Hydrogen-bonded organic supramolecular layered structure for efficient Grotthuss proton conduction in aqueous proton batteries

Abstract

Aqueous-based batteries are among the most promising candidates for sustainable energy storage due to cost, safety and environmental friendliness. Apart from charge carriers, e.g., Li⁺, Na⁺, K⁺, Mg²⁺ and Zn²⁺, which have been predominantly explored for aqueous systems, non-metallic charge carriers, proton (H⁺), have recently gained major attention. Combining with organic electrode materials, which feature redox tunability, structural design flexibility as well as rapid redox kinetics and come from abundant/renewable resources, truly sustainable batteries can be materialized. Herein, we report a nitrogen- and carbonyl-rich highly π-conjugated organic small molecule, hexaazatrianthranylene (HATA)-embedded quinone (HATAQ), with a 2D supramolecular layered structure held together by hydrogen bonding and π–π interactions, as an electrode for aqueous proton batteries. Experimental characterization results, including various kinetic studies, together with molecular and periodic density functional theory (DFT) calculations, reveal Grotthuss fast proton conduction in the hydrogen-bonded network as HATAQ undergoes multistep proton-coupled electron transfer reactions. The compound possesses excellent proton storage capability, delivering a capacity as high as 310 mA h g⁻¹ at 0.75 A g⁻¹ with exceptional cycling stability retaining 90% of its capacity after 10 000 cycles at a high rate of 20 A g⁻¹. All-organic full cells with the HATAQ anode and tetrachloro-1,4-benzoquinone (TCBQ) cathode have also been utilized to demonstrate their suitability for practical applications. The unique interplay between highly dense proton-storing imine and carbonyl redox sites and the hydrogen-bonded supramolecular network creates pathways for very fast proton transport, exhibiting ultra-high capacity and rate capability as well as unparalleled cycling stability in aqueous proton batteries.