Interfacial band-edge engineered TiO₂ protection layer on Cu₂O photocathodes for efficient water reduction reaction

Photoelectrochemical (PEC) water splitting has emerged as a potential pathway to produce sustainable and renewable chemical fuels. Here, we present a highly active Cu₂O/TiO₂ photocathode for H₂ production by enhancing the interfacial band-edge energetics of the TiO₂ layer, which is realized by controlling the fixed charge density of the TiO₂ protection layer. The band-edge engineered Cu₂O/TiO₂ (where TiO₂ was grown at 80 °C via atomic layer deposition) enhances the photocurrent density up to −2.04 mA/cm² at 0 V vs. RHE under 1 sun illumination, corresponding to about a 1,200% enhancement compared to the photocurrent density of the photocathode protected with TiO₂ grown at 150 °C. Moreover, band-edge engineering of the TiO₂ protection layer prevents electron accumulation at the TiO₂ layer and enhances both the Faraday efficiency and the stability for hydrogen production during the PEC water reduction reaction. This facile control over the TiO₂/electrolyte interface will also provide new insight for designing highly efficient and stable protection layers for various other photoelectrodes such as Si, InP, and GaAs. [Figure not available: see fulltext.]