Showing papers by "Jun Lu published in 2019"

Element Replacement Approach by Reaction with Lewis Acidic Molten Salts to Synthesize Nanolaminated MAX Phases and MXenes

Abstract: Nanolaminated materials are important because of their exceptional properties and wide range of applications. Here, we demonstrate a general approach to synthesizing a series of Zn-based MAX phases and Cl-terminated MXenes originating from the replacement reaction between the MAX phase and the late transition-metal halides. The approach is a top-down route that enables the late transitional element atom (Zn in the present case) to occupy the A site in the pre-existing MAX phase structure. Using this replacement reaction between the Zn element from molten ZnCl2 and the Al element in MAX phase precursors (Ti3AlC2, Ti2AlC, Ti2AlN, and V2AlC), novel MAX phases Ti3ZnC2, Ti2ZnC, Ti2ZnN, and V2ZnC were synthesized. When employing excess ZnCl2, Cl-terminated MXenes (such as Ti3C2Cl2 and Ti2CCl2) were derived by a subsequent exfoliation of Ti3ZnC2 and Ti2ZnC due to the strong Lewis acidity of molten ZnCl2. These results indicate that A-site element replacement in traditional MAX phases by late transition-metal halides opens the door to explore MAX phases that are not thermodynamically stable at high temperature and would be difficult to synthesize through the commonly employed powder metallurgy approach. In addition, this is the first time that exclusively Cl-terminated MXenes were obtained, and the etching effect of Lewis acid in molten salts provides a green and viable route to preparing MXenes through an HF-free chemical approach.

A general Lewis acidic etching route for preparing MXenes with enhanced electrochemical performance in non-aqueous electrolyte

Abstract: Two-dimensional carbides and nitrides of transition metals, known as MXenes, are a fast-growing family of 2D materials that draw attention as energy storage materials. So far, MXenes are mainly prepared from Al-containing MAX phases (where A = Al) by Al dissolution in F-containing solution, but most other MAX phases have not been explored. Here, a redox-controlled A-site-etching of MAX phases in Lewis acidic melts is proposed and validated by the synthesis of various MXenes from unconventional MAX phase precursors with A elements Si, Zn, and Ga. A negative electrode of Ti3C2 MXene material obtained through this molten salt synthesis method delivers a Li+ storage capacity up to 738 C g-1 (205 mAh g-1) with high-rate performance and pseudocapacitive-like electrochemical signature in 1M LiPF6 carbonate-based electrolyte. MXene prepared from this molten salt synthesis route offer opportunities as high-rate negative electrode material for electrochemical energy storage applications.

Structural defects on converted bismuth oxide nanotubes enable highly active electrocatalysis of carbon dioxide reduction.

Abstract: Formic acid (or formate) is suggested to be one of the most economically viable products from electrochemical carbon dioxide reduction. However, its commercial viability hinges on the development of highly active and selective electrocatalysts. Here we report that structural defects have a profound positive impact on the electrocatalytic performance of bismuth. Bismuth oxide double-walled nanotubes with fragmented surface are prepared as a template, and are cathodically converted to defective bismuth nanotubes. This converted electrocatalyst enables carbon dioxide reduction to formate with excellent activity, selectivity and stability. Most significantly, its current density reaches ~288 mA cm−2 at −0.61 V versus reversible hydrogen electrode within a flow cell reactor under ambient conditions. Using density functional theory calculations, the excellent activity and selectivity are rationalized as the outcome of abundant defective bismuth sites that stabilize the *OCHO intermediate. Furthermore, this electrocatalyst is coupled with silicon photocathodes and achieves high-performance photoelectrochemical carbon dioxide reduction. Carbon dioxide can be electrochemically reduced to form valuable chemical feedstocks, but efficiency of electrocatalysts should be improved. Here the authors report nanotube-derived bismuth for electrocatalytic reduction of carbon dioxide to formate, with performance that is enhanced by defects.

