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

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.