The structural changes of blood pyropolymers and their beneficial electrocatalytic activity toward oxygen reduction

There is a growing interest in designing more effective fuel cell cathode catalyst precursors. Here the partial pyrolysis of animal bloods has been used to produce the blood pyropolymers, which are an intermediate substance between a polymer and carbonaceous material. These pyropolymers were yielded by carbonization process below 600°C. The structural changes in the pyropolymers were characterized by X-ray diffraction, and their formation was checked by micro-IR spectra, thermogravimetric and differential thermal analysis. Their potential electrocatalytic properties were evaluated using the linear sweep voltammetry in the O₂-saturated KOH solution. It is found that the process of pyropolymer formation began about 200°C and completed around 500°C. The change of particle phase depends on the formation of the pyropolymers, but has no effect to their internal carbon structures which are controlled by pyrolysis process only. Meanwhile, it is confirmed that the crystalline phases in the pyropolymers can exist at the surface of heat-treated materials. It can be also found that the carbon materials are active toward oxygen reduction and their activity is associated with the carbonization level. Our study will stimulate the designers to design the highly active catalysts by using native blood pyropolymers as the precursors.