Hexafluorozirconic Acid -Etched Mxene for Ammonium-Ion Capacitors

Abstract

MXenes have gained significant attention for their exceptional electrochemical properties in applications such as supercapacitors and metal-ion batteries. However, developing mild and efficient liquid-phase methods for synthesizing high-quality MXene nanosheets remains challenging due to the limitations of conventional etching techniques. Herein, we report the successful synthesis of Ti3C2Tx MXene through selective etching of the Al layer from the Ti3AlC2 MAX phase using hexafluorozirconic acid, a safer alternative to hazardous hydrofluoric acid. Both theoretical calculations and experimental results demonstrate that Ti3C2Tx MXene is a highly efficient electrode material with remarkable ammonium ion storage capability. An asymmetric ammonium-ion capacitor, employing Ti3C2Tx MXene as the negative electrode and activated carbon as the positive electrode, achieved impressive energy and power densities, with 86% capacitance retention after 10000 cycles. This work highlights not only the effectiveness of hexafluorozirconic acid as an etching agent but also the substantial potential of Ti3C2Tx MXene in next-generation energy storage devices.

Keywords: MXene, etching agent, DFT calculations, ammonium-ion capacitor