On the Role of Transition Metal Salts During Electrochemical Exfoliation of Graphite: Antioxidants or Metal Oxide Decorators for Energy Storage Applications

A new approach is presented, based on the unexpectedly versatile role of transition metal ions, to produce high-quality graphene via an anodic electrochemical exfoliation route, and the capability of the resultant material in energy storage applications are illustrated. The method is based on graphene exfoliation in the presence of transition metals (Co²⁺ and Fe³⁺) which act as antioxidants, preventing surface oxidation of graphene, while other metals (Ru³⁺, Mn²⁺, Ir³⁺, and Sn⁴⁺) act as metal oxide decorators. The addition of Co²⁺ ions to the exfoliation solution produced few-layer graphene that is two orders of magnitude more conducting and contains 80% less oxygen than the material obtained in the absence of cobalt ion. By contrast, the use of Mn²⁺ and Ru³⁺ in the electrolyte form an interconnected honeycomb lamellar structure of MnO₂ and RuO₂ nanoparticles, respectively. The combination of Mn²⁺ and Ru³⁺ create a uniformly grown Ru–Mn oxide hybrid structure on the graphene sheets in a single stage process, which is found to be an efficient electrode for supercapacitors (specific capacitance of 500 F g⁻¹) and as a bifunctional water splitting electrocatalyst. The use of these inexpensive salts will aid the scalable production of high-quality graphene and functionalized graphene for diverse applications.