V-doped, divacancy-containing β-FeOOH electrocatalyst for high performance oxygen evolution reaction

Improving the oxygen evolution reaction (OER) performance of Fe-based (oxy)hydroxides is vital for the development of cost-effective electrocatalysts. In this work, for the first time, we demonstrate that the OER activity of β-FeOOH is enhanced via V-doping and the generation of both iron and oxygen vacancies. The novel V-doped, divacancy-containing β-FeOOH is obtained in-situ through a pre-OER cyclic voltammetry activation of hydrated layered Fe5V15O39(OH)9·9H2O Various analyses reveal that the vanadium dissolution in basic electrolyte accounts for the in-situ formation of V-doping and divacancy β-FeOOH. The experiment shows that V-doping regulates the formation of oxygen vacancies, subsequently resulting in the modulation of Fe oxidation state and charge transfer characteristics. Metallic Fe in the β-FeOOH also contributes to the enhanced charge transfer. Density functional theory calculation reveals that V-doping and iron vacancy balance the adsorption and desorption of oxygen intermediate species, giving a reduced energy barrier of the rate determining step during OER. As a result, the V-doped, divacancy-containing β-FeOOH exhibits an excellent OER overpotential of 232 mV at 10 mA cm−2, high current density > 450 mA cm−2, no potential decay after 2,000 cycles, and 72 h stability, outperforming the benchmark RuO2 and the other Fe-based catalysts. A water splitting cell consisting of the β-FeOOH anode F(V)OOH and a Pt/C cathode demonstrates an excellent cell voltage of 1.51 V at 10 mA cm−2. This facile method to obtain metal doping and divacancy simultaneously leads to a new approach for further development of electrocatalysts.