Transparently Passivating Catalyst of Hydrated Manganese Phosphate for Photoelectrochemical O₂ Generation

A transparently hydrated manganese phosphate (“Mn–Pi”) catalyst is coated onto a Ti-doped hematite (Ti:Fe2O3) photoanode by the photo-assisted electrochemical deposition. Under a visible light illumination of 100 mW cm–2, the photocurrent density of Ti:Fe2O3/Mn–Pi reaches 0.28 mA cm–2 at 1.2 VRHE, which is around two times higher than that obtained with the pristine Ti:Fe2O3 electrode in a neutral electrolyte, and the “onset” potential reduces by 100 mV. The passivating role of the Mn–Pi catalyst is revealed experimentally. The surface states of hematite are significantly passivated after Mn–Pi deposition, which relieves the degree of Fermi level pinning of hematite and enhances the surface band bending of hematite. Therefore, the photovoltage and the charge separation are improved. Moreover, due to the valence change of the Mn element in Mn–Pi, the charge transfer through the Mn–Pi layer is favorable, which has a low charge transfer resistance for photogenerated holes. The suitability of this transparently passivating catalyst for concentrating light is also identified. This work demonstrates that Mn–Pi can be applied for photoelectrochemical water splitting as a transparently passivating catalyst

Hydrothermally Treating High-Ti Cinder for a Near Full-Sunlight-Driven Photocatalyst toward Highly Efficient H₂ Evolution

A major drawback of conventional photocatalysts like TiO₂ is the limit of only working under ultraviolet irradiation. As a solution, visible-light-driven photocatalysts have been explored in recent years but full-sunlight-driven photocatalysts are still lacking. Herein, multielement-codoped (Mn, Fe, Si, Al, S, F, etc.) TiO₂ nanomaterials were prepared from an industrial high-Ti cinder (HiTi) by a two-step hydrothermal method using NaOH and NH₄F (or H₂O) as morphology controlling agents. The prepared HiTi photocatalyst exhibits a strong absorption at near full-sunlight spectrum (300–800 nm). Among all TiO₂-based photocatalysts without any noble metal cocatalyst, the photocatalytic H₂ evolution rate on NaOH- and H₂O-hydrothermally treated HiTi (HiTi-TiO₂) is remarkably superior to the reference P25 TiO₂ powders by a factor of 3.8 and thus is the highest. However, NaOH- and NH₄F-treated HiTi (HiTi-TiO₂-F) shows a lower photoreactivity than HiTi-TiO₂ does. Mechanistic studies show that the multielement-doped TiO₂ can synergistically harvest full span sunlight to greatly increase light absorption, while suppressing the charge recombination and reducing the reaction barriers for efficient water splitting. Importantly, the amount of produced industrial cinder is huge in China, and it is dumped on the ground in very large mounds, which results in serious pollution. This study may open a promising recycling approach to treat the waste for sustainable energy use