Water‐in‐Salt Electrolyte Supercapacitors with Electrophoretically Deposited Graphene–Biomass Carbon Electrodes

This study explores sustainable alternatives for supercapacitor fabrication by integrating environmentally friendly carbon materials and efficient electrode processing techniques. Traditional supercapacitors rely heavily on expensive, nonrenewable, chemically synthesized carbon nanomaterials and are typically fabricated via time‐intensive N ‐methyl‐2‐pyrrolidone (NMP)‐based slurry casting. To address these limitations, two complementary approaches are presented. First, high‐performance graphene‐like carbon is synthesized from commercial AC (YEC‐8B), using electrochemical exfoliation (EEG). Second, electrophoretic deposition (EPD) is demonstrated as a scalable method for depositing biomass‐based (derived from waste hazelnut shells) activated carbon (BAC) or composites of BAC and EEG onto nickel foam current collectors, achieving a specific capacitance of 150 F g −1 and a power density of 21 kW kg −1 . These electrodes are tested with both pure and hybrid water‐in‐salt electrolytes in A7 pouch cell supercapacitors. The pouch cell configuration that is equipped with commercially sourced composite AC and EEG electrodes shows superior capacitance retention, with 10% improvements at 10–40 A g −1 during cycling, compared to the counterparts prepared from waste biomass.