Partially Reduced Graphite Oxide: A Close Examination of the Contributions to Its Storage Capacity
Authors: Navarro-Suárez Adriana M. , Carretero-González Javier , Rojo Teófilo 
Published: February 2020

Electrical energy storage constitutes an essential component in the development of sustainable energy technologies, given that enables energy to be used on demand. Batteries and supercapacitors have proven to be of crucial importance for advanced and highly efficient energy storage and management.

Graphene-derived materials have been used both in batteries and supercaps because of their high electronic conductivity, intercalation properties and large surface area. (1) The main difference between a battery and a supercapacitor lies in their charge-storage mechanism which is related to the nature of their electrochemical processes. By understanding the mechanisms occurring during the electrochemical cycling we might be able to optimize both the energy and power densities in the energy storage devices containing such materials. In the case of batteries, the process would be diffusion-limited and expected to be proportional to the square root of the scan rate while a strictly capacitive contribution (double-layer and pseudocapacitance) would depend linearly on the scan rate and would be related to supercapacitors. (2) Lately, materials exhibiting charge storage using both capacitive and faradaic means have been of great interest. (3,4)

Herein, we studied the electrochemical properties of a partially reduced graphite oxide, exhibiting quinone moieties.  The identification of both, diffusion-limited and capacitive processes, to the charging storage mechanism in multilayer graphene electrodes in aqueous electrolytes was examined by cyclic voltammetry (Figure 1).  This study provides insightful information about the electron-proton transfer reactions in a unique material as it is the partially reduced graphite oxide, where quinone groups and an electron conducting C-C crystalline lattice coexist together in the same unit.  The identification and quantification of both pseudocapacitance and double layer contributions to the charging storage mechanism in the different electrodes was also possible. 

Figure 1. Capacitive and diffusion-controlled contributions to charge storage in a.) Protic and b.) aprotic electrolyte.

The analysis of cyclic voltammetry curves at different scan rates allowed determining the fraction of the current arising from diffusion-controlled and capacitive processes. For experiments developed in acid electrolytes, a capacitive contribution of up to 85% was found, whereas only about 22% of the stored charge is capacitive in the case of aprotic electrolytes. From these experiments, it can be inferred that about 63% of the current is primarily pseudocapacitive. The electrochemical evaluation of this material would facilitate the preparation of novel graphene-based electrodes for devices based on the properties desired.

 
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Figure 1