WS2 nanosheets vertically grown on Ti3C2 as superior anodes for lithium-ion batteries.

Tungsten disulfide (WS2) is considered as a promising anode material for high-performance lithium-ion batteries (LIBs) result from its inherent characteristics such as high theoretical capacity, large interlayer spacing and weak interlayer Van der Waals force. Nevertheless, WS2 has the drawbacks of easy agglomeration, severe volume expansion and high Li+ migration barrier, which lead to rapid capacity degradation and imperfect rate ability. In this work, a novel two-dimensional (2D) hierarchical composite (Ti3C2/WS2) consisting of WS2 nanosheets vertically grown on titanium carbide (Ti3C2) nanosheets is prepared. Thanks to this distinctive hierarchical structure and synergy between WS2 and Ti3C2, the Ti3C2/WS2 composite demonstrates exceptional electrochemical performance in LIBs. In addition, we investigate the effect of the mass proportion of WS2 in Ti3C2/WS2 composite on the electrochemical performance, and find that the optimal mass ratio of WS2 is 60%. As expected, the optimal electrode exhibits a high specific capacity (650 mAh/g at 0.1 A/g after 100 cycles) and ultra-long cycle stability (400 mAh/g at 1.0 A/g after 5000 cycles).

Endogenous Nb2CTx/Nb2O5 Schottky heterostructures for superior lithium-ion storage.

Schottky heterostructures have significant advantages for exciting charge transfer kinetics at material interfaces. In this work, endogenous Nb2CTx/Nb2O5 Schottky heterostructures with a large active surface area were constructed using an in-situ architectural strategy. The semiconductor Nb2O5 has a low work function, and during the construction of Nb2CTx/Nb2O5 Schottky heterostructures, there was an interfacial electron transfer, which resulted in a built-in electric field. The electrochemical reaction kinetics of Nb2CTx/Nb2O5 Schottky heterostructures were enhanced due to the rapid transfer of charge driven by the electric field. The Nb2CTx/Nb2O5 Schottky heterostructures have a large active surface area, which contributes to excellent electrolyte diffusion kinetics. Therefore, Nb2CTx/Nb2O5 Schottky heterostructures have excellent lithium-ion storage capacity with 575 mAh/g after 200 cycles at 0.10 A/g, and 290 mAh/g after 1000 cycles at 2.00 A/g, without capacity fading. Furthermore, in-situ X-ray diffraction and ex-situ X-ray photoelectron spectroscopy analyses reveal the mechanisms for structure evolution and lithium-ion storage optimization of Nb2CTx/Nb2O5 Schottky heterostructures during the electrochemical reaction. The construction of Schottky heterostructures with excited charge transport kinetics provides a novel idea for optimizing the lithium-ion storage activity of MXenes materials.

In situ artificial solid electrolyte interface engineering on an anode for prolonging the cycle life of lithium-metal batteries.

Lithium, with its high theoretical capacity and low potential, has been widely investigated as the anode in energy storage/conversion devices. However, their commercial applications always suffer from undesired dendrite growth, which forms in the charging process and may puncture the separator, leading to short cycle lives and even security problems. Herein, by an in situ displacement reaction using SnF2 at room temperature, we constructed an artificial solid electrolyte interface (ASEI) of LiF/Li-Sn outside the Li anode. This hybrid strategy can induce a synergy between the high Li+ conductivity of the Li-Sn alloy and good electrical insulation of LiF. Moreover, extreme synergy can be achieved by moderating the thickness of the LiF/Li-Sn ASEI, guiding dendrite-free lithium plating and stripping. As a result, a Li//LiFePO4 battery that is assembled from the LiF/Li-Sn ASEI-engineered Li anode can obtain 1000 cycled lives with 86.3% capacity retention under a charge/discharge rate of 5 C. This work provides an alternative way to construct dendrite-free lithium metal anodes, which significantly benefit the cycle lives of LMBs.

Two-dimensional transition metal carbide (Ti0.5V0.5)3C2Tx MXene as high performance electrode for flexible supercapacitor.

