Gel polymer electrolytes comprising molybdate(VI) salts dispersed in a hydrogel matrix. The hydrogel matrix contains reacted units of an acrylamide (e.g. 2-acrylamido-2-methyl-1-propanesulfonic acid) and optionally an additional monomer. A supercapacitor including the gel polymer electrolyte and electrodes arranged between the electrolyte is also specified. This supercapacitor is evaluated on its specific capacitance, energy density, power density, resistance, as well as cycling stability.