Tailoring surface states by sequential doping of Ti and Mg for kinetically enhanced hematite photoanode

Design of Ti-Pt Co-doped α-Fe2O3 photoanodes for enhanced performance of photoelectrochemical water splitting

This study demonstrates Ti and Pt co-doping can synergistically improve the PEC performance of the α-Fe₂O₃ photoanode. By varying the doping methods, the sample with in-situ Ti ex-situ Pt doping (Ti_i-Pt_e) exhibits the best performance. It demonstrates that Ti doping in bulk facilities charge separation and Pt doping on the surface further accelerates charge transfer. In contrast, Ti doping on the surface inhibits charge separation, and Pt doping in bulk hinders charge separation and transfer. HCl treatment is used to minimize the onset potential further, while it is favorable for the ex-situ doped α-Fe₂O₃, which is more efficient on Ti_e than the Pt_e-doped ones. On the ex-situ Ti-doped α-Fe₂O₃ after HCl treatment, anatase TiO₂ is probed, suggesting that Ti-O bonds accumulate when Fe-O bonds are partly removed, which enhances the charge transfer in surface states. Unfortunately, HCl treatment also induces lattice defects that are adverse to charge transport, inhibiting the performance of in-situ doped α-Fe₂O₃ and excessively treated ex-situ doped ones. Coupled with methanol solvothermal treatment and NiOOH/FeOOH cocatalysts loading, the optimized Ti-Pt/Fe₂O₃ photoanode exhibits an impressive photocurrent density of 2.81 mA cm^-2 at 1.23 V vs. RHE and a low onset potential of 0.60 V vs. RHE.

Ordered Ti-doped FeVO4 nanoblock photoanode with improved charge properties for efficient solar water splitting

Highly photoactive FeVO₄ photoanodes with ordered nanoblock morphology and uniform Ti-doping were prepared by drop-casting mixed Ti and V precursors onto FeOOH nanorod films and following an annealing process. The results indicate that Ti⁴⁺ is uniformly doped into the FeVO₄ lattice by substituting V⁵⁺ and provides an increased number of O₂^- vacancies. The optimized film thickness and doping level are 620 nm and 0.3%, respectively. Compared to the undoped sample, the Ti-doped photoanode showed ~ 219% enhancement in photocurrent at 1.0 V vs Ag/AgCl under back illumination of AM 1.5, reaching a state-of-the-art value of ~ 1.47 mA cm^-2, and also achieved stable and efficient overall water splitting activity with evolution rates of 28.3 and 14.1 μmol cm^-2h^-1 for H₂ and O₂, respectively. The excellent PEC performance could be attributed to the remarkably enhanced charge carrier concentration and conductivity, and the facilitated charge transfer kinetics across the semiconductor/electrolyte interface, as a result of Ti-doping.

Tin and Oxygen-Vacancy Co-doping into Hematite Photoanode for Improved Photoelectrochemical Performances

Hematite (α-Fe₂O₃) material is regarded as a promising candidate for solar-driven water splitting because of the low cost, chemical stability, and appropriate bandgap; however, the corresponding system performances are limited by the poor electrical conductivity, short diffusion length of minority carrier, and sluggish oxygen evolution reaction. Here, we introduce the in situ Sn doping into the nanoworm-like α-Fe₂O₃ film with ultrasonic spray pyrolysis method. We show that the current density at 1.23 V vs. RHE (J_ph@1.23V) under one-sun illumination can be improved from 10 to 130 μA/cm² after optimizing the Sn dopant density. Moreover, J_ph@1.23V can be further enhanced 25-folds compared to the untreated counterpart via the post-rapid thermal process (RTP), which is used to introduce the defect doping of oxygen vacancy. Photoelectrochemical impedance spectrum and Mott-Schottky analysis indicate that the performance improvement can be ascribed to the increased carrier density and the decreased resistances for the charge trapping on the surface states and the surface charge transferring into the electrolyte. X-ray photoelectron spectrum and X-ray diffraction confirm the existence of Sn and oxygen vacancy, and the potential influences of varying levels of Sn doping and oxygen vacancy are discussed. Our work points out one universal approach to efficiently improve the photoelectrochemical performances of the metal oxide semiconductors.