title: Capacitance of carbon-based electrical double-layer capacitors.
abstract: Experimental electrical double-layer capacitances of porous carbon electrodes fall below ideal values, thus limiting the practical energy densities of carbon-based electrical double-layer capacitors. Here we investigate the origin of this behaviour by measuring the electrical double-layer capacitance in one to five-layer graphene. We find that the capacitances are suppressed near neutrality, and are anomalously enhanced for thicknesses below a few layers. We attribute the first effect to quantum capacitance effects near the point of zero charge, and the second to correlations between electrons in the graphene sheet and ions in the electrolyte. The large capacitance values imply gravimetric energy storage densities in the single-layer graphene limit that are comparable to those of batteries. We anticipate that these results shed light on developing new theoretical models in understanding the electrical double-layer capacitance of carbon electrodes, and on opening up new strategies for improving the energy density of carbon-based capacitors.
authors.affiliation: 1] Department of Mechanical Engineering and the Materials Science and Engineering Program, The University of Texas at Austin, 1 University Station C2200, Austin, Texas 78712, USA [2] Department of Materials Science and Engineering and CAS Key Laboratory of Materials for Energy Conversion, University of Science and Technology of China, Hefei 230026, China [3].
authors.forename: Hengxing
authors.initials: H
authors.lastname: Ji
authors.affiliation: 1] Department of Mechanical Engineering and the Materials Science and Engineering Program, The University of Texas at Austin, 1 University Station C2200, Austin, Texas 78712, USA [2] [3].
authors.forename: Xin
authors.initials: X
authors.lastname: Zhao
authors.affiliation: 1] Department of Physics, The University of Texas at Austin, Austin, Texas 78712, USA [2].
authors.forename: Zhenhua
authors.initials: Z
authors.lastname: Qiao
authors.affiliation: 1] Department of Physics, The University of Texas at Austin, Austin, Texas 78712, USA [2].
authors.forename: Jeil
authors.initials: J
authors.lastname: Jung
authors.affiliation: Department of Materials Science and Engineering and CAS Key Laboratory of Materials for Energy Conversion, University of Science and Technology of China, Hefei 230026, China.
authors.forename: Yanwu
authors.initials: Y
authors.lastname: Zhu
authors.affiliation: Department of Materials Science and Engineering and CAS Key Laboratory of Materials for Energy Conversion, University of Science and Technology of China, Hefei 230026, China.
authors.forename: Yalin
authors.initials: Y
authors.lastname: Lu
authors.affiliation: 1] Department of Mechanical Engineering and the Materials Science and Engineering Program, The University of Texas at Austin, 1 University Station C2200, Austin, Texas 78712, USA [2].
authors.forename: Li Li
authors.initials: LL
authors.lastname: Zhang
authors.affiliation: Department of Physics, The University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: Allan H
authors.initials: AH
authors.lastname: MacDonald
authors.affiliation: 1] Department of Mechanical Engineering and the Materials Science and Engineering Program, The University of Texas at Austin, 1 University Station C2200, Austin, Texas 78712, USA [2].
authors.forename: Rodney S
authors.initials: RS
authors.lastname: Ruoff