Pore structure engineering via hard-template synthesis: unlocking the high oxygen reduction reaction activity and stability of Fe-N@C electrocatalysts

abstract

Developing efficient and durable iron-nitrogen-carbon (Fe-N@C) electrocatalysts with optimal pore architecture is crucial for advancing the oxygen reduction reaction (ORR) in fuel cells. In this study, we demonstrate how hard-templating with tailored silica scaffolds (SBA-15, KIT-6, and a dual SBA-15/KIT-6 template) can tune the pore structure of Fe-N@C materials. In these materials, the pore structure influences the formation and accessibility of active sites for the ORR. The mesoporous Fe-N@CMK-3 electrocatalyst, derived from SBA-15, exhibits the highest ORR activity (onset potential: 0.99 VRHE in alkaline media, and 0.82 VRHE in acid) due to its well-defined 2D hexagonal pores, which facilitate efficient oxygen diffusion. In contrast, the microporous Fe-N@CMK-8 (KIT-6-derived) exhibits lower ORR activity due to limited oxygen accessibility to the active sites. The dual-templated Fe-N@CMK-3/8 combines micro/mesoporosity to deliver balanced performance despite its lower surface area and pore volume resulting from the pore connectivity. All electrocatalysts initially follow a quasi-4e- ORR pathway, but their behavior changes during the long-term testing: Fe-N@CMK-8 shifts to the 2e- pathway despite its notably durable activity in acidic media; Fe-N@CMK-3 exhibits the best stability in terms of activity under alkaline conditions also with a slight shift to the 2e- pathway; Fe-N@CMK-3/8 excels in terms of selectivity sustaining a 4e- pathway along time with medium stability in the activity in both acid and alkaline media. These findings establish pore engineering as a powerful tool to tailor Fe-N@C electrocatalysts for specific operational environments, contributing to the development of high-performance non-precious metal catalysts for the ORR in proton exchange membrane and alkaline fuel cell applications.

keywords

POROUS CARBON; TRIBLOCK COPOLYMER; CATALYSTS; SILICA; SBA-15; IRON; POLYANILINE; SITES

subject category

Chemistry; Science & Technology - Other Topics; Materials Science

authors

Gianola, G; Lourenco, MAO; Basile, L; Morais, T; Mafra, L; Pirri, C; Specchia, S; Zeng, JQ

Groups

G1 - Porous Materials and Nanosystems

Projects

CICECO - Aveiro Institute of Materials (UIDB/50011/2020)

CICECO - Aveiro Institute of Materials (UIDP/50011/2020)

Associated Laboratory CICECO-Aveiro Institute of Materials (LA/P/0006/2020)

Unveiling CO2 chemisorption mechanisms in solid adsorbents via surface-enhanced ex(in)-situ NMR (NMR4CO2)

Rationale design of sustainable porous organosilicas for optimal CO2 uptake from biogas (GRACE)

acknowledgements

This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 (DOI https://doi.org/10.54499/UIDB/50011/2020), UIDP/50011/2020 (DOI https://doi.org/10.54499/UIDP/50011/2020) & LA/P/0006/2020 (DOI https://doi.org/10.54499/LA/P/0006/2020), financed by national funds through the FCT/MCTES (PIDDAC). This work has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant Agreement 865974). L. B. acknowledges Politecnico di Torino for supporting his stay@University of Aveiro. T. M. acknowledges FCT for the Doctoral grant (2024.03066.BD). M. A. O. L. acknowledges FCT for the Researcher position CEECIND/01158/2021 (DOI: https://doi.org/10.54499/2021.01158.CEECIND/CP1659/CT0022) and the funding from the European Union's Horizon Europe research and innovation program under the ERA-PF grant agreement no 101090287. J. Z. received a fund under the National Recovery and Resilience Plan (NRRP), Project code: IR0000027, Concession Decree No. 128 of 21/06/2022 adopted by the Italian Ministry of Research, CUP: B33C22000710006, Project title: iENTRANCE.