Interlayer-confined Fe-N 4 sites in the hierarchical carbon structure accelerate mass transport and optimize electronic modulation for enhanced oxygen reduction reaction. Addressing the bottlenecks of catalytic efficiency and cost in clean energy conversion and electrochemical synthesis is critical for low-carbon technology advancement. Herein, we design an iron single atom supported on an inverse opal-structured carbon support (Fe-N-C io ), featuring unique hierarchical pores (micropores, mesopores, macropores) and an interlayer-confined microenvironment that synergistically enhances mass transfer and modulates the electronic structure of Fe-N 4 active sites. We demonstrate that the confined microenvironment in bilayer graphene downshifts the Fe d -band center, weakening the binding strength of oxygen intermediates, favoring O–O bond cleavage and reducing the rate-determining step energy barrier (O* → OH*). Consequently, Fe-N-C io outperforms commercial Pt/C, achieving a half-wave potential ( E 1 / 2 ) of 0.91 V with only 7.87 mV decay after 100,000 cycles. In practical device applications, the aqueous zinc-air batteries (A-ZABs) assembled with Fe-N-C io achieve stable operation for over 1200 h, with a voltage gap change of only 20 mV. The quasi-solid-state zinc-air batteries (QSS-ZABs) exhibit an OCV of 1.48 V, a large peak power density of up to 207.73 mW cm −2 , and also cycling durability for 160 h. In chlor-alkali electrolysis systems, the Fe-N-C io ||RuO 2 chlor-alkali flow cell operates at 1.66 V (80 °C, 300 mA cm −2 ) with stable performance for over 110 h. This work validates the application potential of Fe-N-C io in energy conversion and industrial electrochemistry, while systematically elucidating the regulatory mechanism of the interlayer-constrained microenvironment on single-atom catalyst’s performance, which provides a paradigm for designing high-efficiency non-precious metal catalysts.
Zhao et al. (2026) studied this question.