Ti3C2Tx/CDs@MnO2 Composite as Electrode Materials for Supercapacitors: Synthesis and Electrochemical Performance

Ti3C2Tx/CDs@MnO2 Composite as Electrode Materials for Supercapacitors: Synthesis and Electrochemical Performance | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Ti3C2Tx/CDs@MnO2 Composite as Electrode Materials for Supercapacitors: Synthesis and Electrochemical Performance Tianwang Li, Xiaosong Wei, Yalin Zhang, Yanqing Cai, Xinggang Chen, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4424610/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 10 You are reading this latest preprint version Abstract MXenes are a kind of novel and interesting new materials, and carbon dots (CDs) are also concerned because of their processability, versatility, environmental protection and low cost. Both MXenes and CDs are chemically stable and have a large surface area and high electrical conductivity, which are promising alternative electrode materials for supercapacitors. Moreover, MnO 2 can also improve the energy density of the electrode materials. In this paper, Ti 3 C 2 T x /CDs and Ti 3 C 2 T x /CDs@MnO 2 composites were prepared by a hydrothermal method and their supercapacitor performance were also investigated by a series of electrochemical methods. From the CV profile in a three-electrode system, Ti 3 C 2 T x /CDs@MnO 2 electrode exhibited a high specific capacitance of 281.3 F g − 1 at a scan rate of 5 mV s − 1 , which was higher than that of Ti 3 C 2 T x /CDs (160.3 F g − 1 ). The Ti 3 C 2 T x /CDs showed a good cycling stability with a capacitance retention of 82.38% after 10,000 cycles. Meanwhile, a symmetric supercapacitor was successfully assembled using Ti 3 C 2 T x /CDs@MnO 2 as electrodes, with an energy density of 5.77 Wh kg − 1 at a corresponding power density of 120 W kg − 1 . This work offers a theoretical foundation and a technological path for synthesizing highly effective ternary composite of MXene-based as energy storage materials. Ti3C2Tx Carbon dots MnO2 Supercapacitor Electrochemical performance Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1. Introduction With the energy and environmental challenges posed by fossil fuel depletion, there is an urgent need to promote green and clean energy alternatives. Renewable energy sources such as solar, tidal and wind power have become the key to solving this problem. However, due to the huge volatility and intermittency of the renewable energy sources, they also face the problem of efficient storage of these energy sources [ 1 – 3 ]. In the field of energy storage, batteries and supercapacitors are the two leading electrochemical energy storage technologies that deserve the most attention. Supercapacitors can be charged and discharged quickly at a power density of more than 1 kW kg − 1 , which have a short charging time, a wide range of operating temperatures, and a long cycle life (100,000 cycles) [ 4 – 7 ]. However, although supercapacitors are able to provide a higher energy density than conventional capacitors, it still needs to improve their electrochemical performance. The development of new electrode materials is crucial to improve the performance of supercapacitors [ 8 , 9 ]. MXenes (M n+1 X n T x ) are a kind of general term for two-dimensional (2D) transition metal carbides/nitrides/nitrogen-containing compounds [ 10 – 13 ]. Generally, MXenes are obtained by selectively removing the A atoms in the parent MAX phases interlayer. “M” represents transition metals such as Ti, Mo, V, Cr, etc., “X” represents C and/or N, and “T x ” represents surface terminations introduced during the preparation process, such as -OH, -O, -F [ 14 ]. Among various MXenes, Ti 3 C 2 T x is the most representative and extensively investigated one. Renowned for its elevated specific surface area, superior conductivity, and distinctive layered arrangement, Ti 3 C 2 T x has garnered significant attention in research on electrode materials of supercapacitor. The characteristic layered structure facilitates efficient ion conduction and the intercalation of various small molecules. Therefore, 2D Ti 3 C 2 T x has great potential for use as an electrode material for supercapacitors [ 15 , 16 ]. Nonetheless, challenges persist with etched Ti 3 C 2 T x materials, notably concerning restacking and oxidation, which constrain their widespread utilization in the domain of supercapacitors [ 15 , 17 , 18 ]. Hence, it is necessary to further improve the structure and performance of Ti 3 C 2 T x . Mostly, the intercalation of various small molecules or carbon materials (e.g. carbon dots) is one of the common ways to improve above problems. Carbon dots (CDs) inherently possess rich surface defects, robust chemical stability, abundant raw materials, and cost-effectiveness, rendering them promising for diverse applications within the energy field [ 17 , 19 – 21 ]. Biomass-derived CDs are typically derived from organic small molecules (e.g. glucose, sucrose) abundant in functional groups such as hydroxyl, carboxyl, and carbonyl. Nonetheless, CDs are rarely used alone as electrode materials for supercapacitors, which may be due to the decrease of hydrophilicity and specific surface area caused by agglomeration, as well as the internal resistance of the interface caused by a large number of small size nano effects [ 20 ]. Some researchers found that biomass-derived CDs could expand the interlayer spacing of MXenes, which facilitate the electrolyte ion transport while mitigating the aggregation of MXenes [ 22 , 23 ]. Recently, Devadas et al. [ 24 ] synthesized PPy@CDs and PANI@CDs using the synergistic effect of CDs and conductive polymers, with specific capacitances of 676 and 529 F g -1 at a current density of 1 A g -1 , respectively. Li et al. [ 25 ] prepared CDs/Ti 3 C 2 T x hybrid films with 0D/2D spot motif structure and used them as electrode materials. The optimized freestanding film electrode from pomelo juice as CDs with suitable layer spacing and profuse heteroatom doping indicates a high volumetric capacitance of 984.5 F cm -3 at a scan rate of 2 mV s -1 , and an excellent volumetric energy density of 19.42 Wh L -1 was obtained in the corresponding assembled asymmetric supercapacitor. From previous studies, it can be known that CDs are often used to compound with other materials to improve specific capacitance, which are due to its effect of enhancing electron transport and ion migration in charge/discharge process and accelerating redox reaction. And most importantly, the CDs embedded between Ti 3 C 2 T x layers can prevent the restacking of Ti 3 C 2 T x and improve the electrochemical performances. As a pseudocapacitive material, MnO 2 has a high theoretical specific capacitance of 1370 F g − 1 , abundant reserves, and environmentally friendly characteristics, rendering it a promising candidate for energy storage [ 26 – 28 ]. However, the practical applications of MnO 2 are hindered by its low wettability, conductivity, and cycling stability. Vetrikarasan et al. [ 26 ] prepared Ti 3 C 2 T x @λ-MnO 2 nanoplate electrode with a specific capacitance of 255 F g − 1 , addressing some of these challenges. Therefore, a composite material with high specific capacitance can be prepared by the synergistic action of MnO 2 and Ti 3 C 2 T x . Herein, a novel Ti 3 C 2 T x /CDs@MnO 2 composite was synthesized with a two-step hydrothermal method by coating the Ti 3 C 2 T x /CDs surface with the pseudocapacitive material MnO 2 . Sucrose was chosen as the precursor of CDs, which can expand the interlayer spacing of Ti 3 C 2 T x , and prevent the restacking of layers. Subsequently, the phase, morphology, and specific surface area of composites were comprehensive characterized. Furthermore, the electrochemical performances of the composites were measured by a series of electrochemical test methods. The primary goal is to create a novel composite electrode material that exhibits high specific capacitance, increased energy density, and outstanding cycling stability. According to our findings, CDs has successfully inserted between layers and increased layer spacing of Ti 3 C 2 T x /CDs and electrochemical sites, and higher specific capacitance and cycle stability have obtained finally. Furthermore, incorporating MnO 2 has also improved the capacitance and energy density of Ti 3 C 2 T x /CDs composite. These unique properties of the Ti 3 C 2 T x /CDs@MnO 2 composite result in a high specific surface area, high magnification capability and excellent cycling characteristics for supercapacitors applications. As such, this work offers a promising idea for further research into developing novel MXene-based electrode materials for supercapacitors. 2. Experimental section 2.1 Preparation of Ti 3 C 2 T x /CDs materials The schematic diagram of the preparation process for Ti 3 C 2 T x /CDs and Ti 3 C 2 T x /CDs@MnO 2 was shown in Fig. 1. Ti 3 AlC 2 was prepared by HF-etching method [ 29 ]. 80 mL of HF solution with a 40% volume fraction was utilized to etch 5g of Ti 3 AlC 2 . Firstly, Ti 3 AlC 2 was etched by HF and Ti 3 C 2 was obtained, as shown in Eq. (1)~(3). The Eq. (1)~(3) describes the etching mechanism of Ti 3 AlC 2 and formation of the surface functional groups [ 18 , 30 , 31 ]. TiAlC 2 (s) + 3HF(aq.) → Ti 3 C 2 (s) + AlF 3 (aq.) + 3/2H 2 (g) (1) Ti 3 C 2 (s) + 2HF(aq.) → Ti 3 C 2 F 2 (s) + H 2 (g) (2) Ti 3 C 2 (s) + 2H 2 O(aq.) → Ti 3 C 2 (OH) 2 (s) + H 2 (g) (3) Equation (1) represents the primary reaction for forming the Ti 3 C 2 phase. Equations (2) and (3) correspond to the formation of surface terminal -OH and -F groups, respectively, resulting in the formation of Ti 3 C 2 (OH) 2 and Ti 3 C 2 F 2 . After being heated to 40°C in a magnetic agitator and continuously swirled for 72 hours, the solution was filtered and centrifuged, then adjust the pH to approximately 7.0. It was then dried for 12 hours at 60°C in a vacuum drying oven. Weigh 3g of sucrose and 0.3g of dry Ti 3 C 2 T x and dissolve them in 150 mL of deionized water. After ultrasonic for 30min, the solution was placed in a high-pressure reactor, stirred at a certain rate and constant speed in an oil bath, reacted at 160℃ for 24h, pumped and filtered, and dried at 60℃ for 12h under vacuum to prepare Ti 3 C 2 T x /CDs composite. 2.2 Preparation of Ti 3 C 2 T x /CDs@MnO 2 materials With KMnO 4 as the manganese source, 0.16 g KMnO 4 and 0.2 g of the above prepared Ti 3 C 2 T x /CDs were dissolved in 100mL deionized water, ultrasonic for 30min, the solution was placed in a high-pressure reactor, stirred at a certain rate and constant speed in an oil bath, reacted at 100℃ for 24h, pumped and filtered, and dried in a vacuum at 60℃ for 12h. Ti 3 C 2 T x /CDs@MnO 2 composite was prepared, as was shown in Fig. 1. 2.3 Material Characterization The elements, morphology, and crystal structure of Ti 3 C 2 T x , Ti 3 C 2 T x /CDs, and Ti 3 C 2 T x /CDs@MnO 2 were examined with an electron energy spectrometer (EDS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The pore distribution and specific surface area of Ti 3 C 2 T x /CDs@MnO 2 , Ti 3 C 2 T x /CDs, and Ti 3 C 2 T x were measured and examined by the nitrogen adsorption and desorption test (BET). The phases of Ti 3 C 2 T x /CDs@MnO 2 , Ti 3 C 2 T x /CDs, and Ti 3 C 2 T x were determined through X-ray diffraction (XRD). 