Enhanced Light Absorption and Charge Carrier Management in Core-Shell Fe2O3@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 (Fe2O3) 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 Fe2O3 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 Fe2O3 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 Fe2O3 photoelectrode. Detailed investigation of reaction kinetics suggests an optimum Fe2O3 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.