Robust electrografted interfaces on metal oxides for electrocatalysis - an in situ spectroelectrochemical study
Tomos Gwilym Ab Alun Harris1,2, Robert Götz1,3, Victoria Davis2, Pierre Wrozlek4, Peter Hildebrandt1, Matthias Schwalbe4, Inez Weidinger3, Ingo Zebger1 and Anna Fischer2
1Max-Volmer-Laboratorium, Sekr. PC 14, Technische Universität Berlin, Strasse des 17. Juni 135, 10623, Berlin, GER
2Institut für Anorganische und Analytische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstr. 21, 79104, Freiburg, GER
3Fachrichtung Chemie und Lebensmittelchemie, Technische Universität Dresden, Helholtzstr. 10, 01069, Dresden, GER
4Institut für Chemie, Humboldt-Universität zu Berlin, Brook-Taylor-Str. 2, 12489, Berlin, GER
The immobilisation of functional redox active molecular catalysts on metal oxide surfaces is of major importance in view of exploiting their catalytic properties in the field of electrocatalysis for a broad field of reactions. In this context, the immobilisation of molecular catalysts (and other molecular species such as photosensitisers) on oxides so far relies on their surface attachment via phosphonates, carboxylates, silanes, and their derivatives, which usually suffer from either limited stabilities or poor charge transfer properties. Development of new approaches is hence required to build chemically and electrochemically robust interfaces that allow efficient and fast charge transfer rates. In this context, development of in situ spectroscopic techniques providing real-time monitoring of interface formation, catalyst immobilisation and system evolution under reaction conditions will allow for a rational design of immobilisation strategies, far beyond simple trial and error approaches.
In this work, we have investigated the applicability of diazonium-derived interfaces for the surface functionalisation of transparent conducting oxide (TCO) electrodes, in view of the immobilisation of electrocatalytically active molecular complexes. We thereby used mesoporous ATO electrodes and planar ITO electrodes as model systems. Taking advantage of the transparency and high surface area of the mesoporous electrodes, the formation, structure and stability of these diazonium-derived organic interfaces could be studied by surface sensitive in situ ATR-IR absorption spectroscopy in combination with electrochemistry. Indeed, we could reveal an extremely large stability window in terms of electrochemical potential as well as pH for these covalently attached interfaces.1 Such richness of information cannot be obtained using conventional UV-vis or purely electrochemical methods, and this approach may be very useful for studying inorganic-molecular interfaces on a range of devices, e.g. in photoelectrochemical/dye-sensitised solar cells, electrolyzers, sensors etc.
Furthermore, we could immobilise a model Fe-Hangman oxygen reducing complex on the electrodes, and, with the use of electrochemical techniques and in situ resonance Raman spectroelectrochemistry, demonstrate the high loading and excellent electrochemical accessibility of these immobilised species, as well as fast electron transfer between the active site and the electrode. The electrocatalytic response towards the oxygen reduction reaction revealed onset potentials close to similar catalysts immobilised on carbon electrodes.
T.G.A.A. Harris, et.al., 2018 Submitted↩