2D transition metal carbides and nitrides, known as MXenes, are an emerging class of 2D materials with a wide spectrum of potential applications, in particular in electrochemical energy storage. The ...hydrophilicity of MXenes combined with their metallic conductivity and surface redox reactions is the key for high‐rate pseudocapacitive energy storage in MXene electrodes. However, symmetric MXene supercapacitors have a limited voltage window of around 0.6 V due to possible oxidation at high anodic potentials. In this study, the fact that titanium carbide MXene (Ti3C2Tx) can operate at negative potentials in acidic electrolyte is exploited, to design an all‐pseudocapacitive asymmetric device by combining it with a ruthenium oxide (RuO2) positive electrode. This asymmetric device operates at a voltage window of 1.5 V, which is about two times wider than the operating voltage window of symmetric MXene supercapacitors, and is the widest voltage window reported to date for MXene‐based supercapacitors. The complementary working potential windows of MXene and RuO2, along with proton‐induced pseudocapacitance, significantly enhance the device performance. As a result, the asymmetric devices can deliver an energy density of 37 µW h cm−2 at a power density of 40 mW cm−2, with 86% capacitance retention after 20 000 charge–discharge cycles. These results show that pseudocapacitive negative MXene electrodes can potentially replace carbon‐based materials in asymmetric electrochemical capacitors, leading to an increased energy density.
The complementary working potential windows of MXene and RuO2, along with proton‐induced pseudocapacitance, leads to the design of all‐pseudocapacitive asymmetric devices providing enhanced energy density.
Water electrolysis is regarded as an efficient and green method to produce hydrogen gas, a clean energy carrier that holds the key to solving global energy problems. So far, the efficiency and ...large‐scale application of water electrolysis are restricted by the electrocatalytic activity of applied catalysts. Recently, the reconstruction phenomenon of electrocatalysts during a catalytic reaction has been discovered, which could form reactive sites for both the oxygen evolution and hydrogen evolution reactions. Regulation of the reconstruction process to generate a large number of reactive species with high activity has since been demonstrated as an effective strategy to enhance the catalytic performance of electrocatalysts. This review summarizes recent progress in the regulation strategies for reconstruction reactions. First, the mechanism of water electrolysis is briefly introduced, and the critical factors regarding the reconstruction process are systematically discussed, followed by a brief introduction of advanced characterization for reconstruction. Moreover, the modulation strategies are summarized with reported examples highlighting the promoted effects on the reconstruction process. Finally, the challenges facing surface‐reconstructed catalysts for water electrolysis in the future are discussed.
Regulation of the reconstruction process to generate a large number of reactive species with high activity is demonstrated as an effective method to tune the water electrolysis performance of electrocatalysts. This review summarizes recent advances in water splitting electrocatalyst reconstruction, covering advanced characterization, structural evolution during reconstruction, as well as the modulation strategies to realize controllable reconstruction for enhanced hydrogen evolution reaction and oxygen evolution reaction activity.
Selenide‐based electrocatalysts and scaffolds on carbon cloth are successfully fabricated and demonstrated for enhanced water oxidation applications. A maximum current density of 97.5 mA cm−2 at an ...overpotential of a mere 300 mV and a small Tafel slope of 77 mV dec−1 are achieved, suggesting the potential of these materials to serve as advanced oxygen evolution reaction catalysts.
As a thriving member of the 2D nanomaterials family, MXenes, i.e., transition metal carbides, nitrides, and carbonitrides, exhibit outstanding electrochemical, electronic, optical, and mechanical ...properties. They have been exploited in many applications including energy storage, electronics, optoelectronics, biomedicine, sensors, and catalysis. Compared to other 2D materials, MXenes possess a unique set of properties such as high metallic conductivity, excellent dispersion quality, negative surface charge, and hydrophilicity, making them particularly suitable as inks for printing applications. Printing and pre/post‐patterned coating methods represent a whole range of simple, economically efficient, versatile, and eco‐friendly manufacturing techniques for devices based on MXenes. Moreover, printing can allow for complex 3D architectures and multifunctionality that are highly required in various applications. By means of printing and patterned coating, the performance and application range of MXenes can be dramatically increased through careful patterning in three dimensions; thus, printing/coating is not only a device fabrication tool but also an enabling tool for new applications as well as for industrialization.
Recent progress in the deposition/patterning of MXenes through printing and coating methods is summarized, including issues that are related to the formulation of MXene inks (e.g., dispersion, stability, and tuning of physical–chemical and morphological properties), relevant printing/coating methods, and their applications in energy storage, electronics/optoelectronics, sensing, and actuation.
Pathogens and cellular danger signals activate sensors such as RIG-I and NLRP3 to produce robust immune and inflammatory responses through respective adaptor proteins MAVS and ASC, which harbor ...essential N-terminal CARD and PYRIN domains, respectively. Here, we show that CARD and PYRIN function as bona fide prions in yeast and that their prion forms are inducible by their respective upstream activators. Likewise, a yeast prion domain can functionally replace CARD and PYRIN in mammalian cell signaling. Mutations in MAVS and ASC that disrupt their prion activities in yeast also abrogate their ability to signal in mammalian cells. Furthermore, fibers of recombinant PYRIN can convert ASC into functional polymers capable of activating caspase-1. Remarkably, a conserved fungal NOD-like receptor and prion pair can functionally reconstitute signaling of NLRP3 and ASC PYRINs in mammalian cells. These results indicate that prion-like polymerization is a conserved signal transduction mechanism in innate immunity and inflammation.
