Oxygen evolving reactions catalyzed by different manganese oxides: the role of oxidation state and specific surface area

Abstract A set of the four manganese oxide powders α-MnO 2 (hollandite), δ-MnO (birnessite), Mn O 3 (bixbyite), and 4 (hausmannite) have been synthesized in a phase-pure form tested as catalysts three different oxygen evolution reactions (OER): electrochemical OER KOH (1 mol L −1 ), chemical using aqueous cerium ammonium nitrate, H decomposition. The trends (hollandite >> bixbyite > birnessite hausmannite) are different, which can be explained by differences electric conductivity. decomposition OER, on other hand, showed same trend even linear correlation their initial rates. between catalytic performance oxidation state was observed. Another observed related to specific surface area, highlighting importance these properties for OER. Altogether, hollandite found best performing catalyst this study due combination high large area. Likely, sufficient electrical conductivity, intrinsically is also some extent electrocatalysis example.