Pillaring effect of nanodiamonds and expanded voltage window of Ti3C2T supercapacitors in AlCl3 electrolyte

MXenes have demonstrated excellent performance as constituent materials for supercapacitor electrodes. One of the most outstanding achievements is the capacitance obtained with 2D Ti3C2Tx in H2SO4 electrolyte, which is related to the O/OH titanium surface termination redox process. However, the narrow (under 1 V) potential window of highly acidic electrolytes is a limiting feature for many applications. In this scenario, materials and electrolytes that produce high capacitance and large potential windows are highly sought after. Herein, we used nanodiamonds (NDs) to pillar the Ti3C2Tx structure and obtain superior capacitive storage in AlCl3 electrolytes. The pillaring effect prevents the restacking of MXene layers, reducing diffusion limitations and resulting in a high-rate performance with a capacitance of 235 F/g (561 F/cm3). The use of 3 M AlCl3 provided protons that contributed to the capacitance obtained and allowed an expansion of the potential window to 1.2 V, due to the lowered activity of water in the electrolyte. The results reflect the need for a proper combination of electrode architecture and electrolyte formulation while providing a direction for the exploration of more efficient, safe, and inexpensive supercapacitor devices.