2.4 Electrochemical Characterization For electrochemical tests, the working electrode was first prepared by coating a slurry (Ti 3 C 2 T x , Ti 3 C 2 T x /CDs or Ti 3 C 2 T x /CDs@MnO 2 , acetylene black, PVDF (8:1:1)) onto foamed nickel current collector and dried at 120°C under vacuum for 12h. The slurry was evenly mixed with 0.1g of the active substance (Ti 3 C 2 T x , Ti 3 C 2 T x /CDs or Ti 3 C 2 T x /CDs@MnO 2 ), 0.018g of the conductive agent (acetylene black), 0.006g of the binder (polyvinylidene fluoride, PVDF), and 4mL of the dispersion (N-methyl-2-pyrrolidone). The electrode substrate was sliced with a dry nickel sheet and a microtome with a diameter of 0.5 cm. A button battery was constructed symmetrically from two electrodes of comparable quality, with the electrolyte containing a 6 mol L − 1 KOH solution. A suitable electrode plate was identified to create a three-electrode system for asymmetric electrode testing, with Pt electrode counter electrode, electrode coated with active substance as working electrode, Hg/HgO electrode as reference electrode. and a 6mol L − 1 KOH solution operating as the electrolyte. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge (GCD) tests were carried out by a CHI660e (Shanghai Chenhua Instrument Co, LTD). 3. Results and discussion 3.1 Structural and composition characterization To observe the morphology and composition of the Ti 3 C 2 T x , Ti 3 C 2 T x /CDs, and Ti 3 C 2 T x /CDs@MnO 2 , SEM-EDS and TEM analyses were performed and the results were shown in Fig. 2 and Fig. 3 . Figure 2 a shows the SEM image of Ti 3 C 2 T x obtained after etching with HF. The image reveals that Ti 3 C 2 T x possesses a distinct layered structure with a relatively smooth surface, creating favorable conditions for small molecules to penetrate its interlayers and modify its surface structure [ 12 ]. Figure 2 b displays the morphology of Ti 3 C 2 T x /CDs synthesized via the hydrothermal method. The surface of Ti 3 C 2 T x modified by CDs appears rougher, effectively preventing the restacking of Ti 3 C 2 T x . This rough surface also provides favorable conditions for subsequent surface coating of MnO 2 [ 26 ]. Ti 3 C 2 T x /CDs and KMnO 4 with good hydrophilicity were uniformly dispersed in water. After 30min of ultrasound, the rough surface of Ti 3 C 2 T x /CDs was conducive to the adsorption of MnO- 4, and the reductive property of CDs could reduce KMnO 4 to MnO 2 on the surface of Ti 3 C 2 T x /CDs at high temperature. Furthermore, Fig. 2 c presents the SEM image of the Ti 3 C 2 T x /CDs@MnO 2 composite, the image demonstrates the relatively uniform coverage of MnO 2 on the surface of Ti 3 C 2 T x . In addition, the corresponding EDS of the Ti 3 C 2 T x /CDs@MnO 2 composite in Fig. 2 c are presented in Figs. 2 d-f, which display the elemental mapping for Mn, O, and C. Figure 2 g illustrates the surface scan spectrum and element content of Fig. 2 c. The above results indicated that Ti 3 C 2 T x /CDs@MnO 2 composite was successfully prepared, with carbon and manganese elements distributed relatively uniformly on Ti 3 C 2 T x . Figure 3 a shows the TEM image of Ti 3 C 2 T x /CDs, indicating the successful infiltration of sucrose into Ti 3 C 2 T x to form CDs. The larger shaded areas in the image correspond to well-crystallized CDs. Figure 3 b presents the electron diffraction pattern of Ti 3 C 2 T x /CDs, exhibiting a series of neatly arranged spots. This diffraction pattern consists of concentric rings with varying radii, reflecting the polycrystalline nature of CDs [ 16 ]. Figure 3 c shows the TEM image of Ti 3 C 2 T x /CDs@MnO 2 , illustrating the successful deposition of MnO 2 onto the surface of Ti 3 C 2 T x /CDs. According to the Bragg equation, the measured interplanar spacing d is 0.22nm, which corresponds to the (200) crystal plane of MnO 2 . Lastly, Fig. 3 d exhibits the electron diffraction pattern of Ti 3 C 2 T x /CDs@MnO 2 , showing a series of concentric rings with varying radii [ 26 , 32 ]. It further confirms the successful coating of polycrystalline MnO 2 and demonstrates the successful preparation of Ti 3 C 2 T x /CDs@MnO 2 . Table 1 Structural Parameters and Capacitive Performances of the Samples. samples S BET (m 2 g − 1 ) V t (cm 3 g − 1 ) D a (nm) R e (Ω) R ct (Ω) Ti 3 C 2 T x 7.26 0.055 30.57 5.25 0.2 Ti 3 C 2 T x /CDs 17.31 0.081 18.69 2.94 0.28 Ti 3 C 2 T x /CDs@MnO 2 53.39 0.127 9.48 0.96 0.55 V t : Total pore volume measured at a relative pressure of 0.99. D a : Average pore diameter analyzed using the BJH method. R e : Series resistance. R ct : Charge-transfer resistance. XRD patterns of Ti 3 C 2 T x , Ti 3 C 2 T x /CDs, and Ti 3 C 2 T x /CDs@MnO 2 samples were performed to reveal the combination mechanism, as shown in Fig. 4 a. The distinct peaks observed in Fig. 4 a at 2θ values of 8.9°, 18.1°, 27.3°, and 60.6° correspond to the (002), (006), (008), and (110) crystal planes of Ti 3 C 2 T x , respectively [ 25 , 33 ]. 2theta of 36.8° may indicate that part of Ti 3 C 2 T x was oxidized to TiO 2 .These patterns provide valuable insights into the crystalline structure of Ti 3 C 2 T x samples. In the XRD pattern of Ti 3 C 2 T x /CDs, the characteristic peaks corresponding to Ti 3 C 2 T x exhibit varying degrees of attenuation, reflecting a decrement in the crystallinity of Ti 3 C 2 T x following the integration of polycrystalline CDs. Notably, the characteristic peak associated with the (002) crystal plane shifts slightly from 8.9° to 8.76°. According to the Bragg equation, this shift implies that CDs infiltrate the interlayers of Ti 3 C 2 T x , slightly enlarging the interlayer spacing, thereby exposing more redox-active sites conducive to oxidation-reduction reactions. Moreover, the presence of CDs effectively mitigates the oxidation of Ti 3 C 2 T x , ultimately enhancing the performance of supercapacitors. In contrast, the XRD pattern of Ti 3 C 2 T x /CDs@MnO 2 reveals a significant reduction in the characteristic peaks of Ti 3 C 2 T x . Remarkably, the peak corresponding to the (002) crystal plane undergoes a more pronounced shift from 8.9° to 6.8°. Based on the Bragg equation, this shift indicates that the combined effect of CDs and polycrystalline MnO 2 further widens the interlayer spacing of Ti 3 C 2 T x . The calculation results reveal an enlarged interlayer spacing (Δd) of 0.3202nm, suggesting that Ti 3 C 2 T x /CDs@MnO 2 possesses a greater interlayer spacing, thus exposing even more redox-active sites for oxidation-reduction reactions. Additionally, the coating of MnO 2 contributes additional pseudo-capacitance, further improving the electrochemical performance of supercapacitors. Figure 4 b shows the N 2 adsorption-desorption isotherms of Ti 3 C 2 T x , Ti 3 C 2 T x /CDs, and Ti 3 C 2 T x /CDs@MnO 2 samples. All three samples exhibit distinct type IV adsorption isotherm features and H 3 hysteresis loops within the relative pressure range of 0.45 ~ 1.0. This hysteresis behavior is characteristic of slit-like pores that are formed between the layers of Ti 3 C 2 T x , indicating that all three samples possess mesoporous structures. Table 1 shows the pore structure parameters of the three samples calculated by BET method, the specific surface areas of Ti 3 C 2 T x , Ti 3 C 2 T x /CDs, and Ti 3 C 2 T x /CDs@MnO 2 are 7.26, 17.31, and 53.39 m 2 g -1 , respectively. The introduction of CDs and MnO 2 results in a remarkable increase in the materials' specific surface areas, potentially leading to superior performance in electrochemical applications, such as supercapacitors. The specific surface area of Ti 3 C 2 T x /CDs is notably higher than that of Ti 3 C 2 T x , presumably due to the insertion of CDs into the interlayers of Ti 3 C 2 T x , which enlarges the interlayer spacing and consequently boosts the specific surface area [ 34 ]. Furthermore, Ti 3 C 2 T x /CDs@MnO 2 exhibits an even larger specific surface area, significantly surpassing Ti 3 C 2 T x . This significant enhancement may be attributed to the synergistic effect of CDs and MnO 2 in further expanding the interlayer spacing of Ti 3 C 2 T x , ultimately resulting in a larger specific surface area for Ti 3 C 2 T x /CDs@MnO 2 . From the other structural parameters of the three samples in Table 1 , it shows a gradual increase in the total pore volume (V t ) and a corresponding decrease in the average pore diameter (D a ). These changes are advantageous for electrochemical applications as they enhance the effective contact area between the electrolyte and electrode material. An increased total pore volume and reduced pore diameter promote ion accessibility and charge transfer, significantly improving the electrochemical performance of the composites [ 35 ]. 3.2 Electrochemical Performances in the Three-Electrode System In order to evaluate the electrochemical behavior and quantify the charge storage capacity of Ti 3 C 2 T x /CDs and Ti 3 C 2 T x /CDs@MnO 2 , the above two materials were prepared as active electrode materials for supercapacitors. CV curves and Nyquist plots of the two electrode materials were measured in 6M KOH electrolyte using a three-electrode system, as shown in Fig. 5 . Figure 5 a presents the CV curves of Ti 3 C 2 T x /CDs at various scan rates, revealing an almost rectangular shape within the three-electrode system [ 14 , 17 ]. This observation indicates the excellent capacitive behavior and high reversibility of Ti 3 C 2 T x /CDs, making it a promising candidate for supercapacitor. Figure 5 b displays the CV curves of Ti 3 C 2 T x /CDs@MnO 2 at different scan rates. Compared to Ti 3 C 2 T x /CDs, the image undergoes noticeable distortion due to pseudo-capacitance. For a direct comparison, Fig. 5 c compares the gravimetric capacitance of three samples at different scanning rates, Ti 3 C 2 T x /CDs demonstrates a specific capacitance of 160.3 F g − 1 at a scan rate of 5 mV s − 1 , maintaining a respectable value of 113.5 F g − 1 even at a higher scan rate of 200 mV s − 1 , with a capacitance retention of 70%. This compares favorably to Ti 3 C 2 T x , which exhibits a specific capacitance of 86.1 F g − 1 . In the case of Ti 3 C 2 T x /CDs@MnO 2 , an even higher specific capacitance of 281.3 F g − 1 is achieved at a scan rate of 5 mV s − 1 , retaining a value of 168.9 F g − 1 at 200 mV s − 1 with a capacitance retention of 60%. It is also proved that Ti 3 C 2 T x /CDs@MnO 2 has excellent energy storage performance. Figure 5 d shows the Nyquist plots of the three samples, each exhibiting characteristic capacitive behaviors. The plots exhibit arc shapes in the high-frequency region, followed by straight lines in the low-frequency region, indicative of ideal capacitive performance [ 36 ]. The calculated equivalent series resistance (R e ) of Ti 3 C 2 T x , Ti 3 C 2 T x /CDs and Ti 3 C 2 T x /CDs@MnO 2 are 1.24, 0.937, 0.964Ω and charge transfer resistance (R ct ) 0.32, 0.286, 0.412Ω, respectively. The total resistance (R tot ) is 1.56, 1.22, 1.376Ω, respectively, indicating that Ti 3 C 2 T x /CDs and Ti 3 C 2 T x /CDs@MnO 2 have lower R tot and better electrochemical performance than Ti 3 C 2 T x . 