Enhanced solar water splitting using a TiO2/In2S3 heterojunction coated with NiFe phosphide cocatalyst

A robust photoelectrode is urgently needed for practical solar water splitting. TiO₂ has recognized stability in a wide pH range, but its performance is limited by poor charge separation and low light absorption. In this work, a heterojunction photoelectrode of TiO₂/In₂S₃ has been fabricated through a hydrothermal method and coated with bimetallic NiFe phosphide (NiFeP) cocatalyst derived from NiFe Prussian blue analogue through a low temperature phosphidation process. The TiO₂/In₂S₃/NiFeP photoanode delivers a remarkable photocurrent of 3.18 mA cm⁻² at 1.23 V vs. RHE, which is 92.17 % of its theoretical photocurrent. Stability testing under AM 1.5G illumination reveals that this photoanode retains 97.67 % of its initial photocurrent after 12 h in 1 M KOH electrolyte without the sacrificial reagent. Moreover, the TiO₂/In₂S₃/NiFeP delivers a superior charge separation efficiency of 92.46 % and a high charge injection efficiency of 92.31 %. Due to the use of narrow bandgap In₂S₃, the composite photoanode achieves improved light absorption and efficient charge separation, benefiting from the type-II heterojunction between TiO₂ and In₂S₃. The integration of the NiFeP cocatalyst further accelerates charge transfer through the favorable surface states at the semiconductor-electrolyte interface and protects the In₂S₃ layer from photocorrosion.