Rapid carbothermal shocking fabrication of iron-incorporated molybdenum oxide with heterogeneous spin states for enhanced overall water/seawater splitting

Abstract

Molybdenum dioxide (MoO₂) has been considered as a promising hydrogen evolution reaction (HER) electrocatalyst. However, the active sites are mainly located at the edges, resulting in few active sites and poor activity in the HER. Herein, we first reported on an efficient strategy to incorporate Fe into MoO₂ nanosheets on Ni foam (Fe–MoO₂/NF) using a rapid carbothermal shocking method (820 °C for 127 s). Notably, the different spin states between Fe and Mo atoms could lead to rich lattice dislocations in Fe–MoO₂/NF, exposing abundant oxygen vacancies and the low-oxidation-state of Mo sites during the rapid Joule heating process. As tested, the catalyst exhibited superior activity with ultralow overpotentials (HER: 17 mV@10 mA cm⁻²; oxygen evolution reaction (OER): 310 mV@50 mA cm⁻²) and high OER selectivity in alkaline seawater splitting. Meanwhile, this catalyst was equipped in a home-made anion exchange membrane (AEM) seawater electrolyzer, which achieved a low energy consumption (5.5 kW h m⁻³). More importantly, Fe–MoO₂/NF also coupled very well with a solar-driven electrolytic system and turned out a solar-to-hydrogen (STH) efficiency of 13.5%. Theoretical results also demonstrated that Fe incorporated and abundant oxygen vacancies in MoO₂ can distort the distance of the Mo–O bonds and regulate the electronic structure, thus optimizing the binding energy of H*/OOH* adsorption. This method can be extended to other heterogeneous spin states in MoO₂-based catalysts (e.g. Ni–MoO₂/NF, Co–MoO₂/NF) for seawater splitting, and provide a simple, efficient and universal strategy to prepare highly-efficient MoO₂-based electrocatalysts.