3.3 Electrochemical Properties in Symmetrical System The above analysis results of the structure and morphology of Ti 3 C 2 T x /CDs and Ti 3 C 2 T x /CDs@MnO 2 composites show that they have larger specific surface area and larger pore volume, and are expected to be prepared as electrode materials for supercapacitors with excellent performance. Therefore, the button-type symmetric supercapacitors were assembled with Ti 3 C 2 T x /CDs or Ti 3 C 2 T x /CDs@MnO 2 as positive and negative electrodes, respectively, and then the electrochemical performance was tested to further evaluate their performance. The CV curves of Ti 3 C 2 T x /CDs at different scan rates (5 ~ 200 mV s -1 ) are shown in Fig. 6 a. It can be seen that the CV curves of Ti 3 C 2 T x /CDs exhibit an almost rectangular shape, which remains approximately rectangular as the scan rate increases. This indicates that Ti 3 C 2 T x /CDs possesses good rate capability and ideal capacitive behavior [ 14 , 26 ]. Figure 6 b shows the CV curves of Ti 3 C 2 T x /CDs@MnO 2 across various scan rates. Due to the introduction of the pseudo-capacitor material MnO 2 , the CV curve of Ti 3 C 2 T x /CDs@MnO 2 obviously deviates from the rectangle. These peaks reflect the electrochemical reactions occurring within the material, enhancing its capacitive behavior [ 37 ]. The enclosed area of the CV curves serves as a metric for material capacitance. Figure 6 c compares the CV curves of Ti 3 C 2 T x , Ti 3 C 2 T x /CDs, and Ti 3 C 2 T x /CDs@MnO 2 at a fixed scan rate of 20 mV s -1 . Notably, the enclosed areas increase in the order of Ti 3 C 2 T x , Ti 3 C 2 T x /CDs, and Ti 3 C 2 T x /CDs@MnO 2 , directly correlating with their increasing specific capacitance. This trend underscores the superior capacitive performance of Ti 3 C 2 T x /CDs@MnO 2 compared to the other samples. Figure 6 d presents the calculated specific capacitance values for the three samples across different scan rates. Ti 3 C 2 T x /CDs demonstrates a specific capacitance of 143.6 F g -1 at a scan rate of 5 mV s -1 , maintaining a respectable value of 112.5 F g -1 even at a higher scan rate of 200 mV s -1 , with a capacitance retention of 78%. This compares favorably to Ti 3 C 2 T x , which exhibits a specific capacitance of 86.1 F g -1 . In the case of Ti 3 C 2 T x /CDs@MnO 2 , an even higher specific capacitance of 300.3 F g -1 is achieved at a scan rate of 5 mV s -1 , retaining a value of 137.3 F g -1 at 200 mV s -1 with a capacitance retention of 46%. These results indicate that Ti 3 C 2 T x /CDs@MnO 2 consistently outperforms the other samples regarding specific capacitance. Figures 7 a and b show the GCD curves of Ti 3 C 2 T x /CDs and Ti 3 C 2 T x /CDs@MnO 2 at various current densities. For Ti 3 C 2 T x /CDs, the GCD curve within the voltage range of -0.3 to 0.8 V exhibits a nearly linear and symmetric shape, indicating minimal IR drop[ 10 , 15 ]. Conversely, the GCD curve of Ti 3 C 2 T x /CDs@MnO 2 deviates from linearity and symmetry due to the coexistence of double-layer capacitance and pseudo-capacitance mechanisms [ 37 ]. Ti 3 C 2 T x /CDs@MnO 2 demonstrates a significantly longer discharge time at lower current densities than Ti 3 C 2 T x and Ti 3 C 2 T x /CDs, suggesting a higher specific capacitance. This enhancement in capacitance can be ascribed to the efficient charge transfer occurring at the interface between the Ti 3 C 2 T x layer and MnO 2 . However, it's worth noting that MnO 2 primarily relies on chemical reactions for energy storage, decreasing discharge time for Ti 3 C 2 T x /CDs@MnO 2 at higher current densities [ 38 ]. Figure 7 c shows the specific capacitance of three distinct samples at various current densities. Notably, Ti 3 C 2 T x /CDs@MnO 2 exhibits an impressive mass-specific capacitance of 266 F g -1 at a current density of 0.1 A g -1 . On the other hand, Ti 3 C 2 T x /CDs demonstrates a mass-specific capacitance of 166 F g -1 at 0.1 A g -1 , which gracefully decreases to 120 F g -1 at 4 A g -1 , maintaining a capacitance retention rate of 72.3%. This exceptional rate performance confirms its reliability under varying conditions. Lastly, Fig. 7 d compares the Ragone plots of symmetric capacitors, revealing that Ti 3 C 2 T x achieves an energy density of 2.92 Wh kg -1 at a power density of 125 W kg -1 . Obviously, Ti 3 C 2 T x /CDs and Ti 3 C 2 T x /CDs@MnO 2 surpass this performance, with Ti 3 C 2 T x /CDs reaching an energy density of 5.21 Wh kg -1 at a power density of 114 W kg -1 , and Ti 3 C 2 T x /CDs@MnO 2 achieving an energy density of 5.77 Wh kg -1 at a power density of 120 W kg -1 . In summary, Ti 3 C 2 T x /CDs and Ti 3 C 2 T x /CDs@MnO 2 exhibit superior energy density and storage performance, making them promising candidates for electrochemical applications. The Nyquist plots of three types of samples are shown in Fig. 8 a, which reveal that all three samples exhibit arc shapes in the high-frequency region and linear shapes in the low-frequency region, demonstrating ideal capacitive characteristics. The results show that the R e of Ti 3 C 2 T x , Ti 3 C 2 T x /CDs, Ti 3 C 2 T x /CDs@MnO 2 are 1.06, 0.54, 0.82Ω, and R ct are 0.52, 0.73, 0.5Ω, respectively. Ti 3 C 2 T x /CDs exhibit the smallest R ct but the largest R e among them. This may be attributed to the presence of CDs, which partly improves the hydrophilicity issue of Ti 3 C 2 T x and simultaneously expands the interlayer spacing of Ti 3 C 2 T x to facilitate sufficient contact between Ti 3 C 2 T x /CDs and the electrolyte, thereby promoting charge transfer and resulting in a significant decrease in R ct compared to Ti 3 C 2 T x . However, the nanoscale interface resistance generated by CDs may increase R e [ 39 ]. For Ti 3 C 2 T x /CDs@MnO 2 , the relatively small R ct might be due to the synergistic effect of CDs and polycrystalline MnO 2 , which further expand the interlayer spacing of Ti 3 C 2 T x and increase the pore volume, facilitating better contact with the electrolyte and thus reducing R ct . Nevertheless, the low wettability and conductivity of MnO 2 can increase R ct , with the former effect outweighing the latter, resulting in a macroscopic decrease in R ct [ 37 ]. Moreover, the sloped lines in the low-frequency region represent the ability of ions in the electrolyte to diffuse on the electrode surface, with Ti 3 C 2 T x /CDs exhibiting the steepest slope, indicating that the electrode surface of Ti 3 C 2 T x /CDs is conducive to ion diffusion in the electrolyte [ 25 , 40 ]. Figures 8 b,c respectively illustrate the cyclic stability of Ti 3 C 2 T x /CDs and Ti 3 C 2 T x /CDs@MnO 2 at a current density of 0.4 A g -1 . After 10,000 cycles of constant current charge and discharge, Ti 3 C 2 T x /CDs maintain a capacitance retention rate of 82.38%, indicating excellent electrochemical stability. Ti 3 C 2 T x /CDs@MnO 2 retains 80.77% of its capacitance after 2500 cycles of constant current charge and discharge, displaying relatively superior electrochemical stability. 4. Conclusion To enhance the performance of MXene-based supercapacitors, this work initially utilized sucrose as the precursor of biomass-derived CDs to intercalate into the interlayer of Ti 3 C 2 T x . Subsequently, MnO 2 was coated on the surface of Ti 3 C 2 T x /CDs using KMnO 4 as the manganese source, and a ternary Ti 3 C 2 T x /CDs@MnO 2 composite was synthesized to further enhance the energy storage capabilities of MXene-based materials. The results revealed that CDs prevented the restacking of Ti 3 C 2 T x , widened the interlayer distance, and provided additional redox reaction sites. Ti 3 C 2 T x /CDs demonstrated remarkable mass-specific capacitance (160.3F g − 1 at 5 mV s − 1 ) and long-term cycling stability (82.38% retention rate after 10,000 cycles). Following the surface coating with MnO 2 , Ti 3 C 2 T x /CDs@MnO 2 exhibited a specific surface area of 53.39m 2 g − 1 , increased redox reaction sites, significantly improved energy storage performance (300.3 F g − 1 at 5 mV s − 1 ), and higher energy density (5.77Wh kg − 1 at 120 W kg − 1 ), indicating promising prospects for broad applications in energy storage. The results indicated that organic small molecules, such as sucrose, can serve as precursors to form CDs and hinder the restacking of MXene-based materials. Additionally, surface coating with pseudocapacitive materials like MnO 2 can enhance the energy storage performance of composites. This study offers a pathway for synthesizing MXene-based ternary composite energy storage materials with superior performance. Declarations Competing interests The authors have no relevant financial or non-financial interests to disclose. Funding This work was supported by Hebei Provincial Basic Research Business Fee Research Project for Provincial Universities (No. JST2022005) and Hebei Provincial College Students' Innovation and Entrepreneurship Training Project (T2023006, 202310081003). Author Contribution Tianwang Li: Investigation, Writing—original draft, Methodology, Formal analysis. Yanqing Cai and Xinggang Chen: Writing—review & editing, administration, Formal analysis, Investigation. Xiaosong Wei Wang: Formal analysis. Yalin Zhang: Data Curation, Data analysis. Ying Xu: Data Curation, Investigation. Acknowledgement The authors thank the North China University of Science and Technology for providing the key laboratory. The authors acknowledge the financial support of the Hebei Provincial Basic Research Business Fee Research Project for Provincial Universities (No. JST2022005) and Hebei Provincial College Students' Innovation and Entrepreneurship Training Project (T2023006, 202310081003). 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4424610","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":311550540,"identity":"10563542-d716-4880-89fd-0cb23512c7e3","order_by":0,"name":"Tianwang Li","email":"","orcid":"","institution":"North China University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Tianwang","middleName":"","lastName":"Li","suffix":""},{"id":311550541,"identity":"c08b87ed-c6e8-4a03-a762-d1020641fbea","order_by":1,"name":"Xiaosong Wei","email":"","orcid":"","institution":"North China University of Science and 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samples: (a) Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ex\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e, (b) Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ex\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e/CDs, (c) Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ex\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e/CDs@MnO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e. EDS mapping analyses of Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ex\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e/CDs@MnO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e in (c): (d) Mn element, (e) O, (f) C, and (g) the EDS spectrum of Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ex\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e/CDs@MnO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-4424610/v1/02fcb1b42bbc1100fc6c8b2f.jpeg"},{"id":58146560,"identity":"4516708f-28e8-4664-959f-eda323c8e9cb","added_by":"auto","created_at":"2024-06-11 18:37:08","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1415467,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTEM images for different samples: (a) Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ex\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e/CDs, (c) Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ex\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e/CDs@MnO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e. SAED images of different samples: (b) Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ex\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e/CDs, (d) Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ex\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e/CDs@MnO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-4424610/v1/7c9d69300cdabc4bce5dc3eb.jpeg"},{"id":58147786,"identity":"3e6c8915-1ae2-418d-8354-0609e9e79d17","added_by":"auto","created_at":"2024-06-11 