(Invited) Structural and Mechanistic Details on the Oxygen Evolution Reaction on Nife Layered Double Hydroxide and Ni(OH)2

The incorporation of Fe3+ ions in Ni(OH)2 is responsible for a dramatic oxygen evolution reaction (OER) activity enhancement.1 NiFe based (oxy)hydroxides are among the most active electrocatalysts for the OER in alkaline electrolytes.2 Their crystal structure, known as layered double hydroxide (LDH), is composed of layers of edge sharing metal oxygen octahedra that are intercalated with water molecules and charge balancing anions (Figure 1).3 In contrast, Fe-free Ni(OH)2 can be synthesized in the well defined brucite-like crystal structure, which does not have intercalated species and is indicated as β-M(OH)2. Oxidative deprotonation and possibly the electrocatalytic OER reaction lead to reversible structural changes that are only observable with in operando or in situ methods.1, 4 Several reports investigated the oxidized phases, but key aspects of the catalytically OER active site remain elusive and more investigations are necessary. In this contribution our results obtained using in operando wide angle X-ray scattering (WAXS) on crystalline NiFe LDH nanostructured catalysts and β-Ni(OH)2 catalysts will be presented.5 We identified the structure of the active catalyst state and observed that the lattice spacing under operating conditions changes reaching a similar value for both catalysts (Figure 1). Using a unique differential electrochemical mass spectrometry (DEMS) apparatus and isotope labelled experiments we further unravel mechanistic details on how the OER mechanism proceeds on these catalysts. References D. Friebel, M. W. Louie, M. Bajdich, K. E. Sanwald, Y. Cai, A. M. Wise, M. J. Cheng, D. Sokaras, T. C. Weng, R. Alonso-Mori, R. C. Davis, J. R. Bargar, J. K. Norskov, A. Nilsson and A. T. Bell, J Am Chem Soc, 2015, 137, 1305-1313. M. Gong, Y. G. Li, H. L. Wang, Y. Y. Liang, J. Z. Wu, J. G. Zhou, J. Wang, T. Regier, F. Wei and H. J. Dai, J Am Chem Soc, 2013, 135, 8452-8455. F. Dionigi and P. Strasser, Advanced Energy Materials, 2016, 6. M. Gorlin, J. F. de Araujo, H. Schmies, D. Bernsmeier, S. Dresp, M. Gliech, Z. Jusys, P. Chernev, R. Kraehnert, H. Dau and P. Strasser, J Am Chem Soc, 2017, 139, 2070-2082. F. Dionigi, Z. Zeng, I. Sinev, T. Merzdorf, S. Deshpande, M. B. Lopez, S. Kunze, I. Zegkinoglou, H. Sarodnik, D. X. Fan, A. Bergmann, J. Drnec, J. F. De Araujo, M. Gliech, D. Teschner, J. Greeley, B. Roldan Cuenya and P. Strasser, submitted 2019. Figure 1. Shift of the (003) diffraction peak associated to the interlayer distance for NiFe LDH catalysts between the resting state (black) and OER active state (red).5 3D structural model of the as prepared NiFe LDH. Figure 1