Humic acids as pseudocapacitive electrolyte additive for electrochemical double layer capacitors

•Humic acids (HA) were applied for the first time as electrolyte additive for EDLC.•Capacitances consistently rise with HA addition to 6 M KOH with maximum at 5 wt.%.•Positive effect of humic acids has been ascribed to pseudocapacitive phenomena.•Humic acids are described as low-cost, non-toxic and “green” electrolyte component.

Novel electrolyte additive for electrochemical capacitors has been reported. It has been demonstrated for the first time that addition of humic acids (HA) to KOH-based electrolyte significantly increases capacitance of symmetrical capacitors with electrodes made of activated carbon. Specific capacitances determined by means of galvanostatic charge/discharge, cyclic voltammetry and electrochemical impedance spectroscopy consistently showed increases for HA concentrations ranging from 2% w/w up to saturated solution with maximum positive effect observed for 5% w/w of the additive. The capacitance increase has been attributed to complex faradaic processes involving oxygen-containing groups of HA molecules. Due to abundant resources, low cost and easy processability the reported solution can find application in electrochemical capacitor technologies.

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