Toward the Proper Selection of Carbon Electrode Materials for Energy Storage Applications: Experimental and Theoretical Insights

Identifying the proper carbon material is one of the key requirements in developing high-performance supercapacitor electrodes. Carbon nanotubes (CNTs), graphene nanoplatelets (GNPs), and graphite (Gr) are commonly used carbon allotropes for supercapacitor applications. The performance of those materials depends on the electrolyte used and the operating potential window. However, those parameters have rarely been investigated and explained. Herein, we present a roadmap for the proper selection of carbon materials in supercapacitor applications via the investigation of the behavior of CNTs, GNPs, and Gr in different electrolytes using both electrochemical and computational tools. The charge storage mechanism was found to be electrolyte-dependent. In terms of the operating potential window, the best performance was obtained upon the use of a Na2SO4 electrolyte, which enabled a potential window of -1 to 0.9, while in terms of capacitance, the positive electrodes in a H2SO4 electrolyte exhibited the highest capacitance. H2SO4 enabled keto-enol tautomerism in the positive potential window and can enlarge the potential window to 1 V. Quantum capacitance calculations helped to identify the reasons behind the obtained different performances in the negative and positive potential windows. For example, upon the identification of the proper electrolyte and potential window, it was possible to obtain a capacitance as high as 453.60 F/g at 5 mV/s in a potential window of 1 V for CNTs, which are much higher than those reported in the literature. Moreover, the guidelines were successfully used to develop a symmetric device that delivers a specific energy of 23.3 Wh/kg and a specific power of 475 W/kg with a stability of 97.8% after 5000 cycles over a potential window of 1.9 V, which are much higher than those reported for CNTs-based symmetric devices.

Automated summary

Identifying the proper carbon material is crucial in developing high-performance supercapacitor electrodes. Optimization of electrolyte and operating potential window is essential for enhancing the performance of carbon materials. Quantum capacitance calculations help to explain the differences in carbon material performance under different electrolytes and potential windows.