Simultaneous regulation of Li-ion intercalation and oxygen termination decoration on Ti3C2Tx MXene toward enhanced oxygen electrocatalysis for Li-O2 batteries

Active and robust bifunctional oxygen catalysts are the crucial factors to commercialize Li-O2 batteries (LOBs). However, most of the reported catalysts lack the competence to consistently achieve low overpotentials toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) during long-term cycling under high rates. Here, the bifunctional activity of Ti3C2Tx MXene is subtly motivated by surface engineering via simultaneous regulation of Li-ion intercalation and O termination decoration. The post-treated Ti3C2Tx (t-Ti3C2Tx) MXene catalysts exhibit superior ORR/OER activities to the pristine Ti3C2Tx counterpart, where the conditions of alkalization by 3 M LiOH and annealing under 400 °C offer the optimum performance. The LOB using t-Ti3C2Tx achieves very low ORR/OER overpotentials of 0.16/0.57 V for discharge/charge process, and a large discharge capacity of 17627.3 mAh g−1 at 100 mA g−1, far outperforming that using the pristine Ti3C2Tx (0.19/0.66 V and 13119.7 mAh g−1, respectively). Remarkably, the t-Ti3C2Tx cell achieves unprecedented cycle performances for 300 cycles under the limited capacity of 500 mAh g−1 and 200 cycles under 1000 mAh g−1 at a high rate of 2000 mA g−1, meanwhile outputting the discharge voltages above 2.5 V throughout the whole cycles. The superb catalytic capability of t-Ti3C2Tx is mainly attributed to the synergistic contributions from the uniform O termination groups, abundant intercalated Li ions, expanded interlayer spacing and the consequent increase in active sites for facile formation and decomposition processes of Li2O2 discharge product, and the suppression of excessive oxidation of Ti surface atoms.