Specific Surface versus Electrochemically Active Area of the Carbon/Polypyrrole Capacitor: Correlation of Ion Dynamics Studied by an Electrochemical Quartz Crystal Microbalance with BET Surface

Abstract

Carbon/polypyrrole (PPy) composites are promising electrode materials for energy storage applications such as lightweight capacitors. Although these materials are composed of relatively inexpensive components, there is a gap of knowledge regarding the correlation between surface, porosity, ion exchange dynamics, and the interplay of the double layer capacitance and pseudocapacitance. In this work we evaluate the specific surface area analyzed by the BET method and the area accessible for ions using electrochemical quartz-crystal microbalance (EQCM) for SWCNT/PPy and carbon black Vulcan XC72-R/PPy composites. The study revealed that the polymer has significant influence on the pore size of the composites. Although the BET surface is low for the polypyrrole, the electrode mass change and thus the electrochemical area are large for the polymer-containing electrodes. This indicates that multiple redox active centers in the charged polymer chain are good ion scavengers. Also, for the composite electrodes, the effective charge storage occurs at the polypyrrole-carbon junctions, which are easy to design/multiply by a proper carbon-to-polymer weight ratio. The specific BET surface and electrochemically accessible surface area are both important parameters in calculation of the electrode capacitance. SWCNTs/PPy showed the highest capacitances normalized to the BET and electrochemical surface as compared to the polymer-carbon black. TEM imaging revealed very homogeneous distribution of the nanosized polymer particles onto the CNTs, which facilitates the synergistic effect of the double layer capacitance (CNTs) and pseudocapacitance (polymer). The trend in the electrode mass change in correlation with the capacitance suggest additional effects such as a solvent co-insertion into the polymer and the contribution of the charge associated with the redox activity of oxygen-containing functional groups on the carbon surface.

Comparing Physical and Electrochemical Properties of Different Weave Patterns for Carbon Cloth Electrodes in Redox Flow Batteries

“…Often, there is less surface area accessible to charged species in solution than the physical surface area [15] due to ion size and solvation states [56,57], which would manifest itself during the EDLC measurements. Nevertheless, the morphological measurement is considered an overestimation [58] in the inherit assumption of long, non-overlapping fibers, and the large discrepancy between EDLC and BET is in agreement with prior reports [59][60][61]. We were unable to find a direct comparison between EDLC and MIP in the published literature; however, given that BET and MIP are both measured with uncompressed electrodes and have the same order of magnitude values for a, we estimate that the large discrepancy between EDLC and MIP is physically reasonable.…”

Two‐Step Activated Carbon Cloth with Oxygen‐Rich Functional Groups as a High‐Performance Additive‐Free Air Electrode for Flexible Zinc–Air Batteries

“…The C DL of CC‐A and CC‐C was only 0.78 and 2.48 mF cm −2 , respectively, one order of magnitude less than that of CC‐AC. The highest ECSA of CC‐AC could be the combined result of a porous surface structure, increased amount of OFGs, and high hydrophilic wettability, which further demonstrates the advantage of a two‐step treatment since a larger ECSA plays an important role in enhancing the electrocatalytic activity . The Braunauer–Emmett–Teller (BET) surface areas calculated from their nitrogen adsorption–desorption isotherms confirm an increase trend of surface areas when carbon cloth (CC‐Raw) was treated by mixed acid (CC‐A), calcination (CC‐C), and two‐step method (CC‐AC, Figure S4 and Table S3, Supporting Information).…”

Self-activated cathode substrates in rechargeable zinc–air batteries

“…The remarkable ECSA enhancement of selfactivated CP could be due to the combined effects of the increased amount of oxygen functional groups on CP surface and a porous and reduced hydrophobic surface structure, which further confirmed the advantage of the electrochemical self-activation process since a larger ECSA plays a crucial role in enhancing the overall electrocatalytic activities. [8,46] The galvanostatic discharge curve at a current density of 2.5 mA cm −2 shows a discharge potential of 1.02 V for the ZAB with the self-activated CP as an air-cathode, and with negligible decrease of the discharge potential after 30 hours. The calculated specific capacity during discharge is 571 mAh g −1 for the ZAB with self-activated CP as air cathode (Fig.…”