Activity over time for EQCM experiments
Figure S3. Chronoamperometry results for the MnO2 and Ti-MnO2 catalysts tested in 0.05 M H2SO4 at 1.9
VRHE. 85 % ohmic drop compensation was applied.
ICP-MS results for RDE experiments
To support the tests done with the EQCM system, we also performed Rotating Disk Electrode, RDE,
experiments with the same catalyst films supported by gold polycrystalline disks. The test conditions were
nominally the same as for the EQCM measurements; 0.05 M H2SO4, 2 hours at 1.8 and 1.9 VRHE; aliquots of
electrolyte were taken before and after each test. Furthermore, for the RDE tests, a rotation speed of 1600
RPM was used. The results can be seen in Figure S4a and S4b. After one hour 1t 1.9 V, the Ti-MnO2 sample has
a current density 30 % lower current density than MnO2. However, there decrease in mass loss of 60 %. These
results again support the finding that a better compromise between stability and activity can be obtained by
the incorporation of Ti into MnO2.
Figure S4. a) The activity of MnO2 and Ti-MnO2 after one hour at each potential, measured with an RDE
setup. b) The mass losses for MnO2 and Ti-MnO2 after 2 hours at each potential, evaluated with ICP-MS.
The error bars shown here are ±1 standard deviation from three independent measurements.