Earth-abundant elements doping for robust and stable solar-driven water splitting by FeOOH

The water oxidation reaction (OER) is the key process used for the generation of H-2, and new catalyst systems are needed to achieve considerable efficiency in the OER. In the present work, beta-FeOOH samples, both bare and doped with earth-abundant elements (Ni and Co), were synthesized and confirmed to be promising semiconductors for solar-driven water oxidation. This is the first time that the direct use of beta-FeOOH samples has been reported in a water splitting system, in which beta-FeOOH has always been used as a co-catalyst. From a combination of DFT calculations and experimental results, (a) beta-FeOOH can play two roles, namely, carrier generation and improving the kinetics of water oxidation, owing to the abundance of surface OH groups; (b) doping with Ni or Co can improve the photocatalytic activity of beta-FeOOH, and this enhancement benefits from the separation of photogenerated carriers; (c) samples doped with Ni or Co give better performance in electrocatalytic water oxidation than bare beta-FeOOH. After being doped with these earth-abundant elements, beta-FeOOH delivered saturated photocurrent densities of 4.71 (for Co) and 2.55 (for Ni) mA cm(-2), which are higher than the value of 0.69 mA cm(-2) recorded for bare b-FeOOH at a low external bias of 1.0 V versus RHE.