Magnetometric Characterization of Intermediates in the Solid-State Electrochemistry of Redox-Active Metal-Organic Frameworks

Electrochemical energy storage has been a widely discussed application of redoxactive metal-organic frameworks (MOFs) in the past 5 years. Although MOFs show outstanding performance in terms of gravimetric or areal capacitance and cyclic stability, unfortunately their electrochemical mechanisms are not well understood in most cases. Traditional spectroscopic techniques, such as X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS), have only provided vague and qualitative information about valence changes of certain elements, and the mechanisms proposed based on such information are often highly disputable. In this article, we report a series of standardized methods, including the fabrication of solidstate electrochemical cells, electrochemistry measurements, the disassembly of cells, the collection of MOF electrochemical intermediates, and physical measurements of the intermediates under the protection of inert gases. By using these methods for quantitatively clarifying the electronic and spin state evolution within a single electrochemical step of redox-active MOFs, one can provide clear insight into the nature of electrochemical energy storage mechanisms not only for MOFs, but also for all other materials with strongly correlated electronic structures.

Automated summary

Electrochemical energy storage using redox-active metal-organic frameworks (MOFs) has been extensively studied in the past 5 years. Despite their excellent performance in terms of capacitance and stability, the electrochemical mechanisms of MOFs are still poorly understood. Traditional spectroscopic techniques provide limited and qualitative information, leading to disputed proposed mechanisms. This article presents standardized methods to quantitatively clarify the electronic and spin state evolution within a single electrochemical step of redox-active MOFs, which can provide clear insights into energy storage mechanisms for MOFs and other materials with correlated electronic structures.