Tracking activity behavior of oxygen evolution reaction on perovskite oxides in alkaline solution via 3-dimensional electrochemical impedance spectroscopy

Developing electrocatalysts for the oxygen evolution reaction (OER) is essential for enhancing the efficiency of electrochemical water electrolysis. Among potential candidates, certain metal oxides, such as Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF), undergo structural transformations at their surface during OER operation, and the in situ-formed active layer enhances their OER activities. However, it is challenging to quantitatively evaluate the time-variant electrochemically active surface area (ECSA) and inherent catalytic activity per surface area (area-specific activity) of the oxides. In this study, we utilize the 3-dimentional electrochemical impedance spectroscopy (3D EIS) technique to reveal the variations in the ECSA and area-specific activity of the perovskite oxides during OER operation in an alkaline solution. In BSCF, the diameter of instantaneous Nyquist plots decreases as the number of potential cycling in the OER potential range increases, contrasting with other perovskite oxides, such as La0.5Sr0.5Co0.8Fe0.2O3−δ and LaCoO3. The fitting results of the Nyquist plots demonstrate that in BSCF, the ECSA significantly increases while the area-specific activity drops to less than half of its initial value during OER operation. Consequently, enhanced OER activity of BSCF mainly attributed to the increased ECSA rather than area-specific activity. This study demonstrates the utility of 3D EIS for tracking the ECSA and the area-specific activity of electrocatalysts.