A rechargeable aqueous phenazine-Prussian blue proton battery with long cycle life

Aqueous proton batteries (APBs) are one of the most attractive technologies for grid-scale storage of renewable energy due to their unique merits of a proton as a charge carrier, such as light weight, small ionic radius, and the ability to bind covalently or ionically to various organic/inorganic moieties. Although various types of electrode materials have been employed in APBs, their full cells still show unsatisfactory performance with limited energy density and cycle durability. Herein, we report a novel high-performance APB that operates in a sulfuric acid electrolyte with protons commuting between a Cu-Fe Prussian blue analogue cathode and a fused-ring phenazine derivative anode. The fabricated APB full cell exhibits an energy density of up to 52 W h kg⁻¹, excellent rate performance, and stable cycle life for 10 000 cycles with a capacity retention of ∼65.2% and a round-trip energy efficiency of 87.1%. The proton storage mechanism is studied by ex situ Fourier transform infrared (FTIR) spectroscopy, X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). This work indicates a potential direction to rationally design high-performance APBs.