High durability fuel cell cathodes obtained from cobalt metal organic frameworks

Abstract

Mesoporous carbons doped with Nitrogen and Cobalt were obtained from the pyrolysis of two different Cobalt Metal-Organic Frameworks (MOFs, ZIF-67 and CoNic) and from one linear coordination polymer (CP, Co(CO2)2Pz). (ZIF-67 = catena-(bis(μ2-2-methylimidazolato)-cobalt(II), CoNic = catena-(bis(μ3-nicotinato)-bis(μ2-nicotinato)-(μ2-aqua)-di-cobalt(II), Co(CO2)2Pz = catena-((μ2-pyrazine-2,3-dicarboxylato)-diaqua-cobalt(II) dehydrate). The carbonization products were evaluated as cathode catalysts in polymer electrolyte membrane fuel cell (PEMFC). Membrane Electrode Assemblies (MEAs) prepared with the Co–N doped carbons and Pt 20% supported on Vulcan carbon as anode catalyst, were characterized in a PEMFC and post mortem by SEM, EDX, XPS and X-ray diffraction. The best catalyst was the one derived from the Co(CO2)2Pz polymer, pyrolyzed at 700 °C and acid leached. It reached a maximum power density of 259 mW cm−2, a limiting current of 1.36 A cm−2 and an open cell voltage of 0.86 V. These parameters are comparable to those of Pt 20% on Vulcan. The fuel cell prototype constructed with the Co(CO2)2Pz 700 °C material was able to operate for 500 h, without significant change of its electrochemical parameters and without leaking Co or Pt.