18:45:08","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":165005,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a) XRD patterns of the pure Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ex\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e, Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ex\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e/CDs and Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ex\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e/CDs@MnO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e (b) N\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e adsorption/desorption isotherm of the pure Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ex\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e, Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ex\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e/CDs and Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ex\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e/CDs@MnO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-4424610/v1/ea4c12ac99e56aab9cb98a86.jpeg"},{"id":58146561,"identity":"459ea918-aef5-4e98-9b28-dbc6f94940f1","added_by":"auto","created_at":"2024-06-11 18:37:08","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":324941,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eElectrochemical performance in a three-electrode setup: CV profiles at different scan rates: (a) Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ex\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e/CDs, (b) Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ex\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e/CDs@MnO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e; (c) Gravimetric capacitance of three samples at different scanning rates; (d) Nyquist plots (inset: showing the Nyquist plots expanded in high frequency region and equivalent-circuit diagram).\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-4424610/v1/d14309d71a933d5034a8a8c2.jpeg"},{"id":58146563,"identity":"8734e6cc-e01b-488e-8312-ff1f2b3294e3","added_by":"auto","created_at":"2024-06-11 18:37:08","extension":"jpeg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":322868,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eElectrochemical properties of the AC electrode investigated using the symmetric system in 6 M KOH electrolyte: CV curves of (a) Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ex\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e/CDs and (b) Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ex\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e/CDs@MnO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e performed at different scan rates; (c) CV curves of three samples at a scanning rate of 20mV s\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e-1\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e; (d) Gravimetric capacitance at different scan rates.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-4424610/v1/527098071393c15ea72ed916.jpeg"},{"id":58146565,"identity":"bfb31498-20bb-475d-944d-0f5335a857c2","added_by":"auto","created_at":"2024-06-11 18:37:08","extension":"jpeg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":279976,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eGCD curves of (a) Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ex\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e/CDs, (b) Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ex\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e/CDs@MnO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e at various current densities. (c) Specific capacitance at different current densities; (d) Ragone plots.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage7.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-4424610/v1/d4316df1032361344d358691.jpeg"},{"id":58147787,"identity":"4591d86f-b892-4f4a-a200-6e95f6db22a4","added_by":"auto","created_at":"2024-06-11 18:45:08","extension":"jpeg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":291657,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a) Nyquist plots (inset: showing the Nyquist plots expanded in high frequency region equivalent-circuit diagram); Cyclic stability test of (b) Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ex\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e/CDs, and (c) Ti\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eC\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eT\u003c/strong\u003e\u003csub\u003e\u003cem\u003e\u003cstrong\u003ex\u003c/strong\u003e\u003c/em\u003e\u003c/sub\u003e\u003cstrong\u003e/CDs@MnO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e at 0.4A g\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e-1\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e current density.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage8.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-4424610/v1/22f86d394573da45ad70c879.jpeg"},{"id":58148181,"identity":"148a1388-5c91-4d64-920d-155c0ba9a796","added_by":"auto","created_at":"2024-06-11 18:53:10","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6672203,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4424610/v1/9ab125f1-82c4-4851-9194-8901fb77d8b6.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Ti3C2Tx/CDs@MnO2 Composite as Electrode Materials for Supercapacitors: Synthesis and Electrochemical Performance","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eWith the energy and environmental challenges posed by fossil fuel depletion, there is an urgent need to promote green and clean energy alternatives. Renewable energy sources such as solar, tidal and wind power have become the key to solving this problem. However, due to the huge volatility and intermittency of the renewable energy sources, they also face the problem of efficient storage of these energy sources [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. In the field of energy storage, batteries and supercapacitors are the two leading electrochemical energy storage technologies that deserve the most attention. Supercapacitors can be charged and discharged quickly at a power density of more than 1 kW kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which have a short charging time, a wide range of operating temperatures, and a long cycle life (100,000 cycles) [\u003cspan additionalcitationids=\"CR5 CR6\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. However, although supercapacitors are able to provide a higher energy density than conventional capacitors, it still needs to improve their electrochemical performance. The development of new electrode materials is crucial to improve the performance of supercapacitors [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eMXenes (M\u003csub\u003en+1\u003c/sub\u003eX\u003csub\u003en\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e) are a kind of general term for two-dimensional (2D) transition metal carbides/nitrides/nitrogen-containing compounds [\u003cspan additionalcitationids=\"CR11 CR12\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Generally, MXenes are obtained by selectively removing the A atoms in the parent MAX phases interlayer. \u0026ldquo;M\u0026rdquo; represents transition metals such as Ti, Mo, V, Cr, etc., \u0026ldquo;X\u0026rdquo; represents C and/or N, and \u0026ldquo;T\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e\u0026rdquo; represents surface terminations introduced during the preparation process, such as -OH, -O, -F [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Among various MXenes, Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e is the most representative and extensively investigated one. Renowned for its elevated specific surface area, superior conductivity, and distinctive layered arrangement, Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e has garnered significant attention in research on electrode materials of supercapacitor. The characteristic layered structure facilitates efficient ion conduction and the intercalation of various small molecules. Therefore, 2D Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e has great potential for use as an electrode material for supercapacitors [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Nonetheless, challenges persist with etched Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e materials, notably concerning restacking and oxidation, which constrain their widespread utilization in the domain of supercapacitors [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Hence, it is necessary to further improve the structure and performance of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e. Mostly, the intercalation of various small molecules or carbon materials (e.g. carbon dots) is one of the common ways to improve above problems.\u003c/p\u003e \u003cp\u003eCarbon dots (CDs) inherently possess rich surface defects, robust chemical stability, abundant raw materials, and cost-effectiveness, rendering them promising for diverse applications within the energy field [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan additionalcitationids=\"CR20\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Biomass-derived CDs are typically derived from organic small molecules (e.g. glucose, sucrose) abundant in functional groups such as hydroxyl, carboxyl, and carbonyl. Nonetheless, CDs are rarely used alone as electrode materials for supercapacitors, which may be due to the decrease of hydrophilicity and specific surface area caused by agglomeration, as well as the internal resistance of the interface caused by a large number of small size nano effects [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Some researchers found that biomass-derived CDs could expand the interlayer spacing of MXenes, which facilitate the electrolyte ion transport while mitigating the aggregation of MXenes [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Recently, Devadas et al. [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e] synthesized PPy@CDs and PANI@CDs using the synergistic effect of CDs and conductive polymers, with specific capacitances of 676 and 529 F g\u003csup\u003e-1\u003c/sup\u003e at a current density of 1 A g\u003csup\u003e-1\u003c/sup\u003e, respectively. Li et al. [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] prepared CDs/Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e hybrid films with 0D/2D spot motif structure and used them as electrode materials. The optimized freestanding film electrode from pomelo juice as CDs with suitable layer spacing and profuse heteroatom doping indicates a high volumetric capacitance of 984.5 F cm\u003csup\u003e-3\u003c/sup\u003e at a scan rate of 2 mV s\u003csup\u003e-1\u003c/sup\u003e, and an excellent volumetric energy density of 19.42 Wh L\u003csup\u003e-1\u003c/sup\u003e was obtained in the corresponding assembled asymmetric supercapacitor. From previous studies, it can be known that CDs are often used to compound with other materials to improve specific capacitance, which are due to its effect of enhancing electron transport and ion migration in charge/discharge process and accelerating redox reaction. And most importantly, the CDs embedded between Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e layers can prevent the restacking of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e and improve the electrochemical performances.