Porous carbon electrodes from activated wasted coffee grounds for capacitive deionization

Wasted coffee grounds (WCGs) were activated by a pyrolysis process using KOH, where the porosity increased with temperature, exhibiting a micropore-dominant structure. WCGs upon an activation temperature of 800 °C (AWCG800) showed a surface area up to 1856 m2 g−1 and a specific capacitance of 180.3 F g−1 in 1 M NaCl solution at a scan rate of 10 mV s−1. The AWCG800 electrodes showed an electrosorption capacity up to 12.50 and 16.50 mg g−1 in NaCl solution at cell voltages of 1.2 and 1.4 V, respectively, with an initial concentration of 5 mM. X-ray photoelectron spectroscopy analysis indicated that AWCG800 maintained a high carbon content of 87 at% upon the activation process. The study suggests a practical way for converting WCGs into mesoporous and microporous carbons with large surface area and pore volume, high carbon component, and good wettability to water, which is promising for capacitive deionization application.