Opposite Electron Transfer Induced High Valence Mo Sites for Boosting the Water Splitting Performance of Ir Atoms

Developing highly efficient and low-cost bifunctional electrocatalysts for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in water splitting poses significant challenges. In this study, a novel bifunctional electrocatalyst, Ir-CoMoPO, was achieved via incorporating low-loading Ir single atoms and clusters with the high-valence Mo⁶⁺ modified CoPO nanosheets. The Ir-CoMoPO catalyst demonstrates remarkable low overpotentials of 222 mV and 36 mV for the OER and HER, respectively, in delivering a current density of 10 mA cm^-2. When employed as both the anode and cathode catalyst in overall water splitting, the Ir-CoMoPO∥Ir-CoMoPO configuration exhibits a superior cell voltage of 1.53 V, outperforming the benchmark Pt/C∥IrO₂ electrolytic cell (1.60 V) for achieving the current density of 10 mA cm^-2. Benefiting from the high-valence of Mo species, the metal-support interaction of Ir-CoMoPO was greatly strengthened, resulting in an order of magnitude increase in the mass activity of Ir for the HER. The high valence of non-noble metals plays a crucial role in tuning the local electronic configurations and optimizing the adsorption energies of the intermediates, which synergistically improves the overall performance of Ir in water splitting. The study provides valuable insights for future research in the utilization of Ir-based bifunctional catalysts for overall water electrocatalysis applications.