A PRACTICAL APPROACH TO METAL-FREE OXYGEN REDUCTION CATALYSTS

Efficient oxygen reduction holds the key to practical fuel cells and metal-air batteries. Most of today’s oxygen cathodes are based on platinum catalysts. In theory, fuel cells with such cathodes could power cars for mass transportation – but there is simply not enough platinum on Earth to do this.

We have discovered a new family of nitrogen-doped carbons, characterized by: (1) a particularly simple synthesis, (2) a complex and fascinating microstructure of the carbon, and (3) very good oxygen reduction reaction (ORR) activity at pH 13.

The material is derived from the pyrolysis of simple salts and yields a carbon with hierarchical micro/meso/macro porosity. This porosity results from in situ templating by spontaneously forming MgO nanoparticles and from etching by pyrolysis gases. The mesopores are lined with highly graphitic shells. The high ORR activity is attributed to a good balance between high specific surface area and mass transport through the hierarchical porosity, and to improved electronic conductivity through the graphitic shells. This novel carbon has high surface area (1320 m²/g), and high nitrogen content for a single precursor synthesis (~6%). Importantly, its synthesis is both cheap and easily scalable.

Finally, we demonstrate how this carbon synthesis may serve as a template for an entire research program focused on the rational design of functional carbon materials for electrochemical applications.