Modelling and Ni/Yttria-Stabilized-Zirconia pattern anode experimental validation of a new charge transfer reactions mechanism for hydrogen electrochemical oxidation on solid oxide fuel cell anodes

Abstract

Good understanding of the H2 electrochemical reaction mechanism helps optimize SOFC anode design and improve its performance. Controversies still exist regarding H2 oxidation mechanism despite extensive studies performed. In this work, a new charge transfer reactions mechanism proposed by Shishkin and Ziegler (2010) based on Density Functional Theory (DFT) study was investigated through kinetic modelling and pattern anode experimental validation. The new charge transfer reactions mechanism considers hydrogen oxidation at the interface of Ni and YSZ. It involves a hydrogen atom reacting with the oxygen ions bound to both Ni and YSZ to produce hydroxyl (Charge transfer reaction 1), the latter reacting with the other hydrogen atom to form water (Charge transfer reaction 2). The predictive capability of this reaction mechanism to represent our experimental results was evaluated. The simulated Tafel plots were compared with our experimental data for a wide range of H2 and H2O partial pressures and at different temperatures. Good agreements between simulation and experimental results were obtained. Charge transfer reaction 1 was found to dominate the overall charge transfer reaction under cathodic polarization. Under anodic polarization, a change in the dominating charge transfer reaction from charge transfer reaction 1 to charge transfer reaction 2 was found when increasing the H2O partial pressure.