Photocatalytic hydrogen production using twinned nanocrystals and an unanchored NiS_xco-catalyst

Facilitating charge separation as well as surface redox reactions is considered to be central to improving semiconductor-catalysed solar hydrogen generation. To that end, photocatalysts comprising intimately interfaced photo absorbers and co-catalysts have gained much attention. Here, we combine an efficient Cd 0.5 Zn 0.5 S (CZS) nanotwinned photocatalyst with a NiS_xco-catalyst for photogeneration of hydrogen. We find that an internal quantum efficiency approaching 100% at 425 nm can be achieved for photocatalytic H 2 production from water with Na 2 S/Na 2 SO 3 as hole scavengers. Our results indicate that the NiS_xco-catalyst is not anchored on the surface of the host CZS nanotwins and instead exists in the reaction solution as freestanding subnanometre clusters. We propose that charge transfer is accomplished via collisions between the CZS and NiS x clusters, which aids charge separation and inhibits back reaction, leading to high water reduction rates in the suspension.