Building three-dimensional porous nano-network for the improvement of iron and nitrogen-doped carbon oxygen reduction electrocatalyst

Building three-dimensional (3D) nano-network and improving porous characteristics of nitrogen-doped carbon-based oxygen reduction electrocatalysts can facilitate to the diffusion of oxygen molecule and the enhancement of electrocatalytic performance. In this work, we report a new strategy for preparation of hemin-derived iron and nitrogen co-doped porous carbon electrocatalyst (3D-Fe/N/C-700) with three-dimensional nano-network via using a new hard template of inorganic salts (e.g., NaCl), followed by water-leaching and acid-leaching processes. This catalyst has exhibited a higher BET surface area (∼480 m2 g−1) and a larger total pore volume (∼0.49 cm3 g−1) compared to those of the Fe/N/C catalyst without using a NaCl template. An onset potential of ∼1.0 V vs. RHE and a high long-term stability are achieved for 3D-Fe/N/C-700, but a negative shift of only ∼30 mV exists in the half-wave potential of 3D-Fe/N/C-700 compared to the commercial 20 wt.% Pt/C catalyst. Besides, high electron transfer number (3.9 ± 0.2) and low peroxide species (<18.5%) on 3D-Fe/N/C-700 in the potential range of 0.2-0.8 V indicate a quasi four-electron pathway for electroreduction of O2 molecule. We also suggest that the FeN2 structure may be the active center of our catalyst, but 3D porous network and graphitic-N can play an important role in the enhancement of ORR electrocatalysis. Sustainable conversion of hemin to nitrogen-doped porous carbon and recyclability of NaCl template render a scalable production and practical application of carbon materials for energy storage and conversion.

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