Solvothermal Etching-Assisted Phase and Morphology Tailoring in Highly Porous CuFe2O4 Nanoflake Photocathodes for Solar Water Splitting

Improvization of synthetic strategies for designing novel nanostructures with desirable tailored morphology for efficient solar energy utilization has been at the focus of research on photoelectrochemical water splitting. This work presents a novel fabrication technique comprised of photocathodes comprised of highly porous copper ferrite nanoflake arrays by low-temperature surfactant-assisted solvothermal phase change induced temperature-controlled etching process. Solvothermally predeposited hematite on FTO glass was treated by a second solvothermal step, whereby surfactant-capped Cu2+ ions were forcibly impregnated into the hematite lattice at varying temperatures, resulting in phase change along with a drastic change in nanostructure morphology and crystal phase without the formation of any copper oxide surface impurities causing a temperature-dependent control over the degree of spinel inversion (delta), the underlying electronic properties of which were analyzed using DFT calculations. Analysis of photoelectrochemical (PEC) performance of the fabricated photocathodes was performed under A.M 1.5 G simulated solar illumination under a linear voltage sweep using a potentiostat with the three-electrode setup using 1 M H2SO4 aqueous solution as an electrolyte. The photocathode with delta = 0.77 exhibited the highest photocurrent density of -0.139 mA/cm(2) at 0 V (vs RHE) and -2.57 mA/cm(2) at -1 V (vs RHE). It also exhibited the highest IPCE % of 18.7%, which was higher than that of the photocathode with delta = 0.71, because of the depreciatory effect of high temperature on morphology, thereby emphasizing the precise synergistic influence of phase and morphology control simultaneously upon PEC performance. This work should inspire further research in developing unique wet chemical synthesis strategies for designing porous and highly ordered impurity-free nanostructures with temperature-dependent phase control for photoelectrode applications.