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MXene Electrochemkal capacitor Electrode materials MXene-based composites DevicesMXenes, a family of 20 transition metal carbides/nitrides with a general formula of M.+t X,, T x (n=l ~3), show promising potential for energy storage applications owing to their 20 lamellar structure, impressive density, metallic-liloe conductivity, tunable terminations and intercalation pseudocapacitance charge storage mechanism. Various combinations of transition metals, C and/or N, as well as different n layers result in a broad range of MXenes, but only about a small number have been prepared and used for capacitive energy storage applications (supercapacitors) so far, with Ti 3 Ci T x being the most studied one. This review summarizes the recent advances, achievements and challenges of MXenes for supercapacitors. The preparation methods, composition versatility, material and electrode architectures, chemical modification and hybridization with other active materials ofMX enes are presented. Moreover, the electrochemical characterizations and energy storage mechanisms of MXenes in aqueous and non-aqueous electrolytes are discussed, as well as the preparation of flexible and printable MXene based electrodes and devices. Flnally, perspective is also given, providing guidance for the future development of MXenes with advanced performances for designing the next generation of supercapacitors.

Contact resistance hinders the high performance of electrical devices, especially devices based on two-dimensional (2D) materials, such as graphene and transition metal dichalcogenide. To engineer contact resistance, understanding the resistance distribution and carrier transport behavior at the contact area is essential. Here, we developed a method that can be used to obtain some key parameters of contact, such as transfer length (Lt), sheet resistance of the 2D materials beneath the contacting metal (Rsh), and contact resistivity between the 2D materials and the metal electrode (ρc). Using our method, we studied the contacts between molybdenum disulfide (MoS2) and metals, such as titanium and gold, in bilayer and few-layered MoS2 devices. Especially, we found that Rsh is obviously larger than the sheet resistance of the same 2D materials in the channel (Rch) in all the devices we studied. With the increasing of the back-gate voltage, Lt increases and Rsh, ρc, Rch, and the contact resistance Rc decrease in all the devices we studied. Our results are helpful for understanding the metal–MoS2 contact and improving the performances of MoS2 devices.

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2D MXenes have emerged as promising supercapacitor electrode materials due to their metallic conductivity, pseudo‐capacitive mechanism, and high density. However, layer‐restacking is a bottleneck that restrains their ionic kinetics and active site exposure. Herein, a carbon dots‐intercalated strategy is proposed to fabricate flexible MXene film electrodes with both large ion‐accessible active surfaces and high density through gelation of calcium alginate (CA) within the MXene nanosheets followed by carbonization. The formation of CA hydrogel within the MXene nanosheets accompanied by evaporative drying endow the MXene/CA film with high density. In the carbonization process, the CA‐derived carbon dots can intercalate into the MXene nanosheets, increasing the interlayer spacing and promoting the electrolytic diffusion inside the MXene film. Consequently, the carbon dots‐intercalated MXene films exhibit high volumetric capacitance (1244.6 F cm−3 at 1 A g−1), superior rate capability (662.5 F cm−3 at 1000 A g−1), and excellent cycling stability (93.5% capacitance retention after 30 000 cycles) in 3 m H2SO4. Additionally, an all‐solid‐state symmetric supercapacitor based on the carbon dots‐intercalated MXene film achieves a high volumetric energy density of 27.2 Wh L−1. This study provides a simple yet efficient strategy to construct high‐volumetric performance MXene film electrodes for advanced supercapacitors.

Abstract-When solving constrained optimization problems by evolutionary algorithms, the search algorithm plays a crucial role. In general, we expect that the search algorithm has the capability to balance not only diversity and convergence but also constraints and objective function during the evolution. For this purpose, this paper proposes a composite differential evolution for constrained optimization, which includes three different trial vector generation strategies with distinct advantages. In order to strike a balance between diversity and convergence, one of these three trial vector generation strategies is able to increase diversity, and the other two exhibit the property of convergence. In addition, to accomplish the tradeoff between constraints and objective function, one of the two trial vector generation strategies for convergence is guided by the individual with the least degree of constraint violation in the population, and the other is guided by the individual with the best objective function value in the population. After producing offspring by the proposed composite differential evolution, the feasibility rule and the ε constrained method are combined elaborately for selection in this paper. Moreover, a restart scheme is proposed to help the population jump out of a local optimum in the infeasible region for some extremely complicated constrained optimization problems. By assembling the above techniques together, a constrained composite differential evolution is proposed. The experiments on two sets of benchmark test functions with various features, i.e., 24 test functions from IEEE CEC2006 and 18 test functions with 10 dimensions and 30 dimensions from IEEE CEC2010, have demonstrated that the proposed method shows better or at least competitive performance against other state-of-the-art methods.

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Five new zero-dimensional hybrid manganese halides based on discrete [MnCl4]2- tetrahedrons were prepared and performed as highly efficient green light emitters. Through rationally managing organic cations to tailor the Mn∙∙∙Mn...