Enhanced Light Absorption and Charge Carrier Management in Core‐Shell Fe 2 O 3 @Nickel Nanocone Photoanodes for Photoelectrochemical Water Splitting

Solar driven photoelectrochemical (PEC) water splitting is a clean and sustainable approach to generate green fuel, Hydrogen. Hematite (Fe 2 O 3 ) is considered as potential photoanode because of its abundance, chemical stability and suitable band gap, though its short carrier diffusion length puts a limit on the film thickness and subsequent light absorption capability. In this regard, here we have designed and constructed a unique photoanode by depositing ultrathin films of Fe 2 O 3 on purpose‐built three‐dimensional (3D) nickel nanocone arrays. In this design, 3D nanostructures not only provide ameliorated surface area for PEC reactions but also enhance light absorption capability in ultrathin Fe 2 O 3 films, while ultrathin films promote charge carrier separation and effective transfer to the electrolyte. The 3D electrodes exhibit a substantial improvement in light absorption capability within the entire visible region of solar spectrum, as well as enhanced photocurrent density as compared to the planar Fe 2 O 3 photoelectrode. Detailed investigation of reaction kinetics suggests an optimum Fe 2 O 3 film thickness on 3D nanocone arrays obtained after 6 deposition cycles in achieving maximum charge carrier separation and transfer efficiencies (82 % and 88 %, respectively), mainly ascribable to the increased charge carrier lifetime overcoming recombination losses.