Elucidating the role of interfacial charge transfer on the oxygen incorporation/evolution reactions for solid oxide...

The oxygen incorporation and evolution reactions (OIR/OER) at air electrodes are key challenges limiting the performance of reversible solid oxide cells (SOCs). Surface modification using binary oxides has emerged as a promising strategy to enhance OIR/OER kinetics, with PrO_x as a popular choice of the modification layer. However, the mechanisms behind this improvement of reaction kinetics remain unclear. In this study, we combine insights from electrochemical measurements and operando X-ray absorption spectroscopy to reveal that interfacial charge transfer plays a pivotal role in enhancing the OIR/OER activity in La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) with PrO_x surface modification. The charge transfer increases the hole concentration in LSCF, which can be quantitatively correlated with accelerated OIR/OER kinetics (up to ~70 times enhancement) over a broad range of oxygen chemical potential. We further demonstrate this mechanism in realistic SOCs devices, showing enhanced performance in both fuel cell and electrolysis modes. Our work provides critical insights into the role of interfacial charge transfer and defect chemistry in surface-modified SOCs electrodes, offering a pathway to optimize SOCs performance through surface modifications.