Facile construction of Pt/TiO₂/Se/Ni heterostructure for efficient visible-light-driven PEC water splitting

In this study, a novel Pt/TiO₂/Se/Ni heterostructure photocathode was successfully fabricated via a simple and cost-effective method involving galvanic replacement, thermal annealing, and sequential spin-coating processes. Amorphous selenium was first deposited on nickel foil and subsequently transformed into crystalline trigonal Se through thermal treatment. The TiO₂ and Pt nanoparticles were then uniformly decorated onto the Se surface to form a hierarchical heterostructure. Structural, morphological, and compositional characterizations using XRD, SEM, Raman spectroscopy, and XPS confirmed the formation of trigonal selenium and the successful deposition of TiO₂ and Pt. Optical and photoelectrochemical (PEC) analyses revealed that the crystalline Se exhibited an optimal band gap of 1.89 eV and efficient visible light absorption. The Pt/TiO₂/Se photocathode delivered a significantly enhanced photocurrent density of -5 mA cm^-2 at -0.3 V vs. Ag/AgCl, which is 1.6 times higher than that of the bare Se electrode. Mott-Schottky and EIS analyses demonstrated an increased carrier density and reduced charge transfer resistance, facilitating efficient charge separation and transfer. These findings highlight the great potential of the Pt/TiO₂/Se heterostructure as a high-performance photocathode for solar hydrogen production applications.