Lattice Oxygen Exchange in Transition Metal Oxyhydroxides and Metal Hydroxide Organic Frameworks Elucidated for the Oxygen Evolution Reaction

To achieve the goal of climate neutrality by 2050, it is essential to increase the use of renewable fuels and carbon-neutral energy.1 The anodic oxygen evolution reaction (OER) is a key reaction not only in electrocatalytic production of many renewable fuels,2 but also for next generation of charge storage devices such as metal-air batteries.3 However, the slow kinetics of the OER process result in high energy losses and costs.4 Therefore, the development of more efficient electrocatalysts is critical for making renewable energy via electrocatalysis a viable option in emerging energy systems. Transition metal (TM) oxides are a promising alternative to expensive noble metals due to their high catalytic OER activity under alkaline conditions and wider earth-abundance. Despite extensive research, establishing structure-activity correlations and understanding mechanistic processes is challenging, given the intricate interplay between external and intrinsic parameters. In this study, we investigate the role of lattice oxygens in electrodeposited Ni-Fe, Co-Fe, and Mn-Fe oxyhydroxide (M(OH)xOy, M = TM) electrocatalysts using surface-enhanced Raman spectroscopy (SERS) in conjunction with secondary ion mass spectroscopy (SIMS). By taking advantage of the Raman shift that results from 16O/18O isotope exchange,5–7 we can track the participation of lattice oxygens in the electrocatalytic cycle. Our investigation reveals that, during OER, all the electrocatalysts display minimal exchange of lattice oxygens with the electrolyte (less than 5%). However, many of these electrocatalysts show partial or complete exchange when exposed to non-catalytic potential when in their more reduced states (see Figure 1). Apart from fully inorganic catalysts, we also present results from Ni-derived metal-hydroxide-organic frameworks (MHOFs), which are analogous to M(OH)xOy catalysts but with organic linkers separating the layers.8 Our findings indicate that MHOFs with linkers that have a high π-π stacking energy (and a high structural stability)8 undergo near complete 16O/18O exchange during OER, while MHOFs employing linkers with a low π-π stacking energy (and thus a low stability) show minor or no lattice exchange during OER. Our study suggests that participation oflattice oxygens is closely linked to the oxidation state of the transition metals rather than to the catalytic process. The work provides a detailed picture of the exchange mechanism and elucidates alternative processes involved in lattice oxygen participation and discusses their relation to the mechanisms of the OER process. References IEA (2023), Energy Technology Perspectives 2023, IEA, Paris https://www.iea.org/reports/energy-technology-perspectives-2023, License: CC BY 4.0. Wei, S. Z. et al. Combining theory and experiment in electrocatalysis: Insights into materials design. Science (80-. ). 355, eaad4998 (2017). Li, Y. & Lu, J. Metal–Air Batteries: Will They Be the Future Electrochemical Energy Storage Device of Choice? ACS Energy Lett. 2, 1370–1377 (2017). Song, F. et al. Transition Metal Oxides as Electrocatalysts for the Oxygen Evolution Reaction in Alkaline Solutions: An Application-Inspired Renaissance. J. Am. Chem. Soc. 140, 7748–7759 (2018). Lee, S., Banjac, K., Lingenfelder, M. & Hu, X. Oxygen Isotope Labeling Experiments Reveal Different Reaction Sites for the Oxygen Evolution Reaction on Nickel and Nickel Iron Oxides. Angew. Chemie Int. Ed. 58, 10295–10299 (2019). Moysiadou, A., Lee, S., Hsu, C.-S., Chen, H. M. & Hu, X. Mechanism of Oxygen Evolution Catalyzed by Cobalt Oxyhydroxide: Cobalt Superoxide Species as a Key Intermediate and Dioxygen Release as a Rate-Determining Step. J. Am. Chem. Soc. 142, 11901–11914 (2020). Diaz-Morales, O., Ferrus-Suspedra, D. & Koper, M. T. M. The importance of nickel oxyhydroxide deprotonation on its activity towards electrochemical water oxidation. Chem. Sci. 7, 2639–2645 (2016). Yuan, S. et al. Tunable metal hydroxide–organic frameworks for catalysing oxygen evolution. Nat. Mater. 21, 673–680 (2022). Figure 1