Reversible NH4+ intercalation/de-intercalation with phosphate promotion effect in tunnel (NH4)0.25WO3

With the rapid development of human–machine interfaces and artificial intelligence, the high-performance devices with flexibility, wearable, and lightweight are highly required. In this study, we construct a flexible self-powered sensing system by integrating a pressure sensor with ammonium-ion battery which possesses the advantages of environmental friendliness, low cost, and high theoretical power/energy density. One of the key factors for the self-powered system is the design of flexible bifunctional electrode with ammonium-ion storage and pressure sensor ability in a wide pressure sensing range. Herein, we fabricate a phosphate ion decorated tunnel (NH4)0.25WO3 electrode (denotes as P-NWO) for the first time. Benefiting from the expanded tunnel space, excellent structural stability and enhanced electronegativity upon phosphate ion introduction, the P-NWO exhibits superior NH4+ storage capacity of 148.4 mAh/g at a current density of 0.2 A/g. Spectroscopy studies, electrochemical analysis and theoretical calculation suggest a NH4+ insertion with hydrogen bonds formation/breaking mechanism. Furthermore, the P-NWO//PANI battery provides a stable output power supply to the sensors with an excellent cycle stability.