Chelating agent assisted heat treatment of carbon supported cobalt oxide nanoparticle for use as cathode catalyst of polymer electrolyte membrane fuel cell (PEMFC)

Cobalt-based catalysts for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cell (PEMFC) have been successfully incorporated cobalt oxide (Co₃O₄) onto Vulcan XC-72 carbon powder by thermal decomposition of Co-ethylenediamine complex (ethylenediamine, NH₂CH₂CH₂NH₂, denoted en) at 850 °C. The catalysts were prepared by adsorbing the cobalt complexes Co(en)(H₂O)₄]³⁺, Co(en)₂(H₂O)₂]³⁺ and Co(en)₃]³⁺ on commercial XC-72 carbon black supports, loading amount of Co with respect to carbon black was about 2%, the resulting materials have been pyrolyzed under nitrogen atmosphere to create CoO_x/C catalysts, donated as E1, E2, and E3, respectively. The composite materials were characterized using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). Chemical compositions of prepared catalysts were determined using inductively-coupled plasma-atomic emission spectroscopy (ICP-AES). The catalytic activities for ORR have been analyzed by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The electrocatalytic activity for oxygen reduction of E2 is superior to that of E1 and E3. Membrane electrode assemblies (MEAs) containing the synthesized CoO_x/C cathode catalysts were fabricated and evaluated by single cell tests. The E2 cathode performed better than that of E1 and E3 cathode. This can be attributed to the enhanced activity for ORR, in agreement with the composition of the catalyst that CoO co-existed with Co₃O₄. The maximum power density 73 mW cm⁻² was obtained at 0.3 V with a current density of 240 mA cm⁻² for E2 and the normalized power density of E2 is larger than that that of commercial 20 wt.% Pt/C-ETEK.