Polyoxometalate-incorporated ZnIn2S4 z-scheme heterojunction with enhanced light-driven hydrogen production performances

This work reports a strategy for the rational design of polyoxometalate (SiW9M3, M = Ni, Co, Fe)-based ZnIn2S4 (abbreviated as ZIS) photocatalysts with Z-Scheme heterojunction, under the synergistic effect of polydopamine (abbreviated as PDA), namely ZIS/PDA/SiW9M3 (shorted as ZPM, M = Ni, Co, Fe). Surface loading of SiW9M3 increases expand the light capture capability in the visible range of the composites, providing more active sites for photocatalytic water splitting, and addressing the problem of the easy dissolution and aggregation of the polyoxometalate. Importantly, the close contacting of SiW9M3 and ZIS in the form of Z-Scheme heterojunction creates an internal electric field at the interface due to the difference in Fermi levels, effectively suppressing the recombination of photoinduced electron-hole pairs. Among the ZPM composite materials, ZPNi-20 (20 representing the molar amount of SiW9Ni3 added) exhibits the best hydrogen production performance (13.40 mmol g- 1h- 1, TON = 337 or TOF = 67.4 h- 1). UPS, EPR, and KPFM studies elucidate the efficient charge separation and transfer process in the Z-Scheme structure, where the photo-generated electrons transfer from ZIS (as the electron donor) to SiW9M3 (as the electron acceptor) during illumination, leading to high charge separation and transfer efficiency as well as strong redox capability.