Tofu-derived heteroatom-doped carbon for oxygen reduction reaction in an anion exchange membrane–fuel cell

The oxygen reduction reaction at the cathode of an anion exchange membrane–fuel cell progresses very slowly. Therefore, only platinum-based catalysts with adequate adsorption/desorption binding energy for oxygen are used in practical applications. Because noble metal–based electrocatalysts are very expensive, research is underway to reduce the amount of noble metals used or to replace platinum-based catalysts. Further, to reduce the production cost of fuel cells, a simple fabrication process enabling mass productivity and replacement of noble metals must be developed. Transition metal catalysts with metal–nitrogen-doped carbon have been investigated as an alternative to the noble metal catalysts for oxygen reduction reaction at the cathode of a fuel cell. In this study, to generate metal–nitrogen–carbon sites, protein precipitation was performed by chelating metal cations with the functional groups of proteins. This approach employed a traditional method that uses tofu (made from soy milk) to intake proteins. To separate the proteins dissolved in soy milk in the solid state, a coagulant containing transition metals was added. Tofu containing bimetallic zinc and cobalt ions was prepared and carbonized to synthesize nitrogen- and phosphorus-doped carbon structures and single-atomic cobalt active sites. The prepared tofu-derived catalyst exhibited excellent electrocatalytic performance with a half-wave potential of 0.86 V, an onset potential of 0.981 V, and high durability.