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 /MAPbBr3-x Ix (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.