Hemoglobin pyropolymer used as a precursor of a noble-metal-free fuel cell cathode catalyst

The partial pyrolysis of hemoglobin yielded the hemoglobin pyropolymer, which is an intermediate substance between a polymer and carbonaceous material. The pyropolymer was formed by the heat treatment of hemoglobin below 600 degrees C. The formation behavior of the pyropolymer was examined by thermogravimetry and differential thermal analysis, and the pyropolymer was characterized by elemental analysis and its C-13 nuclear magnetic resonance spectrum. The pyropolymer formation began around 200 degrees C, and aromatic carbon developed with an increase in the heat-treatment temperature through transformation of the aliphatic carbon in hemoglobin. A noble-metal-free cathode catalyst for a polymer electrolyte fuel cell (PEFC) was formed by heat treatment of the hemoglobin pyropolymer in flowing Ar containing 10% CO2. The activity of the catalyst was dependent on the characteristics of the pyropolymer. The carbon matrix developed with an increase in the aromatic carbon, whereas the micropore development was suppressed. The highest activity was observed for the catalyst with the maximized micropore development. The PEFC using the catalyst with the highest activity obtained in this study generated 0.12 and 0.23 W cm(-2) at O-2 partial pressures of 54 and 254 kPa, respectively. Continuous PEFC operations and measurements of the extended X-ray absorption fine structures demonstrated that the current decrease during the operation correlated with the structure of the active site of the catalyst.