The rational design and interface engineering of an electrolyte and current collector for a stable and high-performance aqueous supercapacitor

Characterized by low cost, easy assembly, and excellent ionic properties, the aqueous supercapacitors have been considered promising energy storage devices. However, the absence of any solution for interface engineering between the electrode and electrolyte has been an ongoing performance limitation. Hence, the influence of the electrolyte (KOH and H₂SO₄) and current collector (SUS and graphite) on the electrochemical performance of supercapacitors operating in aqueous electrolytes is examined. Specifically, and for the first time, the outstanding energy-storing performance of an H₂SO₄-based acidic system is described, including excellent ionic properties that provide a large number of electroactive sites and enhanced ionic diffusion performance. Further, an improvement in the cycling stability is achieved by using the graphite current collector to enable the prevention of surface oxidation in the presence of the acidic electrolyte. This strategy results in an outstanding electrochemical performance, including a high specific capacity of 238 F g⁻¹ at a current density of 0.1 A g⁻¹, an excellent high-rate capability, and a remarkable cycling stability of 93% after 3000 cycles. These results suggest that interface engineering using an acidic electrolyte system along with a graphite current collector could be a reasonable strategy for the practical application of aqueous supercapacitors.