The power of operando analysis: Understanding the critical characteristics of OER catalysts from atomistic to systemic scales

Developing high-efficiency and affordable electrocatalysts for the sluggish oxygen evolution reaction (OER) remains a crucial bottleneck on the way to practical applications of water electrolysis toward clean H2. Determining the OER mechanism and understanding the characteristics that affect OER activity and catalyst stability are of vital importance for this endeavor. In this aspect, operando characterization techniques performed under dynamic OER conditions are powerful tools to monitor key reaction intermediates, active sites, charge transfer, and material transformation coupled processes. This mini review covers noble and 3d transition metal-based OER electrocatalysts and their analysis by different operando techniques that span the range from the characterization in half cells to elucidate intrinsic properties to the analysis of phenomena occurring during their technical operation in single cells.