CdSe/ZnS quantum dot–modified activated carbon electrodes for supercapacitors: Light-induced enhancement of capacitance and fluorescence

CdSe/ZnS Quantum Dots (QDs), embedded in supercapacitors (S-C) cells exhibited capacitance amplification that peaked at a certain QD concentration. More than 2.5 peak amplification was demonstrated with cyclic voltammetry (C-V), Charge-Discharge and Electrochemical Impedance Spectroscopy. The peak was obtained when the mass ratio of the dots to the active-carbon electrode (A-C) in the sample was 20 μg to 100 mg in 1 ml of toluene - a ratio of 1–5000. Fluorescence signals from dry (without electrolyte) and wet (with electrolyte) cells, exhibited a correlated, substantial peak enhancement vs QD concentration, as well. Additionally, in the case of wet samples, fluorescence line narrowing was demonstrated, indicating a fluorescence gain. Through experiments and analysis one could show that these effects are consistent with the formation of dot-array at the electrode/electrolyte interface. Embedding QDs at the electrolyte/electrode interface has an added value that it may be further enhanced by white light illumination, and indeed, this was the case here. Probing the electrolyte/electrode interface with fluorescing materials adds to our basic knowledge of the interface and could be useful for light-sensitive S-C cells. (a) Gravitonic specific capacitance as a function of quantum dot concentration for 1 M Na 2 SO 4 filled super-capacitor. Red dots were obtained upon exposure to a 75 W white-light source situated at 30 cm from the sample surface while the black dots were obtained without it. (b) Fluorescence line narrowing as a function of quantum dot concentration. • Small amount of semiconductor quantum dots (QDs) were introduced into super-capacitor (S-C) cell. • The cell capacitance, measured by various techniques exhibited peak amplification at a particular QD concentration. • Further capacitance increase was demonstrated when illuminating the cell with white light. • A substantial fluorescence peak enhancement and line narrowing was also noted. • The above is explained by the formation of dot-arrays at the electrode/electrolyte interface.