Ammonium ion pre-intercalation stabilized tunnel h-WO3 for fast NH4+ storage

Abstract

The development of aqueous electrochemical energy storage devices based on ammonium ion (NH₄⁺) carriers has received increasing attention. However, the easy dissolution of electrode materials in an aqueous solution leads to the collapse of the host structure, which seriously hinders its application. Here, we report a pre-intercalated non-metal ion (NH₄⁺) stabilized tunnel h-WO₃ anode for fast NH₄⁺ storage. The (NH₄)_xWO₃ anode and the α-MnO₂ cathode with a tunnel structure constitute a novel ammonium-ion hybrid supercapacitor (A-HSC). The newly developed (NH₄)_xWO₃//α-MnO₂ A-HSC delivers an ultra-high areal capacitance of 2239.7 mF cm⁻² and a peak areal energy density of 1010.1 μWh cm⁻². First-principles calculations show that ammonium ion pre-intercalated tunnel structured WO₃ can effectively enhance the NH₄⁺ adsorption energy and reduce the NH₄⁺ diffusion energy barrier. Ex situ characterization confirmed that the intercalation/deintercalation of NH₄⁺ is accompanied by the formation/breaking of hydrogen bonds. These findings provide a new prototype for NH₄⁺-based energy storage and facilitate a basic understanding of the storage mechanism of NH₄⁺-tunnel structured metal oxide.