Diffusion-free Grotthuss topochemistry for high-rate and long-life proton batteries

Abstract: The design of Faradaic battery electrodes that exhibit high rate capability and long cycle life equivalent to those of the electrodes of electrical double-layer capacitors is a big challenge. Here we report a strategy to fill this performance gap using the concept of Grotthuss proton conduction, in which proton transfer takes place by means of concerted cleavage and formation of O–H bonds in a hydrogen-bonding network. We show that in a hydrated Prussian blue analogue (Turnbull’s blue) the abundant lattice water molecules with a contiguous hydrogen-bonding network facilitate Grotthuss proton conduction during redox reactions. When using it as a battery electrode, we find high-rate behaviours at 4,000 C (380 A g−1, 508 mA cm−2), and a long cycling life of 0.73 million cycles. These results for diffusion-free Grotthuss topochemistry of protons, in contrast to orthodox battery electrochemistry, which requires ion diffusion inside electrodes, indicate a potential direction to revolutionize electrochemical energy storage for high-power applications. This Article presents a battery with protons as the charge carrier, as opposed to Li-ion batteries, which rely on the transport of Li-ions. Protons are conducted by means of the Grotthuss mechanism in a hydrated Prussian blue analogue electrode, offering potential for ultrafast rate and long-life batteries.

Bridging the academic and industrial metrics for next-generation practical batteries.

Abstract: Batteries have shaped much of our modern world. This success is the result of intense collaboration between academia and industry over the past several decades, culminating with the advent of and improvements in rechargeable lithium-ion batteries. As applications become more demanding, there is the risk that stunted growth in the performance of commercial batteries will slow the adoption of important technologies such as electric vehicles. Yet the scientific literature includes many reports describing material designs with allegedly superior performance. A considerable gap needs to be filled if we wish these laboratory-based achievements to reach commercialization. In this Perspective, we discuss some of the most relevant testing parameters that are often overlooked in academic literature but are critical for practical applicability outside the laboratory. We explain metrics such as anode energy density, voltage hysteresis, mass of non-active cell components and anode/cathode mass ratio, and we make recommendations for future reporting. We hope that this Perspective, together with other similar guiding principles that have recently started to emerge, will aid the transition from lab-scale research to next-generation practical batteries. This Perspective discussed the best practices for reporting lab-scale performance metrics in battery papers.

In situ quantification of interphasial chemistry in Li-ion battery

Abstract: The solid-electrolyte interphase (SEI) is probably the least understood component in Li-ion batteries. Considerable effort has been put into understanding its formation and electrochemistry under realistic battery conditions, but mechanistic insights have mostly been inferred indirectly. Here we show the formation of the SEI between a graphite anode and a carbonate electrolyte through combined atomic-scale microscopy and in situ and operando techniques. In particular, we weigh the graphitic anode during its initial lithiation process with an electrochemical quartz crystal microbalance, which unequivocally identifies lithium fluoride and lithium alkylcarbonates as the main chemical components at different potentials. In situ gas analysis confirms the preferential reduction of cyclic over acyclic carbonate molecules, making its reduction product the major component in the SEI. We find that SEI formation starts at graphite edge sites with dimerization of solvated Li+ intercalation between graphite layers. We also show that this lithium salt, at least in its nascent form, can be re-oxidized, despite the general belief that an SEI is electrochemically inert and its formation irreversible.

Reverse Dual-Ion Battery via a ZnCl2 Water-in-Salt Electrolyte.

Abstract: Dual-ion batteries are known for anion storage in the cathode coupled to cation incorporation in the anode. We flip the sequence of the anion/cation-storage chemistries of the anode and the cathode...

Identification of MRP2 as a targetable factor limiting oxaliplatin accumulation and response in gastrointestinal cancer.

