Role Of Topological Defects And Dopants Of Carbon For Electrical Double-layer Capacitance

Supercapacitor storing energy by electrical double-layer at the interface between electrode and electrolyte is a key component of power-source technologies,and may realize further gains if their energy density can be promoted.Introducing topological defects and dopants to the carbon materials could improve the capacitive properties by enhancing the gravimetric capacitance per mass of the electrode.However,the main mechanisms governing the capacitance improvement are still ambiguous.Using CVD-derived single-layer graphene,we fabricated planar electrodes with controlled topological defects and nitrogen dopants,respectively.The electrical double-layer capacitance(C_EDL)of the graphene electrodes with different concentrations of topological defects and N dopant was measured by electrochemical impedance spectroscopy?EIS?at various potentials with respect to a reference electrode.The relationship between C_EDL and V_EDL of graphene for different defect concentrations shows a concave shape,the C_EDL increasing rate with the potential,increases significantly as a function of the defect concentration,accompanying with an increase of the C_EDL minima to 1.70 ?F cm^-2.However,the potential of the C_EDL minimum slightly upper-shifts to around 0.05 V.The concave-shaped curves of graphene with N dopants behave dramatically different from those of the defected graphene.the potential corresponding to the C_EDL Tminimum increases almost linearly to be 0.46 V along with the increase of doping level though the value of the C_EDL minimum upper-shifts to 1.78 ?F cm^-2.In order to give a deep understanding of the measured C_EDL in these defected or doped graphene systems,in this study we theoretically investigate the CQ of graphene with topological defects and N dopants by using the first-principles calculation methods and tight-binding model calculation.Our experimental study together with theoretical calculations show that although the increase of electrical double-layer capacitance by topological defects and nitrogen dopants are both intimately related to the same improvement of the quantum capacitance,the mechanisms of them are differ from each other.The topological defects improve the DOS and the dopants can tune the Fermi-level of the graphene systems,both of which can significantly mediate the quantum capacitance connected in series with a Helmholtz capacitance,hence the EDL capacitance.Our finding provides a better understanding of the correlation between the carbon microstructure and the EDL capacitance for energy storage,presents a new strategy on developing experimental and theoretical models of electrical double-layer capacitance of carbon electrodes,and finally sheds light on designing application-specific carbon electrodes.