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

Abstract

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 (Co 2+ and Fe 3+ ) which act as antioxidants, preventing surface oxidation of graphene, while other metals (Ru 3+ , Mn 2+ , Ir 3+ , and Sn 4+ ) act as metal oxide decorators. The addition of Co 2+ 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 Mn 2+ and Ru 3+ in the electrolyte form an interconnected honeycomb lamellar structure of MnO 2 and RuO 2 nanoparticles, respectively. The combination of Mn 2+ and Ru 3+ 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.

Formation of a CoMn‐Layered Double Hydroxide/Graphite Supercapacitor by a Single Electrochemical Step

“…The presence of both Na + and Co 2+ drives the cathodic exfoliation of graphite foil through the intercalation of these cations at very negative potentials (<−3 V). The electrochemical exfoliation of graphite in the presence of Co 2+ has been reported, but by applying positive potentials [25] . We find that a very negative potential is a prerequisite and the driving force for the exfoliation of the GF.…”

“…The electrochemical exfoliation of graphite in the presence of Co 2+ has been reported, but by applying positive potentials. [25] We find that a very negative potential is a prerequisite and the driving force for the exfoliation of the GF. It is evident that at this negative potential the generation of hydrogen also contributes to the exfoliation of the graphite sheets.…”

Unravelling and quantifying the aging processes of commercial Li(Ni 0.5 Co 0.2 Mn 0.3 )O 2 /graphite lithium-ion batteries under constant current cycling

“…As reported in ref. 30 and 31 , the Co deposits on the graphite surface can also accelerate the exfoliation of graphite, leading to a severe degradation of the full cell.…”

Graphene Oxide Thin Films: Synthesis and Optical Characterization

“…Therefore, DFT simulations show that in GO sheets the electron donor abilities are more abundant than electron acceptor abilities, like p‐type narrow gap semiconductor behavior and these results suggests that the main contribution of the band‐gap energy can be attributed to epoxy group presence in GO films. Understanding the effect of epoxy groups in electrical and optical properties of molecular GO is of great interest in the basic interpretation of rGO behavior in many applications, like energy storage, catalyst binder, batteries, and micro‐lattices among others . Also, some challenges of GO thin films in organic photovoltaic solar cells may be, the evaluation of film versatility as interface material for electronics, the device compatibility of solvents and the influence of film homogeneity in the electronic devices.…”