Work function-tunable graphene/WO3 heterojunctions for high-performance photoelectrochemical cell: UV-treatment effect and defective graphene.

Designing hybrid photoelectrodes with graphene capable of efficient charge-carrier transfer and excellent chemical stability is an effective strategy for developing high-performance photoelectrochemical (PEC) cells. However, it remains unclear how the PEC properties are enhanced and how to control the junction properties in graphene/metal oxide heterojunction-based photoelectrodes. Here, we develop a deterministic junction to enhance PEC performance in graphene/tungsten trioxide (WO 3)-based photoelectrodes by tuning the work function of graphene. It reveals that the band structure of graphene/WO 3 heterojunctions can be modified by ultraviolet (UV) treatment on WO 3 thin films. This modification is supported by the observation that a single-layer graphene/UV-treated WO 3 photoelectrode exhibits significantly enhanced PEC activities toward the oxygen evolution reaction (OER) (evidenced by features like a threefold increase in photocurrent, an onset potential shift, and improved stability), whereas the single-layer graphene/untreated WO 3 electrode demonstrates improved properties for the hydrogen evolution reaction (HER). Additionally, defects in the graphene layer formed during PEC water splitting contribute to high catalytic activities of the graphene/WO 3 photoelectrode due to a decrease in the Gibbs free energy for OER and HER. These results emphasize that band structure engineering via work function tuning in graphene/WO 3 heterostructures can provide multiple benefits for high PEC performance and long-term stability. [Display omitted] • Graphene offers efficient charge transfer and chemical stability in photoelectrode. • The work function of graphene is tuned with a deterministic junction. • UV treatment on WO 3 modifies the band structure of graphene/WO 3 heterojunctions. • The SLG/WO 3 (UV)/Nb:STO exhibits outstanding water oxidation performance. • Graphene also serves as surface passivation and co-catalyst layer. [ABSTRACT FROM AUTHOR]