Hydrogen evolution from water based on plasmon-induced charge separation at a TiO/Au/NiO/Pt system.

Metal-semiconductor plasmonic nanostructures are capable of converting light energy through plasmon-induced charge separation (PICS), providing fruitful new strategies to utilize solar energy in various fields, including photocatalysis. Here, we enhance the PICS efficiencies for hydrogen evolution from water at a Pt cathode coupled with a TiO/Au photoanode by coating the TiO/Au with a p-type NiO layer on which a Pt co-catalyst is deposited. PICS occurs at the Au-TiO interface under visible light. The electrons injected from the Au nanoparticles into TiO are transported to the Pt cathode and cause hydrogen evolution from water, the action spectrum of which matches the plasmonic extinction spectrum of the Au nanoparticles. The NiO layer extracts the separated positive charges from the Au nanoparticles, accumulates the charges and drives methanol oxidation at the Pt co-catalyst on NiO with the positive charges. As a result of the introduction of the Pt-modified NiO layer, the rates of methanol oxidation and accompanying hydrogen evolution at zero bias voltage were improved by ∼3.5 times. The NiO layer may also protect the Au nanoparticles from self-oxidation.