Exploring Fibrin Protein Hydrogels for the Production of Heteroatom-Doped Porous Carbon Nanoarchitectures as Efficient Metal-Free Oxygen Reduction Reaction Catalysts

Although protein hydrogels are excellent carbonization precursors for synthesizing carbon nanoarchitectures as efficient metal-free oxygen reduction reaction (ORR) catalysts, research on this topic has rarely been conducted. In this study, fibrin protein hydrogels templated with sodium chloride (NaCl) crystals are proposed as novel precursors for the manufacture of heteroatom-doped planar carbon nanostructures containing internal pores. By systematically adjusting the carbonization conditions, it is revealed that their effects on material properties and ORR characteristics. The catalyst carbonized at 900 degrees C for 12 hr demonstrated excellent performances in an alkaline solution, including onset potential (Eon; 0.86 V vs. reversible hydrogen electrode), diffusion-limited current (-4.0 mA cm-2 at 0.05 V), electron transfer number (2.84), and durability (-18 mV shift in Eon after 30,000 cycles). This is attributed to the synergistic action of fast out-of-plane electron transport, sufficient adsorption sites, enhanced activity by heteroatom doping, and effective mass transfer through interconnected pores.