Intrinsic Catalytic Activity and Active Phase for Oxygen Evolution in Layered Double Hydroxide Electrocatalysts

The NiFe layered double hydroxides (LDHs) are among the most active electrocatalysts for the oxygen evolution reaction (OER) in alkaline electrolytes.1 The incorporation of Fe dramatically increases the catalytic activity of Ni hydroxides.2 However, even the most active NiFe LDH catalyst still shows a considerable overpotential for the OER. Understanding the nature of the catalytic active sites and the catalytic mechanism are key challenges to develop better OER electrocatalysts. In this contribution, atomic-scale details of the catalytic active phase will be presented, showing that NiFe LDHs are oxidized under applied anodic potentials from as-prepared α-phases to activated γ-phases.3 The interlayer and in-plane lattice parameters of the OER-active γ-phase were obtained by performing wide angle X-ray scattering (WAXS) measurements on NiFe LDH nanoplatelets during operating electrochemical conditions and were characterized by a contraction of about 8%. Operando WAXS was then performed for other selected catalysts belonging to the transition metal LDH family of materials. Structural similarities of the catalytically active phases will be highlighted. Finally, in order to derive activity-structure relationships, an approach is presented to calculate intrinsic catalytic activities, which are challenging to evaluate for this class of materials. The presented method is based on electrochemical active surface area normalization obtained by impedance spectroscopy measurements under OER.4 References F. Dionigi and P. Strasser, Advanced Energy Materials, 2016, 6 1600621. L. Trotochaud, S. L. Young, J. K. Ranney and S. W. Boettcher, Journal of the American Chemical Society, 2014, 136: 6744-6753. F. Dionigi, Z. Zeng, I. Sinev, T. Merzdorf, S. Deshpande, M. B. Lopez, S. Kunze, I. Zegkinoglou, H. Sarodnik, D. Fan, A. Bergmann, J. Drnec, J. Ferreira de Araujo, M. Gliech, D. Teschner, J. Zhu, W.-X. Li, J. Greeley, B. Roldan Cuenya and P. Strasser, Nat Commun, 2020, 11 2522. F. Dionigi, J. Zhu, Z. Zeng, T. Merzdorf, H. Sarodnik, M. Gliech, L. Pan, W.-X. , Li, J. Greeley, and P. Strasser, Angew Chem Int Edit, 60, 14446 – 14457 (2021).