Unveiling the role of defects in iron oxyhydroxide for oxygen evolution

Compared with defect-free FeOx, the ultrafine FeOx in the FeOx(0.03)@HG-110 with abundant surface defects shows lower energy barrier and higher OER activity. [Display omitted] •The FeOx(0.03)@HG-110 exhibits an OER overpotential as low as 342 mV at 10 mA cm−2.•The average particle size of FeOx is ca. 1.6 nm.•FeOx(0.03)@HG-110 possesses a low Ea of 35.9 kJ mol−1.•The rate-determining step is *O → *OOH with the energy barriers of 0.79 eV. 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 (FeOx(n)@HG-T), providing abundant active sites for the OER. The optimal FeOx(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 FeOx(0.03)@HG-110 is due to its stronger charge transfer ability and lower OER energy barrier than defect-free FeOx nanoparticles. This work demonstrates that the OER performance of oxyhydroxide-based electrocatalysts can be improved by surface defect engineering.