Fabrication of MEA based on optimum amount of Co in Pd_xCo/C alloy nanoparticles as a new cathode for oxygen reduction reaction in passive direct methanol fuel cells

摘要

Carbon supported Pd and Pd_xCo alloy electrocatalysts of different Pd_xCo atomic ratios (x = 1, 2, 3 and 10) were prepared by the impregnation synthesis method at room temperature without heat treatment by ethylene glycol (EG) reduction. As prepared Pd_xCo bimetallic nanoparticles show a single-phase face-centered-cubic (fcc) disordered structure. The performance of these electrodes in the ORR was measured with cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), chronoamperometry (CA), inductive coupled plasma (ICP), X-ray diffraction (XRD); scanning electron microscopy coupled to energy dispersive X-ray (SEM-EDX) and transmission electron microscope (TEM). For synthesized Pd_xCo/C electrocatalysts, the highest catalytic activity for the ORR, was found for a Pd:Co atomic ratio of 3:1 in acid media at the presence and absence of methanol with optimal Pd-Pd bond distance (0.2729 nm). Since the Pd_xCo/C alloy electrocatalysts are inactive for the adsorption and oxidation of methanol, it can act as a methanol-tolerant ORR catalyst in a direct methanol fuel cell (DMFC). A membrane-electrode assembly (MEA) has been prepared by employing of the Pd_3Co/C as a cathode for passive direct methanol fuel cell and characterized by polarization curves and impedance diagrams. The DMFC test results indicate that the MEA prepared from Pd_3Co/C cathode exhibits better performance compared to the MEA prepared from Pt/C (Electrochem) and an in-house Pd/C catalyst synthesized, in terms of maximum power density and minimum charge transfer resistance.