Unveiling the Synchronized Effect of Bulk and Surface Dual Modification of In Situ Nb-Doping and Microwave-Assisted Co(OH)x Cocatalyst for Boosting Photoelectrochemical Water Splitting of Fe2O3 Photoanodes

Herein, in order to improve the conductivity and slack water oxidation kinetics of the hematite (alpha-Fe2O3) photoanode, we propose the Nb-doped and Co(OH)x cocatalyst-deposited alpha-Fe2O3 thin film photoanode (Nb-HT/Co(OH)x) via in situ diluted hydrothermal and microwave-assisted methods. The as-prepared Nb-HT/ Co(OH)x thin-film photoanode exhibited a photocurrent density of 1.78 mA cm-2 at 1.23 V versus a reversible hydrogen electrode (RHE), which is 1.7-fold higher than that of the Bare-Fe2O3 photoanode. The dual effect of Nb-doping and Co(OH)x deposition markedly improved the PEC performance through enhancing the charge carrier mobility and donor density in hematite, as well as accelerating the interfacial charge transfer kinetics at the electrode/electrolyte interface of the alpha-Fe2O3 thin film photoanode. The Nb-HT/Co(OH)x photoanode displayed a high charge separation efficiency of 90% (at 1.23 VRHE) and excellent stability over a 10 h period without any decrease. Detailed electrochemical analyses using electrochemical impedance spectroscopy (EIS), open circuit potential (OCP), and accumulated charge density techniques disclosed the charge separation and transfer processes. This strategy of bulk and surface modification highlights a new approach to constructing a stable photoanode for sustainable solar energy conversion.