Hole extraction and injection pathways constructed by the in situ growth of ultra-thin Fe-doped NiOOH Co-catalysts on a fluorine-doped α-Fe2O3 photoanode

Abstract Hematite can be used as an efficient photoanode for solar water oxidation, but its oxygen evolution kinetics are quite slow. Herein, we developed an efficient hole transport photoanode via the in situ growth of ultrathin Fe-doped NiOOH on fluorine-doped hematite arrays using a natural growth strategy. The resulting FeNiOOH/F–Fe2O3 photoanode showed a high charge separation and injection efficiency. It achieved a stable photocurrent density of 2.52 mA cm−2 at 1.23 V vs. RHE, which was approximately 4.1-fold higher than that of pristine α-Fe2O3. Systematic studies revealed that the excellent photoelectrochemical activity was due to heteroatom doping and interactions between the co-catalyst (FeNiOOH) and F–Fe2O3. Fe doping primarily changed the lattice strain of the co-catalyst, while F doping decreased surface charge recombination and enhanced the intrinsic conductivity of hematite by increasing the carrier density. An ultrathin, amorphous layer of FeNiOOH further accelerated photogenerated hole extraction and the water oxidation kinetics. This work provides a method to produce new, cost-effective photoanodes for clean hydrogen production.