MnO2. Both the currents and mass losses shown are averages for three independent
measurements with the EQCM setup and the error bars are ±1 standard deviation.
Time resolved measurements of the corrosion were obtained with the electrochemical quartz crystal
microbalances when the catalyst was subjected to the testing procedure described above. The time
resolved change in mass can be seen in Figure 7. The mass losses during the first 20 minutes are
similar between the pure MnO2 and the Ti-MnO2. However, the slope progressively diverges between
the two samples: by the last 20 minutes of the experiment, the slope of the Ti-MnO2 is 40% less steep
than the MnO2 sample, indicating a lower rate of mass loss. In other words; since the slopes are
significantly different toward the end of the test, it indicates that fewer undercoordinated sites are
now available for MnO4
- formation. It is likely that at the beginning, a small fraction of the
undercoordinated sites have not been successfully covered with TiO2, therefore, MnO2 can corrode
away until a front of TiO2 is reached. If it was the case that TiO2 simply prevent the electrolyte from
being in contact with the MnO2, then the oxygen evolution activity would decrease by the same
proportion as the corrosion rate. However, this is not the case, as we see a 40 % lower mass losses,
but only 10 % lower OER current. These results substantiate the notion that the TiO2 can stabilize
MnO2.
Figure 7. Change in mass during the experiment based on the resonant frequency of the
quartz oscillator. The frequency measurements have been converted into mass changes using
the Sauerbrey equation.78 The blue line shows the MnO2 while the red line shows the TiO2-