Abstract: Oxaliplatin is important for the clinical treatment of colorectal cancer and other gastrointestinal malignancies, but tumour resistance is limiting. Several oxaliplatin transporters were previously identified but their relative contributions to determining oxaliplatin tumour responses and gastrointestinal tumour cell sensitivity to oxaliplatin remains unclear. We studied clinical associations between tumour expression of oxaliplatin transporter candidate genes and patient response to oxaliplatin, then experimentally verified associations found with MRP2 in models of human gastrointestinal cancer. Among 18 oxaliplatin transporter candidate genes, MRP2 was the only one to be differentially expressed in the tumours of colorectal cancer patients who did or did not respond to FOLFOX chemotherapy. Over-expression of MRP2 (endogenously in HepG2 and PANC-1 cells, or induced by stable transfection of HEK293 cells) decreased oxaliplatin accumulation and cytotoxicity but those deficits were reversed by inhibition of MRP2 with myricetin or siRNA knockdown. Mice bearing subcutaneous HepG2 tumour xenografts were sensitised to oxaliplatin antitumour activity by concurrent myricetin treatment with little or no increase in toxicity. In conclusion, MRP2 limits oxaliplatin accumulation and response in human gastrointestinal cancer. Screening tumour MRP2 expression levels, to select patients for treatment with oxaliplatin-based chemotherapy alone or in combination with a MRP2 inhibitor, could improve treatment outcomes.

A Single-Atom Iridium Heterogeneous Catalyst in Oxygen Reduction Reaction.

Abstract: Combining the advantages of homogeneous and heterogeneous catalysts, single-atom catalysts (SACs) are bringing new opportunities to revolutionize ORR catalysis in terms of cost, activity and durability. However, the lack of high-performance SACs as well as the fundamental understanding of their unique catalytic mechanisms call for serious advances in this field. Herein, for the first time, we develop an Ir-N-C single-atom catalyst (Ir-SAC) which mimics homogeneous iridium porphyrins for high-efficiency ORR catalysis. In accordance with theoretical predictions, the as-developed Ir-SAC exhibits orders of magnitude higher ORR activity than iridium nanoparticles with a record-high turnover frequency (TOF) of 24.3 e- site-1 s-1 at 0.85 V vs. RHE) and an impressive mass activity of 12.2 A mg-1 Ir , which far outperforms the previously reported SACs and commercial Pt/C. Atomic structural characterizations and density functional theory calculations reveal that the high activity of Ir-SAC is attributed to the moderate adsorption energy of reaction intermediates on the mononuclear iridium ion coordinated with four nitrogen atom sites.

Challenges in Zinc Electrodes for Alkaline Zinc–Air Batteries: Obstacles to Commercialization

Abstract: Alkaline zinc–air batteries are promising energy storage technologies with the advantages of low cost, ecological friendliness, and high energy density. However, the rechargeable zinc–air battery has not been used on a commercial scale because the zinc electrode suffers from critical problems such as passivation, dendrite growth, and hydrogen evolution reaction, which limit the practical applications of zinc–air batteries. Herein, the Perspective summaries the solutions to minimize the negative effects of zinc electrodes on discharge performance, cycling life, and shelf life. The future direction of academic research based on current studies of the existing challenges is proposed.

High temperature shockwave stabilized single atoms.

Abstract: The stability of single-atom catalysts is critical for their practical applications. Although a high temperature can promote the bond formation between metal atoms and the substrate with an enhanced stability, it often causes atom agglomeration and is incompatible with many temperature-sensitive substrates. Here, we report using controllable high-temperature shockwaves to synthesize and stabilize single atoms at very high temperatures (1,500–2,000 K), achieved by a periodic on–off heating that features a short on state (55 ms) and a ten-times longer off state. The high temperature provides the activation energy for atom dispersion by forming thermodynamically favourable metal–defect bonds and the off-state critically ensures the overall stability, especially for the substrate. The resultant high-temperature single atoms exhibit a superior thermal stability as durable catalysts. The reported shockwave method is facile, ultrafast and universal (for example, Pt, Ru and Co single atoms, and carbon, C3N4 and TiO2 substrates), which opens a general route for single-atom manufacturing that is conventionally challenging. A repeated on–off high-temperature shockwave is shown to be a generalizable way of efficiently synthesizing and stabilizing single atoms at high temperatures.

Electrochemically activated spinel manganese oxide for rechargeable aqueous aluminum battery.