MXenes have gained widespread interest in flexible supercapacitor due to their rich electrochemical activity and free-standing electrode structure. However, it has been a challenge to obtain an electrode with high (mass and volumetric) specific capacitance, high rate and long cycle life simultaneously. Herein, we have prepared a novel few-layer double transition metal carbide (Ti0.5V0.5)3C2Tx MXene. Multivalent V atoms with high electrochemical activity were constructed in stable M3C2-type MXene to obtain the (Ti0.5V0.5)3C2Tx electrode with excellent performance in flexible supercapacitors. The (Ti0.5V0.5)3C2Tx film has an excellent specific capacitance of 387F g-1 (1625 mF cm-3) at 1.0 A g-1, and 267 F g-1 (1121 mF cm-3) even at a high current density of 20.0 A g-1, demonstrating superior rate performance (69%). Moreover, the capacitance of the (Ti0.5V0.5)3C2Tx film remains stable during 100,000 cycles. The symmetric supercapacitor assembled using (Ti0.5V0.5)3C2Tx film has high energy and power densities, up to 5.6 Wh kg-1 and 5210.3 W kg-1. And the all-solid-state (Ti0.5V0.5)3C2Tx flexible SC maintains stable electrochemical performance after 200 bending cycles. This work shows the huge potential of (Ti0.5V0.5)3C2Tx in flexible supercapacitor, and provides a new idea for the design of high performance flexible electrodes.

Tuning Li Nucleation by a Hybrid Lithiophilic Protective Layer for High-Performance Lithium Metal Batteries.

Lithium (Li) metal has been recognized as the most promising anode material for next-generation rechargeable batteries. However, the practical application of Li anodes is hampered by the growth of Li dendrites. To address this issue, a robust and uniform Sb-based hybrid lithiophilic protective layer is designed and built by a facile in situ surface reaction approach. As evidenced theoretically and experimentally, the as-prepared hybrid protective layer provides outstanding wettability and fast charge-transfer kinetics. Moreover, the lithiophilic Sb embedded in the protective layer provides a rich site for Li nucleation, which effectively reduces the overpotential and induces uniform Li deposition. Consequently, the symmetric cell exhibits a long lifespan of over 1600 h at 1 mA cm-2 and 1 mAh cm-2 with a low voltage polarization. Furthermore, excellent cycling stability is also obtained in Li-S full cells (60% capacity retention in 800 cycles at 1 C) and Li||LFP full cells (74% capacity retention in 500 cycles at 5 C). This work proposed a facile but efficient strategy to stabilize the Li metal anode.

Highly stable few-layer V2CTx MXene/Carbon nanotube structure with restrained restacking for lithium ion storage.

V2CTx MXene has shown potential as an electrode material for lithium-ion batteries (LIBs) due to its high theoretical capacity. However, most reports on V2CTx are confined to multilayer structures in LIBs, and V2CTx nanosheets have a serious restacking problem, which results in their low cyclic stability. Herein, we report the synthesis of few-layer V2CTx/carbon nanotubes (CNTs) composite by tetramethylammonium hydroxide (TMAOH) delamination and electrostatic flocculation of NH4+ ions. Few-layer V2CTx nanosheets with crimped structure can effectively restrain restacking and guarantee full utilization of active surface area. Moreover, with the introduction of CNTs, a developed electrical conductivity network was formed, and CNTs provided structural support for the sheets further restraining their restacking, and ensuring their stable structure during the charge and discharge process even at high rates. This made the few-layer V2CTx/CNT to exhibit a high specific capacitance of 621 mAh/g after 100 cycles at 0.1 A/g, and outstanding rate performance of 290 mAh/g at 5 A/g. Furthermore, the few-layer V2CTx/CNT electrode showed excellent cycling stability with 82.1 % capacitance retention after 2000 cycles at 5 A/g. This shows it has significant potential for lithium-ion batteries applications.

Boosted charge transfer in ReS2/Nb2O5 heterostructure by dual-electric field: Toward superior electrochemical reversibility for lithium-ion storage.

Heterostructures with the electric field effect can excite the charge transfer kinetics of materials due to the driving force of the electric field. Herein, we report a new ReS2/Nb2O5 heterostructure of rhenium disulfide coupled to niobium oxide with a mutually compatible band structure and enriched oxygen vacancies. The unique heterostructure can facilitate the redistribution of charges to induce built-in electric fields and microlocalized electric fields. As expected, the ReS2/Nb2O5 heterostructure shows a superior lithium-ion reversible capacity of 805 mAh g-1 after 2400 h at 0.10 A g-1, and 414 mAh g-1 at 2.00 A g-1. In addition, in situ X-ray diffraction and ex situ X-ray photoelectron spectroscopy analysis reveal the phase transition process of the ReS2/Nb2O5 heterostructure during the electrochemical reaction. This provides deeper insights into the construction of high-performance lithium-ion storage materials based on heterostructures with dual-electric field-driven charge transfer.

Modulating Electron Conducting Properties at Lithium Anode Interfaces for Durable Lithium-Sulfur Batteries.

