Direct observation of the CO2 formation and C–H consumption of carbon electrode in an aqueous neutral electrolyte supercapacitor by in-situ FTIR and Raman

Electrical double-layer capacitors (EDLCs) consist of energy storage devices that present high-power and moderate energy density. The electrolyte and electrode physicochemical properties are crucial for improving their overall energy storage capabilities. Therefore, the stability of the EDLCs’ materials is the primary focus of this study. Since energy storage depends on the specific capacitance, and also on the square of the maximum capacitive cell voltage (UMCV). Thus, electrodes with high specific surface area (SSA) and electrolytes with excellent electrochemical stability are commonly reported in the literature. Aqueous electrolytes are safer and green devices compared to other organic-based solutions. On the other hand, their UMCV is reduced compared to other electrolytes (e.g., organic-based and ionic liquids). In this sense, spanning the UMCV for aqueous-based electrolytes is a ‘hot topic’ research. Unfortunately, the lack of protocols to establish reliable UMCV values has culminated in the publishing of several conflicting results. Herein, we confirm that multiwalled carbon nanotubes (MWCNTs) housed in cells degrade and produce CO2 under abusive polarisation conditions. It is probed by employing electrochemical techniques, in-situ FTIR and in-situ Raman spectroscopies. From these considerations, the current study uses spectro-electrochemical techniques to support the correct determination of the electrode and electrolyte stability conditions as a function of the operating electrochemical parameters.