A polyaniline/polyvinyl acetate composite film electrode for highly sensitive electrochemical sensing of pH

The electrochemical performances of three types of polyaniline (PANI)-based films developed as pH-sensing electrodes were evaluated and compared. PANI emeraldine base (PANI-EB), PANI emeraldine salt (PANI-ES), and PANI-ES/polyvinyl acetate (PVAc) composite films were spin coated on fluorine-doped tin oxide (FTO) glass substrates to fabricate pH-sensing electrodes. The surface morphology, wetting properties, and electrochemical properties were characterized and compared. Unprotonated PANI-EB films had a regular structure with residual flakes, whereas protonated PANI-ES and PANI-ES/PVAc films exhibited globular and porous structures, respectively. All PANI-based films adhered well to the FTO substrate. Water contact angles indicated the hy-drophobic characteristic of the PANI-EB films and the hydrophilicity of the PANI-ES films, which could affect their stability in buffered solutions of different pH. The PANI-ES/PVAc films exhibited improved stability because of the hydrophobic PVAc. The PANI-ES/PVAc electrodes exhibited a significantly higher pH sensitivity of 100 mV pH-1 than those of the single-component PANI-EB and PANI-ES electrodes (57 and 65 mV pH-1, respectively) in the pH range of 3.0-8.0, which could be attributed to the non-equilibrium protonation/depro-tonation of nitrogen atoms in the PANI structure. Moreover, the PANI-ES/PVAc electrodes also exhibited good reproducibility and selectivity to H+ over certain other ions and molecules (e.g., glucose).