Hirotatsu Watanabe

In this study, Ni cathode oxidation during electrochemical CO₂ reduction (CO₂ electrolysis) in a solid oxide electrolysis cell was studied via ex situ and operando X-ray diffraction (XRD) analyses as well as first-principles density functional theory (DFT) calculations. The XRD NiO-Ni peak ratio was used to compare the degree of Ni oxidation. Ex situ XRD analysis was performed to study a Ni/yttria-stabilized zirconia (YSZ) cathode surface after CO₂ electrolysis at 1073 K, revealing that Ni oxidation was inhibited with increasing current density. Operando XRD analysis was performed to characterize the Ni/YSZ cathode surface during CO₂ electrolysis at 873 K, revealing that the NiO(200)-Ni(111) peak ratio was low (2 electrolysis and rapidly increased to 0.7 without electrolysis after 10 min CO₂ exposure. These findings indicated that electrolysis enhanced the oxidation tolerance of the Ni cathode immediately after electrolysis initiation. DFT calculations showed that CO₂ reduction (CO₂ → CO + O (O was filled into a electrolyte vacancy)) at the triple-phase boundary was more favorable than Ni oxidation (Ni + CO₂ → NiO + CO) at the Ni (100) surface, suggesting that an increase in the CO₂ reduction rate improved oxidation tolerance.