In Situ Transformed Organic Redox Molecules for a Hydrogen Battery Operated at −70 °C

Rechargeable hydrogen batteries using organic materials and aqueous protonic electrolytes are sustainable and safe candidates for large-scale energy storage systems. 1,2-Naphthoquinone (1,2-NQ) is a promising organic molecule with a high theoretical capacity of 339 mAh g^-1 via a highly reversible heterogeneous enolization reaction between C═O and C-OH moieties through uptake/removal of H⁺. Nevertheless, the mainstream synthetic route of 1,2-NQ is restricted to oxidizing 1- and 2-naphthol precursors, which involves expensive catalysts and toxic organic solvents. Herein, we propose a green and economical in situ transformation strategy to synthesize 1,2-NQ from a 2-nitro-1-naphthol (2N1N) precursor in an electrochemical manner for high-performance hydrogen batteries. The structural evolution from the 2N1N precursor to 1,2-NQ is confirmed by operando synchrotron radiation Fourier transformed infrared (SR-FTIR) characterization. As a result, the NQ-H₂ battery delivers a high specific capacity of 323.4 mAh g^-1 at 0.2 A g^-1, approaching the theoretical capacity of 1,2-NQ, along with 10000 stable life cycles at 10 A g^-1. It also exhibits a capacity of 155.9 mAh g^-1 at low temperatures down to -70 °C. Moreover, an NQ-H₂ pouch cell with an expanded capacity of 375.4 mAh as well as a high areal capacity of 6.3 mAh cm^-2 is fabricated to demonstrate its potential for practical application. This work provides a feasible strategy in building sustainable hydrogen battery chemistry for practical applications.