Engineering π-Electron Bridge Enables Low-Potential 2D Redox Polymer Anodes for High-Voltage Aqueous All-Organic Batteries.

ABSTRACT

Here, we propose a novel π-electron bridge engineering strategy to explore a class of dioxin-bridged 2D redox covalent organic polymer (RCOP) as trade-off-breaking anodes for high-voltage aqueous all-organic batteries (AAOBs). By establishing a tunable RCOP platform, we perform theoretical study to scrutinize how bridge units between active sites affect the electrode potential and redox activity for the first time. We discover that compared to common pyrazine bridge, the weakened conjugation and strong electron donor character of the proposed dioxin bridge can induce elevated LUMO level and enriched π-electron populations in active sites, heralding a low electrode potential and enhanced redox activity. Besides, nonaromaticity induced molecular flexibility of dioxin bridge mitigates intermolecular stacking for sufficient active site exposure and charge carrier uptake. To experimentally corroborate this, a new dioxin-bridged RCOP (D-HATN) and its pyrazine-bridged analogue (P-HATN) are synthesized for proof-of-concept demonstration. Hence, D-HATN displays excellent compatibility with Na+/Zn2+/NH4+/H3O+ and obviously lower redox potentials in various electrolytes compared to P-HATN, while affording rapid Grotthuss-type proton conduction and unprecedented durability in acid. Thus,  the D-HATN-involved all-organic proton battery delivers an average output voltage of 0.75 V, which can be further elevated to 1.63 V with alkaline-acidic hybrid electrolyte design, affording markedly-increased specific energy.