Hematite nanobelts with ordered oxygen vacancies for bifunctional electrocatalytic water splitting†

The development of inexpensive and stable hydrogen evolution reaction (HER)/oxygen evolution reaction (OER) bifunctional electrocatalysts is extremely important to advance the commercial application of alkaline water electrolysis (AWE). However, the majority of bifunctional catalysts exhibit optimal activity in only one reaction, leading to suboptimal overall water splitting efficiency. The development of a satisfactory bifunctional catalyst capable of simultaneously accelerating both HER and OER kinetics remains an ongoing challenge. Here, we report efficient bifunctional electrocatalytic water splitting by constructing long-range ordered oxygen vacancies in hematite nanobelt arrays. Notably, HNBs-30 with long-range ordered oxygen vacancies exhibits lower OER (317 mV @ 10 mA cm⁻², 369 mV @ 100 mA cm⁻²) and HER (178 mV @ 10 mA cm⁻², 321 mV @ 100 mA cm⁻²) overpotentials, and exhibits a low overpotential of 2.22 V and long-term stability of 40 hours at 100 mA cm⁻² in overall water splitting. This study shows that long-range ordered oxygen vacancies not only optimize the adsorption/desorption kinetics of intermediates, but also establish a highly efficient conduit for charge transport, which can simultaneously accelerate the kinetics of HER and OER. This is a key factor in HNBs-30 achieving bifunctional and high catalytic activity.