{"paper_id":"3d33eaf3-7c1a-4400-a24c-574e1ecfc71e","body_text":"Consequences of Overtones in Raman Spectra for Structural Assignment of Nickel Anodes during Alkaline Electrolysis | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Consequences of Overtones in Raman Spectra for Structural Assignment of Nickel Anodes during Alkaline Electrolysis Justus Leist, Annika Neufischer, Timo Jacob, Albert K. Engstfeld This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8205080/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Surface-enhanced Raman spectroscopy (SERS) is a valuable technique, particularly for in situ and operando studies. However, anharmonic features, such as overtones, while rare and often overlooked, may complicate structural interpretations. This aspect is illustrated for Nickel oxyhydroxide (NiOOH), a vividly discussed oxygen evolution reaction (OER) catalyst for application as anode material in alkaline electrolysers. Based on in situ SERS measurements in common electrolytes, including isotope-labeled water and Density Functional Theory (DFT) calculated Raman spectra, we question the presence of NiOOH upon electrochemical oxidation of Ni(OH) 2 and instead suggest that the catalytically active surface consists of Nickel dioxide (NiO 2 ) instead. Additional bands in the experimental spectrum, which were previously assigned to superoxide species, are attributed to overtones and combination bands. Possible reasons for the appearance of overtones are discussed. Previously observed shifts of these bands at varying pH and more positive OER potentials are rationalized by a vibrational Stark effect rather than changes in the material or adsorbate structure. Physical sciences/Energy science and technology/Renewable energy/Hydrogen energy/Hydrogen fuel Physical sciences/Materials science/Materials for energy and catalysis/Electrocatalysis Physical sciences/Physics/Condensed-matter physics/Structure of solids and liquids Physical sciences/Chemistry/Theoretical chemistry/Density functional theory Physical sciences/Chemistry/Physical chemistry/Optical spectroscopy/Raman spectroscopy Full Text Additional Declarations There is NO Competing Interest. Supplementary Files 2025JULENiRamansupportinginformation.pdf Supporting information Cite Share Download PDF Status: Under Review Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {\"props\":{\"pageProps\":{\"initialData\":{\"identity\":\"rs-8205080\",\"acceptedTermsAndConditions\":true,\"allowDirectSubmit\":false,\"archivedVersions\":[],\"articleType\":\"Article\",\"associatedPublications\":[],\"authors\":[{\"id\":558289884,\"identity\":\"82720f4d-2906-4512-82e0-11e4d16b957c\",\"order_by\":0,\"name\":\"Justus Leist\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Institute of Electrochemistry, Ulm University, D-89081 Ulm, Germany\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Justus\",\"middleName\":\"\",\"lastName\":\"Leist\",\"suffix\":\"\"},{\"id\":558289885,\"identity\":\"39a09b1a-c58d-4be1-8bd1-3eadb6626545\",\"order_by\":1,\"name\":\"Annika Neufischer\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Institute of Electrochemistry, Ulm University, D-89081 Ulm, Germany\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Annika\",\"middleName\":\"\",\"lastName\":\"Neufischer\",\"suffix\":\"\"},{\"id\":558289886,\"identity\":\"da9bb143-a8af-4bee-9f01-99e5ee81e68e\",\"order_by\":2,\"name\":\"Timo Jacob\",\"email\":\"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA20lEQVRIiWNgGAWjYDACZhDBA8QSzAcYGAwYGPhAbHw6eBBa2BLAWtgIaoGzJHgMwDRBLfbs3IkPGGTs5Pmle75JFxQwJLaJHWC88QGvw3g3GzDwJBvOnHN2m/QMA6AW6QRmyxn4tWyTAJIJBjdyt0nzGPwHaWGT5iGspR6oJecZUAsDRMsfwloOg7SwIbTg8z7PYaBfEniOA/1yzNgaqMW4TTqx2bIHjxb2/rMbH3zsqQaGWPPD2zx/GGT7pZMP3viBzxoQSEQ1lLGBkAYgIGjoKBgFo2AUjGgAAMLSPAsCigvCAAAAAElFTkSuQmCC\",\"orcid\":\"https://orcid.org/0000-0001-7777-2306\",\"institution\":\"Institute of Electrochemistry, Ulm University, D-89081 Ulm, Germany\",\"correspondingAuthor\":true,\"prefix\":\"\",\"firstName\":\"Timo\",\"middleName\":\"\",\"lastName\":\"Jacob\",\"suffix\":\"\"},{\"id\":558289883,\"identity\":\"0c474b82-da85-40cc-b128-1a83055f9122\",\"order_by\":3,\"name\":\"Albert K. 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However, anharmonic features, such as overtones, while rare and often overlooked, may complicate structural interpretations. This aspect is illustrated for Nickel oxyhydroxide (NiOOH), a vividly discussed oxygen evolution reaction (OER) catalyst for application as anode material in alkaline electrolysers. Based on \\u003ci\\u003ein situ\\u003c/i\\u003e SERS measurements in common electrolytes, including isotope-labeled water and Density Functional Theory (DFT) calculated Raman spectra, we question the presence of NiOOH upon electrochemical oxidation of Ni(OH)\\u003csub\\u003e2\\u003c/sub\\u003e and instead suggest that the catalytically active surface consists of Nickel dioxide (NiO\\u003csub\\u003e2\\u003c/sub\\u003e) instead. Additional bands in the experimental spectrum, which were previously assigned to superoxide species, are attributed to overtones and combination bands. Possible reasons for the appearance of overtones are discussed. 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