Phase evolution of an alpha MnO₂-based electrode for pseudo-capacitors probed by in operando Raman spectroscopy

In operando Raman spectroscopy has been used to monitor the phase changes of non-stoichiometric α-MnO₂, α-Mn_0.98O₂, electrode materials in a pseudo-capacitor during the charging/discharging process. Results indicate that the α-Mn_0.98O₂ can be converted to MnO₂ and Mn₃O₄ when placed in electrolyte exposed to laser for the Raman measurements. Both the phases contribute to the energy storage process through reversible phase transformation which involves hydrated cations M⁺, protons H⁺ and Mn²⁺ intercalation/deintercalation during the charging/discharging process.