Abstract
The specific energy of an aqueous carbon supercapacitor is generally small, resulting mainly from a narrow potential window of aqueous electrolytes. Here, we introduced agarose, an ecologically compatible polymer, as a novel binder to fabricate an activated carbon supercapacitor, enabling a wider potential window attributed to a high overpotential of the hydrogen-evolution reaction (HER) of agarose-bound activated carbons in sulfuric acid. Assembled symmetric aqueous cells can be galvanostatically cycled up to 1.8 V, attaining an enhanced energy density of 13.5 W h/kg (9.5 µW h/cm2) at 450 W/kg (315 µW/cm2). Furthermore, a great cycling behavior was obtained, with a 94.2% retention of capacitance after 10,000 cycles at 2 A/g. This work might guide the design of an alternative material for high-energy aqueous supercapacitors.
Highlights
A supercapacitor (SC) is an energy-storage system that has attracted great research interest because of its superior properties of ultra-high density of output power, excellent cycling stability, and safety consideration compared with batteries [1,2,3], but the small energy density of a SC creates difficulty for widespread applications
There remain, serious drawbacks to be remedied, such as a limited rate of charge and discharge resulting from a smaller electrolyte conductivity and the requirement of a moisture-free environment to build devices to ensure the stability of organic electrolytes [8,9]
Another slurry, named ACPVDFSpP, was prepared as a reference sample, which was basically composed of the same carbon powder, except that the binder and solvent were replaced with polyvinylidene fluoride (PVDF) and N-methyl-2-pyrrolidone (NMP), respectively
Summary
A supercapacitor (SC) is an energy-storage system that has attracted great research interest because of its superior properties of ultra-high density of output power, excellent cycling stability, and safety consideration compared with batteries [1,2,3], but the small energy density of a SC creates difficulty for widespread applications. The energy density of a SC is determined by its specific capacitance and the corresponding operating voltage. A commercial SC, classified as an electrical double-layer capacitor (EDLC) using activated carbon electrodes in an organic electrolyte, is mostly available on the market. The features of large surface area, effective chemical stability, and excellent electrical conductivity make carbon materials significant as electrode materials in energy storage [6]. The large voltage window of an organic electrolyte (e.g., 2.5–2.7 V for tetraethylammonium tetrafluoroborate in acetonitrile), achieving an attainable energy density, matches the demands for commercial use [7]. The operating voltage of an aqueous electrolyte is Nanomaterials 2021, 11, 1731.
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