Dendritic CuBi₂O₄ Array Photocathode Coated with Conformal TiO₂ Protection Layer for Efficient and Stable Photoelectrochemical Hydrogen Evolution Reaction

Short carrier diffusion length and poor photostability are two major bottlenecks limiting the application of CuBi₂O₄ as a competitive candidate for photoelectrochemical (PEC) hydrogen evolution reaction (HER). To overcome the bottlenecks, we develop a novel template-assisted synthesis strategy to prepare the CuBi₂O₄ dendrites and then protect the dendritic structure with a conformal nanometer-thick TiO₂ passivation layer. The obtained CuBi₂O₄/TiO₂ composite dendrites exhibit high activity for the PEC HER with a photocurrent density of ca. 0.90 mA cm⁻² at 0.200 V vs reversible hydrogen electrode (RHE) in neutral solution, and this value is among the highest reported on CuBi₂O₄-based photocathodes at the same potential. Moreover, the CuBi₂O₄/TiO₂ dendrites show a high photostability with the photocurrent density being stabilized at ca. 0.36 mA cm⁻² (88.8% of its original value) after 6 h measurements at a high applied potential of 0.600 V vs RHE, which is superior to all CuBi₂O₄-based photocathodes reported recently in the literature. This work provides an effective strategy to improve the activity and stability of the copper-oxide-based materials for the HER via constructing a dendritic structure and protecting the structure with a nanoscale TiO₂ passivation layer.