Investigation of macromolecule-metal complexes as cathode catalyst in polymer electrolyte membrane fuel cell system

• Published in: Polymers for advanced technologies 2011-08, Vol.22 (8), p.1235-1241
• Main Authors: Yuasa, M., Kondo, T., Mori, D., Arikawa, S.
• Format: Article
• Language: English
• Subjects: Catalysts; cathode catalyst; Cathodes; Chelates; Cobalt; cobalt polypyrrole; cobalt porphyrin; Density; Fuel cells; Heat treatment; macromolecule-metal complex (MMC); Membranes; oxygen reduction reaction (ORR); polymer electrolyte membrane fuel cell (PEMFC)
• ISSN: 1042-7147; 1099-1581; 1099-1581
• DOI: 10.1002/pat.1933

Search for non‐platinum metal catalyst as the cathode of polymer electrolyte membrane fuel cell (PEMFC) is an important subject in the recent fuel cell research. Macromolecule–metal complexes with macrocyclic ligands such as porphyrin and macromolecular ligands such as polypyrrole, all of which contain four nitrogen donors (Co‐N4 chelates) and are adsorbed on carbon, were prepared and heat‐treated in the hope that they can be an alternate to the conventional carbon‐supported platinum catalyst. Carbon‐supported cobalt (5,10,15,20‐tetraethylporphyrin) (HT‐CoTEtP/C), poly(cobalt (5‐mono(3‐thienyl)‐10,15,20‐triethylporphyrin)) (HT‐P(CoM3ThTEtP)/C), and cobalt‐(polypyrrole) (HT‐CoPPy/C) were chosen as candidate heat‐treated catalysts based on the electrocatalytic activity tests on the prepared macromolecule–metal complexes. The rotating ring‐disk method revealed that these catalysts reduce oxygen mainly with four electrons. Characterization using X‐ray photoelectron spectroscopy showed that the catalysts maintain the Co‐N4 chelate structure, strongly suggesting a major contribution of the Co‐N4 chelate to the four‐electron reduction of oxygen. Membrane electrode assemblies (MEAs) of PEMFCs were then constructed using HT‐CoTEtP/C, HT‐P(CoM3ThTEtP/C), and HT‐CoPPy/C as the cathode catalysts and the current density‐cell voltage and current density‐power density relationships were examined for the PEMFC. HT‐CoTEtP/C exhibited a much higher performance than the other macromolecule–metal complexes. Although the open circuit voltage and power density values of the PEMFCs were lower than those of the conventional carbon supported platinum catalyst, the power density per unit metal weight was almost comparable for the cobalt and platinum catalysts. Copyright © 2011 John Wiley & Sons, Ltd.