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Porphyrin derivatives represent an emerging class of redox-active materials for sustainable electrochemical energy storage. However, their structure–performance relationship is poorly understood, which confines their rational design and thus limits access to their full potential. To gain such understanding, we here focus on the role of the metal ion within porphyrin molecules. The A$_2$B$_2$-type porphyrin 5,15-bis(ethynyl)-10,20-diphenylporphyrin and its first-row transition metal complexes from Co to Zn are used as models to investigate the relationships between structure and electrochemical performance. It turned out that the choice of central metal atom has a profound influence on the practical voltage window and discharge capacity. The results of DFT calculations suggest that the choice of central metal atom triggers the degree of planarity of the porphyrin. Single crystal diffraction studies illustrate the consequences on the intramolecular rearrangement and packing of metalloporphyrins. Besides the direct effect of the metal choice on the undesired solubility, efficient packing and crystallinity are found to dictate the rate capability and the ion diffusion along with the porosity. Such findings open up a vast space of compositions and morphologies to accelerate the practical application of resource-friendly cathode materials to satisfy the rapidly increasing need for efficient electrical energy storage.

Development of practical rechargeable Mg batteries (RMBs) is impeded by their limited cycle life and rate performance of cathodes. As demonstrated herein, a copper‐porphyrin with meso‐functionalized ethynyl groups is capable of reversible two‐ and four‐electron storage at an extremely fast rate (tested up to 53 C). The reversible four‐electron redox process with cationic‐anionic contributions resulted in a specific discharge capacity of 155 mAh g−1 at the high current density of 1000 mA g−1. Even at 4000 mA g−1, it still delivered >70 mAh g−1 after 500 cycles, corresponding to an energy density of >92 Wh kg−1 at a high power of >5100 W kg−1. The ability to provide such high‐rate performance and long‐life opens the way to the development of practical cathodes for multivalent metal batteries., Self‐conditioning: The metalloporphyrin based electrodes exhibit reversible insertion/deinsertion of Mg2+ and bulky anions as well as excellent capacity retention over several hundred cycles at very fast charge‐discharge rates. This opens the pathway for development of new organic electrode materials for stable high‐energy and high‐power multivalent metal‐based energy storage systems.

We present FIB/SEM tomography combined with an optimized embedding procedure and osmium tetroxide staining to trace and visualize the initial self-conditioning step as well as degradation processes of [5,15-bis(ethynyl)-10,20-diphenylporphinato]copper(II) (CuDEPP) composite electrodes for the first time. Staining with osmium tetroxide allowed visualizing chemical changes of the active CuDEPP material. Four composite electrode samples prior and after cycling with different cycle numbers in LiPF6 electrolyte (i.e., pristine, one, 200 and 2000 charging cycles) were investigated and for all samples 3D reconstructions with a voxel size of 7.15 × 7.15 × 20 nm3 were performed. The samples were further analyzed by wavelength-dispersive X-ray (WDX) spectroscopy revealing the insertion of the electrolyte into the active material of the electrode. The formation of an interphase adjacent to the inner pore space of the active CuDEPP material could be unambiguously identified. In addition, Raman spectroscopy results confirmed the self-conditioning and degradation processes of the metalloporphyrin complex.