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 perspective. 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 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 mAh g^-1 at 0.75 A g^-1 with exceptional cycling stability retaining 90% of its capacity after 10000 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 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.