Mechanism for reversible CO/CO2 electrochemical conversion on a patterned nickel electrode

摘要

The patterned Ni negative electrode on single-crystal YSZ in CO-CO2 atmosphere is investigated in both the solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) modes. The effects of the temperature T, partial pressure of CO and CO2 (pCO and pCO(2)) on the electrochemical performance are measured to, obtain the intrinsic kinetic parameters by natural logarithm linear fitting. The strong dependency of surface diffusion resistance on pCO implies that surface diffusion could be related to CO(Ni). The electrochemical performance had an obviously positive correlation with T and pCO. The limitation of CO2 adsorption leads to a weak dependency of polarization on pCO(2). The electrochemical performance of SOEC mode in the atmosphere without CO is 1.21 times higher than that in the atmosphere without CO2, which implies that CO electrochemical reduction could be more significant than CO2 electrochemical reduction in the patterned Ni electrode. An analytical calculation is performed for the speculation of rate limiting steps. In the SOFC mode, CO oxidation into CO2 is speculated to be rate-determining, besides, adsorbed carbon oxidation into CO could be also non-ignorable. In the SOEC mode, CO reduction into carbon could be more probably the major electrochemical reaction on the pure Ni surface. (C) 2017 Published by Elsevier B.V.