Modulating NH4+ in vanadium oxide framework for high-efficient aqueous NH4+ storage

Aqueous energy storage systems have garnered significant attention due to their inherent advantages, including low cost, high eco-sustainability, and enhanced safety profiles. Nonmetal ion as a charge carrier is a fascinated paradigm shift just recently. Vanadium-based materials for ammonium ion (NH4+) storage have received considerable interest and have been demonstrated to serve as highly efficient NH4+ (de)intercalation host materials. However, tuning their structure for enhanced NH4+ storage presents significant challenges. Herein, we report a strategy for the pre-intercalation of NH4+ in vanadium oxide framework to study on the influence of the amount of ammonium ions on their NH4+ storage properties. The results from the experiments and density functional theory (DFT) calculations demonstrate that the appropriate quantity of pre-inserted ammonium ions boosts the (de)intercalation of NH4+ and exhibits the superior electrochemical properties. Moreover, excessive pre-inserted ammonium ions in vanadium oxide framework occupy the active sites for storing NH4+, whereas insufficient pre-inserted ammonium ions in vanadium oxide framework do not support the interlayer space enough for rapid (de)intercalation of NH4+. All results elucidate that modulating NH4+ in vanadium oxide framework enables highly efficient aqueous ammonium ion storage for supercapacitors (SCs). At 0.5 A·g−1, the specific capacitance of 341F·g−1 (171 mAh·g−1) and stable cycle performance of nearly 100 % after 10,000 cycles are achieved. The assembled hybrid supercapacitor exhibits the capacitance with 330 mF·cm−2 at 1 mA·cm−2, and energy density with 13.7 Wh·kg−1 at 22.1 W·kg−1, complemented by commendable mechanical durability and energy output characteristics. The profound insights gleaned from this study illuminate the strategic modulation of NH4+ ions, unveiling the vast potential of vanadium-based materials for efficient NH4+ storage applications.