Ionic Liquid-Assisted Electrodeposition of MnO2 Films on Nickel Foam for Enhanced Supercapacitor Applications

MnO2 is widely investigated for electrochemical capacitors; however, its practical performance is often limited by low electrical conductivity and inefficient charge utilization in thick films. In this work, we investigate the combined effects of controlled electrodeposition and ionic liquid (IL)-assisted growth of MnO2 films onto nickel foam at 0.6 V vs. Ag/AgCl for supercapacitor applications. The deposition time revealed a non-linear structure–performance relationship, with optimal electrochemical response obtained at an intermediate deposition time (240 s). The incorporation of ILs (e.g., [TEA-PS][BF4] and [BMIM][BF4]) enabled direct modulation of nucleation and growth dynamics. While [TEA-PS][BF4] resulted in decreased performance, adding [BMIM][BF4] significantly enhanced the electrochemical response. Our results reveal that without additives the films were dense and cracked; with [BMIM][BF4], they became more open and nanostructured. Consequently, the optimized electrode exhibited a 25% higher specific capacitance, totaling 149.83 F·g−1 at 10 mV·s−1, compared to 119.87 F·g−1 for the unmodified electrode. These findings demonstrate that IL-assisted electrodeposition is an effective strategy for optimizing MnO2-based supercapacitor electrodes.