Investigations of multilayer polyoxometalates-modified carbon nanotubes for electrochemical capacitors

A simple and effective method to improve over previous approaches to add pseudocapacitance to carbon substrates through deposition of polyoxometalates (POMs) was demonstrated on multi-walled carbon nanotubes (MWCNTs). By superimposing layers of different pseudocapacitive polyoxometalates, SiMo12O40-4 (SiMo12) and PMo12O40-3 (PMo12). the POMs exhibited continuous overlapped oxidation/reduction reactions and achieved an up to fourfold increase in area specific capacitance when compared with the double layer capacitance of bare MWCNTs. The superimposed SiMo12 and PMo12 layers were studied by Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS). Analyses of the potential/pH relationship provided important insights into the deposition mechanism and suggested that the layer closest to the electrode substrate was dominating in terms of chemistry and kinetics of the coated MWCNT. (C) 2011 Elsevier Ltd. All rights reserved.