Molecular Engineering of Metalloporphyrins for High‐Performance Energy Storage: Central Metal Matters

Abstract

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 A2B2‐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.

High Active Material Loading in Organic Electrodes Enabled by an in‐situ Electropolymerized π‐Conjugated Tetrakis (4‐Aminophenyl) Porphyrin

“…The incorporation of Zn(II) and Cu(II) metal atoms greatly improves the discharge capacity and rate capability of TAPP. This could be attributed to the changes in the physical properties of the porphyrin material, [21] including solubility, molecule planarity and crystallinity, which will be further explored in the study. At 0.2 A/g the achieved discharge capacity of CuTAPP was around 130 mAh/g in the 2 nd cycle and was well above the ones from ZnTAPP (∼120 mAh/g) and TAPP (∼75 mAh/g).…”

π‐Conjugated Metal Free Porphyrin as Organic Cathode for Aluminum Batteries

“…Herein, [TDPP] delivers an initial charge/discharge capacity of 830/132 mAh g −1 at 0.1 A g −1 . Irreversible charge/discharge capacities are frequently observed in porphyrin‐based electrodes, it is attributed to the formation of solid electrolyte interphase and due to side reactions because of the initial incorporation of the anions [15a,d, 18, 23] . A stable discharge capacity is around 125 mAh g −1 after the first cycle at a current density of 100 mA g −1 (2 nd to 5 th cycle) was recorded, equal to the theoretical capacity calculated for six e − processes.…”

“…This porphyrin-based system further provides the opportunity to improve their performance through molecular engineering. [18] This can involve the introduction of metals or the alteration of their substituents to enhance both conductivity and stability.…”

“…Moreover, TDPP is obtained by a straightforward method with a good yield, opposite to most of the prior studied systems, in which a multi‐step synthesis is required, increasing their cost and resulting in poor yields. This porphyrin‐based system further provides the opportunity to improve their performance through molecular engineering [18] . This can involve the introduction of metals or the alteration of their substituents to enhance both conductivity and stability.…”

Single Pyrrole Unit Functionalized Electron Deficient Porphyrins and Their Metal Complexes: Synthesis, Structural, Spectral and Electrochemical Properties

“…The optical absorption properties of electron deficient βdisubstituted-meso-tetraphenylporphyrins [H 2 TPP(R) 2, [wherein R = CF 3 & CN] were determined in distilled CH 2 Cl 2 at 298 K. The electronic absorption spectra of porphyrin macrocycles are impacted significantly by the existence and nature of peripheral substituents, degree of macrocyclic conjugation, conformation of the macrocyclic core as well the type of central metal ion. [31,48,80] The Soret band, also known as the B band, is a characteristic band of porphyrins and arises from the S 0 to S 2 transitions. The newly synthesized series of single pyrrole unit β-disubstituted porphyrins showed expected absorption features with free base porphyrins reflecting a characteristic Bband along with three to four Q-bands in their electronic absorption spectra.…”