Surface metal valence state regulating on hematite to weaken dependence of charge transport to catalyst loading

Generally, the loading of oxygen evolution catalyst (OEC) must be carefully controlled to an extremely thin level or the photo-generated holes will mainly charge the catalyst rather than oxidizing water. To overcome the extreme sensitivity of charge transport to catalyst thickness, we proposed the iron valence state regulating on hematite to negatively shift the surface defect state, thereby suppressing the severe OEC charging. In detail, a fluorine layer (FeOxFy) was inserted between Fe2O3and OEC (ZIF-67) to reduce the oxidation state of iron atoms, forming a case where only part of Co(II) can be oxidized (build a rapid Co(II)/Co(III) cycle). Even in the case of thicker OEC (~10 nm), Fe2O3@F@ZIF-67 exhibits increased photocurrent density of 2.56 mA cm−2at 1.23VRHE(~170% higher than Fe2O3@ZIF-67), accompanied by a rapid decrease in sensitivity to OEC loading. Above pretreatment not only relaxed the catalyst process requirements, but also provide new insights into interfacial catalysis process.