Decoration of CdS nanowires with Ni3S4 nanoballs enhancing H2 and H2O2 production under visible light

Much work in the past four decades has focused on CdS as photocatalyst for water splitting. Recently, Ni3S4 has been reported to be more active than IrO2 as an electrocatalyst for water oxidation. Herein we report a positive role of Ni3S4 in CdS photocatalysis. Reaction was conducted in aqueous suspension under a 420 nm light, either for proton reduction to H2 in presence of Na2S and Na2SO3, or for O2 reduction to H2O2 without addition of any sacrifices. In both cases, Ni3S4 were nearly not active. After Ni3S4 loading, however, the rates of H2 and H2O2 production on CdS increased by factors as much as 21 and 3, respectively. Furthermore, Ni3S4/CdS was more efficient than CdS for proton and O2 reduction on a cathode, respectively, while Ni3S4/CdS was less efficient than CdS for the photoelectron accumulation on an electrode at open circuit potential. Based on the solid photoluminescence spectra and band edge potentials, a possible mechanism is proposed, involving the interfacial electron transfer from CdS to Ni3S4, followed by an increased surface reaction, for proton (oxygen) reduction on Ni3S4 sites, and for sulfide (water) oxidation on CdS sites, respectively.