Structural, optical, and bifunctional applications: Supercapacitor and photoelectrochemical water splitting of Ni-doped ZnO nanostructures

Abstract

Over the past few decades, doped ZnO structures have attracted significant attention because of their distinctive properties and a wide range of applications in catalysis and energy-storage devices. However, effective simple synthesis of doped ZnO structures for photoelectrocatalytic and supercapacitor applications still remains challenging. In this study, Ni-doped ZnO structures were synthesized at different Ni concentrations. Analysis of the obtained samples confirmed the formation of Ni-doped ZnO; 1.5 mol% Ni-doped ZnO showed enhanced water splitting activity and supercapacitor properties. The highest photocurrent density of 4.6 mA/cm(2) was obtained in a 0.1 M KOH solution at an applied bias photon-to-current efficiency of 4.2%, which is almost twice that obtained with pristine ZnO (2.8%), indicating an enhanced electron-hole separation. Doped ZnO exhibits a photocurrent 1.78 times higher than pristine ZnO under light illumination. Ni-doping induces effective charge separation and transfer, efficiently diminishing the recombination rate and reducing intrinsic defects. Further, the highest specific capacity of similar to 96 F g(-1) was observed for 1.5% Ni-doped ZnO at an applied scan rate of 10 mV s(-1). The optimized sample, 1.5% Ni-doped ZnO, exhibited a high specific capacitance retention and coulombic efficiency of similar to 98% and similar to 99.2%, respectively. These results are expected to be very helpful in developing cheap and simple fabrication methods and efficient electrode materials for photoelectrochemical water splitting and supercapacitor applications.