MnO2-x naturally exists in various polymorphs with various amounts of defects. Each of them has different electrocatalytic performance. Poor electronic conductivity, which is very important for good water splitting catalysts, is also one of the issues with these materials. These catalysts remain a long way from successful implementation within electrolysers, even with enormous potential of usage. It is important that these materials are studied in situ in order to understand performance and limitations under the operando conditions.
In situ Surface Enhanced Raman Spectroscopy is used to track the structural changes of the lattice of hydrous MnOx, while sweeping the potential in the range of 0 - 2.2 V vs RHE. MnOx catalyst is prepared by electrochemical deposition on the surface of roughened gold. It was done by passing an anodic current of 50 mC/cm2 at 1.6 V vs RHE in 0.5 M MnSO4 solution. By following the Mn-O-Mn stretching at various potentials in various electrolytes, the structural conformation of the catalyst was studied. For each electrolyte a unique catalyst structure was finally established. Various electrolytes (alkaline, neutral and acidic) containing alkali metal ions (Li, Na, K, Cs), alkaline earth metal ions (Ca, Sr, Ba) and anions such as borates, phosphates and sulphates were used to study OER under in situ Raman conditions. Catalysts were also studied under conditions of duteration of the electrolytes.