[{"doi":"10.1021/acscatal.5c08785","main_file_link":[{"url":"https://pubs.acs.org/doi/10.1021/acscatal.5c08785","open_access":"1"}],"article_number":"acscatal.5c08785","language":[{"iso":"eng"}],"date_updated":"2026-02-16T14:25:00Z","publication_status":"published","article_type":"original","title":"Role of Defects in Reversible Surface Restructuring and Activity of Co<sub>3</sub>O<sub>4</sub> Oxygen Evolution Electrocatalysts","year":"2026","publication_identifier":{"issn":["2155-5435","2155-5435"]},"author":[{"full_name":"Scharf, Carl Hendric","last_name":"Scharf","first_name":"Carl Hendric"},{"first_name":"Alex","last_name":"Chandraraj","full_name":"Chandraraj, Alex"},{"last_name":"Dyk","first_name":"Konrad","full_name":"Dyk, Konrad"},{"last_name":"Stebner","first_name":"Felix","full_name":"Stebner, Felix"},{"full_name":"Lepin, Sören","last_name":"Lepin","first_name":"Sören"},{"full_name":"Tian, Jing","last_name":"Tian","first_name":"Jing"},{"full_name":"El Bergmi Byaz, Laila","first_name":"Laila","last_name":"El Bergmi Byaz"},{"full_name":"Stettner, Jochim","first_name":"Jochim","last_name":"Stettner"},{"last_name":"Leppin","first_name":"Christian","full_name":"Leppin, Christian","id":"117722"},{"first_name":"Anastasiia","last_name":"Kotova","full_name":"Kotova, Anastasiia"},{"id":"117727","full_name":"Reinke, Sebastian","last_name":"Reinke","first_name":"Sebastian"},{"orcid":"0000-0001-6883-5424","first_name":"Julia","last_name":"Linnemann","full_name":"Linnemann, Julia","id":"116779"},{"full_name":"Maroun, Fouad","last_name":"Maroun","first_name":"Fouad"},{"last_name":"Magnussen","first_name":"Olaf M.","full_name":"Magnussen, Olaf M."}],"keyword":["electrocatalysis","oxygen evolution reaction","cobalt spinel","operando characterization"],"type":"journal_article","department":[{"_id":"985"}],"date_created":"2026-02-16T14:22:15Z","abstract":[{"lang":"eng","text":"Overcoming the slow kinetics of the oxygen evolution reaction at the anode is a key challenge for the production of hydrogen via electrolysis. This reaction operates at very positive potentials, where the electrocatalyst is exposed to highly oxidative conditions and prone to potential-dependent transformation of the near-surface region. While substantial evidence for such surface restructuring exists, its extent and relevance for the catalyst’s activity are unclear. We address this topic for the case of Co3O4, one of the best-known electrocatalysts exhibiting surface restructuring, by studies of epitaxial (111)-ordered electrodeposited films with combined operando X-ray surface diffraction and absorption spectroscopy, electrochemical impedance spectroscopy, and electrochemical measurements on rotating disk electrodes. Comparison of the as-prepared and annealed state of the same samples, which both are stable even under long-term oxygen evolution conditions, provides clear insight into the role of surface defects. Our results show that defect-free annealed Co3O4(111) surfaces are structurally stable over a wide potential range and hydroxylate via adsorption at surface oxygen and Co sites. Potential-induced surface restructuring of the Co3O4 lattice occurs only in the presence of surface defects, leading to the formation of the well-known nanometer-thick oxyhydroxide skin layer. The presence of this skin layer promotes oxygen evolution at low overpotentials but results in higher Tafel slopes. As a result, highly ordered Co3O4(111) surfaces are more active at high current densities than defective Co3O4 surfaces that undergo surface restructuring. These results highlight that strategies for catalyst surface defect engineering need to be application-oriented."