Engineering CuSe nanosheet/TiO₂ heterostructures toward high-performance photocathodes for solar hydrogen production

Two-dimensional copper selenide (CuSe) nanosheet arrays were successfully synthesized on FTO substrates via an electrochemical deposition route, followed by Se vapor thermal treatment and subsequent TiO₂ decoration. Structural and surface analyses confirmed the formation of crystalline CuSe, with XPS revealing the coexistence of Cu²⁺ and Se²⁻ species, while the bandgap values estimated from optical absorption spectra ranged from 1.45 to 1.7 eV depending on post-treatments. Photoelectrochemical (PEC) measurements demonstrated that the photocurrent density of as-grown CuSe nanosheets (−0.8 mA cm⁻²) was markedly improved after Se vapor annealing (−2.1 mA cm⁻²) and further enhanced with TiO₂ decoration (−3.0 mA cm⁻²), corresponding to nearly a fourfold increase. Incident photon-to-electron conversion efficiency (IPCE) spectra revealed a similar absorption onset at 680 nm but significantly higher conversion efficiencies for the CuSe–Se/TiO₂ heterostructure. Mott–Schottky analyses confirmed the p-type semiconducting behavior, with variations in flat-band potential and carrier concentration indicating enhanced charge separation upon TiO₂ modification. Gas chromatographic measurements further verified solar-driven water splitting, yielding H₂ gas with Faradaic efficiencies of ∼80 % under simulated AM 1.5 G irradiation. These findings highlight that Se vapor treatment combined with TiO₂ decoration provides an effective strategy to boost the PEC performance of CuSe nanosheets, demonstrating their potential as efficient photocathodes for solar hydrogen generation.