Two kinds of Ti 3 C 2 /TiO 2 hybrids were synthesized by room temperature oxidation methods, named as Ti 3 C 2 /TiO 2 -nanoparticles and Ti 3 C 2 /TiO 2 -nanowires, respectively. Effects of reaction time and concentration of NaOH solution on the microstructures and electrochemical performances of Ti 3 C 2 /TiO 2 composites were studied in details. When used as electrodes for supercapacitors, both Ti 3 C 2 /TiO 2 -nanoparticles and Ti 3 C 2 /TiO 2 -nanowires exhibit enhanced supercapacitive performances. The electrochemical measurement results show that the specific capacitances of Ti 3 C 2 /TiO 2 -nanoparticles and Ti 3 C 2 /TiO 2 -nanowires electrodes are 128 and 143 F/g at 2 mV/s, respectively, which are larger than that of Ti 3 C 2 MXene (91 F/g). Furthermore, after 6000 charge-discharge cycles at 5 A/g, 88% and 80% of the initial capacitances are retained for Ti 3 C 2 /TiO 2 -nanoparticles and Ti 3 C 2 /TiO 2 -nanowires, respectively. Therefore, this work not only enhances the understanding of the surface states and morphology structures of Ti 3 C 2 MXene at different reaction condition in the aqueous solutions, but also provides simple and facile ways to fabricate photocatalysts, 5-8 lithium-ion batteries 9-11 and supercapacitors.
12-14MXenes are produced by selective etching of "A" layers from M n+1 AX n (n = 1, 2, 3) phase, where M belongs to an early transition metal, A represents a IIIA or IVA element, and X is C and/or N. [15][16][17] The structures of the etched resultants are similar to the exfoliated graphite.15 Typically, MXenes are terminated by -OH, -O and/or -F surface groups (denoted as T x ), and so their general formula is M n+1 X n T x , 15,17,18 such as Ti 3 C 2 T x and Ti 2 CT x . MXenes show significant potential in energy storages benefiting from their layered structure, hydrophilic surfaces, outstanding electrical conductivity and excellent chemical stability. 10,12,13,[17][18][19][20] MXene-derived nanoribbons, formed in simultaneous oxidation and alkalization processes, also show high-performances in sodium and potassium ion batteries. 21 In addition, the electrochemical properties of MXenes and MXenesbased materials have been extensively investigated in aqueous 13,22,23 and nonaqueous electrolytes. 24,25 Notably, MXenes have been demonstrated to exhibit large pseudocapacitance, which is caused by ion intercalation between their two-dimensional nanosheets. 26,27 In order to satisfy the increasing strict requirements of energy storage devices, MXenes are motivated to exploit much better electrochemical performances. Recent studies reported that introduction of transition metal oxides into MXenes is an efficient way to improve the electrochemical properties in supercapacitors 28-31 and lithium-ion batteries 32,33 . Among the transition metal oxides, titanium dioxide (TiO 2 ) is one of the most widely investigated electrode materials, owing to its low cost, abundant availability and convenient synthesis in nanoscale sizes. [34][35][36][37] Many studies have reported different preparation...
