Surface active sites and interphase engineering into metal oxide hydrates enabled by ions substitution for efficient water splitting

The expanding requirement of energy-effective and cost-efficient water electrolysis has prompted studies of earth-abundant metal-based electrocatalysts. In this study, we study the typical substitution strategies of cation (Pt) or anion (Se) for modifying surface active sites or interphase engineering to tune electronic structure of bimetallic nickel molybdenum oxide hydrates (NiMoO₄·xH₂O), thus effectively improving catalytic properties toward hydrogen evolution reaction (HER) or oxygen evolution reaction (OER). Result of the cation substitution achieves Pt_SA–NiMoO₄·xH₂O catalyst with abundant doped Pt single atoms on surface, which promotes high HER activity with a small overpotential of 73 mV at a current yield of 10 mA cm⁻² in alkaline medium. Meanwhile, Se–NiMoO₄·xH₂O catalyst, an outcome of the anion substitution approach, has unique interfaces of NiSe-NiMoO₄ heterostructure and thus exhibits a desired overpotential of only 297 mV for OER. The combination of Pt_SA–NiMoO₄·xH₂O_(–)//Se–NiMoO₄·xH₂O₍₊₎ couple results in a two-electrode electrolyzer cell, which requires a small cell voltage of 1.48, 1.54 and 1.59 V to deliver a response of 10 mA·cm⁻² at 75, 50 and 25 °C, respectively, along with negligible performance decay during 50 h operation. These results highlight the potential of our catalyst engineering strategies to achieve high-performance green hydrogen production.