A holomolecule conjugated and electron delocalized organic compound for superior proton-storage redox capability

Aqueous proton batteries (APBs) offer realistic possibilities for reliable and sustainable energy technologies owing to their unique "Grotthus mechanism". Organic compounds with tunable molecular structures are candidate electrode materials, but their unsatisfactory proton-storage redox behaviors hinder the practical application in APB devices. Herein, a holomolecule conjugated organic compound (PZQN) composed of pyrazine and quinone rings is synthesized and used for APB application. Such reasonable configuration bestows the PZQN molecule with extended π-conjugation, overall molecular rigidity and optimized electronic structure with a small energy gap (∼3.12 eV). Localized orbital locator-π (LOL-π) and iso-chemical shielding surfaces (ICSS) techniques reveal the extraordinary electron delocalization in the PZQN molecule, enabling its high-kinetic redox activity and superior electron affinity. As such, the PZQN compound as an electrode material exhibits a fast, stable and unrivaled proton-storage redox capability with a competitive capacity of 262.5 mAh g−1 in aqueous acidic electrolyte, which is comparable among various proton-inserted organic electrodes. In-situ dynamic analysis combined with theoretical calculations illustrate the proton-storage redox mechanism and corresponding protonation pathway. Finally, a high-performance APB device is fabricated with superior electrochemical properties and an ultralong lifespan over 40,000 cycles, further confirming its promising application prospect.