Nb-Doped TiO₂ Supports Ir Nanoparticles with Strong Metal–Support Interaction as Bifunctional Electrocatalysts for Acidic Overall Water Splitting

The practical application of acidic water splitting is limited by the lack of bifunctional catalysts that combine high activity, long-term stability, and reduced noble metal usage. To address this, we designed an Ir-based catalyst via a two-step hydrothermal synthesis, where ultrafine Ir nanoparticles (NPs) are anchored on Nb-doped TiO2 (Ir NPs/Nb–TiO2) to exploit strong metal–support interactions and electronic modulation. The optimized catalyst exhibits outstanding bifunctional performance in 0.5 M H2SO4, requiring low overpotentials of 37 (hydrogen evolution reaction) and 253 mV (oxygen evolution reaction) at 10 mA cm–2, outperforming most reported Ir-based catalysts. Remarkably, Ir NPs/Nb–TiO2 demonstrates exceptional stability, with almost no change in potential after 40 h of chronoamperometric testing for both oxygen evolution reaction and hydrogen evolution reaction. Furthermore, as a bifunctional catalyst for overall water splitting, it achieves a current density of 10 mA cm–2 at a low cell voltage of 1.531 V, with negligible loss in catalytic activity after 40 h of chronoamperometric testing. Density functional theory calculations reveal that Nb doping enhances electron transfer to Ir, optimizing oxygen intermediate adsorption while strong metal–support interaction prevents Ir dissolution. This work offers a high-performance catalyst for acidic water splitting and a general framework for minimizing noble metal usage through synergistic electronic and interfacial engineering.