Monitoring Copper Ion Leaching from a Metalloporphyrin-Based Cathode for Rechargeable Magnesium Batteries

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Great efforts are being undertaken to characterize the fundamental processes of solid electrolyte interphase (SEI) formation, degradation, and initial conditioning steps of battery electrode materials, including organic electrode materials.[1] Imaging techniques, such as focused ion beam / scanning electron microscopy (FIB/SEM) tomography in combination with element mapping using energy- and wavelength-dispersive X-ray spectroscopy are employed to gain insight into distribution, interconnectivity, and porosity of active materials as well as electrolyte penetration and their influence on degradation processes after longer cycling times.[2] Additionally, electrochemical impedance spectroscopy[3] and anodic stripping voltammetry[4] are used to shed light on those processes. The metalloporphyrin-based material [5,15-bis(ethynyl)-10,20-diphenylporphinato]copper(II) (CuDEPP) has been used as an interesting material for cathodes and anodes of various battery chemistries. These materials undergo initial self-conditioning by electro-polymerization for monovalent ions. With respect to multivalent ions, like magnesium, this polymerization is far less pronounced and an exchange of the copper from the CuDEPP by magnesium ions appears to be occurring.[5] Gaining insight into this trans- or demetallation process induced by parameters like the electrochemical driving force during galvanostatic cycling is a complex analytical challenge.We report the use of Hg ultramicroelectrodes and anodic stripping voltammetry as a sensitive strategy to detect copper ion leaching from metalloporphyrin-based CuDEPP composite electrodes. We demonstrate in-situ/intermittent monitoring of copper ion release during the initial self-conditioning step of the active material while galvanostatic cycling of the battery electrode in dimethoxy ethane. This method could be used to assess the release of an ionic species from complex systems, like composite battery electrodes.