Development of Co-, Fe- and N-Doped Mesoporous Carbon Catalysts for Anion-Exchange Membrane Fuel Cell Cathode
Authors: Lilloja Jaana , Piir Johanna Katariina , Mooste Marek , Kibena-Põldsepp Elo , Sarapuu Ave , Kikas Arvo , Kisand Vambola , Käärik Maike , Kozlova Jekaterina , Treshchalov Alexey , Paiste Päärn , Aruväli Jaan , Leis Jaan , Tamm Aile , Kukli Kaupo , Holdcroft Steven , Tammeveski Kaido 
Published: December 2024

Hydrogen has a lot of promise to be utilized in sustainable transportation and energy production using low-temperature polymer electrolyte membrane fuel cells. While proton-exchange membrane fuel cells are already commercialized, they still have issues with needed substantial amount of platinum as electrocatalyst. By switching to alkaline electrolyte, cheaper and more sustainable electrocatalysts can be used for cathodic oxygen reduction reaction (ORR). For instance, transition metal and nitrogen doped nanocarbons (M-N-C, M = Fe, Co, Mn, etc.) have shown very good ORR activity in alkaline media. Anion-exchange membrane fuel cell (AEMFC) technology, however, is still in research phase, and any further developments in electrocatalysts is necessary.1-3

Herein the focus is on developing mesoporous M-N-C electrocatalysts for the ORR and studying the effect of carbon support porous structure on the AEMFC performance. Mesoporous carbons (MCs) are prepared by combining phloroglucinol with glyoxal/glyoxylic acid. In the first part, soft-templating approach by Pluronic F127 is taken,4 in the second part of the work, effect of additional hard template (MgO) is investigated through dual-templating. We have limited the amount of harsh and environmentally unfriendly chemicals, offering more sustainable approaches beyond the silica-templating for synthesizing mesoporous carbons. The prepared MCs have high specific surface area (up to 900 m2 g-1) and have high content of mesopores in 5-8 nm range. To further study the effect of porous structure of carbon support on the AEMFC performance, nanocarbon composites with MC (prepared in first part) and either highly microporous carbide-derived carbon (CDC) or carbon nanotubes (CNTs) are also prepared (Figure 1a).
Our previous works have shown that bimetallic materials, containing iron and cobalt, perform the best in AEMFC.5-6 Thus herein, all prepared nanocarbon supports are doped with nitrogen (1,10-phenanthroline as source), cobalt and iron (Co- and Fe-acetate) via high-temperature pyrolysis, which yields electrocatalyst with atomically dispersed metal centers (Figure 1b). Rotating disc electrode (RDE) method is employed for preliminary ORR-activity testing with the prepared CoFe-N-C materials showing high electrocatalytic activity in 0.1 M KOH (E
1/2 up to 0.84 V vs RHE) and good stability after 10,000 potential cycles. In the first part, using nanocarbon composites with varying porous structure yielded electrocatalysts with almost identical performance in the RDE test. However, the effect of porous structure came evident during AEMFC testing, wherein presence of more mesoporous structure was beneficial.4 In the second part using dual-templating approach, the most optimal ratio of two templates (F127 and MgO) was found, together with promising AEMFC performance.
In conclusion, we have employed three different mesoporous carbon synthesis routes (soft- or dual-templating), optimized the conditions, and after doping obtained highly active ORR electrocatalysts with great promise for the AEMFC application.

References

[1] H. A. Firouzjaie and W. E. Mustain, ACS Catal. 10 (2020) 225-234.
[2] A. Sarapuu, J. Lilloja, S. Akula, J. H. Zagal, S. Specchia, and K. Tammeveski, ChemCatChem 15 (2023) e202300849.
[3] M. M. Hossen, M. S. Hasan, M. R. I. Sardar, J. B. Haider, Mottakin, K. Tammeveski, and P. Atanassov, Appl. Catal. B: Environ. 325 (2023) 121733.
[4] J. Lilloja, M. Mooste, E. Kibena-Põldsepp, A. Sarapuu, A. Kikas, V. Kisand, M. Käärik, J. Kozlova, A. Treshchalov, P. Paiste, J. Aruväli, J. Leis, A. Tamm, S. Holdcroft, and K. Tammeveski, Electrochim. Acta 439 (2023) 141676.
[5] J. Lilloja, E. Kibena-Põldsepp, A. Sarapuu, J. C. Douglin, M. Käärik, J. Kozlova, P. Paiste, A. Kikas, J. Aruväli, J. Leis, V. Sammelselg, D. R. Dekel, and K. Tammeveski, ACS Catal. 11 (2021) 1920-1931.
[6] J. Lilloja, E. Kibena-Põldsepp, A. Sarapuu, A. Konovalova, M. Käärik, J. Kozlova, P. Paiste, A. Kikas, A. Treshchalov, J. Aruväli, A. Zitolo, J. Leis, A. Tamm, V. Kisand, S. Holdcroft, and K. Tammeveski, ACS Appl. Energy Mater. 6 (2023) 5519−5529.

Figure 1