Chemically etched ZnO thin films, with surface-evolved nano-ridges, for efficient photoelectrochemical splitting of water

The report explores the effect of surface properties of nanostructured ZnO thin films, especially the effective surface area, on the conversion of UV light to hydrogen energy via photoelectrochemical (PEC) splitting of water. It deals with the sol–gel synthesis of films from zinc acetate dihydrate [(CH3·COO)2Zn·2H2O], followed by a controlled surface etching using five different acids. The XRD, SEM, and AFM analysis of pristine and etched films revealed the dominant growth of hexagonal wurtzite ZnO with uniquely evolved nano-ridges at the surface. Average crystallite size ranged from 40 to 51 nm with marginal drop in etched samples. Etching did not influence optical bandgap energy, which lied in the expected range. Nonetheless, effective surface area increased significantly and it directly correlated with the enhancement in PEC photocurrent. The hallmark of the study is that it highlights the fact that compared to exotic combinations, viz., mixing, doping or layering, the low-cost simple method of surface etching can also lead to a matching gain in the performance of ZnO towards the hydrogen energy generation from UV light by photosplitting of water.