Unravelling the synergy of oxygen vacancies and gold nanostars in hematite for the electrochemical and photoelectrochemical oxygen evolution reaction

The development of hematite-based electrocatalysts (EC) and photoelectrocatalysts (PEC) for oxygen evolution reaction (OER) is highly promising on account of the low-cost and favorable chemical properties. Herein, we report a unique inverse opal framework hematite-based bi-functional catalyst for both EC and PEC water oxidation in alkaline media. Under the combined action of oxygen vacancies (Vo) and gold nanostars (AuNSs) on hematite, the catalyst exhibited excellent activity and stability on both EC and PEC. The composite showed superior electrocatalytic performance for OER with a low overpotential of 281 mV at 10 mA cm−2. Density functional theory (DFT) studies reveal that the coverage of Vo controls the d-band center of surface Fe sites, and the OER activity displays a volcano relationship with the Vo coverage. The addition of gold nanoparticles on the hematite with low Vo coverage improves the adsorption strength of oxygen-containing intermediates to the optimal point and increases the OER activity. Furthermore, the as-prepared photoanode exhibits a ∼3.13 fold increase in current (1.46 mA cm−2) at 1.23 V versus RHE. It is proposed that Vo promotes bulk conductivity and surface catalysis and exhibits reduced activation energy under high light intensity. AuNSs efficiently inhibits the bulk recombination and improves carrier concentration because of the Fermi level equilibration and plasmonic resonance, and the surface catalysis compensates the deterioration of interfacial recombination of carriers induced by Vo, playing a synergistic role.