Phase Engineering Modulates the Electronic Structure of the IrO₂/MoS₂ Heterojunction for Efficient and Stable Water Splitting

The engineering of dual-functional catalytic systems capable of driving complete water dissociation in acidic environments represents a critical requirement for advancing proton exchange membrane electrolyzer technology, yet significant challenges remain. In this work, we investigate an IrO₂/MoS₂/CNT heterostructure catalyst demonstrating enhanced bifunctional performance for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) under acidic conditions. Strategic incorporation of IrO₂ into the MoS₂/CNT heterojunction induces a partial phase transformation from 2H to the metastable 1T configuration in MoS₂, thereby modulating the electronic structure of IrO₂ and improving the catalytic performance for overall water splitting. The optimized IrO₂/MoS₂/CNT catalyst exhibited exceptional overpotentials of 9 mV (HER) and 182 mV (OER) at a current density of 10 mA cm^-2 in acidic media. Full-cell evaluations further confirmed its practical potential, showing a 1.47 V operation voltage that outperforms standard Pt/C||IrO₂ counterparts by 120 mV. The experimental results revealed that the n-n heterojunction between IrO₂/CNT and MoS₂/CNT generates a built-in electric field, enhancing charge redistribution and electron transport. Moreover, density functional theory simulations further identify iridium centers as dominant catalytic loci, with a metastable 1T-MoS₂ phase mediating charge equilibration at atomic interfaces. This modification facilitates *OH adsorption and *OOH deprotonation and lowers the kinetic barrier during the water-splitting process.