Cation-Dependent Stabilization of Electrogenerated Naphthalene Diimide Dianions in Porous Polymer Thin Films and Their Application to Electrical Energy Storage

• Published in: Angewandte Chemie (International ed.) Vol. 54; no. 45; pp. 13225 - 13229
• Main Authors: DeBlase, Catherine R., Hernández-Burgos, Kenneth, Rotter, Julian M., Fortman, David J., dos S. Abreu, Dieric, Timm, Ronaldo A., Diógenes, Izaura C. N., Kubota, Lauro T., Abruña, Héctor D., Dichtel, William R.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 02.11.2015; WILEY‐VCH Verlag; Wiley Subscription Services, Inc; Wiley
• Edition: International ed. in English
• Subjects: Anions; Capacitance; Carbonyl compounds; Carbonyl groups; Carbonyls; Cationic polymerization; Cations; Coalescing; Diimide; electrical energy storage devices; Electrochemistry; Electrolytes; Energy density; Energy storage; Flux density; Inspection; Ion transport; Magnesium; Monomers; Naphthalene; Nondestructive testing; Polymer films; Polymers; porous polymers; Potassium; redox processes; Reduction; Reduction (electrolytic); supercapacitors; Thin films; porous polymers; redox processes; electrical energy storage devices; electrochemistry; supercapacitors
• ISSN: 1433-7851; 1521-3773; 1521-3773
• DOI: 10.1002/anie.201505289

Porous polymer networks (PPNs) are attractive materials for capacitive energy storage because they offer high surface areas for increased double‐layer capacitance, open structures for rapid ion transport, and redox‐active moieties that enable faradaic (pseudocapacitive) energy storage. Here we demonstrate a new attractive feature of PPNs—the ability of their reduced forms (radical anions and dianions) to interact with small radii cations through synergistic interactions arising from densely packed redox‐active groups, only when prepared as thin films. When naphthalene diimides (NDIs) are incorporated into PPN films, the carbonyl groups of adjacent, electrochemically generated, NDI radical anions and dianions bind strongly to K+, Li+, and Mg2+, shifting the formal potentials of NDI’s second reduction by 120 and 460 mV for K+ and Li+‐based electrolytes, respectively. In the case of Mg2+, NDI’s two redox waves coalesce into a single two‐electron process with shifts of 240 and 710 mV, for the first and second reductions, respectively, increasing the energy density by over 20 % without changing the polymer backbone. In contrast, the formal reduction potentials of NDI derivatives in solution are identical for each electrolyte, and this effect has not been reported for NDI previously. This study illustrates the profound influence of the solid‐state structure of a polymer on its electrochemical response, which does not simply reflect the solution‐phase redox behavior of its monomers. Charge me up: Thin films of a naphthalene diimide porous polymer exhibit 20 % greater energy density in the presence of counter cations that stabilize their reduced forms in the solid‐state. Such behaviour is not observed for the monomer in solution, pointing to the importance of polymer structure in electrical energy storage devices.