Reversible Complexing-Enabled Coordination Networks for the Retention of Redox Species

Reversible coordination between polymers and multivalent metal cations offers a potential route to reduce the dissolution and migration of mobile redox species while preserving their electrochemical accessibility. Here, we establish a reversible complexing strategy using branched polyethyleneimine (PEI) to construct coordination-crosslinked PEI-metal networks for retaining redox-active species. Using Al³⁺ as a model cation, the resulting PEI/Al³⁺ network effectively immobilizes anthraquinone molecules while maintaining their reversible electrochemical activity. The observed capacity evolution and charge-discharge asymmetry are consistent with a possible state-dependent retention process, although the identity and redox state of the migrating species are not directly resolved by the present measurements. Systematic comparison shows that coordination stability depends on cation-specific aqueous coordination chemistry, with the Zn²⁺-based complex exhibiting more dynamic and electrolyte-sensitive behavior than the PEI/Al³⁺ network under the tested conditions. Extending this concept, PEI-based complexes with redox-active cations such as Mn²⁺ and Cu²⁺ directly function as electrode materials with long-term cycling stability. Moreover, the coordination structures exhibit chemically responsive dissolution under chloride-containing conditions, enabling the release of associated species. This work presents a functional proof-of-concept for coupling reversible polymer-metal complexation with the association, electrochemical utilization, and chemically responsive release of redox-active species.