Formation of Platinum-Free Fuel Cell Cathode Catalyst with Highly Developed Nanospace by Carbonizing Catalase

The amount of platinum in the catalyst for the electrodes of polymer electrolyte fuel cells must be minimized to widely substitute this new energy system for conventional ones. In this study, a platinum-free catalyst for the cathodic oxygen reduction was formed from a natural organic compound, catalase. We carbonized catalase to produce a catalyst active in the superacidic atmosphere of the polymer electrolyte. Nitrogen adsorption onto the carbonized material revealed that the material had highly developed internal nanospaces, which were essential for exposing active sites to oxygen reduction on the pore surface. The carbonized material was also characterized by X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, and Mössbauer spectroscopy. The activity for oxygen reduction was evaluated using rotating disk electrodes, forming a catalyst layer from the carbonized material and the polymer electrolyte on the electrode surface and immersing the layer in oxygen-saturated perchloric acid. The activity increased with the increase in the specific surface area and possibly the increase in the activity of the respective active sites. A preliminary fuel cell test using the material in the cathode confirmed the electricity generation, although the performance was inferior to a Pt-based fuel cell.