First principles study on the electronic structure properties of Keggin polyoxometalates on Carbon substrates for solid-state devices

Abstract

Carbon has shown to give excellent performance in electrodes of energy storage devices, such as Li-ion batteries and supercapacitors. The grafting of polyoxometalates (POM) at carbon has scarcely been explored at the theoretical and experimental level, and the mechanism behind the chemical bonding between POM and carbon has not been fully understood. In order to give insights into these issues, an electronic structure study was carried out on the following POM systems adsorbed on carbon: PdMo12, RuNb12, SiMo12, PMo12 and SiW12. The prediction of the existence and chemical stability of PdMo12 and RuNb12 systems is reported for the first time. All systems were fully optimized with the nominal charges and also neutralized with counterions, as a benchmark to elucidate an optimal scheme that models the interaction in these nanocomposite systems. The POM/carbon attraction lies at about 250 pm in average, which may be addressed to a non-covalent bonding of the electrostatic-type, where the van der Waals contribution may also play a role. The density of states is evidently increased around the Fermi level in all POM/carbon systems. This may be due to the rising of new trajectories that ions may follow at the electrode of a solid-state device, such as a supercapacitor, giving as a result the strengthening of density current values and pseudocapacitive properties than those observed in pristine carbon systems. It was found that the SiWO12 and RuNb12 POM systems may be more feasible to be adsorbed on carbon substrates and may not require functional groups to allow POM retention. These systems represent potential candidates to be considered in nanohybrid electrodes for solid-state applications.