Intrinsic Activity and Ni-O-Fe Catalytic Active Site in Ni-Based (Oxy)Hydroxides for the Oxygen Evolution Reaction

NiFe layered double hydroxides (LDHs) and (oxy)hydroxides are among the most active electrocatalysts for the oxygen evolution reaction (OER) in alkaline electrolytes. 1 However, they still show considerable overpotentials for the OER, i.e. 350 mV at 10 mA cm -2 in pH 13. 1, 2 Understanding the nature of the catalytic active sites and the catalytic mechanism in NiFe LDHs 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-phase to activated γ-phase. 2 The OER active γ-phase was characterized by operando wide angle X-ray scattering (WAXS) in alkaline electrolytes. 2 The intrinsic activity was then obtained by an electrochemical impedance method through electrochemical surface area (ECSA) normalization. 3 Comparison with other Ni- and Co- based LDHs revealed that NiFe LDH shows the highest intrinsic activity. 4 Our density functional theory (DFT) calculations on a γ-phase atomic model showed that O-bridged Ni-Fe reaction centers (Ni-O-Fe) stabilize OER intermediates that are unfavourable on Ni-O-Ni centers and single Fe sites, fundamentally accounting for the high catalytic activity. Furthermore, our DFT calculations predicts that γ-NiFe LDH is close to, but not on, the top of the OER volcano. 2,4 Strategies to modify the catalytic active site to approach the top of the volcano will be presented, together with preliminary experimental results. These strategies will involve the design of active sites involving subsurface metal sites and electronic modulation of the Ni-O-Fe sites by introduction of a third transition metal element. References F. Dionigi and P. Strasser, Advanced Energy Materials, 6, 1600621 (2016). 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., 11, 2522 (2020). S.S. Jeon, P.W. Kang, M. Klingenhof, H. Lee, F. Dionigi, P. Strasser, ACS Catal., 13, 1186-1196 (2023). F. Dionigi, J. Zhu, Z. Zeng, T. Merzdorf, H. Sarodnik, M. Gliech, L. Pan, W.-X. Li, J. Greeley, and P. Strasser, Angew. Chemie IE, 60, 14446 – 14457 (2021)