Birnessite study offers insights for electrochemistry, energy storage

Credit: CC0 Public Domain It is an all-purpose process that can be used to adsorb ions from electrolytes at electrode surfaces. This is useful for both current and future electrochemical energy technologies. What happens when these ions penetrate small spaces? Researchers at NC State examined the behavior of birnessite, a classic material to answer this question. Birnessite, a hydrated, layered manganese oxide form, can store and release many positive ions from electrolytes in a matter of seconds. It is a promising material for high-power electrochemical energy storage or emerging electrochemical technologies like desalination and rare elements recovery from water. It is easy to make and non-toxic, making it a plentiful material. Birnessite's ability to absorb and release cations can be described as either faradaic (involving charge transfer) or non-faradaic, which involves only electrostatic ion absorption. The researchers employed both experimental and computer-based approaches to address this issue. Shelby Boyd, a North Carolina State University postdoctoral researcher and first author of the paper, said that charge storage is normally categorized as either faradaic, or non-faradaic. "At planar interfaces faradaic refers specifically to the adsorption and transfer of an ion to an electrolyte with corresponding charge transfer. This is similar to a redox reaction. Non-faradaic is purely electrostatic adsorption that does not involve charge transfer. These mechanisms of charge storage have been largely viewed as mutually exclusive. We found that the intercalated cation and birnessite interact with each other through the interlayer structural water. This creates an intermediate behavior between the two types at planar interfaces. Researchers were also able experimentally and theoretically to show that water between layers of birnessite acts as a buffer, making capacitive behavior possible while avoiding significant structural changes in the birnessite. The researchers conclude that the findings point to two possible future directions in the field of electrochemistry. "The field is experiencing a renaissance in electrochemistry," said Veronica Augustyn (co-author of the paper) and assistant professor of materials science, engineering at NC State. "The ability to link experimental results with atomistic scale modeling of the electrochemical interface allows for us to probe deeper than ever and ask questions such as: What role is the solvent playing? What happens when the reaction takes place under confinement? Understanding the capacitive mechanism in a material such as birnessite opens the door to more complicated electrochemical reactions. Nature Materials will soon publish the paper "Effects on Interlayer Confinement & Hydration on Capacitive Charge Storage in Birnessite." Continue reading Researchers uncover relationship between supercapacitors and magnetic field More information: Effects of interlayer confinement and hydration on capacitive charge storage in birnessite, Nature Materials, DOI: 10.1038/s41563-021-01066-4 , Journal information: Nature Materials Effects of interlayer confinement and hydration on capacitive charge storage in birnessite,