Enhancement of Stability and Activity of MnOx/Au Electrocatalysts for Oxygen Evolution through Adequ

Oxygen evolution and catalyst corrosion were studied side by side for electrodeposited MnOx catalysts. Measurements using a combination of electro-chemical flow cell, atomic absorption spectroscopy, and rotating ring disk electrode reveal a high sensitivity of oxygen evolution and of manganese oxide corrosion toward the presence of ions (alkali-metal cations and anions) in the electrolyte. The charge to radius ratio of alkali-metal ions affected the reactivity of the oxides and was seen to influence the reaction under both potentiostatic and potentiodynamic conditions, with Li+- and (K+,Cs+)-containing electrolytes showing the lowest and highest activities, respectively. Thermogravimetry in combination with mass spectrometry showed significant differences between samples treated in different electrolytes. Raman spectroscopy showed that the material transformed during the oxygen evolution reaction, with multiple phases α-MnO2 and birnessite-MnO2 being present in the catalyst during oxygen evolution reaction. Electronic structure (XANES) studies revealed the significant influence of alkali-metal ions on the oxidation state of Mn, with the OER-inactive Mn2+ oxidation state being stabilized with the Li+ ion. It was found that selected combinations of anions and cations in the electrolyte and suitable potential can significantly stabilize the electrode during OER application.