102 The benecial interaction between Au and MnOx
Figure 6.4: Volcano shaped activity plot for OER. The predicted overpotential is
plotted as function of the calculated dierence in free energy for the O and OOH
steps. The solid green lines are based on scaling relations from 98. The green points
indicate calculations for specic oxides when proton transfer is not included in the
analysis. Black points indicate the predicted overpotential for each surface when proton
transfer is included. The dashed sloped line indicate how the scaling relations
would predict overpotential if the OOH binding energy could be optimized independently
from the other intermediates. The horizontal dashed line indicate the potential
where proton transfer to Au can be expected and at the same time a lower bound of
the overpotential that can be expected from including such a transfer mechanism with
Au.
6.2 Experimental investigation of Au-MnOx cat-
alysts
To understand the interaction between Au and Mn our approach was to maximise
the number of neighbouring Mn-Au sites in catalytically active thin lms.
To this end, mixed Au-MnOx thin lms were prepared with a co-sputtering deposition
procedure. The thickness of the lms was again nominally 40 nm and
glassy carbon disks were used as substrates. Adhesion to the glassy carbon was
found to be enhanced by a sputter cleaning procedure of the carbon surface prior
to deposition. This was done for 10 minutes in the sputter chamber with a 50 W