GQDs assisted Ba6Co25S27/MWCNT composite as a promising candidate for supercapacitor and a perspective Pt-free counter electrode in DSSC for enhancing the short circuit current

Bifunctional barium cobalt sulfide (BCS) spherical like structure composites with and without carbon materials (MWCNT and GQDs) are synthesized via hydrothermal method and are used as a counter electrode (CE) for DSSC and working electrode for supercapacitors. Crystalline structure, shape and chemical state of the prepared samples are examined by XRD, SEM, TEM and XPS analysis. BCS/MWCNT/GQDs CE based device delivers the short circuit current (JSC) of 10.57 mA/cm2 and open circuit voltage (VOC) of 0.73 V and Fill Factor (FF) of 0.58 and Power Conversion Efficiency (PCE) of 4.48%, which shows two-fold increment than pristine BCS CE. The same composites are tested under cyclic voltammetry and charge/discharge characteristic due to analyze the charge storage performance. Among the three composites, the GQDs embedded BCS/MWCNT composite exhibits the highest specific capacitance of 191 C/g. The findings show that GQDs supported BCS/MWCNT composites are not only a feasible option for Pt-free counter electrodes, but also provide a better outlook for energy storage devices.