In Situ Surface Enhanced Raman Spectroscopic Studies on Manganese Oxide

Non noble metal "earth abundant" electrocatalysts will significantly reduce the costs and make it possible to use electrochemical water splitting on a very large scale. Non noble metal catalysts can be an effective replacement even if their electrochemical activities are a fraction of their noble metal counterparts. If these catalysts can be developed to an extent where their operational lifetime would become comparable to their noble metal counterparts, a large part of the problem would be solved.  

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 MnO_xcluster 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 MnO_2-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 MnO_x while changing the potential in the range of 0 - 2,0 V. Electrodeposition of MnO_x 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 MnO_x 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.