A eutectic salt-assisted semi-closed pyrolysis route to fabricate high-density active-site hierarchically porous Fe/N/C catalysts for the oxygen reduction reaction

Abstract

Here we demonstrate a “eutectic salt-assisted semi-closed carbonization” technique for fabricating a high-density active-site hierarchically porous Fe/N/C catalyst by using a ZnCl₂/KCl eutectic salt as the template. Our technique allows for the pyrolysis of the Fe/N/C precursor under the protection of the molten ZnCl₂/KCl eutectic salt, which can not only provide an ionic liquid-confined space to suppress the large weight loss and N evaporation of the precursor in a very wide temperature range from 390 °C to 923 °C, but also play a key role in modulating the porous structure, specific surface area and graphitization degree of the Fe/N/C catalyst. Accordingly, the as-prepared Fe/N/C catalyst exhibits excellent ORR activity and stability in both acidic (half-wave potential of 0.803 V versus reversible hydrogen electrode) and alkaline (half-wave potential of 0.918 V versus reversible hydrogen electrode) media. More importantly, real cathodes made from the Fe/N/C catalysts further demonstrated superior performance in H₂–O₂ fuel cells and zinc–O₂ batteries. This strategy provides a new avenue for the design and development of advanced porous carbon materials for different applications.