Facile Synthesis of Ag₂S Quantum Dots for Energy Storage and Sensing Applications.

Herein, we report the synthesis of Ag₂S Quantum dots by co-precipitation method using the silver, thiol molecules (stabilizing agent) and sulfur (S) S-complex in molarities. The synthesized Ag₂S Quantum dots were characterized by different techniques by using optical absorption, wavelength tunable photoluminescence emissions in the visible range, FTIR, PXRD, TEM, HRTEM, SAED and EDX. From XRD patterns estimated particle sizes are found of 6.50 nm with a monoclinic phase of the Ag₂S quantum dots. The morphological study was made by performing transmission electron microscopy (TEM) images to confirm a spherical shape and the average particle size estimated from the micrographs is 7 nm. The electrochemical measurements as cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Galvanostatic charge/discharge (GCD) and differential pulse voltammetry (DPV) profile in a three-electrode configuration system for prepared nickel mesh electrode. Initially, the CV curves of Ag₂S QDs electrodes were performed at scan rates ranging from 20 to 100 mVs^-1. A consistent enhancement in current responsiveness can be observed for 1M KOH electrolyte [27]. The regression values (R²) of Ag₂S QDs (0.99807) are enhanced. These values signify a reversible and diffusion-controlled redox reaction of the electrodes. The impedance spectra demonstrated that charge transfer resistance (R_ct) is enhanced with a low capacitance value of Ag₂S. There is a distinctive depressed semicircle representing the charge transfer resistance in the high-frequency region, along with a slope that is associated with the Warburg impedance observed in the low-frequency range. Nyquist plot of Ag₂S electrode, after and before cycling was carried out [28]. Galvanostatic charge/discharge (GCD) exhibited supercapacitor performances with high specific capacitance at different current density (140 Fg⁻¹ at 1 Ag⁻¹) with the potential window 0-4 V and it shows a maximum specific capacity compared to other reported sulfur-based materials. The potential generated in Ag₂S electrode was observed from GCD curves of the first 20 and 200 cycles. After 200 cycles of charge discharge, the coulombic efficiency of was 96% [22,29]. The Differential Pulse Voltammetry (DPV) technique was used to sense the tartaric acid of 0.1M with a linear range of 50 to 1000mM and shows the Limit of Detection about 84.9mM, this shows an extraordinary sensing behaviour of Tartaric acid in the KOH solution with the sensitivity of the sensor about 1.51×10^-7 A/cm^-2, stability (25 days) and the surface coverage area is 7.23×10^-10mol cm^-2. This Organic acid sensor shows a high selectivity among (Oxalic acid, Citric acid, Mallic acid and Ascorbic acid)[. As a result, Ag₂S Quantum dots, synthesized through co-precipitation, show promise as high-performance supercapacitor electrode materials. They offer high capacitance and efficient charge transfer, making them a compelling alternative to toxic materials. Additionally, they exhibit remarkable sensitivity and selectivity as a tartaric acid sensor. Overall, this research underscores their versatility in energy storage and chemical sensing applications.