Accelerating Oxygen Evolution Reaction Kinetics by Reconstructing Layered and Defective Ni3FeOOH/FeOOH in a Hematite Photoanode

Surface engineering has outstanding advantages for improving the carrier exaction of photoelectrodes in the photoelectrochemical water splitting field. NiFe-layered double hydroxides (NiFe-LDH), as promising catalysts for water oxidation, can facilitate carrier transport. But surface collapse and structural deformation limit their applications. In this work, a hematite (alpha-Fe2O3) photoanode is sequentially cumulatively modified with NiFe-LDH (Ni3FeOOH), Ag/SiO2, and FeOOH, and exhibits a high photocurrent density, which increases from 0.92 to 4.54 mA cm(-2) at 1.23 V relative to the standard hydrogen electrode (V-RHE). The mechanism studies demonstrate that the introduction of FeOOH suppresses the electrochemical self-reduction of Ni3FeOOH, remedies the obvious valley formed in the current density and voltage curve, reduces recombination, and facilitates the OH- transformation, which increases the catalytic activities of the photoanode. The Ag@SiO2 nanoparticles can reduce the interface defects between Ni3FeOOH and FeOOH. The density-functional theory calculation reveals that the valley is caused by the direction of the internal electric field formed between Ni3FeOOH and alpha-Fe2O3, which is opposite to that of solid-liquid junction, resulting in serious carrier recombination. FeOOH possesses a higher electrostatic potential than that of Ni3FeOOH and alpha-Fe2O3 and forms an internal electric field directing from alpha-Fe2O3/Ni3FeOOH to FeOOH, which synergistically promotes carrier separation with solid-liquid junction.