\u003c/p\u003e \u003cp\u003eAs a pseudocapacitive material, MnO\u003csub\u003e2\u003c/sub\u003e has a high theoretical specific capacitance of 1370 F g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, abundant reserves, and environmentally friendly characteristics, rendering it a promising candidate for energy storage [\u003cspan additionalcitationids=\"CR27\" citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. However, the practical applications of MnO\u003csub\u003e2\u003c/sub\u003e are hindered by its low wettability, conductivity, and cycling stability. Vetrikarasan et al. [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e] prepared Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e@λ-MnO\u003csub\u003e2\u003c/sub\u003e nanoplate electrode with a specific capacitance of 255 F g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, addressing some of these challenges. Therefore, a composite material with high specific capacitance can be prepared by the synergistic action of MnO\u003csub\u003e2\u003c/sub\u003e and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003eHerein, a novel Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e composite was synthesized with a two-step hydrothermal method by coating the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs surface with the pseudocapacitive material MnO\u003csub\u003e2\u003c/sub\u003e. Sucrose was chosen as the precursor of CDs, which can expand the interlayer spacing of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e, and prevent the restacking of layers. Subsequently, the phase, morphology, and specific surface area of composites were comprehensive characterized. Furthermore, the electrochemical performances of the composites were measured by a series of electrochemical test methods. The primary goal is to create a novel composite electrode material that exhibits high specific capacitance, increased energy density, and outstanding cycling stability. According to our findings, CDs has successfully inserted between layers and increased layer spacing of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs and electrochemical sites, and higher specific capacitance and cycle stability have obtained finally. Furthermore, incorporating MnO\u003csub\u003e2\u003c/sub\u003e has also improved the capacitance and energy density of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs composite. These unique properties of the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e composite result in a high specific surface area, high magnification capability and excellent cycling characteristics for supercapacitors applications. As such, this work offers a promising idea for further research into developing novel MXene-based electrode materials for supercapacitors.\u003c/p\u003e"},{"header":"2. Experimental section","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Preparation of Ti\u003c/b\u003e\u003csub\u003e3\u003c/b\u003e\u003c/sub\u003eC\u003c/b\u003e\u003csub\u003e2\u003c/b\u003e\u003c/sub\u003eT\u003c/b\u003e\u003csub\u003ex\u003c/b\u003e\u003c/sub\u003e/CDs materials\u003c/b\u003e\u003c/h2\u003e \u003cp\u003eThe schematic diagram of the preparation process for Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e was shown in Fig.\u0026nbsp;1. Ti\u003csub\u003e3\u003c/sub\u003eAlC\u003csub\u003e2\u003c/sub\u003e was prepared by HF-etching method [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. 80 mL of HF solution with a 40% volume fraction was utilized to etch 5g of Ti\u003csub\u003e3\u003c/sub\u003eAlC\u003csub\u003e2\u003c/sub\u003e. Firstly, Ti\u003csub\u003e3\u003c/sub\u003eAlC\u003csub\u003e2\u003c/sub\u003e was etched by HF and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e was obtained, as shown in Eq.\u0026nbsp;(1)~(3). The Eq.\u0026nbsp;(1)~(3) describes the etching mechanism of Ti\u003csub\u003e3\u003c/sub\u003eAlC\u003csub\u003e2\u003c/sub\u003e and formation of the surface functional groups [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTiAlC\u003csub\u003e2\u003c/sub\u003e(s)\u0026thinsp;+\u0026thinsp;3HF(aq.) \u0026rarr; Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e(s)\u0026thinsp;+\u0026thinsp;AlF\u003csub\u003e3\u003c/sub\u003e(aq.)\u0026thinsp;+\u0026thinsp;3/2H\u003csub\u003e2\u003c/sub\u003e(g) (1)\u003c/p\u003e \u003cp\u003eTi\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e(s)\u0026thinsp;+\u0026thinsp;2HF(aq.) \u0026rarr; Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e2\u003c/sub\u003e(s)\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003e(g) (2)\u003c/p\u003e \u003cp\u003eTi\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e(s)\u0026thinsp;+\u0026thinsp;2H\u003csub\u003e2\u003c/sub\u003eO(aq.) \u0026rarr; Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e(OH)\u003csub\u003e2\u003c/sub\u003e(s)\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003e(g) (3)\u003c/p\u003e \u003cp\u003eEquation (1) represents the primary reaction for forming the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e phase. Equations\u0026nbsp;(2) and (3) correspond to the formation of surface terminal -OH and -F groups, respectively, resulting in the formation of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003e(OH)\u003csub\u003e2\u003c/sub\u003e and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eF\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003eAfter being heated to 40\u0026deg;C in a magnetic agitator and continuously swirled for 72 hours, the solution was filtered and centrifuged, then adjust the pH to approximately 7.0. It was then dried for 12 hours at 60\u0026deg;C in a vacuum drying oven. Weigh 3g of sucrose and 0.3g of dry Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e and dissolve them in 150 mL of deionized water. After ultrasonic for 30min, the solution was placed in a high-pressure reactor, stirred at a certain rate and constant speed in an oil bath, reacted at 160℃ for 24h, pumped and filtered, and dried at 60℃ for 12h under vacuum to prepare Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs composite.\u003c/p\u003e\u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Preparation of Ti\u003c/b\u003e\u003csub\u003e3\u003c/b\u003e\u003c/sub\u003eC\u003c/b\u003e\u003csub\u003e2\u003c/b\u003e\u003c/sub\u003eT\u003c/b\u003e\u003csub\u003ex\u003c/b\u003e\u003c/sub\u003e/CDs@MnO\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e materials\u003c/b\u003e\u003c/h2\u003e \u003cp\u003eWith KMnO\u003csub\u003e4\u003c/sub\u003e as the manganese source, 0.16 g KMnO\u003csub\u003e4\u003c/sub\u003e and 0.2 g of the above prepared Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs were dissolved in 100mL deionized water, ultrasonic for 30min, the solution was placed in a high-pressure reactor, stirred at a certain rate and constant speed in an oil bath, reacted at 100℃ for 24h, pumped and filtered, and dried in a vacuum at 60℃ for 12h. Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e composite was prepared, as was shown in Fig.\u0026nbsp;1.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Material Characterization\u003c/h2\u003e \u003cp\u003eThe elements, morphology, and crystal structure of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e, Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs, and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e were examined with an electron energy spectrometer (EDS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The pore distribution and specific surface area of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e, Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs, and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e were measured and examined by the nitrogen adsorption and desorption test (BET). The phases of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e, Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs, and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e were determined through X-ray diffraction (XRD).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Electrochemical Characterization\u003c/h2\u003e \u003cp\u003eFor electrochemical tests, the working electrode was first prepared by coating a slurry (Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e, Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs or Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e, acetylene black, PVDF (8:1:1)) onto foamed nickel current collector and dried at 120\u0026deg;C under vacuum for 12h. The slurry was evenly mixed with 0.1g of the active substance (Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e, Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs or Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e), 0.018g of the conductive agent (acetylene black), 0.006g of the binder (polyvinylidene fluoride, PVDF), and 4mL of the dispersion (N-methyl-2-pyrrolidone). The electrode substrate was sliced with a dry nickel sheet and a microtome with a diameter of 0.5 cm. A button battery was constructed symmetrically from two electrodes of comparable quality, with the electrolyte containing a 6 mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e KOH solution. A suitable electrode plate was identified to create a three-electrode system for asymmetric electrode testing, with Pt electrode counter electrode, electrode coated with active substance as working electrode, Hg/HgO electrode as reference electrode. and a 6mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e KOH solution operating as the electrolyte. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge (GCD) tests were carried out by a CHI660e (Shanghai Chenhua Instrument Co, LTD).\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Structural and composition characterization\u003c/h2\u003e \u003cp\u003eTo observe the morphology and composition of the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e, Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs, and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e, SEM-EDS and TEM analyses were performed and the results were shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2\u003c/span\u003ea shows the SEM image of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e obtained after etching with HF. The image reveals that Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e possesses a distinct layered structure with a relatively smooth surface, creating favorable conditions for small molecules to penetrate its interlayers and modify its surface structure [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2\u003c/span\u003eb displays the morphology of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs synthesized via the hydrothermal method. The surface of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e modified by CDs appears rougher, effectively preventing the restacking of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e. This rough surface also provides favorable conditions for subsequent surface coating of MnO\u003csub\u003e2\u003c/sub\u003e [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs and KMnO\u003csub\u003e4\u003c/sub\u003e with good hydrophilicity were uniformly dispersed in water. After 30min of ultrasound, the rough surface of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs was conducive to the adsorption of MnO- 4, and the reductive property of CDs could reduce KMnO\u003csub\u003e4\u003c/sub\u003e to MnO\u003csub\u003e2\u003c/sub\u003e on the surface of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs at high temperature. Furthermore, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2\u003c/span\u003ec presents the SEM image of the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e composite, the image demonstrates the relatively uniform coverage of MnO\u003csub\u003e2\u003c/sub\u003e on the surface of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e. In addition, the corresponding EDS of the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e composite in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2\u003c/span\u003ec are presented in Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2\u003c/span\u003ed-f, which display the elemental mapping for Mn, O, and C. