Stability of Pseudocapacitive 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. However, one obstacle facing pseudocapacitors is their shorter lifetime than commercial supercapacitors using the double-layer charge storage mechanism. In MXene-based pseudocapacitors, this concern is pronounced particularly at high temperatures due to the limited stability of the active material in aqueous solutions. This work shows that Ti₃C₂T<i>_x</i> MXene thin-film electrodes in 5 M H₂SO₄ possess excellent rate capabilities from -50 °C to 70 °C but also a sufficient lifetime at 70 °C using a float test holding at -0.9 V vs. Hg/Hg₂SO₄. 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 Ti₃C₂T<i>_x</i> MXene as a negative electrode in protic aqueous electrolytes across a wide temperature range rooted in thermodynamics, making it promising for pseudocapacitor energy storage.