}],"publication":"ACS Catalysis","user_id":"116779","publisher":"American Chemical Society (ACS)","_id":"64182","status":"public","oa":"1","quality_controlled":"1","citation":{"mla":"Scharf, Carl Hendric, et al. “Role of Defects in Reversible Surface Restructuring and Activity of Co<sub>3</sub>O<sub>4</sub> Oxygen Evolution Electrocatalysts.” <i>ACS Catalysis</i>, acscatal.5c08785, American Chemical Society (ACS), 2026, doi:<a href=\"https://doi.org/10.1021/acscatal.5c08785\">10.1021/acscatal.5c08785</a>.","ama":"Scharf CH, Chandraraj A, Dyk K, et al. Role of Defects in Reversible Surface Restructuring and Activity of Co<sub>3</sub>O<sub>4</sub> Oxygen Evolution Electrocatalysts. <i>ACS Catalysis</i>. Published online 2026. doi:<a href=\"https://doi.org/10.1021/acscatal.5c08785\">10.1021/acscatal.5c08785</a>","bibtex":"@article{Scharf_Chandraraj_Dyk_Stebner_Lepin_Tian_El Bergmi Byaz_Stettner_Leppin_Kotova_et al._2026, title={Role of Defects in Reversible Surface Restructuring and Activity of Co<sub>3</sub>O<sub>4</sub> Oxygen Evolution Electrocatalysts}, DOI={<a href=\"https://doi.org/10.1021/acscatal.5c08785\">10.1021/acscatal.5c08785</a>}, number={acscatal.5c08785}, journal={ACS Catalysis}, publisher={American Chemical Society (ACS)}, author={Scharf, Carl Hendric and Chandraraj, Alex and Dyk, Konrad and Stebner, Felix and Lepin, Sören and Tian, Jing and El Bergmi Byaz, Laila and Stettner, Jochim and Leppin, Christian and Kotova, Anastasiia and et al.}, year={2026} }","apa":"Scharf, C. H., Chandraraj, A., Dyk, K., Stebner, F., Lepin, S., Tian, J., El Bergmi Byaz, L., Stettner, J., Leppin, C., Kotova, A., Reinke, S., Linnemann, J., Maroun, F., &#38; Magnussen, O. M. (2026). Role of Defects in Reversible Surface Restructuring and Activity of Co<sub>3</sub>O<sub>4</sub> Oxygen Evolution Electrocatalysts. <i>ACS Catalysis</i>, Article acscatal.5c08785. <a href=\"https://doi.org/10.1021/acscatal.5c08785\">https://doi.org/10.1021/acscatal.5c08785</a>","ieee":"C. H. Scharf <i>et al.</i>, “Role of Defects in Reversible Surface Restructuring and Activity of Co<sub>3</sub>O<sub>4</sub> Oxygen Evolution Electrocatalysts,” <i>ACS Catalysis</i>, Art. no. acscatal.5c08785, 2026, doi: <a href=\"https://doi.org/10.1021/acscatal.5c08785\">10.1021/acscatal.5c08785</a>.","short":"C.H. Scharf, A. Chandraraj, K. Dyk, F. Stebner, S. Lepin, J. Tian, L. El Bergmi Byaz, J. Stettner, C. Leppin, A. Kotova, S. Reinke, J. Linnemann, F. Maroun, O.M. Magnussen, ACS Catalysis (2026).","chicago":"Scharf, Carl Hendric, Alex Chandraraj, Konrad Dyk, Felix Stebner, Sören Lepin, Jing Tian, Laila El Bergmi Byaz, et al. “Role of Defects in Reversible Surface Restructuring and Activity of Co<sub>3</sub>O<sub>4</sub> Oxygen Evolution Electrocatalysts.” <i>ACS Catalysis</i>, 2026. <a href=\"https://doi.org/10.1021/acscatal.5c08785\">https://doi.org/10.1021/acscatal.5c08785</a>."}},{"citation":{"ieee":"J. Linnemann and C. Leppin, “The catalyst that stores charge first,” <i>Bunsen-Magazin</i>, no. 4, pp. 81–84, 2026, doi: <a href=\"https://doi.org/10.26125/6G4P-8386\">10.26125/6G4P-8386</a>.","apa":"Linnemann, J., &#38; Leppin, C. (2026). The catalyst that stores charge first. <i>Bunsen-Magazin</i>, <i>4</i>, 81–84. <a href=\"https://doi.org/10.26125/6G4P-8386\">https://doi.org/10.26125/6G4P-8386</a>","short":"J. Linnemann, C. Leppin, Bunsen-Magazin (2026) 81–84.","chicago":"Linnemann, Julia, and Christian Leppin. “The Catalyst That Stores Charge First.” <i>Bunsen-Magazin</i>, no. 4 (2026): 81–84. <a href=\"https://doi.org/10.26125/6G4P-8386\">https://doi.org/10.26125/6G4P-8386</a>.","mla":"Linnemann, Julia, and Christian Leppin. “The Catalyst That Stores Charge First.” <i>Bunsen-Magazin</i>, no. 4, Deutsche Bunsen-Gesellschaft für physikalische Chemie e.V., 2026, pp. 81–84, doi:<a href=\"https://doi.org/10.26125/6G4P-8386\">10.26125/6G4P-8386</a>.","bibtex":"@article{Linnemann_Leppin_2026, title={The catalyst that stores charge first}, DOI={<a href=\"https://doi.org/10.26125/6G4P-8386\">10.26125/6G4P-8386</a>}, number={4}, journal={Bunsen-Magazin}, publisher={Deutsche Bunsen-Gesellschaft für physikalische Chemie e.V.