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2\u003c/span\u003eg illustrates the surface scan spectrum and element content of Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e2\u003c/span\u003ec. The above results indicated that Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e composite was successfully prepared, with carbon and manganese elements distributed relatively uniformly on Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003ea shows the TEM image of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs, indicating the successful infiltration of sucrose into Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e to form CDs. The larger shaded areas in the image correspond to well-crystallized CDs. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003eb presents the electron diffraction pattern of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs, exhibiting a series of neatly arranged spots. This diffraction pattern consists of concentric rings with varying radii, reflecting the polycrystalline nature of CDs [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003ec shows the TEM image of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e, illustrating the successful deposition of MnO\u003csub\u003e2\u003c/sub\u003e onto the surface of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs. According to the Bragg equation, the measured interplanar spacing d is 0.22nm, which corresponds to the (200) crystal plane of MnO\u003csub\u003e2\u003c/sub\u003e. Lastly, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003ed exhibits the electron diffraction pattern of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e, showing a series of concentric rings with varying radii [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. It further confirms the successful coating of polycrystalline MnO\u003csub\u003e2\u003c/sub\u003e and demonstrates the successful preparation of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eStructural Parameters and Capacitive Performances of the Samples.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003esamples\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eS\u003csub\u003eBET\u003c/sub\u003e(m\u003csup\u003e2\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eV\u003csub\u003et\u003c/sub\u003e(cm\u003csup\u003e3\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eD\u003csub\u003ea\u003c/sub\u003e(nm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eR\u003csub\u003ee\u003c/sub\u003e(Ω)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eR\u003csub\u003ect\u003c/sub\u003e(Ω)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTi\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e7.26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.055\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e30.57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e5.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTi\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e /CDs\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e17.31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.081\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e18.69\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.28\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTi\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e53.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.127\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e9.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eV\u003c/b\u003e \u003csub\u003e \u003cb\u003et\u003c/b\u003e \u003c/sub\u003e: \u003cb\u003eTotal pore volume measured at a relative pressure of 0.99. D\u003c/b\u003e\u003csub\u003e\u003cb\u003ea\u003c/b\u003e\u003c/sub\u003e: \u003cb\u003eAverage pore diameter analyzed using the BJH method. R\u003c/b\u003e\u003csub\u003e\u003cb\u003ee\u003c/b\u003e\u003c/sub\u003e: \u003cb\u003eSeries resistance. R\u003c/b\u003e\u003csub\u003e\u003cb\u003ect\u003c/b\u003e\u003c/sub\u003e: \u003cb\u003eCharge-transfer resistance.\u003c/b\u003e\u003c/p\u003e \u003cp\u003eXRD patterns of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e, Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs, and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e samples were performed to reveal the combination mechanism, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003ea. The distinct peaks observed in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003ea at 2θ values of 8.9\u0026deg;, 18.1\u0026deg;, 27.3\u0026deg;, and 60.6\u0026deg; correspond to the (002), (006), (008), and (110) crystal planes of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e, respectively [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. 2theta of 36.8\u0026deg; may indicate that part of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e was oxidized to TiO\u003csub\u003e2\u003c/sub\u003e.These patterns provide valuable insights into the crystalline structure of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e samples. In the XRD pattern of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs, the characteristic peaks corresponding to Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e exhibit varying degrees of attenuation, reflecting a decrement in the crystallinity of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e following the integration of polycrystalline CDs. Notably, the characteristic peak associated with the (002) crystal plane shifts slightly from 8.9\u0026deg; to 8.76\u0026deg;. According to the Bragg equation, this shift implies that CDs infiltrate the interlayers of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e, slightly enlarging the interlayer spacing, thereby exposing more redox-active sites conducive to oxidation-reduction reactions. Moreover, the presence of CDs effectively mitigates the oxidation of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e, ultimately enhancing the performance of supercapacitors. In contrast, the XRD pattern of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e reveals a significant reduction in the characteristic peaks of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e. Remarkably, the peak corresponding to the (002) crystal plane undergoes a more pronounced shift from 8.9\u0026deg; to 6.8\u0026deg;. Based on the Bragg equation, this shift indicates that the combined effect of CDs and polycrystalline MnO\u003csub\u003e2\u003c/sub\u003e further widens the interlayer spacing of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e. The calculation results reveal an enlarged interlayer spacing (Δd) of 0.3202nm, suggesting that Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e possesses a greater interlayer spacing, thus exposing even more redox-active sites for oxidation-reduction reactions. Additionally, the coating of MnO\u003csub\u003e2\u003c/sub\u003e contributes additional pseudo-capacitance, further improving the electrochemical performance of supercapacitors.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003eb shows the N\u003csub\u003e2\u003c/sub\u003e adsorption-desorption isotherms of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e, Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs, and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e samples. All three samples exhibit distinct type IV adsorption isotherm features and H\u003csub\u003e3\u003c/sub\u003e hysteresis loops within the relative pressure range of 0.45\u0026thinsp;~\u0026thinsp;1.0. This hysteresis behavior is characteristic of slit-like pores that are formed between the layers of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e, indicating that all three samples possess mesoporous structures. Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows the pore structure parameters of the three samples calculated by BET method, the specific surface areas of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e, Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs, and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e are 7.26, 17.31, and 53.39 m\u003csup\u003e2\u003c/sup\u003e g\u003csup\u003e-1\u003c/sup\u003e, respectively. The introduction of CDs and MnO\u003csub\u003e2\u003c/sub\u003e results in a remarkable increase in the materials' specific surface areas, potentially leading to superior performance in electrochemical applications, such as supercapacitors. The specific surface area of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs is notably higher than that of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e, presumably due to the insertion of CDs into the interlayers of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e, which enlarges the interlayer spacing and consequently boosts the specific surface area [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. Furthermore, Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e exhibits an even larger specific surface area, significantly surpassing Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e. This significant enhancement may be attributed to the synergistic effect of CDs and MnO\u003csub\u003e2\u003c/sub\u003e in further expanding the interlayer spacing of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e, ultimately resulting in a larger specific surface area for Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e. From the other structural parameters of the three samples in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, it shows a gradual increase in the total pore volume (V\u003csub\u003et\u003c/sub\u003e) and a corresponding decrease in the average pore diameter (D\u003csub\u003ea\u003c/sub\u003e). These changes are advantageous for electrochemical applications as they enhance the effective contact area between the electrolyte and electrode material. An increased total pore volume and reduced pore diameter promote ion accessibility and charge transfer, significantly improving the electrochemical performance of the composites [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Electrochemical Performances in the Three-Electrode System\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn order to evaluate the electrochemical behavior and quantify the charge storage capacity of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e, the above two materials were prepared as active electrode materials for supercapacitors. CV curves and Nyquist plots of the two electrode materials were measured in 6M KOH electrolyte using a three-electrode system, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e5\u003c/span\u003e. