Band engineering of hematite photoanode for effective photoelectochemical water splitting

Photoelectrochemical (PEC) water splitting provides a green zero carbon footprint technique to produce hydrogen. Among the currently studied photoanodes, hematite is one of the most promising material with multiple advantages i.e. earth abundance, suitable band gap of ~2.1eV which is capable of utilising nearly 40% of incident solar light and suitable band edge position for oxidizing water to oxygen. However, its full potential is not realised due to bottleneck of small hole diffusion length and high recombination. Herein, photoelectrochemical property of electrodeposited α-Fe₂O₃ on FTO (Fluorine doped tin oxide) has been investigated. The SnO₂ heterojunction underlayer has been formed to retard the electron hole recombination process. Photoanodes has been characterized by XRD, AFM and Raman spectroscopy. Photo-response of photoanode materials were performed by Chopped Light Voltammetry (CLV) technique. The fabricated photoelectrode showed enhanced photo-response. In order to understand the mechanism of the photo electrocatalytic activity, donor density measurement, photo electrochemical impedance spectroscopy (PEIS), incident photon to current efficiency (IPCE) has been performed. Insertion of SnO₂ heterojunction shows improvement in Tafel slope from 258 mV to 240 mV, donor density by 4 times, decrease in charge transfer resistance and considerable improvement in IPCE (from ~20% to ~28%) in SnO₂-Fe₂O₃ compared to bare Fe₂O₃. Further, the stability test of SnO₂/Fe₂O₃ photoanode was performed by chronoamperometry method for continuous light illumination for 7200 s. The photoanode material is stable over appreciable period of time. Therefore, the band engineering of hematite photoanode by heterojunction formation is an effective technique to reduce electron hole recombination to enhance the efficiency of hematite photoanode