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The decoupled synthesis of Fe-NC single-site electrocatalysts mediated by Lewis acids enables high active site density and utilization. However, current approaches often rely on small organic molecules and suffer from low synthesis yields due to the high Lewis acid-to-precursor ratios required to achieve highly porous carbons. Here, a porous organic polymer (POP) based on 2,4,6-Triaminopyrimidine (TAP) is utilized as a carbon-nitrogen-based scaffold for the synthesis of Fe─NC electrocatalysts. By tuning the amounts of MgCl2 ·6H2O used both as porogen and active site templating agent, synthetic yields exceeding 45% are achieved, a significant improvement compared to the 6% yield from the molecular analogue and the highest reported forMg2+ templated systems. Subsequent low-temperature exchange with Fe leads to atomically dispersed FeNx, minimizing Fe aggregation. The resulting materials exhibit high specific surface areas (>1000 m2 g−1) with micro-, meso-, and macropores, which promote mass transport and active site accessibility. Compared to Fe─NC synthesized via direct pyrolysis of Fe-coordinated POP, the decoupled method enables significantly higher catalytic activity in both alkaline and acidic media, and delivers 1 A cm−2 at 0.687 ± 0.004 VRHE in an alkaline gas diffusion electrode, highlighting its potential for practical oxygen reduction devices.
Atomically dispersed Fe in N-doped carbon (Fe–N–C) catalysts are leading platinum-group-metal-free candidates for the O2 reduction reaction in proton exchange membrane fuel cells (PEMFCs). Zeolitic imidazolate framework (ZIF-8) derived Fe–N–C present the most promising performance; however, they possess a narrow distribution of small micropores, which limits active site accessibility. Here, to induce hierarchical porosity in Fe–N–C, we report a systematic study on MgCl2·6H2O-templated ZIF-8-derived Fe–N–C catalysts for the O2 reduction reaction. MgCl2·6H2O addition induced complete Zn removal, collapse of the ZIF-8 framework, and formation of large micro- and mesopores, with graphene-like structures. N content was markedly reduced, with conversion from pyridinic to pyrrolic N species. Rotating disc electrode tests showed a progressive increase in O2 reduction activity with MgCl2·6H2O, which is strongly correlated (R2 = 0.98) to the formation of large micropores and small mesopores (1–4 nm). This introduces an indirect structure–activity design principle for Fe–N–Cs. The enhanced Fe–N–C porosity also leads to increased degradation rates under accelerated stress test conditions, which we attributed to the oxidation of disordered carbon domains and active Fe loss. This study highlights a key trade-off between porosity-driven O2 reduction activity and durability in Fe–N–C catalysts.
