Efficient and stable piezo-photocatalytic splitting of water and seawater by interfacial engineering of Na0.5Bi0.5TiO3/Na0.5Bi4.5Ti4O15 self-generated heterojunctions

Seawater splitting by piezocatalysis and piezo-photocatalysis recently has been developed as a strategy for efficient energy conversion from mechanical energy and/or renewable solar energy. However, the piezocatalytic hydrogen evolution reaction (HER) performance currently remain worse than those from electrolysis or photocatalysis, suffering from serious charge recombination and catalyst leaching in seawater. Herein, the present work reveals a novel nanostructure with self-generated Na0.5Bi0.5TiO3/Na0.5Bi4.5Ti4O15 (NBT/NBT4) heterojunctions, which can be engineered systematically by regulating the NaOH precursor concentration (2.5 M, 7.5 M, 12.5 M) during hydrothermal synthesis. This engineering facilitates the substitution of Bi3+ by Na+ in the NBT solid solution, which also enables the regulation of oxygen vacancy and modification of the band structure. Experimental results and associated theoretical simulation reveal the formation of heterojunction between NBT and NBT4, thereby promoting both charge transfer and charge separation. Consequently, the heterojunction (NBT-12.5 M) exhibited an efficient HER rate of 140 μmol/g/h from DI water through piezo-photocatalysis. More significantly, the heterojunction also causes notable seawater splitting capability, with the HER rates of 68 μmol/g/h from simulated seawater and 58 μmol/g/h from natural seawater. The unique nanostructure effectively suppresses the leaching of Na+ ions in simulated seawater, indicating the potential for durable and practical seawater splitting.