Ultrathin Amorphous Ni(OH)₂ Nanosheets on Ultrathin α‐Fe₂O₃ Films for Improved Photoelectrochemical Water Oxidation

Hematite ( α ‐Fe 2 O 3 ) is a promising photoanode material for photoelectrochemical (PEC) water splitting, however, its performance is largely limited by the short hole diffusion length that requires the thin active layer and efficient catalysts. In this work, ultrathin α ‐Fe 2 O 3 films are fabricated using atomic layer deposition technology, and then ultrathin amorphous Ni(OH) 2 nanosheets are decorated on α ‐Fe 2 O 3 films through a hydrothermal method. The microscopic morphology, phase, and composition are characterized by scanning electron microscopy, X‐ray diffraction, X‐ray photoelectron spectra, and high resolution transmission electron microscopy. The quantity of Ni(OH) 2 is adjusted by controlling the growth time. The results show that the onset potential of the optimum thick Ni(OH) 2 /Fe 2 O 3 films demonstrate a cathodical shift by 400 mV, and the photocurrent density at 1.23 V is enhanced from 0.21 to 0.37 mA cm −2 compared with the pristine ultrathin α ‐Fe 2 O 3 films. The Ni(OH) 2 /Fe 2 O 3 films show the superior stability up to 20 h. The enhanced PEC performances are attributed to the amorphous Ni(OH) 2 nanosheets that do not affect obviously the light utilization, maintain large specific area to the electrolyte, and store holes produced in Fe 2 O 3 for oxidizing water efficiently in situ with fast regeneration of Ni 2+ .