}, author={Linnemann, Julia and Leppin, Christian}, year={2026}, pages={81–84} }","ama":"Linnemann J, Leppin C. The catalyst that stores charge first. <i>Bunsen-Magazin</i>. 2026;(4):81-84. doi:<a href=\"https://doi.org/10.26125/6G4P-8386\">10.26125/6G4P-8386</a>"},"popular_science":"1","oa":"1","conference":{"end_date":"2026-04-01","start_date":"2026-03-30","name":"Bunsen Conference 2026","location":"Dresden"},"status":"public","user_id":"116779","publisher":"Deutsche Bunsen-Gesellschaft für physikalische Chemie e.V.","_id":"66488","page":"81-84","abstract":[{"lang":"eng","text":"Alkaline oxygen evolution on Co3O4 involves more than adsorption and electron transfer at a fixed surface. The article draws on operando electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D), surface X-ray diffraction (SXRD), Raman, UV/Vis and impedance spectroscopy. On this basis, it discusses pseudocapacitive oxidation of cobalt ion sites, electrolyte uptake and near-surface transformation, and asks which of these changes are kinetically coupled to electrocatalysis."}],"publication":"Bunsen-Magazin","issue":"4","department":[{"_id":"985"}],"keyword":["electrocatalysis","oxygen evolution reaction","cobalt spinel","operando characterization","spectroelectrochemistry"],"type":"journal_article","date_created":"2026-07-14T14:59:31Z","article_type":"review","date_updated":"2026-07-14T15:02:05Z","author":[{"full_name":"Linnemann, Julia","last_name":"Linnemann","first_name":"Julia","orcid":"0000-0001-6883-5424","id":"116779"},{"first_name":"Christian","last_name":"Leppin","full_name":"Leppin, Christian","id":"117722"}],"year":"2026","title":"The catalyst that stores charge first","doi":"10.26125/6G4P-8386","language":[{"iso":"eng"}],"main_file_link":[{"url":"https://bunsen.de/bmo/the-catalyst-that-stores-charge-first","open_access":"1"}]},{"type":"journal_article","keyword":["electrocatalysis","oxygen evolution reaction","cobalt spinel","operando characterization","spectroelectrochemistry"],"department":[{"_id":"985"}],"date_created":"2025-10-24T07:49:21Z","abstract":[{"text":"Doped Co3O4 nanoparticles are investigated via spectro-electrochemistry in the (pre-) oxygen evolution reaction (OER) regime by tracing the absorption signal of the Co3+ d–d transition under applied bias for getting insight into the catalysts activation and the formation of catalytically active phases. In the low potential regime up to 1.37 VRHE, a rise in the optical absorption signal of the [Co3+]oct d–d transition is observed and attributed to a structural change from [Co2+]tet to [Co3+]oct due to an electrochemically induced surface restructuring with water. For applied potentials higher than 1.37 VRHE an overall offset of the absorption spectra in the UV–vis range, equivalent to a darkening of the materials is detected. This is attributed to the formation of a CoOx(OH)y skin layer as supported by high-energy X-ray diffraction (HE-XRD) measurements. We found that the kinetics of the Co3+ states are heavily influenced by the type of dopant with V-doped Co3O4 exhibiting stable Co3+ states (>20 min) while the Mn-doped Co3O4 Co3+ states reduce within 36 s under reductive bias. We conclude that doping Co3O4 with transition metals affects the formation and potential-dependent thickness of the CoOx(OH)y skin layer as the catalytically active phase and the formation of long-time stable surface Co3+ states after activation in the first OER cycle.","lang":"eng"}],"publication":"ACS Catalysis","issue":"21","doi":"10.1021/acscatal.5c03900","language":[{"iso":"eng"}],"publication_status":"published","date_updated":"2025-12-07T17:15:53Z","article_type":"original","intvolume":"        15","year":"2025","title":"Operando Analysis of the Pre-OER Activation of Metal-Doped Co<sub>3</sub>O<sub>4</sub> Nanoparticle Catalysts","publication_identifier":{"issn":["2155-5435","2155-5435"]},"author":[{"full_name":"Kampermann, L.","first_name":"L.","last_name":"Kampermann"},{"last_name":"Klein","first_name":"J.","full_name":"Klein, J."