Stimulation of surface terminating group by carbon quantum dots for improving pseudocapacitance of Ti3C2Tx MXene based electrode

Abstract

Enhancing pseudocapacitance of Ti3C2Tx MXene-based electrode materials induced by sufficient surface terminating groups (such as Ti–O bonding) becomes one promising way for fabricating high energy-density supercapacitors. However, most of terminating group activity cannot be excited well in the multilayer Ti3C2Tx due to the layer stacking feature, which limits its further performance improvement. In this paper, a CQDs@Ti3C2Tx hybrid material is synthesized by modifying few-layer Ti3C2Tx MXene matrix with highly dispersed carbon quantum dots (CQDs). In this unique hybrid model, the Ti3C2Tx MXene matrix with high conductivity and high specific surface area is just like the “paddy field”, which not only promotes the charge rapid transfer, but also provides the high double layer capacitance by ion adsorption. More importantly, the CQDs act as “rice seedlings” firmly anchored to the Ti3C2Tx matrix, and greatly stimulate the activity of the termination groups of Ti3C2Tx. As expected, this hybrid achieves a harmonious coexistence of high conductivity and high pseudocapacitance. As a result, the CQDs@Ti3C2Tx electrode delivers high reversible capacitances of 441.3 F g−1 at 1 A g−1 and 310.1 F g−1 at 20 A g−1, and a relatively stable cyclability with almost 100% capacitance retention after 10 000 cycles at 10 A g−1.