A Highly Porous Fe-N-C-based Proton Exchange Membrane Fuel Cell: Effect of Ionomer Loading Probed by in situ Electrochemical Methods

Angus Pedersen^a^,^b^,^c^,^d, Rifael Snitkoff-Sol^d, Yan Yurko^d, Jesús Barrio^a^,^b, Rongsheng Cai^e, Theo Suter^e, Guangmeimei Yang^a, Sarah Haigh^e, Dan Brett^c, Rhodri Jervis^c, Magda Titirici^b, Ifan Stephens^a, Lior Elbaz^d

^aDepartment of Materials, Royal School of Mines, Imperial College London, London SW7 2AZ, England

^bDepartment of Chemical Engineering, Imperial College London, London SW7 2AZ, England, UK.

^cElectrochemical Innovation Lab, Department of Chemical Engineering, University College London, London WC1E 7JE, England

^dDepartment of Nanotechnology and Advanced Materials and the Department of Chemistry, Bar-Ilan University, Ramat Gan, Israel

^eDepartment of Materials, University of Manchester, Manchester, M13 9PL, England

Proceedings of 24th International Conference on Solid State Ionics (SSI24)

Advanced characterisation techniques: fundamental and devices

London, United Kingdom, 2024 July 14th - 19th

Organizers: John Kilner and Stephen Skinner

Oral, Angus Pedersen, presentation 300
Publication date: 10th April 2024

The next generation of proton exchange membrane fuel cells (PEMFCs) require a substantial reduction or elimination of Pt-based electrocatalyst from the cathode,[1], [2] where O₂ reduction takes place. The most promising alternative to Pt is atomic Fe embedded in N-doped C (Fe-N-C). Successful incorporation of Fe-N-C in PEMFCs relies on a thorough understanding of the catalyst layer properties, both ex situ and in situ, with tailored electrode interface engineering.[3] Here, it is demonstrated that a previously developed high pore volume Fe-N-C [4] requires a sufficiently high ionomer to catalyst mass ratio (I/C, 2.8≤I/C≤4.2) for optimum PEMFC performance under H₂/O₂. Advanced in situ electrochemical techniques (distribution of relaxation times[5] and Fourier transform alternating current voltammetry[6]) were used to deconvolute for the first time the trade-off between proton and electron resistance and in situ FeN_x active site density with increasing ionomer loading. These findings highlight the significant impact of tuning the I/C ratio based on the catalyst layer properties and feature the power of emerging in situ electrochemical tools for optimising performance in PEMFCs and other electrochemical devices.

References:

[1] S. T. Thompson and D. Papageorgopoulos, ‘Platinum group metal-free catalysts boost cost competitiveness of fuel cell vehicles’, Nat. Catal., 2019, 2, 558–561

[2] A. Pedersen et al., ‘Comparative techno-economic and life-cycle analysis of precious versus non-precious metal electrocatalysts: The case of PEM fuel cell cathodes’. Green Chem., 2023, 25, 10458–10471.

[3] D. Banham, J. Y. Choi, T. Kishimoto, and S. Ye, ‘Integrating PGM-Free Catalysts into Catalyst Layers and Proton Exchange Membrane Fuel Cell Devices’, Adv. Mater., 2019, 31, 1804846.

[4] J. Barrio et al., ‘FeNC Oxygen Reduction Electrocatalyst with High Utilization Penta‐Coordinated Sites’, Adv. Mater., 2023, 35, 2211022.

[5] Q. Meyer, S. Liu, Y. Li, and C. Zhao, ‘Operando detection of oxygen reduction reaction kinetics of Fe–N–C catalysts in proton exchange membrane fuel cells’, J. Power Sources, 2022, 533, 231058.

[6] R. Z. Snitkoff-Sol et al., ‘Quantifying the electrochemical active site density of precious metal-free catalysts in situ in fuel cells’, Nat. Catal., 2022, 5, 163–170.

Acknowledgements:

The authors acknowledge financial support from the Engineering and Physical Sciences Research Council (EPSRC) (EP/W031019/1, EP/S023259/1 and EP/V001914/1), the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement no. 866402 and no. 715502, EvoluTEM). A. P. thanks the EPSRC Centre for Doctoral Training in the Advanced Characterisation of Materials (grant number EP/L015277/1) and the British/Israel Council/Wohl Clean Growth Alliance Foundation for supporting and funding travel in this collaboration. J. B. acknowledges financial support from Imperial College London through the Imperial College Research Fellowship. Electron microscopy access was supported by the Henry Royce Institute for Advanced Materials, funded through EPSRC grants EP/R00661X/1, EP/S019367/1, EP/P025021/1 and EP/P025498/1. R.Z.S.-S. thanks the Israeli Ministry of Energy for his fellowship.

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