Conformally Coupling CoAl-Layered Double Hydroxides on Fluorine-Doped Hematite: Surface and Bulk Co-Modification for Enhanced Photoelectrochemical Water Oxidation

Abstract

Earth-abundant hematite is an attractive photoanode for photoelectrochemical water splitting, whereas the intrinsic properties of inferior charge transfer and slow water oxidation kinetics still hinder its application. In response, an integrated photoanode has been constructed with hematite nanorod arrays modified by fluorine anion doping and further decorated with amorphous CoAl-layered double hydroxides (CoAl-LDH). This novel CoAl-LDH/F–Fe2O3 photoanode exhibited an excellent photocurrent density of 2.46 mA cm–2 at 1.23 V versus reversible hydrogen electrode (VRHE), five times enhanced than that of pristine α-Fe2O3. Systematic investigations reveal that fluorine anion serving as a donor dopant dramatically enhances the density of charge carrier and reduces the resistance of hematite for rapid charge transfer. Furthermore, the cocatalyst of CoAl-LDH could effectively passivate the surface defects of F–Fe2O3 and facilitate the water oxidation kinetics through an alternative pathway of holes trapped by Co species. As a consequence, the charge separation efficiencies of the bulk and surface were improved to 32.6 and 81.8%, respectively, compared with those of α-Fe2O3 (9.7 and 31.7%). Our results demonstrate that the dual modification of the bulk and surface is an attractive maneuver to ameliorate the water oxidation activity of hematite.