Defatted spent coffee grounds-supported cobalt catalyst as a promising supercapacitor electrode for hydrogen production and energy storage

The effect of several parameters, such as different Co2+ ratios, burning temperatures, and burning times, was examined by using defatted spent coffee grounds (DSCG) as organic waste to obtain the most effective catalyst for producing hydrogen. Under optimum conditions, the most active catalyst/metal ratio was obtained by burning 50% Co 2+ at 400 °C for 90 min. To measure the time-dependent amounts of hydrogen, 0.1 g of DSCG-Co catalyst was dissolved in 10 mL of a methanol solution containing 0.25 g sodium borohydride (NaBH4) at 30 °C. The maximum hydrogen generation rate obtained from the methanolysis of NaBH4 at 30 and 60 °C was found to be 8749 and 17,283 mL min−1 gcat−1, respectively, and the activation energy of the catalyst was found to be 23.2 kJ mol−1. FTIR, ICP-OES, XRD, BET, and SEM–EDX analyses were performed for the characterization of the prepared DSCG-Co-Cat catalyst. Furthermore, a supercapacitor cell was constructed by using this catalyst as an active substance for electricity storage. The specific capacitance of the electrode at the current density of 1 A/g was calculated as 67 F/g for two-electrode systems. The results of electrochemical analysis of the prepared supercapacitor were found to be similar to the ideal supercapacitor curves. The obtained capacitance values are at very good levels in terms of the capacity and cost factors. The results indicated that the multifunctional capacitor-catalyst material produced by Co-doped waste coffee could constitute an important element in a hybrid system that includes capacitor and catalyst systems that can be installed in the future.