Co₄N/nitrogen-doped graphene: A non-noble metal oxygen reduction electrocatalyst for alkaline fuel cells

Cobalt-nitride (Co₄N) nanoparticle-decorated nitrogen-doped graphene sheets were obtained via the nitrogen doping of a graphene-oxide precursor and simultaneous nitride formation. The non-precious metal catalyst formed in this one-step synthesis exhibits high electrocatalytic oxygen reduction activity and hence provides a promising alternative to conventional Pt/C alkaline fuel cell cathode catalysts. The reported composites were formed from the mixture of lyophilized graphene-oxide nanosheets and cobalt(II) acetate in ammonia atmosphere at 600 °C. The average Co₄N particle size increased from 14 to 201 nm with the increase in cobalt content. The oxygen reduction activity of the new catalysts was comparable to that of non-noble metal systems described in the literature, and also to the widely-used carbon black supported platinum catalysts. The highest reduction current density under alkaline conditions was found to be as high as 4.1 mA cm⁻² with the corresponding electron transfer number of 3.6. Moreover, the new system outperformed platinum-based composites in terms of methanol tolerance, thus eliminating one of the major drawbacks (besides high price and limited availability), of noble metal catalysts.