Alkali Cation Interactions with Superoxide Intermediates during the Oxygen Evolution Reaction on Ni1–xFexOOH

Alkali-cation-dependent kinetics have been widely observed for the oxygen evolution reaction (OER); however, reported trends and the underlying mechanism lack consensus. Herein, the OER activity on Ni1–xFexOOH was determined to follow the order Cs+ > K+, Na+ > Li+. Coupling operando surface-enhanced Raman spectroscopy (SERS) with X2O (X = H or D) and H2YO (Y = 16 or 18) isotope labeling revealed scavenging of superoxide (O–O–) intermediates in the presence of Li+ leading to the formation of Li2CO3, resulting in a modified reaction path and subgrade activity. Ni1–xFexOOH catalytic films revealed stable performance during 18 days of anodic polarization in 1 M XOH at 60 °C. Conversely, severe degradation was observed in 6 M XOH due to delamination of the catalytic coating as well as loss of active sites and formation of unwanted FeOOH and NiOx moieties, regardless of alkali metal cation type.