CoFe Amorphous Double Hydroxides Modified Hematite Photoanode with the Synergism of Co and Fe for Enhanced Photoelectrochemical Water Oxidation

In this study, a hematite photoanode with a CoFe-ADH co-catalyst loaded on the surface was successfully prepared through hydrothermal treatment, annealing, and electrodeposition. We investigated the influence of the deposition time and Co/Fe molar ratio for CoFe-ADH on the performance of alpha-Fe2O3 in photoelectrochemical (PEC) water oxidation. With an optimized condition of CoFe-ADH, the prepared CoFe-ADH/alpha-Fe2O3 photoanode exhibited a high photocurrent density of 1.58 mA/cm2 at 1.23 VRHE, which is about 2.5 times as high as that of alpha-Fe2O3. A series of characterization results and detailed mechanism studies reveal that surface modification of hematite by introducing CoFe-ADH can boost the surface charge transfer efficiency, which can be attributed to the good optical transparency, the amorphous structure of CoFe-ADH, and the synergism of Co and Fe in CoFe-ADH. The good optical transparency contributes to decreasing the loss of light absorption by the photoanodes; the amorphous structure could prevent the formation of grain boundaries and provide more active catalytic sites for PEC water oxidation; and the synergism of Co and Fe in CoFe-ADH enhances photogenerated carriers effective separation and the hole's injection. This work provides valuable insights into the influence of bimetallic co-catalysts on the PEC performance of photoanodes, offering guidance for photoanodes to achieve excellent performance.