We have synthesized vanadium sulfide nanoparticle (VS2) through a simple solvothermal method. Nyquist plot( impedence spectroscopy) shows that VS2 modified glassycarbon electrode (VS2/Nf/GCE) showed lower charge transfer resistance (Rct) implying the faster electron transfer rate than bare GCE. Vanadium sulfide is a semiconductor and such material should have low conductivity. What is probable reason behind this type of behavior of vanadium sulfide nanoparticles?
What solution did you test this in? Populating the GC surface with VS2 nanoparticles can do at least two things: increase the surface area available for redox reactions, and catalyze those redox reactions. I would guess the latter, but without knowing more about your system, it's hard to say.
In addition to what PM asked: Do you use 3 electrode scheme (in that case what was your polarizing potential) or 2 electrode? What is the amplitude of the signal you've used? Have you measured IV curve for the system? Have you measured kinetics of the process i.e. time dependence?
W/o all this info no reasonable assumption on the electrode transfer process mechanism can be made :(
I second the opinions provided by PM and PT. It is highly possible that the size of your charge transfer semicircle in the Nyquist plot is influenced by added adsorption due to increased surface area.
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