<p>The formation of the spinel phase and the successful incorporation of Cu2⁺ ions into the A-site of the CuMn₂O₄ spinel were investigated through powder X-ray diffraction analysis. The crystallization of CuMn₂O₄ in the cubic phase was confirmed by calculating the lattice parameter value (~8.32 Å). The specific capacitance (<i>C</i>sp) computed from the current–potential plots for stiff and flexible devices exhibited reproducible electrochemical characteristics, with a minor difference of less than 5% in the <i>C</i>sp values. The influence of KCl concentration on <i>C</i>sp was minimal, remaining below 5%, which affirms the potential use of CuMn₂O₄ as a sustainable electrode material over a range of electrolyte concentrations. The small variation in <i>C</i>sp, ranging from 497 to 512 F/g for rigid current collectors and from 507 to 523 F/g for flexible current collectors, illustrates the minimal influence of scan rate. The <i>C</i>sp values of CuMn₂O₄/PVA–KCl/CuMn₂O₄ supercapacitors fabricated on stiff and flexible copper current collectors were calculated to be 1115 F/g and 1253 F/g, respectively, with a difference in specific capacitance of approximately 11.1%. The retention ratios estimated from the current–potential plots for stiff and flexible current collectors coated with CuMn₂O₄ remained above 88% even after 5000 cycles, confirming the suitability of CuMn₂O₄ as a superior and sustainable electrode material for supercapacitors.</p>