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.