Browsing by Author "De, R."

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    Cyanide linkage isomerization induced by cobalt oxidation-state changes at a Co-Fe prussian-blue analogue/ZnO interface
    (Wiley-VCH Verlag GmbH & Co. KGaA, 2024-10-28) De, R.; Hermesdorf, M.; Bera, A.; Phul, Ruby; Gawlik, A.; Plentz, J.; Oschatz, M.; Karadaş, Ferdi; Dietzek-Ivanšić, B.
    Understanding the interfacial composition in heterostructures is crucial for tailoring heterogenous electrochemical and photoelectrochemical processes. This work aims to elucidate the structure of a series of Co-Fe Prussian blue analogue modified ZnO (PBA/ZnO) electrodes with interface-sensitive vibrational sum frequency generation (VSFG) spectroscopy. Our measurements revealed, for the first time, a cyanide linkage isomerism at the PBA/ZnO interface, when the composite is fabricated at elevated temperatures. In situ VSFG spectro-electrochemistry measurements correlate the ${Co}^{II}→{Co}^{III}$ oxidation with the flip of the bridging CN ligand from Co-NC-Fe coordination mode to a Co-CN-Fe one. Photoluminescence measurements and X-ray photoelectron spectroscopy reveal that this unprecedented linkage isomerism originates from surface defects, which act as oxidation sites for the PBA. The presence of such surface defects is correlated with the fabrication temperature for PBA/ZnO. Thus, this contribution identifies the interplay between the surface states of the ZnO substrates and the chemical composition of PBA at the ZnO surface, suggesting an easily accessible approach to control the chemical composition of the interface.
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    Probing the interfacial molecular structure of a Co-Prussian blue in situ
    (Wiley-VCH Verlag GmbH & Co. KGaA, 2024-04-29) Bera, A.; De, R.; Schmidt, H.; Leistenschneider, D.; Ulusoy Ghobadi, Türkan Gamze; Oschatz, M.; Karadaş, Ferdi; Dietzek-Ivansic, B.
    Molecular-level insight into the interfacial composition of electrodes at thesolid-electrolyte and the solid-electrode interface is essential to understanding the charge transfer processes, which are vital for electrochemical (EC) and photoelectrochemical (PEC) applications. However, spectroscopic access toboth interfaces, particularly upon application of an external bias, remains achallenge. Here, in situ surface sensitive vibrational sum-frequency generation (VSFG) spectroscopy is used for the first time to directly access the interfacial structure of a cobalt-containing Prussian blue analog (Co-PBA) incontact with the electrolyte and TiO₂/Au surface. Structural and compositional changes of the Prussian blue layer during electrochemicaloxidation are studied by monitoring the stretching vibration of the CN group. At open circuit potential, VSFG reveals a non-homogeneous distribution ofoxidation states of metal sites: Feᴵᴵᴵ–CN–Coᴵᴵ and Feᴵᴵ –CN–Co coordinationmotifs are dominantly observed at the Co-PBA|TiO₂ interface, while it is onlythe Feᴵᴵ–CN–Coᴵᴵ unit at the electrolyte interface. Upon increasing the potential applied to the electrode, the partial oxidation of Feᴵᴵ–CN–Coᴵᴵ to Feᴵᴵᴵ–CN–Coᴵᴵ is observed followed by its transformation to Feᴵᴵ–CN–Coᴵᴵᴵ via charge transfer and, finally, the formation of Feᴵᴵᴵ–CN–Coᴵᴵᴵ species at the interface with TiO2 and the electrolyte.