关键词: Pt_xCu_y/C电催化剂, 甲醇氧化反应, CuO相

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 <PtCu/C < PtCu₃/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.

Key words: Pt_xCu_y/C electrocatalyst, methanol oxidation reaction, CuO