4.2 Activity measurements 67
Figure 4.2: X-ray Diraction in Glancing Angle mode used to measure on the MnOx
thin lm, which is compared to an MnO2 reference. No peaks are observed for both
substrate and thin lm.
For the analysis of XPS on manganese oxides several groups have shown that
the oxide stoichiometry can be determined from the Mn3s and Mn2p peaks
151,192,193. This analysis method was adopted and for the thin lms described
here the Mn3s multiplet splitting was determined to be 4.7 eV and the Mn2p 1
2
satellite 11.4 eV away from the main peak. From comparison with literature, see
table 3.1, the observed values are consistent with a Mn:O ratio of 1:2, indicating
that a dioxide has formed. However, from the XRD results no peaks were
identied and it was therefore concluded that the lms are highly disordered or
even amorphous.
4.2 Activity measurements
To ensure that the deposited lms are relevant in terms of activity, they were
tested with a Rotating Disk Electrode, RDE, set up. Results from these tests
can be seen as a cyclic voltammogram in gure 4.3. A voltammogram for the
same type of lm on the EQCM substrates is also included. By comparing the
two results, it is evident that the RDE test yields higher current densities. This
could be due to more facile removal of oxygen formed on the catalyst when the
electrode is rotated. However, the onsets of OER are very close for the two
tests.
Comparison between literature results is often problematic due to dierent fabrication
methods and testing parameters. The OER onset potential or the overpotential
needed for achieving 10 mA/cm2 are typical metrics for evaluating