The lithium (Li) ion and electron diffusion behaviors across the actual solid electrolyte interphase (SEI) play a critical role in regulating the Li nucleation and growth and improving the performance of lithium-sulfur (Li-S) batteries. To date, a number of researchers have pursued an SEI with high Li-ion conductivity while ignoring the Li dendrite growth caused by electron tunneling in the SEI. Herein, an artificial anti-electron tunneling layer with enriched lithium fluoride (LiF) and sodium fluoride (NaF) nanocrystals is constructed using a facile solution-soaking method. As evidenced theoretically and experimentally, the LiF/NaF artificial SEI exhibits an outstanding electron-blocking capability that can reduce electron tunneling, resulting in dendrite-free and dense Li deposition beneath the SEI, even with an ultrahigh areal capacity. In addition, the artificial anti-electron tunneling layer exhibits improved ionic conductivity and mechanical strength, compared to those of routine SEI. The symmetric cells with protected Li electrodes achieve a stable cycling of 1500 h. The LiF/NaF artificial SEI endows the Li-S full cells with long-term cyclability under conditions of high sulfur loading, lean electrolyte, and limited Li excess. This study provides a perspective on the design of the SEI for highly safe and practical Li-S batteries.

V2CTX catalyzes polysulfide conversion to enhance the redox kinetics of Li-S batteries.

Lithium-sulfur (Li-S) batteries have the potential to become the future energy storage system, yet they are plagued by sluggish redox kinetics. Therefore, enhancing the redox kinetics of polysulfides is key for the development of high-energy density and long-life Li-S batteries. Herein, a Ketjen Black (KB)/V2CTX modified separator (KB/V2CTX-PP) based on the catalytic effect in continuous solid-to-liquid-to-solid reactions is proposed to accelerate the conversion of sulfur species during the charge/discharge process in which the V2CTX can enhance the redox kinetics and inhibit polysulfide shuttling. The cells assembled with KB/V2CTX-PP achieve a gratifying first discharge capacity of 1236.1 mA h g-1 at 0.2C and the average capacity decay per cycle reaches 0.049% within 1000 cycles at 1C. The work provides an efficient idea to accelerate redox conversion and suppress shuttle effects by designing a multifunctional catalytic separator.

Interfacial electronic modulation of CoP-CoO p-p type heterojunction for enhancing oxygen evolution reaction.

Heterojunction can effectively improve oxygen evolution reaction (OER) activity by regulating the interfacial electronic structure of catalysts. However, p-p type heterojunction OER catalysts have obtained less attention, and the corresponding catalytic mechanisms are unclear either. Herein, the self-supported CoP-CoO p-p type heterojunction arrays are fabricated on carbon cloth substrate (CoP-CoO/CC). Band structure analysis shows that the formation of p-p heterojunction can drive the electrons from CoO to flow into CoP. This electronic modulation contributes to positively charged regions on the CoO and enhances the OH- adsorption during OER, proven by X-ray photoelectron spectroscopy and methanol molecular detection, respectively. As a result, the CoP-CoO/CC electrode only needs 210 mV overpotential to drive a current density of 10 mA cm-2 in an alkaline medium, superior to the most reported OER catalysts. Additionally, the CoP-CoO/CC also exhibits an ideal hydrogen evolution reaction response, and a water splitting system has been successfully constructed which can drive a 10 mA cm-2 within 1.65 V. This study supplies insight for catalytic origins p-p type heterojunctions OER catalyst, which provides a reference value for the efficient and reasonable design of heterojunction catalysts.

CoS nanowires grown on Ti3C2Tx are promising electrodes for supercapacitors: High capacitance and remarkable cycle capability.

Benefitting from the large interlayer spacing, ultrahigh conductivity and abundant surface chemistry, Ti3C2Tx has been a promising electrode material for supercapacitors (SCs). CoS has attracted much attention due to its low cost, weak Co-S bond and relatively high theoretical capacity. Herein, CoS nanowires were grown on few-layered Ti3C2Tx by one-step solvothermal method as a SC electrode. Within the composite, Ti3C2Tx could function as conductive network and buffer matrix to provide ultra-fast electronic transport and relieve volume expansion of CoS nanowires. Simultaneously, the active CoS nanowires with high capacitance act as interlayer spacer to restrain the restacking of Ti3C2Tx nanosheets. As a result, CoS/Ti3C2Tx-5 electrode exhibits a remarkable improvement specific capacitance of 528 F g-1 at a current density of 1 A g-1 and ultrahigh capacitance retention of 99.3% after 20 000 cycles at a current density of 10 A g-1. The attempts and efforts made in this work provide a prototype for achieving excellent electrochemical properties.

