86 Towards a stable and inexpensive catalyst for OER in acid
The lms were subjected to the same tests as described in section 5.1. From
the initial CVs it was observed that the activity was slightly lower for the mixed
lms. Ideally the activity could be kept at the same level, which would require an
optimization of the Ti concentration and likely a ne-tuning of the temperature
treatment. Optimally, the amount of Ti atoms added would match the number
of undercoordinated sites since any excess of Ti is likely to lower the activity.
Therefore, the current density could decrease with up to 20 % due to the Ti
concentration. A deactivation is certainly observed from the CVs in gure 5.8a.
However, after prolonged tests the current densities become more similar to each
other as observed from the chronoamperometry test in gure 5.8b.
MnO2
1,41,51,61,71,8
4
3
2
1
0
OERcurrentsforMnO2andTi-MnO2
020406080100120
10
8
6
4
2
0
InitialCVsforMnO2andTi-MnO2
Ti-MnO2
jgeo/mA.cm-2
U-iR/V(vs.RHE)
b)
jgeo/mA.cm-2
Time/minutes
Ti-MnO2
MnO2
a)
Figure 5.8: a) Cyclic voltammetry of MnO2 and Ti-MnO2 lms at 5 mV/s. First
anodic scans are shown for both. The potential scale has been corrected for Ohmic
drop. b) Chronoamperometry test at 1.9 VRHE. Test conducted in 0.05 M H2SO4.
For both graphs results for the pure MnO2 lm are in blue and the Ti-MnO2 in red.
The stability test protocol was carried out using both EQCM samples and RDE
samples. For both setups, three samples with and three samples without Ti
were tested. The results were then compared on basis of activity and stability.
For the EQCM tests the results are summarized in gure 5.9. At 1.8 VRHE the
activity goes down with 18 % due to the Ti modication while the mass losses
decrease with 47 %. At 1.9 VRHE the activity is decreased with 10 % and the
mass loss with 40 %. From these values it is clear that modication with Ti
leads to a stabilizing eect for the MnO2 surface, even though the mass losses
are not completely stopped.