How titanium and iron are integrated into hematite to enhance the photoelectrochemical water oxidation: a review.

Hematite has been considered as a promising photoanode candidate for photoelectrochemical (PEC) water oxidation and has attracted numerous interests in the past decades. However, intrinsic drawbacks drastically lower its photocatalytic activity. Ti-based modifications including Ti-doping, Fe2O3/Fe2TiO5 heterostructures, TiO2 passivation layers, and Ti-containing underlayers have shown great potential in enhancing the PEC conversion efficiency of hematite. Moreover, the combination of Ti-based modifications with various strategies towards more efficient hematite photoanodes has been widely investigated. Nevertheless, a corresponding comprehensive overview, especially with the most recent working mechanisms, is still lacking, limiting further improvement. In this respect, by summarizing the recent progress in Ti-modified hematite photoanodes, this review aims to demonstrate how the integration of titanium and iron atoms into hematite influences the PEC properties by tuning the carrier behaviours. It will provide more cues for the rational design of high-performance hematite photoanodes towards future practical applications.

CoMoO4-modified hematite with oxygen vacancies for high-efficiency solar water splitting.

Hematite is a potential photoelectrode for photoelectrochemical (PEC) water splitting. Nevertheless, its water oxidation efficiency is highly limited by its significant photogenerated carrier recombination, poor conductivity and slow water oxidation kinetics. Herein, under low-vacuum (LV) conditions, we fabricated a CoMoO4 layer on oxygen-vacancy-modified hematite (CoMo-Fe2O3 (LV)) for the first time for efficient solar water splitting. The existence of oxygen vacancies can significantly facilitate the electrical conductivity, while the large onset potential along with oxygen vacancies can be lowered by the CoMoO4 with accelerated water oxidation kinetics. Therefore, a high photocurrent density of 3.53 mA cm-2 at 1.23 VRHE was obtained for the CoMo-Fe2O3 (LV) photoanode. Moreover, it can be further coupled with the FeNiOOH co-catalyst to reach a benchmark photocurrent of 4.18 mA cm-2 at 1.23 VRHE, which is increased around 4-fold compared with bare hematite (0.90 mA cm-2). The combination of CoMoO4, FeNiOOH, and oxygen vacancies may be used as a reasonable strategy for developing high-efficiency hematite-based photoelectrodes for solar water oxidation.