Kinetic Study of Formic Acid Electrochemical Oxidation on Supported Pd Based Electrocatalysts

Developing high performance catalyst based on Pd/C catalyst is critical in investigating and commercializing direct formic acid fuel cell. The improvement of the electron-transfer rate of novel catalysts could solve the sluggish reaction kinetics of formic acid electro-oxidation reaction in some extent. We have demonstrated that phosphotungstic acid (PWA) modified Pd/C catalyst could improve the electro-oxidation activity toward formic acid. In this paper, the electrochemical oxidation reaction kinetics of PWA modified Pd/C catalyst were studied by cyclic voltammetry (CV), Tafel polarization, electrochemical impedance spectroscopy (EIS) and rotating disc voltammetry (RDV) at different scanning rates and temperatures. The results showed that smaller apparent activation energy, charge transfer resistance and Tafel slope of formic acid electro-oxidation from Pd/PWA-C electrode catalyst was obtained, which indicated better electrocatalytic kinetics by PWA modification. The rate-determining step of formic acid electro-oxidation is diffusion process and reaction paths are different with potential. The larger diffusion coefficients of Pd/PWA-C electrode catalyst was verified by CV, EIS and RDV, respectively. With the help of electrochemical measurements, it is concluded that PWA modified Pd/C catalyst has better electrocatalytic activity and faster kinetic performance for formic acid electro-oxidation. (C) 2018 The Electrochemical Society.