A crystalline dihydroxyanthraquinone anodic material for proton batteries

As a class of redox-active compounds, anthraquinones (AQs) have been investigated in rechargeable metallic ion batteries. In this work, it is found that protons (H+) can be reversibly intercalated and deintercalated in crystalline 2,6-dihydroxyanthraquinone (DHAQ) at a potential of −0.21 V vs. Ag/AgCl in acidic solution and exhibits a specific capacity of 110 mAh g−1. This unique property is leveraged in a rechargeable proton battery system with a DHAQ anode and an Mn2+ cathode. During battery cycling, a morphology evolution from particulate DHAQ into centimeter-scale nanofibers is observed. It is revealed that the evolution of morphology stems from a realignment of the DHAQ molecule. The quinone proton battery delivers an equilibrium voltage of 1.1 V, and the capacity retention rate could be as high as 100% after 2600 cycles. This study showcases a unique proton (de)intercalation chemistry in crystalline AQ and demonstrates the viability of the organic proton battery system.