Particle size effect in porous film electrodes of ligand-modified graphene for enhanced supercapacitor performance

Graphene-based electrodes for high performance supercapacitors are developed by taking advantage of particle size control, large mass loading, and surface functionalization of reduced graphene oxide (rGO) sheets. Two controlled sizes of graphene sheets (100 nm vs. 45 μm average lateral dimensions) were prepared to study two-electrode system performance. The nano-size graphenes led to the formation of mesoporous films, resulting in higher capacitance, better capacitance retension and lower equivalent series resistance (ESR), indicating better surface usability for diffusion and accessibility of electrolyte ions by shortening transport paths (compared with horizontally stacked films from micro-sized graphenes). For studies using an aqueous electrolyte, the maximum specific capacitance of nano-rGO film was 302 F/g (at 1 A/g with 4.3 mg/cm2 of mass loading), which was ∼2.4 times higher than micro-rGO film, and achieved a ∼67% reduced ESR. With an organic electrolyte, the nano-rGO delivered ∼4.2 times higher capacitance (115 F/g at 2 A/g with 4.3 mg/cm2), 4.0 times lower IR drops, and an order-of-magnitude lower charge-transfer resistance with an energy density of 18.7 Wh/kg. The results of this work indicate that the size control of graphene sheet particles for film deposit electrodes can be a simple but effective approach to improve supercapacitor performance.

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