Operando Studies of Hole-Doped IrNiOx core-shell electrocatalysts for Water Oxidation in acidic Environment

Hong Nhan Nong^a^,^d, Tobias Reier^a, Paul Paciok^b, Detre Teschner^c^,^d, Marc Heggen^b, Valeri Petkov^e, Robert Schlögl^c^,^d, Travis Jones^d, Peter Strasser^a

^aDept. of Chemistry, Technical University Berlin, Strasse des 17. Juni 124, TC 03, 10623 Berlin, Germany

^bForschungszentrum Jülich GmbH, DE, Wilhelm-Johnen-Straße, Jülich, Germany

^cDept. of Inorganic Chemistry, Fritz-Haber-Institute of the Max-Planck-Society, Faradayweg 4-6, 14195 Berlin, Germany

^dMax Planck Institute for Chemical Energy Conversion - Mülheim an der Ruhr, Stiftstraße, 34-36, Mülheim an der Ruhr, Germany

^eDept. of Physics, Central Michigan University, Mt. Pleasant, MI 48859, USA.

Materials for Sustainable Development Conference (MATSUS)
Proceedings of nanoGe Fall Meeting 2018 (NFM18)

S2 Light Driven Water Splitting

Torremolinos, Spain, 2018 October 22nd - 26th

Organizers: Wolfram Jaegermann and Bernhard Kaiser

Oral, Hong Nhan Nong, presentation 140
DOI: https://doi.org/10.29363/nanoge.nfm.2018.140
Publication date: 6th July 2018

The electro-oxidation of water to oxygen (oxygen evolution reaction, OER) in (photo-)electrolytic devices yields the electrons and protons required to form molecular fuels^1,2: This is why it is expected to play a major role in the development of future (photo-)electrochemical energy conversion and storage technologies. However, the slow rate of water oxidation remains a key challenge that requires fundamental understanding and the design of more active and stable OER electrocatalysts^3,4.

To further this development, we probe the local geometric ligand environment and the electronic metal states of O-coordinated Ir centers in Ni-leached IrNi@IrOx metal-oxide core-shell nanoparticles⁵— one of the most active OER electrocatalysts known to date — under catalytic oxygen evolution condition using operando spectroscopic techniques, resonant high-energy XRD and differential atomic pair correlation analysis, with support of density functional theory (DFT) calculations. Ni-leaching generates lattice vacancies, which in turn produce uniquely shortened Ir-O metal-ligand bonds and an unusually large number of d-band holes in the Ir oxide shell under OER. DFT calculations show this increase in formal Ir oxidation state drives the formation of O 2p holes on the oxygen ligands in direct proximity to lattice vacancies, resulting in the highly covalent and uniquely short Ir-O bonds seen experimentally. We argue the electrophilic character of these ligands renders them susceptible to nucleophilic acid-base-type O-O bond formation at reduced kinetic barriers, resulting in strongly enhanced OER reactivities. Together, our findings advance both our fundamental understanding of the exceptional reactivity of bimetallic core-shell Ir catalysts and provide a roadmap to tailoring of other “hole-doped” core-shell catalysts for water oxidation at a molecular level.

References

Dau, H.; Limberg, C.; Reier, T.; Risch, M.; Roggan, S.; Strasser, P. Chemcatchem 2010, 2, 724.

Olah, G. A.; Goeppert, A.; Prakash, G. K. S. J. Org. Chem. 2009, 74, 487.

Suntivich, J.; May, K. J.; Gasteiger, H. A.; Goodenough, J. B.; Shao-Horn, Y. Science 2011, 334, 1383.

Reier, T.; Nong, H. N.; Teschner, D.; Schlögl, R.; Strasser, P. 2017, 7, 1601275.

Nong, H. N.; Gan, L.; Willinger, E.; Teschner, D.; Strasser, P. Chem. Sci. 2014, 5, 2955.

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