Abstract: Aluminum is a naturally abundant, trivalent charge carrier with high theoretical specific capacity and volumetric energy density, rendering aluminum-ion batteries a technology of choice for future large-scale energy storage. However, the frequent collapse of the host structure of the cathode materials and sluggish kinetics of aluminum ion diffusion have thus far hampered the realization of practical battery devices. Here, we synthesize AlxMnO2·nH2O by an in-situ electrochemical transformation reaction to be used as a cathode material for an aluminum-ion battery with a configuration of Al/Al(OTF)3-H2O/AlxMnO2·nH2O. This cell is not only based on aqueous electrolyte chemistry but also delivers a high specific capacity of 467 mAh g−1 and a record high energy density of 481 Wh kg−1. The high safety of aqueous electrolyte, facile cell assembly and the low cost of materials suggest that this aqueous aluminum-ion battery holds promise for large-scale energy applications. The instability of the host structure of cathode materials and sluggish aluminium ion diffusion are the major challenges facing the Al-ion battery. Here the authors show AlxMnO2·nH2O as a cathode that allows for reversible Al3+ (de)intercalation in an aqueous electrolyte and impressive electrochemical performance for a battery device.

Conductivity and lithiophilicity gradients guide lithium deposition to mitigate short circuits

Abstract: Lithium metal anodes hold great promise to enable high-energy battery systems. However, lithium dendrites at the interface between anode and separator pose risks of short circuits and fire, impeding the safe application. In contrast to conventional approaches of suppressing dendrites, here we show a deposition-regulating strategy by electrically passivating the top of a porous nickel scaffold and chemically activating the bottom of the scaffold to form conductivity/lithiophilicity gradients, whereby lithium is guided to deposit preferentially at the bottom of the anode, safely away from the separator. The resulting lithium anodes significantly reduce the probability of dendrite-induced short circuits. Crucially, excellent properties are also demonstrated at extremely high capacity (up to 40 mAh cm−2), high current density, and/or low temperatures (down to −15 °C), which readily induce dendrite shorts in particular. This facile and viable deposition-regulating strategy provides an approach to preferentially deposit lithium in safer positions, enabling a promising anode for next-generation lithium batteries. Here the authors report a deposition-regulating strategy to form conductivity and lithiophilicity gradients which serve to guide the preferential lithium growth away from the interface between anode and separator and mitigate the dendrite-induced short circuits.

Heterojunction Architecture of N-Doped WO3 Nanobundles with Ce2S3 Nanodots Hybridized on a Carbon Textile Enables a Highly Efficient Flexible Photocatalyst

Abstract: The availability of robust, versatile, and efficient photocatalysts is the main bottleneck in practical applications of photocatalytic degradation of organic pollutants. Herein, N‐WO3/Ce2S3 nanotube bundles (NBs) are synthesized and successfully immobilized on a carbon textile, resulting in a flexible and conducting photocatalyst. Due to the large interfacial area between N‐WO3 and Ce2S3, the interwoven 3D carbon architecture and, more importantly, the establishment of a heterojunction between N‐WO3 and Ce2S3, the resultant photocatalyst exhibits excellent light absorption capacity and superior ability to separate photoinduced electron–hole pairs for the photocatalytic degradation of organic compounds in air and water media. Theoretical calculations confirm that the strong electronic interaction between N‐WO3 and Ce2S3 can be beneficial to the enhancement of the charge carrier transfer dynamics of the as‐prepared photocatalyst. This work provides a new protocol for constructing efficient flexible photocatalysts for application in environmental remediation.

Cross-linked beta alumina nanowires with compact gel polymer electrolyte coating for ultra-stable sodium metal battery.

Abstract: Sodium metal batteries have potentially high energy densities, but severe sodium-dendrite growth and side reactions prevent their practical applications, especially at high temperatures. Herein, we design an inorganic ionic conductor/gel polymer electrolyte composite, where uniformly cross-linked beta alumina nanowires are compactly coated by a poly(vinylidene fluoride-co-hexafluoropropylene)-based gel polymer electrolyte through their strong molecular interactions. These beta alumina nanowires combined with the gel polymer layer create dense and homogeneous solid-liquid hybrid sodium-ion transportation channels through and along the nanowires, which promote uniform sodium deposition and formation of a stable and flat solid electrolyte interface on the sodium metal anode. Side reactions between the sodium metal and liquid electrolyte, as well as sodium dendrite formation, are successfully suppressed, especially at 60 °C. The sodium vanadium phosphate/sodium full cells with composite electrolyte exhibit 95.3% and 78.8% capacity retention after 1000 cycles at 1 C at 25 °C and 60 °C, respectively. Here the authors show a beta alumina nanowires/gel polymer composite electrolyte design. The dense and homogeneous solid-liquid hybrid sodium-ion transportation channels promote uniform sodium deposition and stripping and significantly improve the performance of a Na metal battery.

