Boosting the energy storage performance of aqueous NH4+ symmetric supercapacitor based on the nanostructured molybdenum disulfide nanosheets

Abstract

Nanostructured molybdenum disulfide (MoS2-2H phase) is a well-known metal dichalcogenide and promising material for electrochemical energy storage due to its unique properties, including structural stability, tuneable bandgap, and dangling-bond free basal surface. However, electrochemical devices based on MoS2 suffer from a short lifespan, low power density, and safety. Herein, we proposed 2H-MoS2 nanosheets as a capacitive energy storage material for aqueous ammonium-ion supercapacitors (AASCs) to address the above-mentioned issues. MoS2 nanosheets were grown on carbon cloth (MoS2@CC) with a wet-chemical method as binder-free capacitive electrodes, and a symmetric supercapacitor (SSC) was assembled to evaluate its energy storage performance. According to our simulation results with density functional theory (DFT), the ammonium sulfate (NH4)2SO4 aqueous solution was selected as the ammonium-ion electrolyte. The MoS2@CC electrode exhibits outstanding NH4+ ion storage by achieving a high capacitance of 1,010 Fg−1 at 1 Ag−1 and ultra-high rate performance (60% at 50-folded high current density) with 98% capacitance retention after 10,000 cycles. The pseudocapacitive charge storage process governs the NH4+ intercalation/deintercalation mechanism through the bounding/breaking of H with S atoms. A symmetric AASC was fabricated using the MoS2@CC and an aqueous (NH4)2SO4 electrolyte to assess the practical performance. The assembled AASC can operate at a wide potential window (0.0–1.5 V) and demonstrates high charge storage performance (237 Fg−1 at 1 Ag−1 and 133 Fg−1 at 50 Ag−1) with extremely stable rate and cycling performance of ∼ 99% up to 50,000 cycles. This study would give an effective and a succinct technique for creating metal dichalcogenide with porous structure for advanced NH4+ storage.