Oxygen reduction reaction (ORR) catalysts play a critical role in energy storage and conversion devices and have been attracted enormous interests, and however, it remains challenging to develop highly active cheap catalysts in a simple and green route. Inspired by the heme-copper oxidases (HOCs), in which the ORR active center is originated from the incorporation of Fe-N₄ with copper atom, we here developed a fine manganese oxide nanosheets (MnO_x NSs) integrated with iron phthalocyanine (FePc) anchored on highly conductive graphene (MnO_x/FePc-G) through a green route only involve ethanol as the reagent. The bio-inspired catalyst MnO_x/FePc-G demonstrated high ORR activity with a half-wave potential (E_1/2) of 0.887 V, about 57 mV more positive than that of Pt/C. And the current density (j) at 0.9 V is about 1.9 mA cm⁻², which is three times of Pt/C and FePc-G. More importantly, the bio-inspired systems show superior stability in comparison to commercial Pt/C, showing a potential of 0.863 V to deliver a j of 3 mA cm⁻² after 18 000 s polarization, about 80 mV higher than that of 0.783 V for Pt/C. The high activity is contributed by the integration of the FePc and MnO_x NSs that plays the role to assist the cleavage of the O₂ bond. Our approach provides a new evidence to develop highly efficient ORR catalysts through imitate the naturally involved systems through a simple route.

The electrochemical carbon dioxide reduction reaction (CO₂RR), which can produce value-added chemical feedstocks, is a proton-coupled-electron process with sluggish kinetics. Thus, highly efficient, cheap catalysts are urgently required. Transition metal oxides such as CoO_x, FeO_x, and NiO_x are low-cost, low toxicity, and abundant materials for a wide range of electrochemical reactions, but are almost inert for CO₂RR. Here, we report for the first time that nitrogen doped carbon nanotubes (N-CNT) have a surprising activation effect on the activity and selectivity of transition metal-oxide (MO_x where M = Fe, Ni, and Co) nanoclusters for CO₂RR. MO_x supported on N-CNT, MO_x/N-CNT, achieves a CO yield of 2.6–2.8 mmol cm⁻² min⁻¹ at an overpotential of −0.55 V, which is two orders of magnitude higher than MO_x supported on acid treated CNTs (MO_x/O-CNT) and four times higher than pristine N-CNT. The faraday efficiency for electrochemical CO₂-to-CO conversion is as high as 90.3% at overpotential of 0.44 V. Both in-situ XAS measurements and DFT calculations disclose that MO_x nanoclusters can be hydrated in CO₂ saturated KHCO₃, and the N defects of N-CNT effectively stabilize these metal hydroxyl species under carbon dioxide reduction reaction conditions, which can split the water molecules and provide local protons to inhibit the poisoning of active sites under carbon dioxide reduction reaction conditions.

Elucidating the reaction mechanism of hydrazine oxidation reaction (HzOR) over carbon-based catalysts is highly propitious for the rational design of novel electrocatalysts for HzOR. In present work, isolated first-row transition metal atoms have been coordinated with N atoms on the graphite layers of carbon nanotubes via a M-N₄-C configuration (MSA/CNT, M=Fe, Co and Ni). The HzOR over the three single atom catalysts follows a predominant 4-electron reaction pathway to emit N₂ and a negligible 1-electron pathway to emit trace of NH₃, while their electrocatalytic activity for HzOR is dominated by the absorption energy of N₂H₄ on them. Furthermore, FeSA/CNT reverses the passivation effect on Fe/C and shows superior performance than CoSA/CNT and NiSA/CNT with a recorded high mass activity for HzOR due to the higher electronic charge of Fe over Co and Ni in the M-N₄-C configuration and the lowest absorption energy of N₂H₄ on FeSA/CNT among the three MSA/CNT catalysts.