Transferred monolayer MoS onto GaN for heterostructure photoanode: Toward stable and efficient photoelectrochemical water splitting.

Solar-driven photoelectrochemical water splitting (PEC-WS) using semiconductor photoelectrodes is considered a promising solution for sustainable, renewable, clean, safe and alternative energy sources such as hydrogen. Here, we report the synthesis and characterization of a novel heterostructure MoS/GaN to be used as a photoanode for PEC-WS. The heterostructure was synthesized by metal-organic chemical vapor deposition of single crystalline GaN onto a c-plane sapphire substrate, followed by the deposition of a visible light responding MoS monolayer (E = 1.9 eV) formed by a Mo-sulfurization technique. Our experimental results reveal that MoS/GaN photoanode achieved efficient light harvesting with photocurrent density of 5.2 mA cm at 0 V vs Ag/AgCl, which is 2.6 times higher than pristine GaN. Interestingly, MoS/GaN exhibited a significantly enhanced applied-bias-photon-to-current conversion efficiency of 0.91%, whereas reference GaN yielded an efficiency of 0.32%. The superior PEC performance of the MoS/GaN photoelectrode is mainly related to the enhanced light absorption due to excellent photocatalytic behavior of MoS, which reduces charge transfer resistance between the semiconductor and electrolyte interface, and the improvement of charge separation and transport. This result gives a new perspective on the importance of MoS as a cocatalyst coated onto GaN to synthesize photoelectrodes for efficient solar energy conversion devices.