A stable suspension of polyaniline nanoparticles (nPANI) in acidic solution can be used in various applications. For the first time, the electrochemical behavior of nPANI as a dispersed phase in phosphoric acid (H3PO4) solution on a gold electrode has been investigated using a series of electrochemical methods including cyclic voltammetry (CV), chronoamperometry and electrochemical impedance spectroscopy. The prepared suspensions were stable during a long time. The electrochemical results confirmed two redox transformations within the nPANI structure occurred at the potentials of about 0.20 and 0.50 V (vs. Ag|AgCl) which are controlled by the irreversible diffusion and the adsorption mechanism of nPANI particles at the gold surface, respectively. Two main electrochemical parameters including total numbers of redox active sites per nPANI particle (4.2 × 105) and electron-transfer rate constant (9.7 × 10−6 cm s−1) have been determined using CV method. The adsorption process of nPANI particles obeys Langmuir isotherm; additionally, the quantum chemical calculations and Monte Carlo simulation demonstrated that polyaniline macro molecules can replace water and phosphoric acid molecules from the surface upon its adsorption to the gold substrate. The surface analyses of the electrode using Raman spectroscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy confirm the adsorption phenomenon.

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