In Situ Fluorescence Imaging of Oxygen Evolution on Epitaxial Perovskite Films with Composition Gradients

The oxygen evolution reaction (OER) is critical for the efficient electrochemical conversion of earth-abundant molecules and materials into more useful energy carriers, fuels, and value-added commodities. However, the sluggish kinetics of the OER leads to high overpotentials needed to catalyze the reaction, despite significant efforts to rationally design highly active OER catalysts. To date, most OER catalyst discovery has relied on human-driven approaches that have led to an understanding of only a small proportion of all possible materials. In recent years, the advent of high-throughput virtual screening and machine learning has significantly increased the space that has been explored, but methods for experimentally validating the OER activities at scale are still limited and challenging. In this work, we report a fluorescence-based high-throughput screening method for OER catalysts. We detailed a simple, custom-built cell with a fluorescent detector that changed colors upon O2 contact to screen the La0.6Sr0.4FexCo1–xO3 composition space. Using kinetic measurements of the fluorescence evolution as a function of the O2 evolved, apparent OER rates for the entire composition space were extracted, which revealed that x = 0.20 ± 0.05 appears to be the most active within the chemical space. Density functional theory calculations revealed a decrease in the computed OER overpotential on both Co and Fe sites of La0.5Sr0.5FexCo1–xO3 (001) with increasing Co doping, where x = 0.25 was found to be the most active, hence validating the observed trend and demonstrating the validity of the setup for screening the entire composition space simultaneously.