National Research Council of Canada. Nanotechnology
Electrochemical oxygen reduction and evolution reactions (ORR and OER) play a vital role in the field of energy conversion and storage. The problem is that both processes are sluggish, requiring precious-metal catalysts. Here, starting from abundant precursors and using a simple synthesis approach, we report the preparation of a good bifunctional oxygen electro-catalyst: a composite nanorod of manganese oxides and nitrogen-doped carbon. This material has hierarchical porosity, facilitating the mass transfer within the electrode. The nitrogen-doped carbon forms contiguous 3D network, connecting the isolated MnOx nanoparticles and ensuring superior electrical conductivity. Importantly, the MnOx particles contain manganese of mixed oxidation states; aligned with the nitrogen-doped carbon, this hybrid is among the best non-noble-metal ORR/OER catalysts in alkaline media, outperforming even Pt and RuO2 catalysts.