Dynamic surface self-reconstruction is the key of highly active perovskite nano-electrocatalysts for water splitting

Abstract

The growing need to store increasing amounts of renewable energy has recently triggered substantial R&D efforts towards efficient and stable water electrolysis technologies. The oxygen evolution reaction (OER) occurring at the electrolyser anode is central to the development of a clean, reliable and emission-free hydrogen economy. The development of robust and highly active anode materials for OER is therefore a great challenge and has been the main focus of research. Among potential candidates, perovskites have emerged as promising OER electrocatalysts. In this study, by combining a scalable cutting-edge synthesis method with time-resolved X-ray absorption spectroscopy measurements, we were able to capture the dynamic local electronic and geometric structure during realistic operando conditions for highly active OER perovskite nanocatalysts. Ba0.5Sr0.5Co0.8Fe0.2O3−δ as nano-powder displays unique features that allow a dynamic self-reconstruction of the material’s surface during OER, that is, the growth of a self-assembled metal oxy(hydroxide) active layer. Therefore, besides showing outstanding performance at both the laboratory and industrial scale, we provide a fundamental understanding of the operando OER mechanism for highly active perovskite catalysts. This understanding significantly differs from design principles based on ex situ characterization techniques.

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Figure 1: Microstructure and OER activities of BSCF-FS, LSC-FS and CoO-FS.
Figure 2: Operando XANES spectra.
Figure 3: Operando EXAFS and postmortem HAADF-STEM and EDX spectroscopy of the BSCF-FS electrode.
Figure 4: Relationship between OER activity and local electronic/structural changes.
Figure 5: OER/LOER and dissolution/re-deposition mechanism leading to the formation of a self-assembled active surface layer, rich in CoO(OH) and FeO(OH).
Figure 6: Performance comparison of BSCF-FS and IrO2 anode OER catalysts under alkaline membrane water electrolyser operating conditions.

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Acknowledgements

The authors gratefully acknowledge the Swiss National Science Foundation through its Ambizione Program (grant No. PZ00P2_148041 and grant No. PZ00P2_171426), the Swiss Competence Center for Energy Research (SCCER) Heat & Electricity Storage, the Swiss National Science Foundation within NCCR Marvel, and the Paul Scherrer Institute for financial contributions to this work. The authors thank I. Puente Orench from D1B/ILL/Grenoble for her assistance with the neutron diffraction experiments and R. Haumont from SP2M/ICMMO/Université Paris-sud for his help with neutron diffraction refinement. Furthermore, the authors thank the Swiss Light Source for providing beamtime at the SuperXAS beamline and ScopeM of ETH Zurich for the use of their transmission electron microscopes.

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E.F., T.B. and T.J.S. developed the concept. M.N. refined the argumentation. F.B. synthesized the nanocatalysts. E.F., X.C., B.-J.K. and J.D. carried out sample physical characterizations and electrochemical measurements. E.F., M.N., J.D. and X.C. carried out the experiments at the SuperXAS beamline. M.N. guided the operando XAS measurements. R.S. helped with the TEM investigation. L.W., M.P., N.D. and K.E.A. performed and supervised the electrolyser tests. E.F., M.N., T.B. and T.J.S. discussed the results and co-wrote the paper. All of the authors have revised the manuscript.

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Correspondence to Emiliana Fabbri or Thomas J. Schmidt.

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Fabbri, E., Nachtegaal, M., Binninger, T. et al. Dynamic surface self-reconstruction is the key of highly active perovskite nano-electrocatalysts for water splitting. Nature Mater 16, 925–931 (2017). https://doi.org/10.1038/nmat4938

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