Cyclic voltammetry of porous carbon is impacted by charge redistribution - understanding the mechanism and effects on performance metrics

Ion-transport limitations in porous carbon can cause charge redistribution (CR) that significantly impacts cyclic voltammetry (CV) results and associated figures of merit. We elucidate these effects and the underlying mechanism using Vulcan XC 72 carbon and a Transmission Line Circuit (TLC). During the initial anodic scan, charge redistributes into the pores. The charged pores then act as a charge reservoir during the cathodic sweep and all subsequent CV cycles. Thus, pristine electrodes exhibit more positive currents than previously-cycled electrodes, causing higher anodic charge (capacity), capacitance and energy but lowering the cathodic charge, capacitance and energy, and the coulombic- and energy-efficiencies. When multiple sweep rates are run on the same electrode, there is a residual effect of the previous sweep rate; we show that applying sweep rates in order of decreasing magnitude must be avoided to eliminate significant bias in the data. Suggestions are made for designing CV protocols that minimize CR-based impacts on the CV profile and associated figures of merit. These considerations are vital to prevent erroneous conclusions due to CR and to allow comparisons between literature results. While this work focusses on carbon, the findings herein apply equally to other highly porous conductive materials and pseudocapacitive films. (C) 2020 Elsevier Ltd. All rights reserved.