Novel Keplerate type polyoxometalate-surfactant-graphene hybrids as advanced electrode materials for supercapacitors

The development of novel materials for enhanced electrochemical energy storage applications, in particular for the fabrication of supercapacitors (SCs) displaying increased properties, is a milestone of both fundamental and technological relevance. Among nanostructured materials, polyoxometalates (POMs) combined with various carbon-based nanostructures represent a very promising class of hybrid systems for energy storage, yet, guidelines for their rational design and synthesis leading to high-performance SCs is still lacking. Here, we have produced a novel hybrid architecture based on Keplerate type POM (Mo132) functionalized with dodecyltrimethylammonium bromide (DTAB), which upon mixing with electrochemically exfoliated graphene (EEG) nanosheets results in the formation of porous 3D superstructures. Mo132-DTAB-EEG combines the redox activity of POMs and high electrical conductivity of graphene, all synergically mediated by the surfactant-assisted porosity enhancement, to form new electrode materials for SCs. Cyclic voltammetry and galvanostatic charge/discharge electrochemical studies on Mo132-DTAB-EEG performed in aqueous H2SO4 electrolyte revealed that the unique combination of these three components yields highly efficient energy storage materials. In particular, our highly porous hybrids system exhibits high specific capacitance of 65 F g−1 (93 F cm−3, 93mFcm−2) combined with excellent stability (99% of specific capacitance retained) after 5000 charge/discharge cycles at different current densities, overall displaying significantly improved performance compared to pristine electrochemically exfoliated graphene material. Strong non-covalent interactions between Keplerate type polyoxometalate Mo132-DTAB and graphene surface offer higher stability compared to other hybrid POM/carbon-based systems, and unique electrical properties of the multicomponent structure, thereby paving the way towards the development of novel, and potentially multifunctional, POM-based architectures to be exploited as SC electrode materials