Solar water splitting can form the basis of a sustainable hydrogen based energy economy, however the system requires optimisation in terms of cost and performance on a scale commensurate with the global energy demand. Photocatalysts consist of solar spectrum absorber semiconductor materials and co-catalysts as the redox mediator for hydrogen and oxygen evolution reactions. The key factors for efficient solar water splitting process to occur with such photocatalysts are a semiconductor with a sufficiently narrow band gap to absorb visible lights, a suitable thermodynamic potential for the redox reactions, and stability against photocorrosion. However, current photocatalysts also suffer from undesirable photoelectron-hole (charge carrier) recombination within the semiconductor due to their short diffusion path lengths and lifetimes, which results in fewer than 10% of the incident photons being used for water splitting.

Cuprous Oxide (Cu₂O), one of the few naturally occurring p-type metal oxides, is the most promising candidate for an efficient photocathode because of its earth abundance, a band gap of 2.0 eV, which enables efficient visible light absorption, a scalable CMOS compatible deposition technique (e.g., electrodeposition), and favourable energy band position i.e. conduction band lies 0.7 eV negative of the hydrogen evolution potential that drives off half of the water reduction reaction without of any external bias. However, the application of Cu₂O as photocathode is limited by two drawbacks; fast photoelectron–hole recombination owing to short carrier diffusion length and self-photo corrosion in aqueous solution under illumination since the potentials of Cu₂O reduction and oxidation to metallic Cu and CuO, respectively, lie within the bandgap. Hence, the solar-to-fuel conversion efficiency on Cu₂O depends on how fast the photoelectron can be extracted to the reduction reaction sites and inhibition of electrolyte access to Cu₂O surface. A thin protective coating and a heterostructure in the seed layer of the electrochemically deposited Cu₂O film enhance the overall photocatalytic performance versus the Cu₂O film alone. The thickness of the Cu₂O film was optimised to avoid the charge carrier recombination towards the efficient and stable photocatalytic performance. The photocatalytic performance of Cu₂O thin film is shown in Fig 1, in which the film performance is unexpectedly high and only dropped to 22% after the first cycle at 0.0 V_RHE, after which it stabilises. This presentation will discuss our current research to develop cheap and efficient photocatalysts and their enhancement mechanism towards photocatalytic water splitting reactions.