Performance and Mechanism of Pt_xCu_y/C Electrocatalyst for Methanol Oxidation

Authors

Jia Tang, 1. Chinese Academy of Sciences, Dalian Institute of Chemical Physics, Dalian 116023, Liaoning, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;
Xiao-Ming Zhang, 1. Chinese Academy of Sciences, Dalian Institute of Chemical Physics, Dalian 116023, Liaoning, China;
Shan-Sheng Yu, 3. Jilin University, School of Materials Science and Engineering, Changchun 130012, Jilin, China;
Su-Li Wang, 1. Chinese Academy of Sciences, Dalian Institute of Chemical Physics, Dalian 116023, Liaoning, China;Follow
Gong-Quan Sun, 1. Chinese Academy of Sciences, Dalian Institute of Chemical Physics, Dalian 116023, Liaoning, China;Follow

Corresponding Author

Su-Li Wang(suliwang@dicp.ac.cn);
Gong-Quan Sun(gqsun@dicp.ac.cn)

Abstract

Direct methanol fuel cell (DMFC), which directly converts the chemical energy of methanol fuel into electrical energy, has the advantages of high energy conversion efficiency, environmental friendliness, and abundance of fuel sources. DMFC is considered as the promising substitutes in the field of portable devices, military applications, and stationary power stations, while the broad application is severely hindered by the sluggish kinetic of methanol oxidation reaction (MOR) in the anode and the high cost of platinum (Pt)-based anodic electrocatalysts. Herein, a series of carbon supported Pt_xCu_y (Pt_xCu_y/C) binary metal electrocatalysts, featured with high activity and low consumption of precious metal, were prepared under the ambient environment by a simple liquid phase impregnation reduction method using ethanol as the solvent and sodium borohydride as the reducing agent. Uniform distribution of Pt_xCu_y nanoparticles in the range of 2 ~ 4 nm was achieved by rationally optimizing the dropping rate, stoichiometric ratio, and reaction time. As revealed by XRD and TEM characterizations, adding way of the reducing agent into the metal salt precursor carbon slurry had a significant impact on the morphology. Compared with dumping, adding the reducing agent in a dropwise way was beneficial for obtaining nanoparticles with a smaller size and uniform distribution. By adjusting the amount of the reducing agent up to 20 times the molar amount of metal precursors, the complete reduction, signifying a higher loading and less waste of Pt precursors, can be safely ensured. When increasing the content of Cu precursors, those metal nanoparticles tended to connect into worm-like structures and the individual CuO phase was observed in PtCu₃/C and PtCu₄/C samples. MOR activity of as-prepared electrocatalysts was determined by systematically electrochemical measurements and an activity order of commercial Pt/C < Pt₃Cu/C < PtCu₄/C 3/C was revealed. In particular, the specific area activity of PtCu₃/C was 2.86 mA·cm^-2, which was 3.74 times higher than that of commercial Pt/C (0.94 mA·cm^-2), while the electrochemical active area (ECSA) was only half of commercial Pt/C. It indicated the enhanced performance stemmed from the accelerated reaction process instead of the increased reaction site. This was further confirmed by density functional theory (DFT) calculations that the introduction of Cu as well as the formation of CuO phase can promote the hydrolysis reaction, and the subsequent produced *OH can promote the oxidation of CO-like intermediate species into CO₂ through the bifunctional mechanism. The current work opens a new avenue for the convenient and controllable synthesis of binary Pt-Cu alloy electrocatalysts on MOR and facilitates the development of high-efficient and low-cost DMFC devices.

Graphical Abstract

Keywords

PtxCuy/C electrocatalyst, methanol oxidation reaction, CuO

DOI Link

https://doi.org/10.13208/j.electrochem.210317

Publication Date

2021-10-28

Online Available Date

2021-10-28

Revised Date

2021-04-25

Received Date

2021-03-17

Recommended Citation

Jia Tang, Xiao-Ming Zhang, Shan-Sheng Yu, Su-Li Wang, Gong-Quan Sun. Performance and Mechanism of Pt_xCu_y/C Electrocatalyst for Methanol Oxidation[J]. Journal of Electrochemistry, 2021 , 27(5): 508-517.
DOI: Direct methanol fuel cell (DMFC), which directly converts the chemical energy of methanol fuel into electrical energy, has the advantages of high energy conversion efficiency, environmental friendliness, and abundance of fuel sources. DMFC is considered as the promising substitutes in the field of portable devices, military applications, and stationary power stations, while the broad application is severely hindered by the sluggish kinetic of methanol oxidation reaction (MOR) in the anode and the high cost of platinum (Pt)-based anodic electrocatalysts. Herein, a series of carbon supported Pt_xCu_y (Pt_xCu_y/C) binary metal electrocatalysts, featured with high activity and low consumption of precious metal, were prepared under the ambient environment by a simple liquid phase impregnation reduction method using ethanol as the solvent and sodium borohydride as the reducing agent. Uniform distribution of Pt_xCu_y nanoparticles in the range of 2 ~ 4 nm was achieved by rationally optimizing the dropping rate, stoichiometric ratio, and reaction time. As revealed by XRD and TEM characterizations, adding way of the reducing agent into the metal salt precursor carbon slurry had a significant impact on the morphology. Compared with dumping, adding the reducing agent in a dropwise way was beneficial for obtaining nanoparticles with a smaller size and uniform distribution. By adjusting the amount of the reducing agent up to 20 times the molar amount of metal precursors, the complete reduction, signifying a higher loading and less waste of Pt precursors, can be safely ensured. When increasing the content of Cu precursors, those metal nanoparticles tended to connect into worm-like structures and the individual CuO phase was observed in PtCu₃/C and PtCu₄/C samples. MOR activity of as-prepared electrocatalysts was determined by systematically electrochemical measurements and an activity order of commercial Pt/C < Pt₃Cu/C < PtCu₄/C 3/C was revealed. In particular, the specific area activity of PtCu₃/C was 2.86 mA·cm^-2, which was 3.74 times higher than that of commercial Pt/C (0.94 mA·cm^-2), while the electrochemical active area (ECSA) was only half of commercial Pt/C. It indicated the enhanced performance stemmed from the accelerated reaction process instead of the increased reaction site. This was further confirmed by density functional theory (DFT) calculations that the introduction of Cu as well as the formation of CuO phase can promote the hydrolysis reaction, and the subsequent produced *OH can promote the oxidation of CO-like intermediate species into CO₂ through the bifunctional mechanism. The current work opens a new avenue for the convenient and controllable synthesis of binary Pt-Cu alloy electrocatalysts on MOR and facilitates the development of high-efficient and low-cost DMFC devices.

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