A Near‐Perfect Pt Cocatalyst with a Spatially Oriented Distribution of Pt ²⁺ /Pt ⁰ for Photocatalytic Water Splitting

Abstract Loading the cocatalyst, e.g., Pt, is a promising strategy for photocatalytic overall water splitting, in which metallic state Pt° facilitates proton reduction and positive valence state Pt ²⁺ inhibits H ₂ /O ₂ recombination. However, simultaneously leveraging the advantages of Pt ⁰ and Pt ²⁺ in Pt‐photocatalyst hybrids for photocatalytic water splitting is challenging. Herein, a universal strategy is demonstrated for modulating Pt valence state, obtaining a spatially oriented distribution of Pt ²⁺ /Pt ³ and a close to zero proton reduction barrier, along with isolated O ₂ adsorption. As a proof of concept, Pt undergoes electron transfer to ZnIn ₂ S ₄ , accompanied by partial oxidation from Pt ⁰ to Pt ²⁺ through the introduction of electron‐deficient centers in ZnIn ₂ S ₄ via vanadium doping and sulfur vacancy (V‐Sv‐ZIS). Reverse electron transfer induces Pt ²⁺ dominating 83% of the region near the Pt/V‐Sv‐ZIS interface and Pt ⁰ dominating in the remaining 17% near the Pt cluster center, which can be extended to other Pt‐based catalyst systems. The dominant Pt ²⁺ inhibits O ₂ adsorption and induces the lowest H ₂ /O ₂ recombination rate of 4%, and the minimal Pt ⁰ obtains a 152.2‐fold increase in photogenerated electron density, ultimately realizing a 45.4‐fold increase in photocatalytic activity. A 10 m ² large‐area photocatalytic system is fabricated, producing 6.4 L of H ₂ per day under natural sunlight.