Amino-rich surface-modified MXene as anode for hybrid aqueous proton supercapacitors with superior volumetric capacity

Supercapacitors (SCs) have attracted considerable attention due to their outstanding power density and cycling performance. In this work, the amino-rich surface functional groups (–NH– and –N+H-) surface modified Ti3C2Tx MXene nanosheets (N–Ti3C2Tx-200) are synthesized via the solvothermal method, which is accompanied by the generation of surface titanium atom defects. Moreover, kinetic analysis confirms that the surface amino-rich functional groups are in favor of the rapid hydrogen ions transmission within electrode, leading to an enhancement of capacitive capacitance. Specifically, the flexible N–Ti3C2Tx-200 electrode exhibits a volumetric capacity of 936.0 C cm−3, which is 1.49 times that of the pristine Ti3C2Tx. Further, the modified electrode even can keep a volumetric capacity of 839.7 C cm−3 at 1 V s−1, which is much higher than that of the pristine Ti3C2Tx (277.7 C cm−3). More importantly, the hybrid aqueous proton supercapacitors (HAPSs), constructed by N–Ti3C2Tx-200 anode and copper hexacyanoferrate (CuHCF) cathode, achieve a 2 V wide voltage window and an ultrahigh volumetric energy density of 104.9 Wh L−1 at 0.38 kW L−1. This work offers a basic understanding of the amino-rich surface-modified flexible Ti3C2Tx film electrodes with high volumetric energy density and high-rate performance, providing a strategy to fabricate HAPSs with superior volumetric capacity. [Display omitted] •Amino-rich surface-modified flexible Ti3C2Tx (–NH–, –N+H-) films are prepared.•The flexible N–Ti3C2Tx-200 film electrode shows a maximum capacity of 936.0 C cm−3.•The volumetric capacity of N–Ti3C2Tx-200 film can maintain 89.7% even at 1 V s−1.•The HAPSs are constructed by flexible N–Ti3C2Tx anode and CuHCF cathode.•The HAPSs achieve an energy density of 104.9 Wh L−1 with a 2 V wide voltage window.