Collection of Super Capacitors(202409)
MXenes with two-dimensional layered structure are widely used in the field of potassium ion supercapacitors because of their excellent electrical properties and adjustable surface functional groups, but their limited dual-capacitor storage capacity severely retards the application of MXenes materials in electrode materials. In this work, the strategy of “Lewis acid molten salt pre-etching + liquid phase etching + in situ hydrothermal recombination” was used to prepare the Ti3C2-based heterojunction with Ti3C2 as matrix and MnO2 coated surface to improve the storage of potassium ions in electrode materials. The connection mode, electrical properties and the change of potassium adsorption law at Ti3C2-based heterojunction interfaces were studied by using the first principles calculation method based on density functional theory. The results show that the maximum adsorption capacity of potassium ions in the constructed Ti3C2-based heterojunction is about 3 times that of Ti3C2. The presence of Ti-O-H-O connecting channel increases the number of free electrons in MnO2, causing Ti3C2-based heterojunction exhibiting excellent electrical properties. The electrochemical test results of the three-electrode system show that, at a current density of 1 A·g-1, Ti3C2-based heterojunction can provide 431 F·g-1 specific capacitance which is much higher than 128 F·g-1 of bare Ti3C2. At a voltage sweep rate of 100 mV·s-1, the contribution of pseudocapacitance is up to 89%. In addition, the Ti3C2-based heterojunction exhibits lower electrochemical impedance, which improves the potassium ion transport rate and electron transfer rate. Therefore, this study demonstrates that the electrochemical performance of Ti3C2 matrix can be improved by constructing Ti3C2-based heterojunction, and the corresponding energy storage mechanism can provide a theoretical basis for the design of other MXenes-based electrode materials.
Supercapacitors, distinguished by their unique advantages, including high power performance, stable cycling behavior, and excellent safety, emerge as highly promising energy storage devices in the fields of new energy vehicles and mobile electronic applications. However, the issue of relatively low energy density continues to constrain their practical applications. To enhance electrochemical activity, CoS nanosheets were deposited onto ZnCo2O4-ZnO microspheres coated with carbon (ZCO-ZO@C@CoS) using a facile solvothermal method, calcination treatment, and electrochemical deposition reaction. Carbon layer not only promoted electron transport to enhance electrical conductivity, but also improved the stability of the structure. The open network space formed between CoS nanosheets facilitated rapid ion transport. Additionally, CoS nanosheets possessed abundant electroactive sites, enabling rapid reversible redox reactions. The co-effect of nanowires of the core-shell structure, the carbon layer, and the outer nanosheets effectively enhanced the overall electrochemical performance. Consequently, ZCO-ZO@C@CoS exhibited a specific capacitance of 1944 F·g-1 (972.0 C·g-1) at 1.5 A·g-1, with an initial capacity retention of 75% after 10000 cycles at high current density of 20 A·g-1. The asymmetric supercapacitor device, comprising ZCO-ZO@C@CoS (positive electrode) and activated carbon (negative electrode), also demonstrated excellent specific capacitance, high-rate performance, and exceptional cycling stability, indicating significant potential for practical applications.
Excessive emission of greenhouse gases has serious adverse effects on global climate. How to reduce carbon emissions has become a global problem. Supercapacitors have advantages of long cycle life, high power density and relatively low carbon emissions. Developing supercapacitor energy storage is an effective measure to build the reliable future energy system. In recent years, MXene materials have achievedgreat popularity in the field of supercapacitor energy storage applications due to their excellent hydrophilicity, electrical conductivity, high electrochemical stability, and surface chemical tunability. However, the serious self-stacking problem of MXene limits its performance in energy storage. Developing advanced MXene materials is critical for next generation high-performance electrochemical energy storage devices. This paper reviews the research progress of MXene material in the field of supercapacitor energy storage. Firstly, the structure and energy storage properties of MXene are introduced, followed by analysis of the energy storage mechanism of MXene. Secondly, nanoengineering of structure design to improve the performance of MXene electrode is depicted. Thirdly, structure-performance relationship of MXene composite materials and its latest research progress in application of supercapacitor are summarized. Finally, research and development trends of MXene as an electrode for supercapacitor are broadly prospected.
