Synthesis of Highly Porous Metal-Free Oxygen Reduction Electrocatalysts in a Self-Sacrificial Bacterial Cellulose Microreactor

Bacterial cellulose (BC) is often used as a carbon source for in situ carbonization into carbon nanofibers (CNFs). The main challenge for such CNFs lies in the low yield and very low apparent density of the product, which hamper their applications as electrode materials in batteries and fuel cells. Herein, BC pellicles (8 wt%) are simultaneously employed as a substrate and a sacrificial microreactor, thus allowing the carbonization in its unique porous network. Ethylenediaminetetraacetic acid serves as a carbon source and a nitrogen source, while cobalt plays the role of a recyclable pore-creating template to create a 3D nitrogen-doped graphite carbon with hierarchically porous structure (HPGC). The resultant HPGC exhibits a large specific surface area, high porosity, and large amount of structural defects, which translate into very high oxygen reduction reaction (ORR) activity and stability. The synthesis route, the catalyst structure, and the proposed mechanism open novel avenue and insights to develop next-generation metal-free ORR catalysts.