-assisted synthesis of PtAg nanoflowers on reduced

reaction, Electrochim. Acta, 133 (2014) 407-413.

-p

graphene oxide and their enhanced electrocatalytic activity toward oxygen reduction

re

[33] Q. Liu, Y. Lin, J. Fan, D. Lv, Y. Min, T. Wu, Q. Xu, Well-dispersed palladium nanoparticles on three-dimensional hollow N-doped graphene frameworks for

lP

enhancement of methanol electro-oxidation, Electrochem. Commun., 73 (2016) 75-79. [34] C. Hu, X. Zhai, Y. Zhao, K. Bian, J. Zhang, L. Qu, H. Zhang, H. Luo,

na

Small-sized PdCu nanocapsules on 3D graphene for high-performance ethanol oxidation, Nanoscale, 6 (2014) 2768-2775. [35] Y. H. Ahmad, K, Eid, K. A. Mahmoud, S. Y. Al-Qaradawi, Controlled design of

ur

PtPd nanodendrite ornamented niobium oxynitride nanosheets for solar-driven water splitting, New. J. Chem., 42 (2018) 14239-14245.

Jo

[36] H.M. An, Z.L Zhao, L.Y. Zhang, Y. Chen, Y.Y. Chang, C.M. Li, Ir-alloyed ultrathin ternary PdIrCu nanosheet-constructed flower with greatly enhanced catalytic performance toward formic acid electrooxidation, ACS Appl. Mater. Interfaces, 10 (2018) 41293-41298. [37] M. M. A. Abualrejal, K. Eid, R. Tian, L. Liu, H. Chen, A.M. Abdullah, Z. Wang, Rational synthesis of three-dimensional core–double shell upconversion nanodendrites with ultrabright luminescence for bioimaging application, Chem. Sci.,

DOI: 10.1039/C9SC01586H. [38] K. Eid, V. Malgras, H. Pei, K. Wang, A. Aldalbahi, S.M. Alshehri, Y. Yamauchi, L. Wang, One-step synthesis of trimetallic Pt–Pd–Ru nanodendrites as highly active electrocatalysts RSC Adv., 5(2015) 31147-31152. [39] K. Eid, H. Wang, V. Malgras, S. M. Alshehri, T. Ahamad, Y. Yamauchi, L. Wang, One-step solution-phase synthesis of bimetallic PtCo nanodendrites with high electrocatalytic activity for oxygen reduction reaction, J. Electroanal. Chem. 779 (2016) 250-255.

ro of

[40] C. Wang, K. Zhang, H. Xu, Y. Du, M.C. Goh, Anchoring gold nanoparticles on poly(3,4-ethylenedioxythiophene) (PEDOT) nanonet as three-dimensional

electrocatalysts toward ethanol and 2-propanol oxidation, J. Colloid Interface Sci.

Jo

ur

na

lP

re

-p

541(2019) 258-268.