Display omitted
•MAVS and ASC exhibit hallmarks of prions in yeast and mammalian cells•The prion forms of MAVS and ASC activate downstream signaling•Mutations that impair MAVS and ASC prion formation abolish their functions•Signaling through prion-like polymerization is conserved from fungi to mammals
The adaptor proteins MAVS and ASC form self-perpetuating prion-like polymers to propagate innate immune and inflammatory signaling. Prion-like switch is a conserved mechanism of signal transduction from fungi to mammals.
MXenes are a class of two‐dimensional (2D) transition metal carbides, nitrides and carbonitrides that have shown promise for high‐rate pseudocapacitive energy storage. However, the effects that ...irreversible oxidation have on the surface chemistry and electrochemical properties of MXenes are still not understood. Here we report on a controlled anodic oxidation method which improves the rate performance of titanium carbide MXene (Ti3C2Tx, Tx refers to ‐F, =O, ‐Cl and ‐OH) electrodes in acidic electrolytes. The capacitance retention at 2000 mV s−1 (with respect to the lowest scan rate of 5 mV s−1) increases gradually from 38 % to 66 % by tuning the degree of anodic oxidation. At the same time, a loss in the redox behavior of Ti3C2Tx is evident at high anodic potentials after oxidation. Several analysis methods are employed to reveal changes in the structure and surface chemistry while simultaneously introducing defects, without compromising electrochemically active sites, are key factors for improving the rate performance of Ti3C2Tx. This study demonstrates improvement of the electrochemical performance of MXene electrodes by performing a controlled anodic oxidation.
Good made better: Controllable anodic oxidation of 2D Ti3C2Tx improves the rate performance of supercapacitor electrodes. The capacitance retention at 2000 mV s−1 increases gradually from 38 % to 66 % by tuning the degree of anodic oxidation.
We demonstrate that poly(vinylidene fluoride) (PVDF)-based percolative composites using two-dimensional (2D) MXene nanosheets as fillers exhibit significantly enhanced dielectric permittivity. The ...poly(vinylidene fluoride-trifluoro-ethylene-chlorofluoroehylene) (PVDF-TrFE-CFE) polymer embedded with 2D Ti3C2T x nanosheets reaches a dielectric permittivity as high as 105 near the percolation limit of about 15.0 wt % MXene loading, which surpasses all previously reported composites made of carbon-based fillers in the same polymer. With up to 10 wt % MXene loading, the dielectric loss of the MXene/P(VDF-TrFE-CFE) composite indicates only an approximately 5-fold increase (from 0.06 to 0.35), while the dielectric constant increased by 25 times over the same composition range. Furthermore, the ratio of permittivity to loss factor of the MXene–polymer composite is superior to that of all previously reported fillers in this same polymer. The dielectric constant enhancement effect is demonstrated to exist in other polymers as well when loaded with MXene. We show that the dielectric constant enhancement is largely due to the charge accumulation caused by the formation of microscopic dipoles at the surfaces between the MXene sheets and the polymer matrix under an external applied electric field.
Rechargeable zinc‐ion batteries (ZIBs) have shown great potential as an alternative to lithium‐ion batteries. The ZIBs utilize Zn metal as the anode, which possesses many advantages such as low cost, ...high safety, eco‐friendliness, and high capacity. However, on the other hand, the Zn anode also suffers from many issues, including dendritic growth, corrosion, and passivation. These issues are largely related to the surface and interface properties of the Zn anode. Many efforts have therefore been devoted to the modification of the Zn anode, aiming to eliminate the above‐mentioned problems. This review gives a comprehensive summary on the mechanism behind these issues as well as the recent progress on Zn anode modification with focus on the strategies of surface and interface engineering, covering the design and application of both the Zn anode supports and surface protective layers, along with abundant examples. In addition, the promising research directions and perspective on these strategies are also presented.
Zn anodes in aqueous Zn‐ion batteries suffer from dendritic growth, corrosion, and passivation issues. A comprehensive review of the recent progress in Zn anode modification with focus on the design and application of both Zn anode supports and surface protective layers is presented. Additionally, promising research directions are also suggested to promote the development of highly reversible Zn anodes.
A catalytic domino spirocyclization of 1,7-enynes with simple cycloalkanes and cyclo-1,3-dicarbonyls has been established via multiple C–C bond formations from alkynyl/alkenyl functions and dual ...α,α-C(sp3)-H abstraction/insertion. The reaction involves addition, 6-exo-dig cyclization and radical coupling sequences under convenient catalytic conditions and provides a concise access to spiro cyclopentacquinolines in good to excellent yields.
PDF
