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.