Nanostructured Fe-N-C as bifunctional catalysts for oxygen reduction and hydrogen evolution

The development of electrocatalysts for energy conversion and storage devices is of paramount importance to promote sustainable development. Among the different families of materials, catalysts based on transition metals supported on a nitrogen-containing carbon matrix have been found to be effective catalysts toward oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) with high potential to replace conventional precious metal-based catalysts. In this work, we developed a facile synthesis strategy to obtain a Fe-N-C bifunctional ORR/HER catalysts, involving wet impregnation and pyrolysis steps. Iron (II) acetate and imidazole were used as iron and nitrogen sources, respectively, and functionalized carbon black pearls were used as conductive support. The bifunctional performance of the Fe-N-C catalyst toward ORR and HER was investigated by cyclic voltammetry, rotating ring disk electrode experiments, and electrochemical impedance spectroscopy in alkaline environment. ORR onset potential and half-wave potential were 0.95 V and 0.86 V, respectively, indicating a competitive performance in comparison with the commercial platinum-based catalyst. In addition, Fe-N-C had also a good HER activity, with an overpotential of 478 mV @10 mAcm(-2) and Tafel slope of 133 mVdec(-1), demonstrating its activity as bifunctional catalyst in energy conversion and storage devices, such as alkaline microbial fuel cell and microbial electrolysis cells.