Non-stoichiometric problem of photocatalytic water splitting on γ-Ga2O3: Cause and solution

Abstract

Photocatalytic water splitting on metal oxides often faces oxygen evolution inefficiency, reflecting the complex interplay of its two half-reactions. Strategies like heterojunctions, cocatalyst loading, or noble metal nanoparticles addition have been explored to address this. Using γ-Ga₂O₃ nanosheets as a model, we uncovered the formation of −O-O- species as the key barrier to stoichiometric splitting. To tackle this, a strategy was devised, Sr-doping to inhibit surface peroxidation. The resultant Sr-doped γ-Ga₂O₃ (Sr-Ga₂O₃) significantly improved activity and stability, achieving balanced H₂ and O₂ production under 125 W mercury lamp light. Upon further enhancement with Rh/Cr₂O₃ cocatalyst via photoreduction, the Sr-Ga₂O₃/(Rh/Cr₂O₃) composite demonstrated a remarkable 8.7 mmol·g⁻¹·h⁻¹ H₂ and 4.4 mmol·g⁻¹·h⁻¹ O₂ evolution rate, 8.3 times higher than γ-Ga₂O₃ alone, with a 34.1 % quantum efficiency under 260 nm light. This represents a record performance for Ga₂O₃-based photocatalytic water splitting. Mechanistically, Sr doping alters surface chemistry to favor direct oxygen release. Our study elucidates molecular-level insights into non-stoichiometric splitting mechanisms and offers a potent strategy to boost metal oxide photocatalysts’ water-splitting efficiency.