5.4 Conclusion 95
Figure 5.16: Change in mass for MnO2, blue, and Ti-MnO2, red, in 0.05 M H2SO4
when the potential is scanned cathodically from 1.4 to 1 VRHE at 0.5 mV/s. The mass
change is plotted as percentage of the original mass that is left on the electrode as
function of the potential. The shaded areas indicate 1 standard deviation from three
independent measurements.
it is promising that the stabilization strategy is likely to improve both cathodic
and anodic stability of MnO2.
5.4 Conclusion
In this chapter the stability and activity towards oxygen evolution of Mn oxide
thin lms have been characterized in acidic environment. The motivation behind
this study is the lack of active non-noble metal based catalysts for OER that can
work in the acidic environment of PEM cells. MnO2 is a unique material since
it is an active OER catalyst and is stable in acid in the potential region relevant
for water oxidation. Regarding activity, the lms are signicantly less active in
sulfuric acid compared to in potassium hydroxide. More specically they suer
from a high Tafel slope of 170 mV/decade in acid compared to approximately
70 mV/decade in alkaline. Furthermore, at 400 mV overpotential the current
density in acid is around half the one achieved in alkaline. However, even with
this deactivation it was shown that the lms prepared for this project are among
the most active non-precious metal oxides for oxygen evolution, albeit still far
from the performance of Ru or Ir based electrodes. The stability of the lms
was characterized with EQCM and ICP-MS measurements using a rigorous test
protocol. The mass losses due to anodic dissolution were found to be the same