Electrochemical characteristics of solid oxide fuel cells supplied with CO-rich fuel gases

CO2 biomass gasification is an attractive option for reducing CO2 emission which produces gas mixtures with higher CO concentrations than typical syngas compositions. However, carbon deposition and catalyst degradation may occur when CO-rich fuel gas is supplied to a Ni-Yttria-stabilized Zirconia solid oxide-based fuel cell. In this study, the electrochemical performance of an SOFC (anode: NiO-YSZ/NiO-GDC) with various CO-rich gas compositions was experimentally investigated. Four distinct gas mixtures were tested using electrochemical experiments at 1073 K. Impedance and steady-state polarization measurements were taken, and electric power generation was assessed at 100 mA·cm-2 under the 4 gas mixtures. Gas 1, a mixture of H2 (38%), CO (19%), CO2 (9.5%), and H2O (5%) was prepared as a reference gas to model a typical syngas mixture obtained from biomass gasifier. It generated the highest voltage without any degradation of the anode over 8 h. Gas 2, containing CO (19%), CO2 (9.5%), and H2O (5%), caused serious anode degradation compared with Gas 1. Gas 3, containing CO (19%) and H2O (5%) showed good performance with a relatively small polarization resistance and good stability in long-term electric power generation test. Gas 4, consisting of CO (20%) and CO2 (10%), exhibited the largest charge-transfer resistance at low overpotential and a significant diffusion resistance at high overpotential. Additionally, Gas 4 had the worst stability in the electric power generation test. Based on these results, we conclude that biomass gasification gas is a promising fuel for use in SOFCs. CO direct oxidation can provide electric power generation, although it appears to be unstable and shows high resistance at both low and high overpotentials. H2O addition can efficiently improve the stability of the CO direct oxidation process.