Comparison of Cu and Pt point-contact electrodes on proton conducting BaZr0.7Ce0.2Y0.1O3−δ
Abstract The hydrogen oxidation kinetics of Cu and Pt point contact-electrodes on proton conducting BaZr0.7Ce0.2Y0.1O3−δ (BZCY72) were studied over a range of temperatures and hydrogen pressures using impedance spectroscopy. Characteristic capacitances were used to identify process contributions as charge and mass transfer, then Langmuir adsorption theory and Butler-Volmer charge transfer formalism were used to propose a hydrogen oxidation model to describe the experimental data. The charge transfer hydrogen pressure dependencies were p H 2 3 / 4 for Cu, attributed to a high occupancy of adsorbed oxygen at three-phase boundary sites in the water-vapor containing atmosphere, and p H 2 - 1 / 4 for Pt, corresponding to a hydrogen saturated interface. The Cu and Pt point contact electrodes exhibit similar temperature dependencies for charge transfer, with activation enthalpies of 0.82 and 0.93 eV, and pre-exponentials of approximately 160 and 1000 Ω−1cm−1, respectively. Mass transfer dominated the total polarization resistance of both metal point contact electrodes, exhibiting a p H 2 1 / 2 hydrogen pressure dependency. The activation enthalpies are 1.21 eV for Cu and 0.73 eV for Pt, reflecting the higher catalytic activity generally expected for Pt. Pre-exponentials for mass transfer of approximately 10,000 Ω−1cm−1 for Cu and 2.6 Ω−1cm−1 for Pt, indicate that Cu utilizes a much larger active interface. Cu may be a suitable candidate electrode material for use in carbonaceous atmospheres, but the results of this work indicates that it suffers from a high activation enthalpy for mass transfer in the hydrogen oxidation reaction.