A Rhodium-Doped PbTiO ₃ Photocathode Applicable to Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) water splitting using pair-conjugated dual-electrodes is a promising approach for converting solar energy to hydrogen. However, the development of stable photocathode materials capable of harvesting visible light remains challenging. Herein, rhodium-doped lead titanate (Rh:PbTiO3) was synthesized via a vacuum-condition solid-state reaction. Rh doping converted the n-type PbTiO3 host into a p-type one, accompanied by a transition from an anodic to cathodic PEC response. The switching mechanism was thoroughly investigated using Kelvin probe force microscopy and in situ surface photovoltage spectroscopy. Spontaneously formed Rh on the Rh:PbTiO3 particle was conducive to enhancing surface charge injection efficiency (86% at 0.2 V vs RHE). The onset potential of the optimized 4% Rh:PbTiO3 photocathode reached 1.06 V vs RHE after modification with a layered Pt@Rh cocatalyst. An unbiased parallel cell established by the Rh:PbTiO3 photocathode and Mo:BiVO4 photoanode exhibited stoichiometric and continuous water splitting under simulated sunlight illumination with a Faradaic efficiency of unity. This work not only outlines the dopant-dominated n/p-type transition for semiconducting materials but also shows their priority in achieving stable and visible light-responsive PEC water splitting.