Browsing by Author "Oschatz, M."

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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-Ivansic, 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 CoII -> CoIII 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 understandingthe charge transfer processes, which are vital for electrochemical (EC) andphotoelectrochemical (PEC) applications. However, spectroscopic access toboth interfaces, particularly upon application of an external bias, remains achallenge. Here, in situ surface sensitive vibrational sum-frequencygeneration (VSFG) spectroscopy is used for the first time to directly access theinterfacial structure of a cobalt-containing Prussian blue analog (Co-PBA) incontact with the electrolyte and TiO 2 /Au surface. Structural andcompositional 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: Fe III –CN–Co II and FeII –CN–Co III coordinationmotifs are dominantly observed at the Co-PBA|TiO 2 interface, while it is onlythe FeII –CN–Co II unit at the electrolyte interface. Upon increasing thepotential applied to the electrode, the partial oxidation of Fe II –CN–Co II toFeIII –CN–Co II is observed followed by its transformation to FeII –CN–Co III viacharge transfer and, finally, the formation of Fe III –CN–Co III species at theinterface with TiO2 and the electrolyte.