The microreactor was constructed by using the block copolymer (P123)/sodium dodecyl sulfate (SDS) hybrid emulsion. Horseshoe-shaped hollow porous carbon was prepared by hydrothermal carbonization of xylose. The results showed that hydrothermal reaction of xylose occurred at interface between microreactor and solution. Hydrophilicity of PEO (hydrophilic block in P123) decreased at hydrothermal temperature of 160 ℃. Hybrid emulsion was swelled and destroyed gradually because PEO ran into the interior of emulsion. Furthermore, the morphology of microreactor could be regulated by the mass ratio of P123/SDS and the opening angle, and cavity diameter could be controlled by the hydrothermal time. Owing to the open cavity, the capacity of charges and ions was magnified and transport distance was reduced. In addition, specific capacitance and energy density of porous carbons were improved and showed positive correlation with cavity diameter. The horseshoe-shaped hollow porous carbon with largest opening angle (63°), cavity diameter (80 nm) and optimal supercapacitor performance was obtained at a P123/SDS mass ratio of 1.25 : 1 by hydrothermal method for 12 h. In a three-electrode system, the product showed a high specific capacitance of 292 F·g-1 at a current density of 1 A·g-1. In a two-electrode system, the product showed an excellent energy density (6.44 Wh·kg-1), specific capacitance of 185 F·g-1 at a current density of 0.2 A·g-1 and outstanding cycling stability (94.83%) after 5000 cycles at a current density of 5 A·g-1.
N/S doped carbon nanotubes were prepared with natural mineral fibrous brucite as template, sucrose as carbon source, and thiourea as nitrogen and sulfur source. Experimental results indicate that the doped carbon nanotubes inherit the one-dimensional columnar structure of the fibrous brucite template. In addition, it presents a hollow tubular structure, which increases the specific surface area and pore volume of the template carbon. In 6 mol·L-1 KOH electrolyte, the electrochemical performance significantly improves after doping. CNT-N/S presents a high specific capacity of 172.0 F·g-1 at current density of 1 A·g-1, higher than those of CNT (62.2 F·g-1) and CNT-N (97.0 F·g-1). The capacitance of the N/S doped carbon nanotubes remains 89% after 1000 charge-discharge cycles. Furthermore, the assembled symmetrical supercapacitor also shows good capacitance performance.
Carbon materials are favorable for supercapacitors but suffer from insufficient capacitance. Heteroatom doping, especially nitrogen (N) doping, is an effective method to significantly improve the electrochemical performance, but it is still a big challenge to achieve high active nitrogen content in carbon materials. This work successfully tuned nitrogen species and content by interaction between Si-O-Si network and aluminum oxide. Besides, the structure of carbon materials varies from a coral-like network to three-dimensional structure by adjusting the precursor composition. Oxygen (O) in oxides bonds with N in carbon materials during the reaction, which makes it difficult to escape, achieving high nitrogen content of 5.29at% at 1000 ℃. On the other hand, the interaction empowers the carbon material with large pore volume of ~1.78 cm3·g-1 and broad pore size distribution of 0.5-60 nm. Thus, the N-rich carbon material harvests high capacitance of 302 F·g-1 at 1 A·g-1 and excellent rate capability of 177 F·g-1@120 A·g-1. This unique nitrogen fixation method is a promising strategy for preparing high performance electrode materials of supercapacitors.
High-entropy oxides have attracted more and more attention due to their unique structures and potential applications. In this work, M3O4(M=FeCoCrMnMg) high entropy oxide powders were synthesized by a facile solid-state reaction method. The powders were characterized by different methods. Furthermore, M3O4/Ni foam (M3O4/NF) electrode was prepared by a coating method, followed by investigation of its supercapacitor performance. The results showed that, with the increase of calcining temperature, Fe2O3(H)/Co3O4(S)/Cr2O3(E) and Mn2O3(B) dissolved successively in the crystal lattice of spinel structure. After M3O4 powders being calcined at 900 ℃ for 2 h, single spinel structure (FCC, Fd-3m, a=0.8376 nm) was obtained with uniform distribution of Fe, Co, Cr, Mn, and Mg elements, the typical characteristic of high entropy oxide. In addition, the mass specific capacitance of M3O4/NF composite electrode is 193.7 F·g-1, with 1 mol/L KOH as electrolyte and 1 A·g-1 as current density, which indicated that the M3O4 high entropy oxide can be considered as a promising candidate for the electrode material in the field of supercapacitor applications.