Selective deposition of zinc hexacyanoferrate on the metal impurity sites of a SWCNT/glassy carbon electrode

In this work, we report for the first time that multi-metal impurities present in SWCNTs aid ZnHCF-modification of the electrode and the charge–discharge characteristics of the composite. The multi-metal impurities in the as-supplied SWCNTs serve as nucleating centres or provide active sites for electrocrystallization of ZnHCF. ZnHCF-SWCNT/GCE was characterized using cyclic voltammetry, X-ray photoelectron spectroscopy and transmission electron microscopy. Interestingly, the deposition of ZnHCF is restricted only to the metal impurity surface sites and not to the surface of the walls of SWCNT, confirming again that the deposition does not take place on the carbon surface of the nanotube. Intimate contact established between the metal impurities and ZnHCF is inferred to be responsible for the reduced charge-transfer resistance observed in the ac impedance measurements performed on the composite electrode. The calculated specific capacitance values of ZnHCF-SWCNT/GCE are 5 times higher than those obtained for SWCNT/GCE.