Unlocking Grotthuss Proton Energy Storage in Pyrochlore-Type Tungsten Oxide

It is of momentous significance to identify suitable proton-storage electrode materials inherent with Grotthuss topochemistry toward high-power aqueous proton batteries. However, currently reported oxide electrode materials have seldom conformed to the Grotthuss mechanism. Here Grotthuss mechanism-dominated proton storage is showcased in a novel 3D-tunnel-structured pyrochlore-type WO₃·0.5H₂O (WOH), together with a reliable and effective approach to amplifying its Grotthuss conduction effect. Different from other phases of tungsten oxide (e.g., orthorhombic, monoclinic, and hexagonal), the zeolitic-water-enriched cubic pyrochlore WOH favors proton-hopping akin to "Newton's cradle" instead of traditional "vehicle-like" transport. Interestingly, introducing trace Ni(II) ions into the WOH (NWOH) is find to notably increase the content of structural water in lattice, thereby reframing the hydrogen-bonding network along with enhanced proton transfer capability as a consequence of its largely reduced activation energy as low as 0.08 eV. Hence, NWOH shows boosted reversible capacity of 71 mAh g^-1 at 100C, ultrafast charging capability up to 500C, and ultralong cycling life over 30,000 cycles. Once coupled with Prussian blue analogue cathodes with identical Grotthuss conduction mechanism, the resultant high-output-voltage full-cells (≈1.1 V) sustain high-rate cycling with high energy/power density and operate at a wide working temperature from -20 to 50 °C.