Modifying Randles circuit for analysis of polyoxometalate layer-by-layer films

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Layer-by-layer (LbL) assembly enables fabrication of functional thin films.
• Understanding charge transport is crucial for applications of multilayer films.
• Phosphomolybdic acid (PMo(12)) clusters offer unique electrochemical properties.

Purpose of the Study:

• To investigate charge transport phenomena in PMo(12) cluster-based multilayer films.
• To correlate film structure and composition with ion diffusion coefficients.
• To elucidate the influence of ionic strength and probe charge on mass transport.

Main Methods:

• Fabrication of multilayer films using electrostatic layer-by-layer (LbL) assembly.
• Electrochemical characterization using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS).
• Analysis of diffusion coefficients using an enhanced Randles equivalent circuit model.

Main Results:

• Lower diffusion coefficients were observed for negatively charged probes ([Fe(CN)(6)](3-/4-)) with increasing ionic strength of deposition solutions.
• The relationship between ionic strength and diffusion was less pronounced for positively charged probes ([Ru(NH(3))(6)](3+/2+)) due to electrostatic interactions.
• Increased PMo(12) loading resulted in lower diffusion coefficients, indicating pathway blockage by the clusters.
• Higher ionic strength solutions led to increased film tortuosity, hindering mass transport.

Conclusions:

• The ionic strength of deposition solutions significantly affects the mass transport properties of PMo(12) multilayer films.
• Electrostatic interactions between the film and redox probes play a critical role in determining diffusion behavior.
• Film tortuosity and the physical presence of PMo(12) clusters are key factors limiting ion diffusion.