Transition Metal Salts Additive as Antioxidant or Metal Oxide Decorator during Electrochemical Exfoliation of Graphite?

Abstract

The preparation of graphene via electrochemical exfoliation in aqueous solution is considered very attractive in terms of cost, scalability and non-toxicity. However, the quality of graphene produced by this method is inferior to the material produced by methods such as mechanical exfoliation due to the functionalisation of carbon by reactive oxygen radical species derived from water oxidation.1 There is a need to alleviate the effect of these radicals in order to capitalize on the use of anodic electrochemical exfoliation in aqueous solution. In this presentation, we will describe the use of a new approach, based on the unexpectedly versatile role of transition metal ions to produce high quality graphene via an anodic electrochemical exfoliation route, using sulfate as the intercalating anion.2 Notably, some of the transition metals (Co2+, Fe3+) acted as antioxidants, preventing surface oxidation of graphene, while others (Ru3+, Mn2+, Ir3+) acted as metal oxide decorators (Figure 1). The graphene obtained by electrochemical exfoliation of graphite in the presence of Co2+ is two orders of magnitude more conducting and defect free than the one obtained in the absence of cobalt ion. This Co-treated graphene found to be an excellent cathode material for Aluminum-based batteries in terms of performance and cycling stability. The use of other transition metal ions (Ru3+, Mn2+, Ir3+) in the electrolysis solution resulted in decoration of graphene with the oxide of that metal in a single stage simultaneous process. This process can also allow for producing graphene functionalised with hybrid metal oxides (G-RuO2-Mn3O4) in a one-pot single step process, which can be used as electrodes for supercapacitors (500 F g-1) and as an efficient electrocatalyst for water splitting. References 1) K. Parvez, Z. S. Wu, R. J. Li, X. J. Liu, R. Graf, X. L. Feng, K. Mullen, J. Am. Chem. Soc. 2014, 136, 6083. 2) A. Ejigu, K. Fujisawa, B. F. Spencer, B. Wang, M. Terrones, I. A. Kinloch, R. A. W. Dryfe, Adv. Funct. Mater. 2018, 28, 1804357. Figure 1