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 H₂ 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 H₂ production, and simultaneous electrocatalytic I₃ ^- reduction and O₂ production. The efficient charge separation, abundant H₂ production active sites, and a small HI splitting energy barrier contribute to the superior photocatalytic H₂ production activity of MoSe₂ /MAPbBr_{3- x} I_x (CH₃ NH₃ ⁺ = MA). Subsequent electrocatalytic I₃ ^- reduction and O₂ 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 H₂ (6.99 mmol g^-1 ) to O₂ (3.09 mmol g^-1 ) produced during the first photocatalytic and electrocatalytic cycle is close to 2:1, and the continuous circulation of I₃ ^- /I^- between the photocatalytic and electrocatalytic systems can achieve efficient and robust pure water splitting.