Bifunctional citrate-Ni0.9Co0.1(OH)x layer coated fluorine-doped hematite for simultaneous hole extraction and injection towards efficient photoelectrochemical water oxidation

Surface modification by loading a water oxidation co-catalyst (WOC) is generally considered an efficient means to optimize the sluggish surface oxygen evolution reaction (OER) of a hematite photoanode for photoelectrochemical (PEC) water oxidation. However, the surface WOC usually exerts little impact on the bulk charge separation of hematite. Herein, an ultrathin citrate-Ni0.9Co0.1(OH)(x) [Cit-Ni0.9Co0.1(OH)(x)] is conformally coated on the fluorine-doped hematite (F-Fe2O3) photoanode for PEC water oxidation to simultaneously promote the internal hole extraction and surface hole injection of the target photoanode. Besides, the conformally coated Cit-Ni0.9Co0.1(OH)(x) overlayer passivates the redundant surface trap states of F-Fe2O3. These factors result in a superior photocurrent density of 2.52 mA cm(-2) at 1.23 V versus a reversible hydrogen electrode (V vs. RHE) for the target photoanode. Detailed investigation manifests that the hole extraction property in Cit-Ni0.9Co0.1(OH)(x) is mainly derived from the Ni sites, while Co incorporation endows the overlayer with more catalytic active sites. This synergistic effect between Ni and Co contributes to a rapid and continuous hole migration pathway from the bulk to the interface of the target photoanode, and then to the electrolyte for water oxidation.

Automated summary

In this study, an ultrathin citrate-Ni0.9Co0.1(OH)(x) overlayer was conformally coated on the fluorine-doped hematite photoanode to promote internal hole extraction and surface hole injection, resulting in a superior photocurrent density. The synergistic effect between Ni and Co contributes to a rapid and continuous hole migration pathway for water oxidation.