Improved capacitance characteristics during electrochemical charging of carbon nanotubes modified with polyoxometallate monolayers

By modification of surfaces of multi-walled carbon nanotubes with ultra-thin monolayer-type films of phosphododecamolybdic acid, H3PMo12O40, an electrode material with improved capacitance properties is produced. It is apparent from three distinct test experiments (based on cyclic voltammetry, galavanostatic charging–discharging and AC impedance) that capacitors utilizing H3PMo12O40-modified carbon nanotubes are characterized by specific capacitances and energy densities on the levels of 40 F g−1 and 1.3 Wh kg−1, whereas the respective values for the systems built from bare carbon nanotubes are lower, 22 F g−1 and 0.7 Wh kg−1. It is reasonable to expect that fast and reversible multi-electron transfers of the Keggin-type H3PMo12O40 account for the pseudocapacitance effect and significantly contribute to the observed overall capacitance.