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  • Final Activity Report Summary - HETEROELECTRANS (Heterogeneous charge-transfer studied by ab initio quantum chemical methods: Application to processes at electrodes and scanning tunnelling images)

Final Activity Report Summary - HETEROELECTRANS (Heterogeneous charge-transfer studied by ab initio quantum chemical methods: Application to processes at electrodes and scanning tunnelling images)

Electron transfer (ET) is no doubt the essential ingredient of all electrochemical processes and of the related technological applications, fuel cells among them. ET is also at the heart of scanning tunnelling microscopy (STM). Nowadays STM provides one of the few instruments permitting one to handle matter at the nanoscopic scale. At the theoretical level a quantitative treatment of heterogeneous electron transfer remains exceedingly difficult since one needs provide an ab initio description of each component of the system, and of their interaction. For example in electrochemical processes, the model must provide a microscopic description of the structure at the electrode interface including the solute, the solvent and the electrode including the interaction between them, and must account for the presence of the bias voltage.

The group at the host institution has shown that it is possible to approach ET at an electrode from a pure ab initio viewpoint and with explicit inclusion of the external electric field. The main goal of the present project has been precisely to continue this exciting research field thus contributing to build up new and more accurate models of heterogeneous ET reactions. In this model the electrode is represented by a cluster of atoms and the both states involved in the ET process (the initial state with the electron on the donor and the final state with the electron on the acceptor) simultaneously computed through a multi-reference method. In the approach an external electric field is applied perpendicular to the surface and its intensity is varied until a crossing between the two states is achieved. The key quantity is represented by the electric field intensity required to achieve the crossing since it corresponds to the electron transfer event.

The ET model developed by the host institution and already applied to the oxidation of halides at a copper anode has been extended to the study of other systems in electrochemical environment. In particular the emphasis has been on the effect of the electrode material on the electrode transfer process. To this end the type of processes considered have been the oxidation of halides on different transition metal electrodes, including Cu, Rh, Pd, Ag, Pt, and Au. On the one hand the work has highlighted the existence of a dependence of the electron transfer process on the electrode material. On the other hand, more generally this study has enabled to draw general considerations on the quality of the model as a predictive and quantitative theory of general use in electrochemistry, and therefore has provided the necessary information to improve the model it-self.

A new and original point has concerned the application of the present ab initio ET model to the prediction of STM images. The result has been a completely new ab initio approach to STM including explicitly the external bias voltage and taking into account the atomistic nature of both the surface and tip.

The project offers perspectives of fundamental and potentially technological importance, since it involves the development of new concepts and models that can find their direct application and employment in the field of nanotechnologies, and renewable energy technologies (e.g., fuel cells).

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C/ Marti i Franquès 1
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