Enhanced visible-light photocatalytic H2 production by Znx Cd1-x S modified with earth-abundant nickel-based cocatalysts.

The application of various earth-abundant Ni species, such as NiS, Ni, Ni(OH)2 , and NiO, as a co-catalyst in a Znx Cd1-x S system for visible-light photocatalytic H2 production was investigated for the first time. The loading of Ni or NiS enhanced the photocatalytic activity of Znx Cd1-x S because they could promote the electron transfer at the interface with Znx Cd1-x S and catalyze the H2 evolution. Surprisingly, Ni(OH)2 -loaded Znx Cd1-x S exhibits a very high photocatalytic H2 -production rate of 7160 μmol h(-1)  g(-1) with a quantum efficiency of 29.5 % at 420 nm, which represents one of the most efficient metal sulfide photocatalysts without a Pt co-catalyst to date. This outstanding activity arises from the pronounced synergetic effect between Ni(OH)2 and metallic Ni formed in situ during the photocatalytic reaction. However, the loading of NiO deactivated the activity of Znx Cd1-x S because of their unmatched conduction band positions. This paper reports the optimization of the Znx Cd1-x S system by selecting an appropriate Ni-based co-catalyst, Ni(OH)2 , from a series of Ni species to achieve the highest photocatalytic H2 -production activity for the first time and also reveals the roles of these Ni species in the photocatalytic activity.