Two-step carbonization as a method of enhancing catalytic properties of hemoglobin at the fuel cell cathode

Recently, there has been increased demand for a polymer electrolyte fuel cell (PEFC) that functions efficiently with far less or no Pt. In this study, the catalyst for the O-2 reduction at the cathode was formed by carbonizing hemoglobin, which could be abundantly and inexpensively obtained. A substantial enhancement of catalytic properties was achieved by a change in the carbonization process from one step to two steps. The PEFC using the carbonized hemoglobin formed in the modified carbonization process generated a high power comparable to those formed using a Pt-free cathode as reported already. The power densities of 0.11 and 0.16 W cm(-2) were attained using H-2 and O-2 gases at atmospheric pressure (H-2 and O-2 partial pressures, 54 kPa) and using pressurized gases (H-2 and O-2 partial pressures, 254 kPa), respectively. The carbonization modification reduced the Fe valence state from 3+ to 2+ in the carbonized hemoglobin, which was demonstrated by X-ray photoelectron spectroscopy. The catalysis enhancement was probably attributed to the increase in Fe(II), which was required as an O-2 bonding site in the first step of the multistep cathodic O-2 reduction process.