One-step synthesis of few-layer niobium carbide MXene as a promising anode material for high-rate lithium ion batteries.

Two-dimensional (2D) few-layer MXene nanosheets have attracted extensive attention due to their great potential for high-rate energy storage devices, but a simplified method to synthesize these structures with good cycling and rate performances is still a challenge for the MXene family. In this work, a one-step method to synthesize 2D few-layer niobium carbide (Nb2CTx) MXene nanosheets by etching Nb2AlC powder is reported for the first time. A sample of the few-layer Nb2CTx electrode shows a high specific capacity of 354 mA h g-1 at 0.05 A g-1 with a long cycling lifetime. The specific capacity can be stabilized at 225 mA h g-1 after 800 cycles at 1.0 A g-1. The one-step synthesis of unassisted few-layer Nb2CTx MXene nanosheets paves the way for the exploration of Nb2CTx-based composite materials and applications.

Chemical Proteomic Characterization of a Covalent KRASG12C Inhibitor.

The KRASG12C protein product is an attractive, yet challenging, target for small molecule inhibition. One option for therapeutic intervention is to design small molecule ligands capable of binding to and inactivating KRASG12C via formation of a covalent bond to the sulfhydryl group of cysteine 12. In order to better understand the cellular off-target interactions of Compound 1, a covalent KRASG12C inhibitor, we have completed a series of complementary chemical proteomics experiments in H358 cells. A new thiol reactive probe (TRP) was designed and used to construct a cellular target occupancy assay for KRASG12C. In addition, the thiol reactive probes allowed us to profile potential off-target interactions of Compound 1 with over 3200 cysteine residues. In order to complement the TRP data we designed Compound 2, an alkyne containing version of Compound 1, to serve as bait in competitive chemical proteomics experiments. Herein, we describe and compare data from both the TRP and the click chemistry probe pull down experiments.

Modular assembly of dimeric HIV fusion inhibitor peptides with enhanced antiviral potency.

The HIV-1 envelope gp120/gp41 glycoprotein complex plays a critical role in virus-host cell membrane fusion and has been a focus for the development of HIV fusion inhibitors. In this Letter, we present the synthesis of dimers of HIV fusion inhibitor peptides C37H6 and CP32M, which target the trimeric gp41 in the pre-hairpin intermediate state to inhibit membrane fusion. Reactive peptide modules were synthesized using native chemical ligation and then assembled into dimers with varying linker lengths using Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) 'click' chemistry. Cell-cell fusion inhibition assays demonstrated that dimers with a (PEG)7 linker showed enhanced antiviral potency over the corresponding monomers. Moreover, the bio-orthogonal nature of the CuAAC 'click' reaction provides a practical way to assemble heterodimers of HIV fusion inhibitors. Heterodimers consisting of the T20-sensitive strain inhibitor C37H6 and the T20-resistant strain inhibitor CP32M were produced that may have broader spectrum activities against both T20-sensitive and T20-resistant strains.

Coupling protein engineering with probe design to inhibit and image matrix metalloproteinases with controlled specificity.

Matrix metalloproteinases (MMPs) are zinc endopeptidases that play roles in numerous pathophysiological processes and therefore are promising drug targets. However, the large size of this family and a lack of highly selective compounds that can be used for imaging or inhibition of specific MMPs members has limited efforts to better define their biological function. Here we describe a protein engineering strategy coupled with small-molecule probe design to selectively target individual members of the MMP family. Specifically, we introduce a cysteine residue near the active-site of a selected protease that does not alter its overall activity or function but allows direct covalent modification by a small-molecule probe containing a reactive electrophile. This specific engineered interaction between the probe and the target protease provides a means to both image and inhibit the modified protease with absolute specificity. Here we demonstrate the feasibility of the approach for two distinct MMP proteases, MMP-12 and MT1-MMP (or MMP-14).

A coupled protein and probe engineering approach for selective inhibition and activity-based probe labeling of the caspases.

