MOF-derived nitrogen-coordinated iron single atoms: A promising ORR electrocatalyst for passive direct ethanol alkaline fuel cells

This study presents a novel electrocatalyst for the oxygen reduction reaction (ORR), featuring single-atom iron-doped nitrogen (Fe-N_x) embedded in a carbon-based framework. The electrocatalyst was derived from a bimetallic zeolitic imidazole framework (Zn/Fe-BZIF), leveraging the high surface area, tunable coordination environments, stability, and cost-effectiveness of metal–organic frameworks (MOFs). Iron incorporation significantly enhanced the onset potential, positioning the material as a promising candidate for high-performance ORR applications. To achieve atomic-level dispersion and prevent agglomeration, the double solvent method was utilized, encapsulating the iron salt precursor within the hydrophilic pores of ZIF-8. This method ensured precise integration and optimized electrocatalyst efficiency. Following pyrolysis, the Fe-s/NC catalyst exhibited outstanding ORR activity and stability in alkaline media, surpassing commercial Pt/C. The catalyst demonstrated high selectivity for the direct 4e⁻ reduction of oxygen to water, achieving an onset potential (E_onset) of 1.03 V_RHE and a half-wave potential (E_1/2) of 0.93 V_RHE. Over 40,000 s of chronoamperometric testing, it maintained 90% of its initial current density. Furthermore, the electrocatalyst showed promising performance in a direct ethanol alkaline fuel cell (DEAFC) and in sensor applications at low ethanol concentrations. In air, it achieved an open-circuit voltage (OCV) of 0.920 V with a peak power density (P_max) of 14.7 mW cm⁻² at 0.320 V, and in oxygen, it reached an OCV of 0.946 V with P_max of 19.3 mW cm² at 0.346 V. This research introduced Fe-s/NC as an innovative catalyst to enhance cathode's electrocatalytic performance in passive DEAFCs.