Low-Temperature pseudocapacitive energy storage in Ti3C2Tx MXene

The use of pseudocapacitive electrode materials can enable devices to store more energy than electrical double-layer capacitors (EDLCs). However, only a few pseudocapacitive materials can maintain excellent performance at low temperatures, which limits their application in harsh climate conditions. Here we demonstrate that a pseudocapacitor with two-dimensional transition metal carbide (MXene) electrode can exhibit excellent low-temperature performance like EDLC. The MXene electrodes contain electrolyte between 2D sheets, and the electrolyte ions can unimpededly reach redox-active sites and interact with surface oxygen groups rapidly, even at low temperatures. With a combination of 40 wt.% sulfuric acid solution as the electrolyte, the working temperature of the MXene electrode extends to -60 degrees C. The electrode exhibits temperature-insensitive performance at a low scan rate, and the capacity of MXene (88 mAh g(-1) at 5 mV s(-1)) stays almost constant when the temperature decreases from 20 to -50 degrees C. Moreover, at -50 degrees C, MXene electrodes show a high capacity retention of > 75% at 100 mV s(-1), indicating good low-temperature rate performance. Interestingly, a broad working potential window of 1.5 V is achieved at -60 degrees C. Such an excellent low-temperature performance demonstrates that MXene is a promising electrode candidate for low-temperature pseudocapacitive energy storage applications.