Methanol electrooxidation performance of nickel-modified polyaniline thin films for direct methanol fuel cells

Abstract

A metal–organic composite thin film composed of polyaniline (PANI) and Ni was prepared and characterized for methanol electrooxidation reaction. First, PANI thin films were electrodeposited on a fluorine-doped tin oxide (FTO) coated glass support in an aqueous acidic solution. Subsequently, the polymer film was modified with Ni particles (FTO/PANI-Ni) by chronoamperometric (CA) technique. The composite film was characterized by structural, morphological and electrocatalytic analyses. X-ray diffraction (XRD) results confirmed the crystallization of Ni according to the cubic structure. Scanning electron microscopy (SEM) images showed that the Ni nanoparticles were uniformly dispersed on the PANI surface. The electrocatalytic performance of the FTO/PANI-Ni composite electrode for the methanol electrooxidation reaction was investigated in 0.5 M KOH solution containing methanol using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA) techniques. The effects of temperature and methanol concentration on the methanol electrooxidation performance were also studied. The modified composite catalyst exhibited an electrochemically active surface area of 0.5235 cm2. The presence of Ni nanoparticles on the polymer surface promoted the adsorption of methanol molecules and facilitated the oxidation process, leading to higher current densities and better overall performance. The maximum current density was 14 mA cm-2 and the electrode maintain 68 % of its initial activity even after 200 cycles, indicating that the FTO/PANI-Ni electrode exhibited good stability. The high methanol oxidation performance of the composite electrode was associated with large real surface area, a possible synergistic effect between the polymer moleucles and Ni particles as well as high intrinsic activity of Ni for this process.