Transferred monolayer MoS₂ onto GaN for heterostructure photoanode: Toward stable and efficient photoelectrochemical...

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 MoS₂/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 MoS₂ monolayer (E_g = 1.9 eV) formed by a Mo-sulfurization technique. Our experimental results reveal that MoS₂/GaN photoanode achieved efficient light harvesting with photocurrent density of 5.2 mA cm^-2 at 0 V vs Ag/AgCl, which is 2.6 times higher than pristine GaN. Interestingly, MoS₂/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 MoS₂/GaN photoelectrode is mainly related to the enhanced light absorption due to excellent photocatalytic behavior of MoS₂, 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 MoS₂ as a cocatalyst coated onto GaN to synthesize photoelectrodes for efficient solar energy conversion devices.