Ammonia-assisted heterocyclic amine exerts soft delamination and interlayer engineering of Ti₃C₂T_x MXene for fabricating stable supercapacitors

Abstract

The application of two-dimensional titanium carbide MXenes (Ti3C2Tx) for electrochemical energy storage and conversion has garnered considerable attention in recent years. For practical applications, gradual delamination, phase shift, and/or structural disintegration of MXene flakes in aqueous conditions are the challenges needed to be addressed. Herein, a unique and effective approach for in situ manipulation of MXene edge and surface by gentle delamination using 5-azaindole (5-Az; a heterocyclic amine) and ammonium hydroxide (NH4OH) has been developed. In the presence of NH4OH, 5-Az enables soft delamination of multilayer MXene without sonication, and more importantly, allows in situ functionalization of its surface and edges via a nucleophilic substitution reaction at the Ti-atom sites at room temperature. In addition, the easy intercalation of 5-Az in the multilayer MXene allows for an increase in its interlayer spacing when it is made into a film or electrode, which is beneficial for various electrochemical applications. The 5-Az functionalization provides exceptional stability of MXenes for up to 500 days in water at room temperature. The NH4OH-treated- and 5-Az-functionalized MXene (NH4OH-5-Az/Ti3C2Tx) shows increased interlayer spacing (1.67 nm) when compared to the MXene treated with NH4OH (NH4OH-Ti3C2Tx) (1.25 nm), enhanced ion- and charge-transport properties resulting in a remarkable specific capacitance of 631 F g(-1) at 2 A g(-1) with capacitance retention of 82 % after 150 days. Having high specific capacitance and excellent stability, the NH4OH-5-Az/Ti3C2Tx prepared through the proposed simple and effective approach holds great potential as high-performance electrodes for supercapacitors.