Interlayer‐Expanded Ti ₃ C ₂ MXene/Mn‐Doped NH ₄ V ₄

ABSTRACT

Non‐metallic charge carriers, especially NH ₄ ⁺ ions, have recently attracted attention for energy storage, with Ammonium Vanadates (NH ₄ V ₄ O ₁₀ ) gaining an early advantage in ammonium‐ion storage due to their large interlayer spacing. Here, we report the fabrication of a nanocomposite involving Ti ₃ C ₂ (MX) and Mn‐doped NH ₄ V ₄ O ₁₀ (MVO). Bare NH ₄ V ₄ O ₁₀ (NVO) has an interlayer spacing of 9.8Å corresponding to the major (001) peak. The interlayer spacing was enhanced to 10.81Å by doping with Mn ²⁺ ions. The H‐bonding interactions between the surface terminations of MX and the N─H bonds of MVO provide intimate contact, allowing faster ion diffusion, and contributing to predominantly diffusion‐controlled charge storage. The MX‐18 composite delivered a maximum specific capacitance of 260 F/g at 1 mA/cm ² in a half‐cell configuration in 1 

NH ₄ Cl, with the lowest charge‐transfer resistance among its counterparts. MX‐18, in an asymmetric device, yielded a maximum energy density (44.4 Wh/kg) at a power density of 289.04 W/kg, with 70% capacitance retention after 5500 cycles. The symmetric configuration of MX‐18 was fabricated as a screen‐printed micro‐supercapacitor with PVA/NH ₄ Cl gel electrolyte, yielding an energy density of 5 µWh/cm ² at a power density of 114 µW/cm ² , showcasing good flexibility and long‐term stability.