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PRINCIPAL PUBLICATION AND AUTHORS

Imaging Heterogeneous Electrocatalyst Stability and Decoupling Degradation Mechanisms in Operating Hydrogen Fuel Cells, I. Martens (a,b), A. Vamvakeros (a,c,d), N. Martinez (e), R. Chattot (a), J. Pusa (a), M.V. Blanco (a), E.A. Fisher (b), T. Asset (f), S. Escribano (e), F. Micoud (e), T. Starr (g), A. Coelho (h), V. Honkimaki (a), D. Bizzotto (b), D.P. Wilkinson (i), S.D.M. Jacques (d), F. Maillard (f), L. Dubau (f), S. Lyonnard (j), A. Morin (e), J. Drnec (a), ACS Energy Lett. 6, 2742-2749 (2021); https:/doi.org/10.1021/acsenergylett.1c00718 (a) ESRF (b) Advanced Materials and Process Engineering Laboratory, University of British Columbia, Vancouver (Canada) (c) University College London, London (UK) (d) Finden Limited, Abingdon (UK) (e) Université Grenoble Alpes, CEA, Grenoble (France) (f) Université Grenoble Alpes, Université Savoie Mont Blanc, CNRS, Grenoble INP, LEPMI, Grenoble (France) (g) Independent researcher, St. Johann im Tirol (Austria) (h) Coelho Software, Brisbane (Australia) (i) Department of Chemical and Biological Engineering, University of British Columbia, Vancouver (Canada) (j) Université Grenoble Alpes, CEA, CNRS, IRIG, SyMMES, Grenoble (France)

REFERENCES

[1] I. Martens et al., J. Phys. Energy 3, 031003 (2021). [2] I. Martens et al., J. Power Sources 437, 226906 (2019). [3] A. Vamvakeros et al., J. Appl. Cryst. 53(6), 1531 (2020).

This study demonstrates that the X-ray scattering tomography techniques developed at the ESRF can be scaled up to image industrially sized fuel cell and battery samples, 5-10x larger than previously feasible. These advances leverage improvements in the brilliance provided by ESRF-EBS, but also from X-ray-compatible electrochemical sample environments [2], and advanced data-analysis strategies [3] developed in collaboration with international partners.

The data help to explain why next-generation fuel cell electrocatalysts reported in the literature have repeatedly failed to reach commercial viability, despite excellent

A new technique to image human organs at the multiscale

Beamline BM05 has been used to develop a new technique called Hierarchical Phase-Contrast Tomography (HiP-CT), which is capable of three- dimensional, non-destructive imaging from the whole human organ (at 25 µm/voxel) down to single- cell resolution in a region of interest anywhere within the intact organ. The technique could revolutionise medical imaging.

Human organs are inherently multiscale and hierarchical. Functional sub-units at different length scales collectively provide biological function and physical integrity (Figure 137). Understanding how healthy or pathological behaviours emerge from interactions across these length scales is a fundamental challenge for imaging science.

HiP-CT is a phase-contrast propagation-based imaging (PBI) [1,2] approach that utilises local tomography to

selectively image high-resolution volumes anywhere within the larger sample. Previously, PBI with local tomography was limited to samples with high density contrast, such as fossilised remains [1]. Soft-tissue imaging, where there is low density contrast, requires a high-energy X-ray beam with high flux to penetrate large samples, coupled with high spatial coherence to enable long propagation distances without geometric blurring. Previously, this combination was not available at any synchrotron beamline worldwide.

HiP-CT combines the advances of the ESRF-EBS with scanning protocols adapted from large fossil local tomography [3,4], modifications to beamline BM05, a single-distance phase-retrieval combined with a 2D unsharp mask reconstruction, and a sample-preparation protocol that physically stabilises organs over long periods. Once prepared, samples are scanned in a hierarchical fashion: the whole organ at 25 µm/voxel, then areas of interest at 6 µm/voxel, and finally at 2.5-1.3 µm/voxel. Multiple regions of interest can be scanned and the

performance in laboratory testing. The heterogeneous environment imprinted by the macroscopic design of the cell, together with the harsher conditions found inside the practical device, can have detrimental effects not seen under idealised conditions. Therefore, a more holistic understanding obtained through multimodal operando characterisation, as shown in this work, is critical in order to understand the chemistry inside complex electrochemical devices. This will guide the optimisation of each component of the cell, as well as the interaction between the components, allowing incorporation of new-generation, high-performance materials in industrial devices and bringing the hydrogen economy closer to reality.