},{"full_name":"Wagner, T.","first_name":"T.","last_name":"Wagner"},{"full_name":"Kotova, A.","last_name":"Kotova","first_name":"A."},{"last_name":"Placke-Yan","first_name":"C.","full_name":"Placke-Yan, C."},{"full_name":"Yasar, A.","first_name":"A.","last_name":"Yasar"},{"first_name":"L.","last_name":"Jacobse","full_name":"Jacobse, L."},{"full_name":"Lasagna, S.","last_name":"Lasagna","first_name":"S."},{"id":"117722","full_name":"Leppin, Christian","last_name":"Leppin","first_name":"Christian"},{"first_name":"S.","last_name":"Schulz","full_name":"Schulz, S."},{"id":"116779","first_name":"Julia","last_name":"Linnemann","orcid":"0000-0001-6883-5424","full_name":"Linnemann, Julia"},{"full_name":"Bergmann, A.","last_name":"Bergmann","first_name":"A."},{"full_name":"Roldan Cuenya, B.","last_name":"Roldan Cuenya","first_name":"B."},{"full_name":"Bacher, G.","first_name":"G.","last_name":"Bacher"}],"quality_controlled":"1","citation":{"short":"L. Kampermann, J. Klein, T. Wagner, A. Kotova, C. Placke-Yan, A. Yasar, L. Jacobse, S. Lasagna, C. Leppin, S. Schulz, J. Linnemann, A. Bergmann, B. Roldan Cuenya, G. Bacher, ACS Catalysis 15 (2025) 18391–18403.","chicago":"Kampermann, L., J. Klein, T. Wagner, A. Kotova, C. Placke-Yan, A. Yasar, L. Jacobse, et al. “Operando Analysis of the Pre-OER Activation of Metal-Doped Co<sub>3</sub>O<sub>4</sub> Nanoparticle Catalysts.” <i>ACS Catalysis</i> 15, no. 21 (2025): 18391–403. <a href=\"https://doi.org/10.1021/acscatal.5c03900\">https://doi.org/10.1021/acscatal.5c03900</a>.","ieee":"L. Kampermann <i>et al.</i>, “Operando Analysis of the Pre-OER Activation of Metal-Doped Co<sub>3</sub>O<sub>4</sub> Nanoparticle Catalysts,” <i>ACS Catalysis</i>, vol. 15, no. 21, pp. 18391–18403, 2025, doi: <a href=\"https://doi.org/10.1021/acscatal.5c03900\">10.1021/acscatal.5c03900</a>.","apa":"Kampermann, L., Klein, J., Wagner, T., Kotova, A., Placke-Yan, C., Yasar, A., Jacobse, L., Lasagna, S., Leppin, C., Schulz, S., Linnemann, J., Bergmann, A., Roldan Cuenya, B., &#38; Bacher, G. (2025). Operando Analysis of the Pre-OER Activation of Metal-Doped Co<sub>3</sub>O<sub>4</sub> Nanoparticle Catalysts. <i>ACS Catalysis</i>, <i>15</i>(21), 18391–18403. <a href=\"https://doi.org/10.1021/acscatal.5c03900\">https://doi.org/10.1021/acscatal.5c03900</a>","bibtex":"@article{Kampermann_Klein_Wagner_Kotova_Placke-Yan_Yasar_Jacobse_Lasagna_Leppin_Schulz_et al._2025, title={Operando Analysis of the Pre-OER Activation of Metal-Doped Co<sub>3</sub>O<sub>4</sub> Nanoparticle Catalysts}, volume={15}, DOI={<a href=\"https://doi.org/10.1021/acscatal.5c03900\">10.1021/acscatal.5c03900</a>}, number={21}, journal={ACS Catalysis}, publisher={American Chemical Society (ACS)}, author={Kampermann, L. and Klein, J. and Wagner, T. and Kotova, A. and Placke-Yan, C. and Yasar, A. and Jacobse, L. and Lasagna, S. and Leppin, Christian and Schulz, S. and et al.}, year={2025}, pages={18391–18403} }","ama":"Kampermann L, Klein J, Wagner T, et al. Operando Analysis of the Pre-OER Activation of Metal-Doped Co<sub>3</sub>O<sub>4</sub> Nanoparticle Catalysts. <i>ACS Catalysis</i>. 2025;15(21):18391-18403. doi:<a href=\"https://doi.org/10.1021/acscatal.5c03900\">10.1021/acscatal.5c03900</a>","mla":"Kampermann, L., et al. “Operando Analysis of the Pre-OER Activation of Metal-Doped Co<sub>3</sub>O<sub>4</sub> Nanoparticle Catalysts.” <i>ACS Catalysis</i>, vol. 15, no. 21, American Chemical Society (ACS), 2025, pp. 18391–403, doi:<a href=\"https://doi.org/10.1021/acscatal.5c03900\">10.1021/acscatal.5c03900</a>."},"user_id":"116779","volume":15,"page":"18391-18403","publisher":"American Chemical Society (ACS)","_id":"61982","status":"public"}]