Ultra‐Narrow Depletion Layers in a Hematite Mesocrystal‐Based Photoanode for Boosting Multihole Water Oxidation

Abstract

Significant charge recombination that is difficult to suppress limits the practical applications of hematite (α‐Fe2O3) for photoelectrochemical water splitting. In this study, Ti‐modified hematite mesocrystal superstructures assembled from highly oriented tiny nanoparticle (NP) subunits with sizes of ca. 5 nm were developed to achieve the highest photocurrent density (4.3 mA cm−2 at 1.23 V vs. RHE) ever reported for hematite‐based photoanodes under back illumination. Owing to rich interfacial oxygen vacancies yielding an exceedingly high carrier density of 4.1×1021 cm−3 for super bulk conductivity in the electrode and a large proportion of ultra‐narrow depletion layers (<1 nm) inside the mesoporous film for significantly improved hole collection efficiency, a boosting of multihole water oxidation with very low activation energy (Ea=44 meV) was realized.

Low-bias photoelectrochemical water splitting via mediating trap states and small polaron hopping

“…5b). We note that the excellent sulfite oxidation performances of the phosphorus-doped BiVO 4 samples at low applied potentials (≤1.0 V RHE ) are not only better than those of the state-of-theart BiVO 4 photoanodes (Supplementary Table 1) but also superior to those of other metal oxide photoanodes to date 33,34 .…”

Photothermal‐boosted polaron transport in Fe2O3 photoanodes for efficient photoelectrochemical water splitting

“…39,40 According to the previous experimental and theoretical research about the effect of O V on the PEC performances of Fe 2 O 3 , the introduction of O v significantly increases the charge carrier density of Fe 2 O 3 . 15,41 However, the positively charged O v can bind the negatively charged electron polaron, thus resulting in severely reduced charge carrier mobility. 42,43 To reveal the effect of O v on the small polarons hopping process, density functional theory calculations were performed.…”

Mechanisms of water oxidation on heterogeneous catalyst surfaces

“…Patzke's group recently observed the 3 rd -order reaction kinetics on hematite photoanode in the presence of two surface states at 0.9 and 1.3 V, respectively, which was later interpreted as that the O-O formation was the RDS [65]. In their other two works on hematite, they observed 2 nd order kinetics on bare hematite nanorods array [66] but 3 rd order kinetics on mesocrystal-based hematite photoanode [67]. For the 4 th -order reaction, it is only reported on Ni/Fe oxyhydroxide films (Fig.…”