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e5\u003c/span\u003ea presents the CV curves of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs at various scan rates, revealing an almost rectangular shape within the three-electrode system [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. This observation indicates the excellent capacitive behavior and high reversibility of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs, making it a promising candidate for supercapacitor. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e5\u003c/span\u003eb displays the CV curves of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e at different scan rates. Compared to Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs, the image undergoes noticeable distortion due to pseudo-capacitance. For a direct comparison, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e5\u003c/span\u003ec compares the gravimetric capacitance of three samples at different scanning rates, Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs demonstrates a specific capacitance of 160.3 F g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at a scan rate of 5 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, maintaining a respectable value of 113.5 F g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e even at a higher scan rate of 200 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, with a capacitance retention of 70%. This compares favorably to Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e, which exhibits a specific capacitance of 86.1 F g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. In the case of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e, an even higher specific capacitance of 281.3 F g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is achieved at a scan rate of 5 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, retaining a value of 168.9 F g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 200 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with a capacitance retention of 60%. It is also proved that Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e has excellent energy storage performance. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e5\u003c/span\u003ed shows the Nyquist plots of the three samples, each exhibiting characteristic capacitive behaviors. The plots exhibit arc shapes in the high-frequency region, followed by straight lines in the low-frequency region, indicative of ideal capacitive performance [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. The calculated equivalent series resistance (R\u003csub\u003ee\u003c/sub\u003e) of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e, Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e are 1.24, 0.937, 0.964Ω and charge transfer resistance (R\u003csub\u003ect\u003c/sub\u003e) 0.32, 0.286, 0.412Ω, respectively. The total resistance (R\u003csub\u003etot\u003c/sub\u003e) is 1.56, 1.22, 1.376Ω, respectively, indicating that Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e have lower R\u003csub\u003etot\u003c/sub\u003e and better electrochemical performance than Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Electrochemical Properties in Symmetrical System\u003c/h2\u003e \u003cp\u003eThe above analysis results of the structure and morphology of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e composites show that they have larger specific surface area and larger pore volume, and are expected to be prepared as electrode materials for supercapacitors with excellent performance. Therefore, the button-type symmetric supercapacitors were assembled with Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs or Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e as positive and negative electrodes, respectively, and then the electrochemical performance was tested to further evaluate their performance.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe CV curves of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs at different scan rates (5\u0026thinsp;~\u0026thinsp;200 mV s\u003csup\u003e-1\u003c/sup\u003e) are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e6\u003c/span\u003ea. It can be seen that the CV curves of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs exhibit an almost rectangular shape, which remains approximately rectangular as the scan rate increases. This indicates that Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs possesses good rate capability and ideal capacitive behavior [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e6\u003c/span\u003eb shows the CV curves of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e across various scan rates. Due to the introduction of the pseudo-capacitor material MnO\u003csub\u003e2\u003c/sub\u003e, the CV curve of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e obviously deviates from the rectangle. These peaks reflect the electrochemical reactions occurring within the material, enhancing its capacitive behavior [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. The enclosed area of the CV curves serves as a metric for material capacitance. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e6\u003c/span\u003ec compares the CV curves of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e, Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs, and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e at a fixed scan rate of 20 mV s\u003csup\u003e-1\u003c/sup\u003e. Notably, the enclosed areas increase in the order of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e, Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs, and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e, directly correlating with their increasing specific capacitance. This trend underscores the superior capacitive performance of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e compared to the other samples. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e6\u003c/span\u003ed presents the calculated specific capacitance values for the three samples across different scan rates. Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs demonstrates a specific capacitance of 143.6 F g\u003csup\u003e-1\u003c/sup\u003e at a scan rate of 5 mV s\u003csup\u003e-1\u003c/sup\u003e, maintaining a respectable value of 112.5 F g\u003csup\u003e-1\u003c/sup\u003e even at a higher scan rate of 200 mV s\u003csup\u003e-1\u003c/sup\u003e, with a capacitance retention of 78%. This compares favorably to Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e, which exhibits a specific capacitance of 86.1 F g\u003csup\u003e-1\u003c/sup\u003e. In the case of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e, an even higher specific capacitance of 300.3 F g\u003csup\u003e-1\u003c/sup\u003e is achieved at a scan rate of 5 mV s\u003csup\u003e-1\u003c/sup\u003e, retaining a value of 137.3 F g\u003csup\u003e-1\u003c/sup\u003e at 200 mV s\u003csup\u003e-1\u003c/sup\u003e with a capacitance retention of 46%. These results indicate that Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e consistently outperforms the other samples regarding specific capacitance.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigures \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003ea and b show the GCD curves of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e at various current densities. For Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs, the GCD curve within the voltage range of -0.3 to 0.8 V exhibits a nearly linear and symmetric shape, indicating minimal IR drop[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Conversely, the GCD curve of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e deviates from linearity and symmetry due to the coexistence of double-layer capacitance and pseudo-capacitance mechanisms [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e demonstrates a significantly longer discharge time at lower current densities than Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs, suggesting a higher specific capacitance. This enhancement in capacitance can be ascribed to the efficient charge transfer occurring at the interface between the Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e layer and MnO\u003csub\u003e2\u003c/sub\u003e. However, it's worth noting that MnO\u003csub\u003e2\u003c/sub\u003e primarily relies on chemical reactions for energy storage, decreasing discharge time for Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e at higher current densities [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003ec shows the specific capacitance of three distinct samples at various current densities. Notably, Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e exhibits an impressive mass-specific capacitance of 266 F g\u003csup\u003e-1\u003c/sup\u003e at a current density of 0.1 A g\u003csup\u003e-1\u003c/sup\u003e. On the other hand, Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs demonstrates a mass-specific capacitance of 166 F g\u003csup\u003e-1\u003c/sup\u003e at 0.1 A g\u003csup\u003e-1\u003c/sup\u003e, which gracefully decreases to 120 F g\u003csup\u003e-1\u003c/sup\u003e at 4 A g\u003csup\u003e-1\u003c/sup\u003e, maintaining a capacitance retention rate of 72.3%. This exceptional rate performance confirms its reliability under varying conditions. Lastly, Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003ed compares the Ragone plots of symmetric capacitors, revealing that Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e achieves an energy density of 2.92 Wh kg\u003csup\u003e-1\u003c/sup\u003e at a power density of 125 W kg\u003csup\u003e-1\u003c/sup\u003e. Obviously, Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e surpass this performance, with Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs reaching an energy density of 5.21 Wh kg\u003csup\u003e-1\u003c/sup\u003e at a power density of 114 W kg\u003csup\u003e-1\u003c/sup\u003e, and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e achieving an energy density of 5.77 Wh kg\u003csup\u003e-1\u003c/sup\u003e at a power density of 120 W kg\u003csup\u003e-1\u003c/sup\u003e. In summary, Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e exhibit superior energy density and storage performance, making them promising candidates for electrochemical applications.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe Nyquist plots of three types of samples are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e8\u003c/span\u003ea, which reveal that all three samples exhibit arc shapes in the high-frequency region and linear shapes in the low-frequency region, demonstrating ideal capacitive characteristics. The results show that the R\u003csub\u003ee\u003c/sub\u003e of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e, Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs, Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e are 1.06, 0.54, 0.82Ω, and R\u003csub\u003ect\u003c/sub\u003e are 0.52, 0.73, 0.5Ω, respectively. Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs exhibit the smallest R\u003csub\u003ect\u003c/sub\u003e but the largest R\u003csub\u003ee\u003c/sub\u003e among them. This may be attributed to the presence of CDs, which partly improves the hydrophilicity issue of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e and simultaneously expands the interlayer spacing of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e to facilitate sufficient contact between Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs and the electrolyte, thereby promoting charge transfer and resulting in a significant decrease in R\u003csub\u003ect\u003c/sub\u003e compared to Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e. However, the nanoscale interface resistance generated by CDs may increase R\u003csub\u003ee\u003c/sub\u003e [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. For Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e, the relatively small R\u003csub\u003ect\u003c/sub\u003e might be due to the synergistic effect of CDs and polycrystalline MnO\u003csub\u003e2\u003c/sub\u003e, which further expand the interlayer spacing of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e and increase the pore volume, facilitating better contact with the electrolyte and thus reducing R\u003csub\u003ect\u003c/sub\u003e. Nevertheless, the low wettability and conductivity of MnO\u003csub\u003e2\u003c/sub\u003e can increase R\u003csub\u003ect\u003c/sub\u003e, with the former effect outweighing the latter, resulting in a macroscopic decrease in R\u003csub\u003ect\u003c/sub\u003e [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. Moreover, the sloped lines in the low-frequency region represent the ability of ions in the electrolyte to diffuse on the electrode surface, with Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs exhibiting the steepest slope, indicating that the electrode surface of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs is conducive to ion diffusion in the electrolyte [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. Figures\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e8\u003c/span\u003eb,c respectively illustrate the cyclic stability of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e at a current density of 0.4 A g\u003csup\u003e-1\u003c/sup\u003e. After 10,000 cycles of constant current charge and discharge, Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs maintain a capacitance retention rate of 82.38%, indicating excellent electrochemical stability. Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e retains 80.77% of its capacitance after 2500 cycles of constant current charge and discharge, displaying relatively superior electrochemical stability.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eTo enhance the performance of MXene-based supercapacitors, this work initially utilized sucrose as the precursor of biomass-derived CDs to intercalate into the interlayer of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e. Subsequently, MnO\u003csub\u003e2\u003c/sub\u003e was coated on the surface of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs using KMnO\u003csub\u003e4\u003c/sub\u003e as the manganese source, and a ternary Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e composite was synthesized to further enhance the energy storage capabilities of MXene-based materials. The results revealed that CDs prevented the restacking of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e, widened the interlayer distance, and provided additional redox reaction sites. Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e /CDs demonstrated remarkable mass-specific capacitance (160.3F g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 5 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and long-term cycling stability (82.38% retention rate after 10,000 cycles). Following the surface coating with MnO\u003csub\u003e2\u003c/sub\u003e, Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e exhibited a specific surface area of 53.39m\u003csup\u003e2\u003c/sup\u003e g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, increased redox reaction sites, significantly improved energy storage performance (300.3 F g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 5 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), and higher energy density (5.77Wh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 120 W kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), indicating promising prospects for broad applications in energy storage. The results indicated that organic small molecules, such as sucrose, can serve as precursors to form CDs and hinder the restacking of MXene-based materials. Additionally, surface coating with pseudocapacitive materials like MnO\u003csub\u003e2\u003c/sub\u003e can enhance the energy storage performance of composites. This study offers a pathway for synthesizing MXene-based ternary composite energy storage materials with superior performance.\u003c/p\u003e"},{"header":"Declarations","content":" \u003ch2\u003eCompeting interests\u003c/strong\u003e \u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose.\u003c/p\u003e \u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThis work was supported by Hebei Provincial Basic Research Business Fee Research Project for Provincial Universities (No. JST2022005) and Hebei Provincial College Students' Innovation and Entrepreneurship Training Project (T2023006, 202310081003).\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eTianwang Li: Investigation, Writing\u0026mdash;original draft, Methodology, Formal analysis. Yanqing Cai and Xinggang Chen: Writing\u0026mdash;review \u0026amp; editing, administration, Formal analysis, Investigation. Xiaosong Wei Wang: Formal analysis. Yalin Zhang: Data Curation, Data analysis. Ying Xu: Data Curation, Investigation.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors thank the North China University of Science and Technology for providing the key laboratory. The authors acknowledge the financial support of the Hebei Provincial Basic Research Business Fee Research Project for Provincial Universities (No. JST2022005) and Hebei Provincial College Students' Innovation and Entrepreneurship Training Project (T2023006, 202310081003).\u003c/p\u003e\u003ch2\u003eData availability\u003c/h2\u003e \u003cp\u003eThe data that support the findings of this study are available from the corresponding author upon reason able request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eZhang L, Hu X, Wang Z, Sun F, Dorrell DG (2018) A review of supercapacitor modeling, estimation, and applications: A control/management perspective. 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Small 15: \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1002/smll.201805235\u003c/span\u003e\u003cspan address=\"10.1002/smll.201805235\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhao S, Zhang H-B, Luo J-Q, Wang Q-W, Xu B, Hong S, Yu Z-Z (2018) Highly Electrically Conductive Three-Dimensional Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e MXene/Reduced Graphene Oxide Hybrid Aerogels with Excellent Electromagnetic Interference Shielding Performances. ACS Nano 12: 11193\u0026ndash;11202. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1021/acsnano.8b05739\u003c/span\u003e\u003cspan address=\"10.1021/acsnano.8b05739\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWen J, Fu Q, Wu W, Gao H, Zhang X, Wang B (2019) Understanding the Different Diffusion Mechanisms of Hydrated Protons and Potassium Ions in Titanium Carbide MXene. ACS Applied Materials \u0026amp; Interfaces 11: 7087\u0026ndash;7095. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1021/acsami.8b21117\u003c/span\u003e\u003cspan address=\"10.1021/acsami.8b21117\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"ionics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Ionics](https://www.springer.com/journal/11581) ","snPcode":"11581","submissionUrl":"https://mc.manuscriptcentral.com/ionics","title":"Ionics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Ti3C2Tx, Carbon dots, MnO2, Supercapacitor, Electrochemical performance","lastPublishedDoi":"10.21203/rs.3.rs-4424610/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4424610/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eMXenes are a kind of novel and interesting new materials, and carbon dots (CDs) are also concerned because of their processability, versatility, environmental protection and low cost. Both MXenes and CDs are chemically stable and have a large surface area and high electrical conductivity, which are promising alternative electrode materials for supercapacitors. Moreover, MnO\u003csub\u003e2\u003c/sub\u003e can also improve the energy density of the electrode materials. In this paper, Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs and Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e composites were prepared by a hydrothermal method and their supercapacitor performance were also investigated by a series of electrochemical methods. From the CV profile in a three-electrode system, Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e electrode exhibited a high specific capacitance of 281.3 F g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at a scan rate of 5 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which was higher than that of Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs (160.3 F g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). The Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs showed a good cycling stability with a capacitance retention of 82.38% after 10,000 cycles. Meanwhile, a symmetric supercapacitor was successfully assembled using Ti\u003csub\u003e3\u003c/sub\u003eC\u003csub\u003e2\u003c/sub\u003eT\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e/CDs@MnO\u003csub\u003e2\u003c/sub\u003e as electrodes, with an energy density of 5.77 Wh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at a corresponding power density of 120 W kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. This work offers a theoretical foundation and a technological path for synthesizing highly effective ternary composite of MXene-based as energy storage materials.\u003c/p\u003e","manuscriptTitle":"Ti3C2Tx/CDs@MnO2 Composite as Electrode Materials for Supercapacitors: Synthesis and Electrochemical Performance","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-11 18:37:03","doi":"10.21203/rs.3.rs-4424610/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-06-15T11:43:11+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-06-12T01:55:48+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-06-10T18:28:15+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"70429345832921670957731703249393074060","date":"2024-06-02T00:53:55+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"200132824372153402680253609946690181645","date":"2024-05-31T03:14:47+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"68532494328210027762810848015346686406","date":"2024-05-29T04:05:47+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-05-28T21:27:51+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-05-27T07:06:45+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-05-27T07:06:45+00:00","index":"","fulltext":""},{"type":"submitted","content":"Ionics","date":"2024-05-15T10:43:21+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"ionics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Ionics](https://www.springer.com/journal/11581) ","snPcode":"11581","submissionUrl":"https://mc.manuscriptcentral.com/ionics","title":"Ionics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"d8263261-c504-4125-85f7-70f262e7fe66","owner":[],"postedDate":"June 11th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2024-07-10T21:23:26+00:00","versionOfRecord":[],"versionCreatedAt":"2024-06-11 18:37:03","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4424610","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4424610","identity":"rs-4424610","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}