Electrical Double Layer Capacitance of Curved Graphite Electrodes

Abstract

To improve the understanding of the relation between electrode curvature and energy storage mechanisms, a systematic investigation of the correlation between convex and concave electrode surfaces and the differential capacitance of an electrochemical double layer capacitor using molecular dynamics simulations is presented. Each electrode consists of three layers of curved graphene sheets with a convex and concave surface to which the constant potential method was applied. The differential capacitance shows a fluctuating behavior with respect to the curvature radius of the convex and concave areas of the electrode. The reasons identified for this are differences in the geometric arrangement and solvation of the adsorbed ions as well as a steric hindrance prohibiting further charge accumulation. Since the total differential capacitance is calculated as a weighted average of contributions from concave and convex surfaces, the influence of individual curvatures on the total capacitance is significantly reduced for the total electrode surface.

Elucidating Curvature-Capacitance Relationships in Carbon-Based Supercapacitors

“…Consequently, the discussion concentrates in the following only on the negative electrode. As previously observed in Seebeck et al [9], number density fluctuations of the imidazole group in the EDL with respect to different applied electric potentials, shown in Fig. S3, correlate to features in the differential capacitance of Fig.…”

“…Such a potential-induced phase transition of the double layer at flat electrodes has also been observed experimentally [28,41,42]. Using CONP simulations, we have previously demonstrated the influence of curved electrodes on the differential capacitance, and found correlations between the electrode curvature and the number densities of the electrolyte components as well as the orientation of the ions [9]. In this work, we employ the histogram reweighting approach to estimate free energies of the electric double layer formation which ultimately allows us to correlate the charge fluctuations with structural changes at the electrode-electrolyte interface.…”

“…The discovery of an anomalously high capacitance in microporous carbons has led to numerous research activities aimed at deciphering the underlying molecular mechanisms [1][2][3][4][5][6][7]. Beyond the sheer increase of the electrode surface area facilitated by microporous carbons-effectively increasing the capacitance-the specific shape of the electrodes, such as pore sizes and curvatures, affects the structure and composition of the EDL and thus the capacitance [8][9][10][11][12][13][14][15].…”

Nanoporous carbon for electrochemical capacitive energy storage

“…A few modeling works have mentioned the effect of curvature over the years. 84,140,[255][256][257] Merlet et al used MD simulation to characterize different sites with various morphology of CDC materials (edge, plane, hollow and pocket) and calculate the degree of confinement of the adsorbed ions. 256 The results showed that at the edge, plane, hollow and pocket sites (with the increased degree of confinement) of CDC samples, the degree of desolvation of anions varies compared to the bulk.…”

Ionic liquid dynamics in nanoporous carbon: A pore-size- and temperature-dependent neutron spectroscopy study on supercapacitor materials

“…The introduction of surface oxide in this intermediate step likely changes the carbon-carbon bonding, such that it is reasonable to assume that this resulted in different pore morphologies and pore walls roughnesses during the vacuum annealing, when surface functional groups-like oxygen-are removed. Indeed, there are hints from molecular dynamics simulations that such differences influence the mesoscopic structure and dynamics of an ionic liquid in carbon nanoconfinement [65][66][67]. Also the broad pore-size distribution is presumably of relevance here, because the QENS methods measure the dynamics averaged over all pores.…”