Manganese oxides are a compelling electrode material to use in electrochemical systems due to the low cost of manganese and the ability to control their crystal structures and particle sizes. Manganese oxides are known to undergo redox reactions coupled to sodium uptake and release, in which Mn(IV) reduction is coupled to sodium ion uptake. These redox reactions can occur at a manganese oxide surface via pseudo-capacitive mechanisms, or they can occur within the manganese oxide structure via intercalation processes that involve structural tunnels or interlayers. In this work, we characterized the electrochemical, structural, and morphological properties for twelve synthetic manganese oxides (β-, γ-, α-, δ-MnO2, birnessite, Mn2O3, and sodium manganese oxide). We examined how the charge storage mechanisms varied as a function of charging rate and manganese oxide structure by examining electrochemical cyclic voltammograms collected at different scan rates. We subsequently tested each manganese electrode in a salinity gradient concentration flow cell for harnessing electrical energy. Results indicate a positive correlation between capacity and BET specific surface area, suggesting that a considerable amount of capacity was attributable to (pseudo-)capacitive reactions occurring at the surface. Scan rate analyses reveal that layered manganese oxides (δ-MnO2 and birnessites) had superior charge storage capacity due to their ability to participate in partial interlayer intercalation reactions. Furthermore, materials that exhibited high capacity derived from fast (pseudo-)capacitive reactions (δ-MnO2 and hexagonal birnessite) outperformed in the concentration flow cell compared to structures that had high capacity resulting from slow faradaic or diffusion-controlled reactions (sodium manganese oxide, triclinic sodium birnessite, and triclinic potassium birnessite).

Elucidating how manganese oxide electrodes store charge in electrochemical systems

Macromolecular Chemistry: The Second Century

[Author Benefits](https://scimeetings.acs.org/?utm_source=pubs_content_marketing&utm_medium=website&utm_campaign=0320_MCF_NPI_Launch_Spring_Homepage&ref=pubs_content_marketing)

[How to use SciMeetings](https://storage.googleapis.com/dl.morressier.com/acs/SciMeetings-ACSSpring2020-HowToGuide_M3020-Final.pdf)

[Frequently Asked Questions](https://storage.googleapis.com/dl.morressier.com/acs/SciMtng_ACSNMSp2020_FAQ_M3120_Final.pdf)

ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.