Carbon-polymer composites have great application potential in the field of organic batteries, capacitors, capacitive water desalination reactors and as the conductive platforms for electrochemical sensors. Although numerous studies have been carried out with respect to the synthesis, the optimization of composition, the carbon type and the morphology control, there is still a lack of understanding about which kind of intermolecular connection between carbon and polymer phases is preferential, and how the system should be designed to achieve the application demand of long-term electrochemical stability. Herein, we propose two model systems that employ the most well-known commercial carbons (SWCNTs and carbon black Vulcan XC72-R) to generate polypyrrole-C composites and validate the type of chemical bonding that is preferential to maintain electrochemical stability. In this work we used a simple oxidative polymerization of pyrrole and generated various formulations (with variable polymer content). Based on the surface XPS combined with bulk TGA-MS analysis we were able to evaluate the concentration and type of oxygen-containing functionalities, revealing a high oxygen content for the carbon black. It was further correlated with XPS analysis of the respective composites showed evidence of the electronic interaction called π-π* stacking between SWCNTs and PPy, and the binding energy shifts associated with the formation of hydrogen bridge bonds in the case of Vulcan XC-72R-PPy. Furthermore, the electrochemical stability of these model samples was investigated by AC impedance spectroscopy. The charge transfer resistance (Rct) was analyzed upon the oxidative potential, revealing SWCNT-PPy as an ultra-stable composite, even for the high polymer content (1 : 4 weight ratio of C-PPy). In contrast, the carbon black-PPy underwent rapid degradation in the whole composition range. The durability is associated with the type and strength of the polymer-carbon bonding as revealed by EIS impedance correlated with spectroscopic studies. The electronic interactions between SWCNTs and PPy result in superior stability while the carbon black-PPy, where the hydrogen bridge bonds are generated, is not stable under the same experimental conditions.

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.