Synthesis and Characterization of Electrodeposited C-PANI-Pd-Ni Composite Electrocatalyst for Methanol Oxidation

Electropolymerization of aniline at the graphite electrodes was achieved by potentiodynamic method. Electrodeposition of Pd (C-PANI-Pd) and Ni (C-PANI-Ni) and codeposition of Pd-Ni (C-PANI-Pd-Ni) microparticles into the polyaniline (PANI) film coated graphite (C-PANI) were carried out under galvanostatic control. The morphology and composition of the composite electrodes were obtained using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) techniques. The electrochemical behavior and electrocatalytic activity of the electrode were characterized using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronoamperometric (CA) methods in acidic medium. The C-PANI-Pd-Ni electrode showed an improved catalytic performance towards methanol oxidation in terms of lower onset potential, higher anodic oxidation current, greater stability, lower activation energy, and lower charge transfer resistance. The enhanced electrocatalytic activity might be due to the greater permeability of C-PANI films for methanol molecules, better dispersion of Pd-Ni microparticles into the polymer matrixes, and the synergistic effects between the dispersed metal particles and their matrixes. 1. Introduction Direct methanol fuel cell (DMFC) is regarded as a potential candidate as portable power sources [1]. Platinum modified polyaniline (PANI) electrocatalysts for methanol electrooxidation have been widely studied in recent years [2]. But, slow methanol oxidation kinetics, high cost, and limited resource do not allow use of Pt at commercial level. In addition, Pt-based electrocatalysts, generally, undergo deactivation/poisoning by the reaction intermediates, particularly by CO molecule in acid medium. The use of non-platinum metal like palladium in fuel cell catalysts is interesting, because it is more widespread in the Earth crust than platinum (abundance of 1.5 × 10？2 versus 5 × 10？3 parts per million by mass, resp.), and it is less expensive than Pt [3]. In addition, it is very stable in the acidic fuel cell environment and also exhibits interesting electrocatalytic properties for CO electrooxidation. These properties have led to considering Pd as a possible catalyst for those reactions in which CO appears as a poisoning intermediate, such as in the methanol [4]. The catalytic activity of Pd can be modified by alloying with other metals such as Ni; the combination of Pd with Ni is expected to further enhance the tolerance of Pd to poisoning as Ni is an oxophilic element [5]. The study of alloy electrodes is motivated primarily from