In Situ Surface Enhanced Raman Spectroscopic Studies on Manganese Oxide
Whether in acidic, alkaline or neutral media, catalyst corrosion remains a significant challenge to oxygen evolution. MnO2 is earth abundant and well known for catalyzing oxygen evolution. A form of MnOxcluster is known to catalyze water oxidation in photosynthesis. The problem is that the catalyst comes with a significant corrosion problem.
MnO2 + 2H2O --> MnO4- + 4H+ + 3e- E0= 1.69V vs. NHE
Besides that MnO2-xnaturally exists in various polymorphs, with various amounts of defects each of which is known to have a different electrocatalytic performance. Poor ballistic electronic conduction (important for good electrode materials) is also a prevalent issue with these oxides. These catalysts although with immense potential remain a long way from successful implementation within electrolysers. In order to understand the limitations of this catalyst under the operational conditions, it is important to study this material in situ.
Setup for in situ Surface Enhanced Raman Spectroscopy is used for tracking the structural changes of hydrous MnOx while changing the potential in the range of 0 - 2,0 V. Electrodeposition of MnOx on the surface of Au was achieved by passing an anodic current of 50 mC/cm2 at 1,6V. The resulting MnO2 phase could be termed as the alpha/MnO2 phase. The structural integrity of the MnOx was studied by following the Mn-O-Mn stretching various potential ranges in various electrolytes. Onset of phase changes and corrosion could be clearly established.