Rapid fabrication of high-quality few-layer graphene through gel-phase electrochemical exfoliation of graphite for high-energy-density ionogel-based micro-supercapacitors

Electrochemical exfoliation has been identified as a promising top-down method for obtaining high-quality graphene from graphite. However, conventional anodic exfoliation introduces undesirable oxidation and defects in resultant graphene while cathodic exfoliation eliminates that issue but is time and energy intensive. Herein we report a versatile and rapid fabrication approach for gentle (<1 h ultrasonication) cathodic exfoliation of graphite using only 0.05 M K₂SO₄ in a polyvinyl alcohol (PVA)-based aqueous gel medium as electrolyte. The few-layer graphene obtained via this route demonstrates high quality (I_D/I_G ratio of 0.07) and minimal oxidation (3.02 at% oxygen). This gel-exfoliated graphene is found to be particularly suitable for micro-supercapacitors (MSCs) achieving a stable working voltage of 1.2 V in aqueous gel electrolyte, good rate capability, high capacitance of 13.7 F cm⁻³ at 10 mV s⁻¹ and energy density of 2.74 mW h cm⁻³. Importantly, gel-exfoliated graphene is also compatible with ionogel electrolyte, achieving a high voltage of 3.4 V and resulting in competitive energy density of 14.5 mW h cm⁻³, outperforming most reported graphene-based MSCs. The MSCs show excellent long cycling performance retaining nearly 100% capacitance over 10,000 cycles. We also demonstrate the mechanical flexibility and integration of the MSCs connected in series and parallel for powering future microscale flexible electronics.