Research will be presented that illustrates the redox chemistry and structural transformations of the Mn oxide, birnessite, for the oxygen evolution reaction (OER) which is part of the water splitting reaction. Emphasis will be placed on the unique redox chemistry occurring within the interlayer region of hexagonal birnessite, due to the nano-confinement of intercalated metal cations and water. Results will be presented that show that intercalated metal cations in birnessite, which include nickel and cobalt, are more active catalysts for the OER than are the respective pure metal (hydr)oxides. For example, the overpotential (measured at 10 mA/cm2) for the OER for birnessite with interlayer nickel is 400 mV, compared to 550 mV and &gt;700 mV, for nickel hydroxide, and birnessite, respectively. Research will also be presented that has investigated the effect of pH on the structure of both the hexagonal and triclinic phases of birnessite and how this ultimately plays a role in the catalytic activity of birnessite. The results show that the Mn(III) redox state of Mn has a high activity for the OER. The relevance of the results for helping to understand the reaction of birnessite in natural settings will also be discussed.

Redox chemistry and structural transformations relevant to birnessite as an electrocatalyst for water oxidation

ACS Spring Meeting 2021

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