Interweaving 3D network binder for high-areal-capacity Si anode through combined hard and soft polymers

Abstract: Si anodes suffer an inherent volume expansion problem. The consensus is that hydrogen bonds in these anodes are preferentially constructed between the binder and Si powder for enhanced adhesion and thus can improve cycling performance. There has been little research done in the field of understanding the contribution of the binder's mechanical properties to performance. Herein, a simple but effective strategy is proposed, combining hard/soft polymer systems, to exploit a robust binder with a 3D interpenetrating binding network (3D-IBN) via an in situ polymerization. The 3D-IBN structure is constructed by interweaving a hard poly(furfuryl alcohol) as the skeleton with a soft polyvinyl alcohol (PVA) as the filler, buffering the dramatic volume change of the Si anode. The resulting Si anode delivers an areal capacity of >10 mAh cm−2 and enables an energy density of >300 Wh kg−1 in a full lithium-ion battery (LIB) cell. The component of the interweaving binder can be switched to other polymers, such as replacing PVA by thermoplastic polyurethane and styrene butadiene styrene. Such a strategy is also effective for other high-capacity electroactive materials, e.g., Fe2O3 and Sn. This finding offers an alternative approach in designing high-areal-capacity electrodes through combined hard and soft polymer binders for high-energy-density LIBs.

Heteroatom-Doped Porous Carbon Materials with Unprecedented High Volumetric Capacitive Performance

Abstract: The design of carbon-based materials with a high mass density and large porosity has always been a challenging goal, since they fulfill the demands of next-generation supercapacitors and other electrochemical devices. We report a new class of high-density heteroatom-doped porous carbon that can be used as an aqueous-based supercapacitor material. The material was synthesized by an in situ dehalogenation reaction between a halogenated conjugated diene and nitrogen-containing nucleophiles. Under the given conditions, pyridinium salts can only continue to perform the dehalogenation if there is residue water remaining from the starting materials. The obtained carbon materials are highly doped by various heteroatoms, leading to high densities, abundant multimodal pores, and an excellent volumetric capacitive performance. Porous carbon tri-doped with nitrogen, phosphorous, and oxygen exhibits a high packing density (2.13 g cm-3 ) and an exceptional volumetric energy density (36.8 Wh L-1 ) in alkaline electrolytes, making it competitive to even some Ni-MH cells.

Correlation between manganese dissolution and dynamic phase stability in spinel-based lithium-ion battery.

Abstract: Historically long accepted to be the singular root cause of capacity fading, transition metal dissolution has been reported to severely degrade the anode. However, its impact on the cathode behavior remains poorly understood. Here we show the correlation between capacity fading and phase/surface stability of an LiMn2O4 cathode. It is revealed that a combination of structural transformation and transition metal dissolution dominates the cathode capacity fading. LiMn2O4 exhibits irreversible phase transitions driven by manganese(III) disproportionation and Jahn-Teller distortion, which in conjunction with particle cracks results in serious manganese dissolution. Meanwhile, fast manganese dissolution in turn triggers irreversible structural evolution, and as such, forms a detrimental cycle constantly consuming active cathode components. Furthermore, lithium-rich LiMn2O4 with lithium/manganese disorder and surface reconstruction could effectively suppress the irreversible phase transition and manganese dissolution. These findings close the loop of understanding capacity fading mechanisms and allow for development of longer life batteries. To unlock the potential of Mn-based cathode materials, the fast capacity fading process has to be first understood. Here the authors utilize advanced characterization techniques to look at a spinel LiMn2O4 system, revealing that a combination of irreversible structural transformations and Mn dissolution takes responsibility.

