Photocatalytic hydrogen production using twinned nanocrystals and an unanchored NiSx co-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 Cd0.5Zn0.5S (CZS) nanotwinned photocatalyst with a NiSx co-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 Na2S/Na2SO3 as hole scavengers. Our results indicate that the NiSx co-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 NiSx clusters, which aids charge separation and inhibits back reaction, leading to high water reduction rates in the suspension.