Key Takeaways & Executive Findings
- •• • The m-Fe/NC catalyst achieves half-wave potentials of 0.81 V (acidic) and 0.88 V (alkaline), outperforming many non-precious metal catalysts and approaching Pt/C performance, critical for fuel cell and metal-air battery efficiency. • • In zinc-air battery tests, m-Fe/NC delivers a specific capacity of 815 mAh g_Zn^-1 and a stable cell voltage of 1.31 V at 10 mA cm^-2, indicating high energy density and operational stability for practical applications. • • Turnover frequency (TOF) for acidic ORR at 0.8 V is 0.26 s^-1 for m-Fe/NC-2, compared to 0.064 s^-1 for microporous Fe/NC, a 4-fold improvement, demonstrating enhanced intrinsic activity due to mesoporosity. • • Density functional theory (DFT) calculations show that Fe-N4 sites on mesoporous surfaces have lower energy barriers (0.66–0.69 eV) for ORR than microporous Fe/NC-1 (0.72 eV), confirming the curvature-induced strain effect weakens intermediate adsorption and facilitates 4e^- reduction.
Abstract
Pore-tuning engineering is an effective strategy for designing catalysts for energy storage and conversion. Here, we report a rhombic dodecahedral iron and nitrogen co-doped carbon (Fe-N-C) material with hierarchical micro-mesoporous structures, synthesized using mesoporous silica as both pore template and iron source. The resulting catalyst (m-Fe/NC) exhibits significantly enhanced oxygen reduction reaction (ORR) activity, with half-wave potentials of 0.81 V and 0.88 V in acidic and alkaline media, respectively. When employed as a cathode in zinc-air batteries, m-Fe/NC delivers a superior specific capacity of 815 mAh g_Zn^-1 and a stable cell voltage of 1.31 V at a current density of 10 mA cm^-2. Advanced characterization and theoretical calculations reveal that the mesoporous structure not only increases active site exposure but also induces a curvature-induced strain effect on concave surfaces, which enhances intrinsic activity. This work provides insights for developing innovative nanoporous electrocatalysts.
1. Introduction
The oxygen reduction reaction (ORR) is a critical bottleneck in fuel cells and metal-air batteries due to its sluggish kinetics. Platinum-based catalysts are the benchmark but suffer from high cost, scarcity, and poor stability, hindering scalable deployment. Non-precious metal catalysts, particularly iron and nitrogen co-doped carbon (Fe-N-C), have emerged as promising alternatives due to their high atom utilization and tunable electronic structure. However, conventional Fe-N-C materials often exhibit limited active site exposure and suboptimal intrinsic activity, restricting their ORR performance.
This work addresses these limitations by engineering hierarchical micro-mesoporous structures in Fe-N-C using mesoporous silica as a template and iron source. The introduction of mesopores not only enlarges the electrochemically accessible surface area, improving mass transport and active site accessibility, but also induces a curvature-induced strain effect on concave surfaces. This strain modulates the electronic structure of Fe-N4 sites, weakening the adsorption of ORR intermediates and lowering the energy barrier, thereby enhancing intrinsic activity. The resulting m-Fe/NC catalyst demonstrates superior ORR performance in both acidic and alkaline media, and excellent zinc-air battery performance, offering a viable pathway for cost-effective and durable energy conversion.
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Qing Li, Jiayuan Tang, Yuhan Yang, Jun Chai, Xiao Zhang, Mingfei Shao, Hangjia Shen (2026). Mesopore-tuned iron and nitrogen co-doped carbon for enhanced oxygen reduction electrocatalysis. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3672-8
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Frequently Asked Questions
What is the specific role of mesoporous silica in the synthesis, and how does it influence the pore structure and iron loading?
Mesoporous silica acts as both a hard template and an iron source. It creates mesopores in the carbon framework after removal, and its iron content is incorporated into the Fe-N-C structure. This dual function ensures a hierarchical micro-mesoporous architecture with high surface area and accessible Fe-N4 active sites, as evidenced by the enhanced TOF and half-wave potentials.
How does the curvature-induced strain effect quantitatively alter the adsorption energies of ORR intermediates on Fe-N4 sites?
DFT calculations show that the energy barriers for ORR on mesoporous Fe-N4 sites are 0.66–0.69 eV, compared to 0.72 eV on microporous Fe/NC-1. This ~0.03–0.06 eV reduction indicates weaker binding of intermediates, which accelerates the rate-determining step and promotes a 4e^- pathway, consistent with the higher TOF observed.
What are the long-term stability and durability of m-Fe/NC under operational conditions, especially in acidic media?
The abstract reports stable cell voltage of 1.31 V at 10 mA cm^-2 in zinc-air batteries, but specific long-term cycling data (e.g., >1000 cycles) are not provided in the excerpt. However, the mesoporous structure is expected to mitigate carbon corrosion and active site leaching, though further accelerated stress tests are needed to confirm durability.
How does the performance of m-Fe/NC compare to commercial Pt/C in terms of half-wave potential and cost?
m-Fe/NC achieves half-wave potentials of 0.81 V (acidic) and 0.88 V (alkaline), which are competitive with Pt/C (typically ~0.85-0.9 V in alkaline). Given the use of earth-abundant Fe and N, the material offers significant cost advantages, potentially reducing catalyst cost by >90% compared to Pt-based systems.
What is the scalability of the synthesis method for industrial production?
The synthesis uses ZIF-8 and mesoporous silica, which are commercially available and amenable to scale-up. The pyrolysis step is standard in catalyst manufacturing. However, the removal of silica template requires HF or NaOH etching, which poses safety and waste management challenges. Alternative template removal methods or recyclable templates would be needed for large-scale production.
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