Unveiling the role of defects in iron oxyhydroxide for oxygen evolution.

Development of earth-abundant and robust oxygen evolution reaction (OER) catalysts is imperative for cost-effective hydrogen production via water electrolysis. Herein, we report ultrafine iron (oxy)hydroxide nanoparticles with average particle size of 2.6 nm and abundant surface defects homogeneously supported on oleum-treated graphite (FeO(n)@HG-T), providing abundant active sites for the OER. The optimal FeO(0.03)@HG-110 exhibits high electrocatalytic OER activity and excellent stability. Electrochemical testing results and theoretical calculations reveal that the outstanding OER activity of FeO(0.03)@HG-110 is due to its stronger charge transfer ability and lower OER energy barrier than defect-free FeO nanoparticles. This work demonstrates that the OER performance of oxyhydroxide-based electrocatalysts can be improved by surface defect engineering.