Effect of annealing environment on the photoelectrochemical water oxidation and electrochemical supercapacitor performance of SnO2 quantum dots

Abstract

SnO2 quantum dots (SQD) were prepared by utilizing the soft-chemical approach. The formed SQD's were annealed in two kinds of environments: air and nitrogen (N2). Each annealing environment resulted in significant improvement in the performance of water oxidation and electrochemical supercapacitor performance. The specific capacitance of the SQD's under the N2 annealing process (SQD-N2) shows significantly better electrochemical performance. A specific capacitance of 79.13 F/g was achieved for SQD-N2 sample by applying a current of 1 mA, which was approximately 1.5 times greater than that of the pristine SQD's. A cycle stability of 99.4% over 5000 cycles was achieved by SQD-N2. The process of nitrogen annealing environment brings down the bandgap from 3.37 to 1.9 eV. The SQD-N2 sample shows the highest photocurrent over SQD and SQD-Air samples. From the LSV study, SQD-N2 shows the photocurrent density of 4.82 mA/cm2, which is 1.43 times greater than pristine SQD sample. The nitrogen-annealing environment provides the optimal environment to tune the average crystallite size and crystallinity nature of SQD's to improve the optical properties like bandgap to enhance the water oxidation and also electrochemical performance.