Dual-strategy modification of NiMoO4 yields high performance bifunctional water splitting catalysts

Abstract

Nickel molybdate is considered a promising alternative to noble-metal catalysts for water splitting because its microstructure and electronic structure can be readily tuned. However, its inherent low catalytic activity limits the OER and HER performance and stability of the catalyst. This work employs a simple one step hydrothermal method to synthesize iron-doped nickel molybdate (FNMO) on a self-assembled Ti₃C₂/NF substrate, followed by phosphorating treatment with PH₃ gas to obtain the phosphorated product Pi/FNMO/Ti₃C₂/NF nanorod array catalyst. The Pi/FNMO/Ti₃C₂/NF catalyst exhibits superior oxygen evolution reaction (OER) activity (189.8 mV @ 10 mA cm⁻², 329.8 mV @ 100 mA cm⁻²) and hydrogen evolution reaction (HER) activity (73 mV @ 10 mA cm⁻²), significantly surpassing commercial RuO₂ and Pt/C catalysts. This may be attributed to the formation of a heterojunction between FNMO and Ti₃C₂ within the Pi/FNMO/Ti₃C₂/NF composite following phosphorylation, which modulates the electronic structure and reduces the overpotentials for both the OER and HER. Meanwhile, as a bifunctional catalyst, Pi/FNMO/Ti₃C₂/NF requires only 1.57 V to drive overall water splitting at a current density of 100 mA cm⁻² and maintain stable output for 180 h with a decay rate of only 5.5%. This work demonstrates the feasibility of enhancing overall water splitting performance through the incorporation of heteroatom doping and phosphorylation modification in nickel molybdate-MXene composites, providing a useful strategy for the design of high-performance NiMoO₄-MXene electrocatalysts for alkaline water splitting.