Fig.3. (a) Raman spectra of MXene, MXene/AAC and AAC; (b) XRD imaged of MXene, MXene/AAC and AAC; (c) Nitrogen adsorption isotherms of MXene and MXene/AAC 2:1; (d) Pore size distribution of MXene and MXene/AAC 2:1; (e) C 1s spectra of MXene/AAC 2:1;(f) Ti 2p spectra of MXene/AAC 2:1
In order to confirm that the enhanced interlayer spacing observed in ATM is statistically significant. X-ray diffraction (XRD) patterms are performed for pure MXene, MXene/AAC 5:1, MXene/AAC 2:1 and AAC composites and shown in Fig.3. (b). The MXene film exhibits a peak (002) at about 2θ=7.5°, corresponding to d-spacing values of 12.62 Å. The peaks corresponding to the (002) plane of MXene/AAC 2:1 and MXene/AAC 5:1 downshift to about 2θ=7.06° and 2θ=6.07° which demonstrates a 3.0 Å and 4.2 Å in the c -lattice parameter (c -LP) and 1.5 Å and 2.1 Å increase the d -spacing, respectively. In the pure AAC, a broad peak at 2θ=25° is observed, demonstrating exceptional graphitization, which further proved the stability of the composite after chemical treatment. In addition, the intensity of (002) peaks decreases with the increase of AAC content, indicating that the order between MXene layers is interrupted due to hybridization with AAC. Besides, all MXene/AAC composites have the broad peak (002) of AAC particles which confirms manufacturing of MXene/AAC. However, the intercalation of AAC into MXene layers could reduce material density and electrical conductivity. As shown in Table S1. The MXene composite has an electrical conductivity of 3206 S cm-1 and a material density of 2.01 g cm-3. Nevertheless, the electrical conductivity and material density decrease with the increase of AAC mass ratio. Besides, the MXene/AAC 2:1 and MXene/AAC 5:1 exhibit a quite low material density of 0.309 and 0.406 g cm-3 with the electrical conductivity of 191 and 357 S cm-1, respectively. In contrast, with the increase of AAC mass ratio, the specific surface area (BET) and specific volume (Vtotal) of MXene/AAC increase. The pure MXene shows a much lower BET (18.92 m2g-1) and Vtotal(0.008 cm3g-1) than MXene/AAC 2:1 hybrid (1651 m2g-1 and 1.07 cm3g-1). Due to the large surface areas and abundant specific volume, the electrochemical performance of MXene/AAC are greatly enhanced.
The microstructure and exposed surface area of the as-prepared hybrid are examined by the nitrogen (77K) adsorption-desorption measurement. Fig.3. (c-d) show the nitrogen adsorption isotherms and pore size distributions of pure MXene and MXene/AAC 2:1. The MXene/AAC 2:1 particles present a combination of type-Ⅰ and type-Ⅱ isotherms, demonstrating that the microporous-mesoporous structure which could be ascribed to the incorporation of AAC between MXene layers. Fig.3. (a) presents Raman spectra of the pure MXene and MXene/AAC composite. The Raman spectra of MXene and MXene/AAC are similar in the range of 100 to 800 cm-1. The MXene has a sharp peak at about 150 cm-1 and broad peaks at about 370 cm-1 and 619 cm-1, which are distinctive feature of MXene. On the other hand, the peaks at about 1275 and 1572 cm-1 represent as the D-band and G-band, respectively which are signatures of carbon and confirm the incorporation of MXene and AAC. The D-band corresponds to defects and relates to zone boundary k -point phonons and the G-band is due to collective symmetric stretching of sp2 carbon lattice. The ratio of the D-band and G-band (I D/I G) which proportional to the defect sites in graphitic carbon is 1.29 which could calculate the corresponding sp2 crystallite size to be 9.8 nm according to the followed formula.
\(L_{a}\left(\text{nm}\right)=560/E_{\text{laser}}^{4}(\frac{I_{D}}{I_{G}})\)-1(6)
Where \(L_{a}\) is the average sp2 crystallite size,E laser is the laster excitation energy in eV.
In order to further investigate the mechanism and chemical compositions of synthesized MXene/AAC interaction, X-ray photoelectron spectroscopy (XPS) was employed to examine the chemical composition and surface electronic states and the corresponding images exhibited in Fig.3. (c-d) and Fig. S3 (a-c). The XPS survey spectra as shown in Fig. S3 (a) demonstrate that the MXene/AAC hybrids are mainly composed of C, Ti, O, N and F. High-resolution XPS spectrum in the Ti 2p region (Fig.3. (d)) core levels of MXene/AAC 2:1 hybrids could be deconvoluted into six peaks with components corresponding to Ti-C, Ti(Ⅱ), Ti(Ⅲ) and Ti-O peaks. The Ti 2p core level can be fitted with three doublets (Ti 2p3/2-Ti 2p1/2) which in agreement with other papers(尚). The Ti 2p3/2 components mainly located at binding energy of 458.6, 459.1, 463.3 and 464.9 eV correspond to Ti-C 2p3/2, Ti-O 2p3/2, C-Ti-Tx 2p1/2 and Ti-O 2p1/2, respectively, demonstrating the interaction between MXene and AAC particles at the sites of oxygen dangling bonds. However, the XRD spectrum exhibits no peaks for TiO2.The Raman pattern of MXene/AAC exhibits similar vibrations in the shift range 100-800 cm-1, demonstrating that the appearance of Ti-O peak mainly comes from the MXene-to-AAC contact area31, 32. The C 1s core level (Fig.3. (c)) could be fitted with five components at binding energy of 284.1, 284.8, 286.3, 286.6, and 288.9 eV, which could be assigned to C-Ti-O, Ti-O, C-C, C-N, C-O and O=C-O bonds, respectively. confirming the interaction between MXene layers and AAC particles33, 34. Fig.S3. (b) exhibits the N 1s core level mainly centered at binding energy of 397.6, 398.8 and 399.9 eV which could be accordingly assigned to Ti-N, pyridinic N and pyrrolic N, respectively. Fig.S3. (c) exhibits the O 1s core level which could be fitted with three components at binding energy of 530.4, 531.8 and 532.9 eV which further confirm the interaction between MXene flake and AAC particles. The result is in good agreement with the TEM observation.