Deriving Efficient Porous Heteroatom-Doped Carbon Electrocatalysts for Hydrazine Oxidation from Transition Metal Ions-Coordinated Casein

In this work, the synthesis of high-performance, metal ion-imprinted, mesoporous carbon electrocatalysts for hydrazine oxidation reaction (HzOR) using casein or a family of phosphoproteins derived from cow's milk as a precursor is shown. The synthesis is made possible by mixing trace amounts of non-noble metal ions (Fe ³⁺ or Co ²⁺ ) with casein and then producing different metal ions-functionalized casein intermediates, which upon carbonization, followed by acid treatment, lead to metal ion-imprinted catalytically active sites on the materials. The materials effectively electrocatalyze HzOR with low overpotentials at neutral pH and exhibit among the highest electrocatalytic performances ever reported for carbon catalysts. Their catalytic activities are also better than the corresponding control material, synthesized by carbonization of pure casein and other materials previously reported for HzOR. This work demonstrates a novel synthetic route that transforms an inexpensive protein to highly active carbon-based electrocatalysts by modifying its surfaces with trace amounts of non-noble metals. The types of metal ions employed in the synthesis are found to dictate the electrocatalytic activities of the materials. Notably, Fe ³⁺ is found to be more effective than Co ²⁺ in helping the conversion of casein into more electrocatalytically active carbon materials for HzOR.