A multi-technique approach towards the mechanistic investigation of the electrodeposition of Prussian blue over carbon nanotubes film

Abstract

A detailed and multi-technique study on the kinetics and mechanism of the electrodeposition of Prussian blue (PB) over iron filled-carbon nanotubes (CNTs) thin films is presented here. PB is electrochemically synthesized through a heterogeneous reaction between iron species encapsulated into CNTs and ferricyanide ion in aqueous solution. The reaction was followed by a combination of in-situ or ex-situ measurements through UV–Vis spectroscopy, cyclic voltammetry, Raman spectroscopy and scanning electron microscopy. The analysis of the evolution of a new parameter that we called coverage ratio as well as an innovative way to associate the data extracted from cyclic voltammetry with the electrochemical reaction, are introduced by the first time. Similar response vs. time profiles are obtained from absorbance, charge, current, band intensity in Raman spectra, particle size, and coverage ratio, yet providing different aspects of the growth mechanism. Electrochemical data demonstrates an initial mixed control process related to the iron releases from the CNTs cavities and nucleation, followed by a diffusion limited regime on the growth of PB. Spectroscopic data indicates pseudo-first order kinetics, dependent on ferricyanide concentration, and the rate limited by the iron releases from the CNTs. Both particle size of PB and coverage ratio show a progressive nucleation of PB corroborating the proposed mechanism. Raman data also confirm the PB growth rate over the CNTs walls and evidence of PB/CNT interactions during voltammetric cycles. This multi-technique approach gives insights on different aspects of PB electrodeposition and can be extended to a wide class of different materials.