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Quantifying the electrochemical active site density of precious metal-free catalysts in situ in fuel cells

Abstract

Advances in the development of precious-group metal-free (PGM-free) catalysts for the oxygen reduction reaction (ORR) in fuel cell cathodes have produced active catalysts that reduce the performance gap to the incumbent Pt-based materials. However, utilization of state-of-the-art PGM-free catalysts for commercial applications is currently impeded by their relatively low durability. Methods designed to study catalyst degradation in the operation of fuel cells are therefore critical for understanding durability issues and, ultimately, their solutions. Here we report the use of Fourier-transform alternating current voltammetry as an electrochemical method for accurate quantification of the electrochemically active site density of PGM-free cathode catalysts, and to follow their degradation in situ during the operation of polymer electrolyte fuel cells. Using this method, we were able to quantify the electrochemical active site density, which will enable the elucidation of degradation mechanisms of PGM-free ORR catalysts in situ in fuel cells.

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Fig. 1: CV of the fuel cell.
Fig. 2: Polarization curves of the cell during the stability test.
Fig. 3: Schematic representation data processing for FTacV measurement.
Fig. 4: Power spectrum obtained from FTacV measurments.
Fig. 5: Harmonics extracted from a single FTacV measurement of the fuel cell.
Fig. 6: The seventh harmonics generated from FTacV measurements at different times during the stability test.
Fig. 7: Analysis of EASD and TOF over the course of the stability measurement.

Data availability

The raw data that support the findings of this study are available from the corresponding author on request.

Code availability

All simulations in this work were conducted using the MECSim simulation package obtained from the following website free of charge: http://www.garethkennedy.net/MECSim.html.

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Acknowledgements

R.Z.S.-S., A.F. and H.C.H. thank the Israeli Ministry of Energy for their fellowships. Part of this work was conducted within the framework of the Israeli Fuel Cells Consortium. L.E. thanks the Israeli Ministry of Energy for funding this project (no. 219-11-132). This research was supported in part by the US Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office. Electron microscopy was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.

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R.Z.S.-S. conceived, analysed, simulated and conducted fuel cell and electrochemical measurements and prepared the manuscript. A.F. and Y.Y. conducted some of the preliminary experiments. A.K. conducted XRD measurements and Raman spectroscopy. H.C.H. conducted XPS measurements and analysis. M.J.Z. conducted TEM and STEM measurements and analysis. A.M.B. gave advice, discussed the results and edited the manuscript. P.Z. discussed the results and edited the manuscript. L.E. conceived and analysed all experiments and discussed the results, supervised the work and edited the manuscript.

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Correspondence to Lior Elbaz.

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Nature Catalysis thanks Frédéric Jaouen and Jianglan Shui for their contribution to the peer review of this work.

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Supplementary Figs. 1–21, Tables 1 and 2, Methods, Discussion and Notes 1–3.

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Snitkoff-Sol, R.Z., Friedman, A., Honig, H.C. et al. Quantifying the electrochemical active site density of precious metal-free catalysts in situ in fuel cells. Nat Catal 5, 163–170 (2022). https://doi.org/10.1038/s41929-022-00748-9

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