Extending potential window of hierarchical heteroatom doped carbon supercapacitor with N,N-dimethylformamide-water electrolyte for enhanced energy-density

Bridging the gap between batteries and supercapacitors is essential for applications that demand both high-energy density and high-power density. We adopt a multipronged strategy that integrates electrode and electrolyte optimization to maximize supercapacitor performance. Melamine-co-formaldehyde (MF) resin serves as a nitrogen- and oxygen-containing carbon precursor. By incorporating ammonium bicarbonate as a thermally labile porogen, MF resin is cross-linked at 120 °C to form macroporous foam (PMF). Pre-carbonization of PMF at 300 °C (PMF-Pc) followed by activation at 950 °C with low carbon:KOH ratio (1:1) yields N, O co-doped hierarchical porous carbon (MF-Ac) with ultrahigh surface area of 2858 m² g −1 . A symmetric device with MF-Ac electrodes and 1 M H₂SO₄ aqueous electrolyte (ΔV = 1 V) delivers a high specific capacitance of 480 F g −1 at 1 A g −1 and an energy density of 66.6 Wh kg −1 . The energy density further increases by using a DMF-H₂O binary solvent system. Optimizing the DMF:H₂O ratio enhances hydrogen-bonding interactions and widens the potential window. A semi-aqueous 1 M H₂SO₄ electrolyte (30 vol% DMF) provides stable potential window of 1.7 V. Symmetric device delivers 404.7 F g −1 at 1 A g −1 and a high energy density of 162.4 Wh kg −1 , approaching battery-level performance.