A Novel Layered WO3 Derived from An Ion Etching Engineering for Ultrafast Proton Storage in Frozen Electrolyte

Abstract Aqueous proton batteries/pseudocapacitors are promising candidates for next‐generation electrochemical energy storage. However, their development is impeded by the lack of suitable electrode materials that facilitate rapid transport and storage of protons. Herein, an open‐layered hydrous tungsten oxide (WO 3 ·nH 2 O) with larger layer spacing from Aurivillius Bi 2 WO 6 via ion etching is proposed. Particularly, the WO 3 ·nH 2 O electrode possesses a unique multi‐level nanostructure and presents superior rate performance (254 F g −1 at 1000 mV s −1 , surpassing most carbon‐based electrode materials known). In situ X‐ray Diffraction combined with crystallography study demonstrate that the open layered structure with negligible structural strain enables fast and reversible (de)intercalation of protons during electrochemical reaction. Furthermore, a full proton pseudocapacitor (Prussian blue analogues//WO 3 ·nH 2 O) operating in a wide temperature range from −40 to 25 °C is fabricated. This device can deliver 70% of the room‐temperature capacitance and stably cycle with negligible capacitance fading over 5000 cycles even in the solid‐phase electrolyte at −20 °C. This study provides a valuable strategy to design electrode materials with layered structures for the development of high‐performance aqueous proton batteries/pseudocapacitors at low temperatures.