Integrating Mixed Halide Perovskite Photocatalytic HI Splitting and Electrocatalysis into a Loop for Efficient and Robust Pure Water Splitting

Abstract Developing a hydrogen economy to replace traditional fossil fuels is essential for sustainable human development. As two promising H ₂ production strategies, photocatalytic and electrocatalytic water splitting with large reaction energy barriers still face the great challenges of poor solar‐to‐hydrogen efficiency and large electrochemical overpotentials, respectively. Herein, a new strategy is proposed to disassemble the difficult pure water splitting into two parts that are easy to implement, namely mixed halide perovskite photocatalytic HI splitting for H ₂ production, and simultaneous electrocatalytic I ₃ ⁻ reduction and O ₂ production. The efficient charge separation, abundant H ₂ production active sites, and a small HI splitting energy barrier contribute to the superior photocatalytic H ₂ production activity of MoSe ₂ /MAPbBr _{3− x} I _x (CH ₃ NH ₃ ⁺ = MA). Subsequent electrocatalytic I ₃ ⁻ reduction and O ₂ production reactions only need a small voltage of 0.92 V to drive, which is far lower than that of the electrocatalytic pure water splitting (>1.23 V). The molar ratio of H ₂ (6.99 mmol g ⁻¹ ) to O ₂ (3.09 mmol g ⁻¹ ) produced during the first photocatalytic and electrocatalytic cycle is close to 2:1, and the continuous circulation of I ₃ ⁻ /I ⁻ between the photocatalytic and electrocatalytic systems can achieve efficient and robust pure water splitting.