(Invited) Energy Storage in Ti₃C₂T _x MXene in a Wide Temperature Range

Pseudocapacitors have the potential to achieve high energy and high power density simultaneously, a holy grail for electrochemical energy storage. MXene-based pseudocapacitors have made major progress in the last decade, achieving better energy and power density than carbon supercapacitors using the double-layer charge storage mechanism. However, one obstacle facing pseudocapacitors is their shorter lifetime. In MXene-based pseudocapacitors, which showed up to 500,000 cycles lifetime in aqueous electrolyte at room temperature, this concern is pronounced particularly at high temperatures due to the limited stability of the active material in aqueous solutions. This work shows that Ti 3 C 2 T x MXene electrodes in 5 M H 2 SO 4 possess excellent rate capabilities from -50 °C to 100 °C but also a sufficient lifetime at 70 °C when using a float test holding at -0.9 V vs. Hg/Hg 2 SO 4 . Post-mortem characterization using X-ray photoelectron spectroscopy and Raman spectroscopy showed negligible signs of oxidation in the bulk of the film. This work suggests sufficient stability of Ti 3 C 2 T x MXene as a negative electrode in protic aqueous electrolytes across a wide temperature range rooted in thermodynamics, making it promising for pseudocapacitor energy storage.