Reduction of charge carrier recombination by Ce gradient doping and surface polarization for solar water splitting

• Gradient Ce doping on Fe 2 O 3 with the construction of built-in electric field. • Surface polarization on gradient Ce doped Fe 2 O 3 reduced the interfacial oxygen vacancies. • The photoanode exhibited a photocurrent of 2.50 mA cm −2 at 1.50 V RHE with a low onset potential of 0.64 V RHE . • DFT calculations demonstrated the elimination of deep trap state and the reduction of charge recombination. Photoelectrochemical (PEC) water splitting is one of the most strategies for solar energy storage and utilization. Hematite as one of the promising candidates for PEC research, has a short hole diffusion length and short carrier lifetime, resulting in PEC conversion efficiency far below the theoretical value. In this work, a facile but efficient strategy was introduced for the growth of gradient Ce doped hematite nanorods, following with the sequent photoactivation process. The gradient Ce doping not only increased the conductivity of bulk material, but also importantly, constructed a built-in electric field by the addition of Ce element, which remarkably enhanced the charge separation and transfer from the bulk to the surface. Moreover, the surface polarization under illumination was applied for the reduction of overpotential and the enhancement of photocurrent density, taking a role of cocatalyst decoration. It reduced the oxygen vacancies concentration at the surface, which further reduced the surface recombination owing to the passivation from photoactivation. According to these, the resulting photoanode exhibited a photocurrent of 1.92 and 2.50 mA cm −2 at 1.23 and 1.50 V RHE , respectively, with onset potential of 0.64 V RHE under AM 1.5G illumination. This work opens a useful strategy of modifying the electronic structure and constructing the interface structure for improving PEC performance on hematite-based photoelectrodes for solar energy storage and utilization.