Caspases are cysteine proteases that play essential roles in apoptosis and inflammation. Unfortunately, their highly conserved active sites and overlapping substrate specificities make it difficult to use inhibitors or activity-based probes to study the function, activation, localization, and regulation of individual members of this family. Here we describe a strategy to engineer a caspase to contain a latent nucleophile that can be targeted by a probe containing a suitably placed electrophile, thereby allowing specific, irreversible inhibition and labeling of only the engineered protease. To accomplish this, we have identified a non-conserved residue on the small subunit of all caspases that is near the substrate-binding pocket and that can be mutated to a non-catalytic cysteine residue. We demonstrate that an active-site probe containing an irreversible binding acrylamide electrophile can specifically target this cysteine residue. Here we validate the approach using the apoptotic mediator, caspase-8, and the inflammasome effector, caspase-1. We show that the engineered enzymes are functionally identical to the wild-type enzymes and that the approach allows specific inhibition and direct imaging of the engineered targets in cells. Therefore, this method can be used to image localization and activation as well as the functional contributions of individual caspase proteases to the process of cell death or inflammation.

Site-specific chemical modification of a glycoprotein fragment expressed in yeast.

Site-specific modification of glycoproteins has wide application in both biochemical and biophysical studies. This method describes the conjugation of synthetic molecules to the N-terminus of a glycoprotein fragment, viz., human immunoglobulin G subclass 1 fragment crystallizable (IgG1 Fc), by native chemical ligation. The glycosylated IgG1 Fc is expressed in a glycosylation-deficient yeast strain. The N-terminal cysteine is generated by the endogenous yeast protease Kex2 in the yeast secretory pathway. The N-terminal cysteine is then conjugated with a biotin thioester to produce a biotinylated, glycosylated IgG1 Fc using native chemical ligation.

Functional characterization of a SUMO deconjugating protease of Plasmodium falciparum using newly identified small molecule inhibitors.

Small ubiquitin-related modifier (SUMO) is implicated in the regulation of numerous biological processes including transcription, protein localization, and cell cycle control. Protein modification by SUMO is found in Plasmodium falciparum; however, its role in the regulation of the parasite life cycle is poorly understood. Here we describe functional studies of a SUMO-specific protease (SENP) of P. falciparum, PfSENP1 (PFL1635w). Expression of the catalytic domain of PfSENP1 and biochemical profiling using a positional scanning substrate library demonstrated that this protease has unique cleavage sequence preference relative to the human SENPs. In addition, we describe a class of small molecule inhibitors of this protease. The most potent lead compound inhibited both recombinant PfSENP1 activity and P. falciparum replication in infected human blood. These studies provide valuable new tools for the study of SUMOylation in P. falciparum.

Synthesis of N-terminally linked protein and peptide dimers by native chemical ligation.

Dimerization can be utilized to double the molecular weight of proteins and peptides and potentially increase their avidity of binding to target receptors. These dimerization effects may be utilized to increase in vivo half-lives in a manner similar to PEGylation and may also improve biological activity. In this paper, we report a new strategy for the synthesis of N-terminally linked protein and peptide homodimers utilizing native chemical ligation to conjugate a short dithioester linker to the N-terminal cysteines of protein and peptide monomers to form dimers in a single step. This strategy is general and has been applied to the production of dimers from three recombinantly expressed polypeptides, the IgG binding domain Protein G, an HIV entry inhibitor peptide C37H6, and human interleukin-1 receptor antagonist (IL-1ra). The biological activities of the C37H6 and IL-1ra dimers produced by these methods were retained or even slightly increased when compared to their corresponding monomers.

Targeting a homogeneously glycosylated antibody Fc to bind cancer cells using a synthetic receptor ligand.

The targeting of a glycosylated antibody Fc fragment to bind to cancer cells by site-selective incorporation of a synthetic ligand is described. Homogeneously glycosylated immunoglobulin G subclass 1 fragment crystallizable (IgG1 Fc) was produced by expression in a glycosylation-deficient yeast strain and subsequent treatment with mannosidase IA. A N-terminal cysteine was generated on the expressed IgG1 Fc by utilizing proteolytic processing enzymes in the yeast secretory pathway. A cyclic RGD peptide thioester 2 was synthesized and then site-selectively attached to the N-terminus of the IgG1 Fc glycoprotein using native chemical ligation. The resulting chemically modified antibody fragment, RGD-Man(5)-IgG1 Fc (5), retained biological activity similar to that of the free cyclic RGD peptide 1 when assayed for its ability to both promote and inhibit the adhesion of alpha(v)beta(3) integrin receptor-expressing WM-115 melanoma cells. In addition, fluorescent microscopy experiments were conducted using FITC-labeled 5 and confirmed binding of 5 to WM-115 melanoma cells. Site-selectively modified antibody fragments such as the one described here may be used to combine the beneficial properties of synthetic receptor ligands with antibody fragments to develop useful biochemical tools and improved therapeutics. The methods described here can also be used to produce glycoprotein fragments for the chemoenzymatic synthesis of homogeneous glycoproteins.