Core-alloyed shell structured Fe@FeCo di-atomic nanoclusters loaded in carbon aerogels as efficient bi-functional catalysts towards ORR and HER

Abstract

In this work, core-alloyed shell structured (CAS) Fe@FeCo di-atomic nanoclusters loaded in carbon aerogels (CAS Fe@FeCo DA-NC/C catalysts) were successfully prepared by utilizing the spatial confinement effect of polyaniline (PANI) hydrogels led by strong chelation among Fe3+ ions, tannic acid (TA), and amino (or imino) groups of PANI polymer chains. The spatial confinement effect can guarantee the formation of CAS Fe@FeCo DA-NCs with sizes between 1.4 and 2.4 nm. Moreover, N4–Fe–O–Co–N4 units are composed of the alloyed shells of the CAS Fe@FeCo DA-NCs, which can act as bi-functional active sites. In addition, N4–Fe–O–Fe–N4 units are the main component of their cores (like Fe-SA-NCs), which would slightly help strengthen the adsorption ability of bi-functional active sites of the CAS Fe@FeCo DA-NCs to the reactants. The core-alloyed shell structure of the CAS Fe@FeCo DA-NCs are demonstrated by results of X-ray photoelectron spectra, X-ray absorption spectroscopy and control experiments. Thus, the CAS Fe@FeCo DA-NC is proposed as a new type of active species with bi-functional active sites for the first time, to the best of our knowledge. Thanks to their unique features as active species (proper size, core-alloyed shell structure, and bi-functional active sites), the as-prepared CAS Fe@FeCo DA-NC/C catalysts show excellent performance as bi-functional catalysts in the oxygen reduction reaction (ORR) with a half-wave potential (E1/2) of 0.895 V (ΔE1/2 = 34 mV vs of Pt/C) in alkaline media and the hydrogen evolution reaction (HER, 133 mV @ 10 mA cm−2) in acidic media.