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Transition metal electrocatalysts are deem to be alternatives for the replacement of commercial Pt/C as highly efficient oxygen reduction reaction (ORR) electrocatalysts in the applications of advanced energy conversion/storage technologies. Herein, we reprecipitate hemin on polypyrrole (PPy) modified carbon materials (R-Hm/PPy@C), which boosts up the ORR performances. A high half-wave potential (E1/2) of 0.896 V (vs. RHE) and kinetic current density (JK) of 40.9 mA·cm−2 at 0.80 V (vs. RHE) of R-Hm/PPy@C outperforms these of commercial Pt/C in a 0.1 M KOH electrolyte. Moreover, the direct ammonia fuel cells (DAFC) and zinc-air batteries (ZAB) assembled by R-Hm/PPy@C deliver remarkable peak power densities of 288.4 mW·cm−2 in an electrolyte containing 3 M NH3 and 3 M KOH, and 180.2 mW·cm−2 with a high capacity of 820 mAh·gcat.−1 in a 6 M KOH solution. Such superior electrocatalytic performances are not only due to the synergistic effect of Fe3S4 particles and FeN4 single sites, but also are improved by enriched N-doped C species, further corroborated by theoretical calculations. Overall, this study delivers an efficacious approach to fabricate non-noble metal electrocatalysts (NNMEs) by engineering the synergistic effect of nanoparticles (NPs) and single-atom species with N-enriched dopants towards elevated electrocatalytic activities for energy conversion/storage devices.
Li et al. (Tue,) studied this question.