82 Towards a stable and inexpensive catalyst for OER in acid
Ti and Ge which can be seen in gure 5.4. The termination energy for each
material is plotted as a function of the surface formation energy of the (110)
rutile surface. The trend shows that the system gains energy by terminating
steps with materials that have a lower surface formation energy than MnO2.
On the other hand a less stable system is created by termination of MnO2 with
materials with a higher surface formation energy.
Figure 5.4: Termination energy for six dierent rutile metal dioxides on the steps of
a rutile (120) MnO2 surface as a function of the surface formation energy. The surface
formation energies are taken from 219. The red arrow indicates that a positive
termination energy means that it will cost the system energy, whereas the blue arrow
indicate an overall lowering of system energy.
The results suggest that termination of the steps with Ti and Ge is feasible.
Modication of MnO2 with TiO2 is particularly promising as TiO2 is abundant
and has been proven a viable protection layer for other electrochemical
systems 220224. The same type of calculations was also performed for kinked
structures and again it was found that termination of Ti was favourable. These
simple calculations indicate that it is feasible to terminate undercoordinated
surface sites of MnO2. In the following an experimental investigation of this
concept will be presented.
5.3 Experimental validation of the concept
To investigate whether the stabilization concept could be realized experimentally,
mixed Ti-MnO2 lms were prepared by sputter deposition. The deposition