A Quasi-Solid-State Flexible Fiber-Shaped Li-CO2 Battery with Low Overpotential and High Energy Efficiency.

Abstract: The rapid development of wearable electronics requires a revolution of power accessories regarding flexibility and energy density. The Li-CO2 battery was recently proposed as a novel and promising candidate for next-generation energy-storage systems. However, the current Li-CO2 batteries usually suffer from the difficulties of poor stability, low energy efficiency, and leakage of liquid electrolyte, and few flexible Li-CO2 batteries for wearable electronics have been reported so far. Herein, a quasi-solid-state flexible fiber-shaped Li-CO2 battery with low overpotential and high energy efficiency, by employing ultrafine Mo2 C nanoparticles anchored on a carbon nanotube (CNT) cloth freestanding hybrid film as the cathode, is demonstrated. Due to the synergistic effects of the CNT substrate and Mo2 C catalyst, it achieves a low charge potential below 3.4 V, a high energy efficiency of ≈80%, and can be reversibly discharged and charged for 40 cycles. Experimental results and theoretical simulation show that the intermediate discharge product Li2 C2 O4 stabilized by Mo2 C via coordinative electrons transfer should be responsible for the reduction of overpotential. The as-fabricated quasi-solid-state flexible fiber-shaped Li-CO2 battery can also keep working normally even under various deformation conditions, giving it great potential of becoming an advanced energy accessory for wearable electronics.

Bamboo-Like Nitrogen-Doped Carbon Nanotube Forests as Durable Metal-Free Catalysts for Self-Powered Flexible Li-CO2 Batteries.

Abstract: The Li-CO2 battery is a promising energy storage device for wearable electronics due to its long discharge plateau, high energy density, and environmental friendliness. However, its utilization is largely hindered by poor cyclability and mechanical rigidity due to the lack of a flexible and durable catalyst electrode. Herein, flexible fiber-shaped Li-CO2 batteries with ultralong cycle-life, high rate capability, and large specific capacity are fabricated, employing bamboo-like N-doped carbon nanotube fiber (B-NCNT) as flexible, durable metal-free catalysts for both CO2 reduction and evolution reactions. Benefiting from high N-doping with abundant pyridinic groups, rich defects, and active sites of the periodic bamboo-like nodes, the fabricated Li-CO2 battery shows outstanding electrochemical performance with high full-discharge capacity of 23 328 mAh g-1 , high rate capability with a low potential gap up to 1.96 V at a current density of 1000 mA g-1 , stability over 360 cycles, and good flexibility. Meanwhile, the bifunctional B-NCNT is used as the counter electrode for a fiber-shaped dye-sensitized solar cell to fabricate a self-powered fiber-shaped Li-CO2 battery with overall photochemical-electric energy conversion efficiency of up to 4.6%. Along with a stable voltage output, this design demonstrates great adaptability and application potentiality in wearable electronics with a breath monitor as an example.

Single-cell microRNA-mRNA co-sequencing reveals non-genetic heterogeneity and mechanisms of microRNA regulation

Abstract: Measuring multiple omics profiles from the same single cell opens up the opportunity to decode molecular regulation that underlies intercellular heterogeneity in development and disease. Here, we present co-sequencing of microRNAs and mRNAs in the same single cell using a half-cell genomics approach. This method demonstrates good robustness (~95% success rate) and reproducibility (R2 = 0.93 for both microRNAs and mRNAs), yielding paired half-cell microRNA and mRNA profiles, which we can independently validate. By linking the level of microRNAs to the expression of predicted target mRNAs across 19 single cells that are phenotypically identical, we observe that the predicted targets are significantly anti-correlated with the variation of abundantly expressed microRNAs. This suggests that microRNA expression variability alone may lead to non-genetic cell-to-cell heterogeneity. Genome-scale analysis of paired microRNA-mRNA co-profiles further allows us to derive and validate regulatory relationships of cellular pathways controlling microRNA expression and intercellular variability. Single-cell RNA sequencing allows characterizing cell-to-cell heterogeneity at transcriptome scale. Here, the authors present an approach that enables microRNA and mRNA sequencing in the same single cell, providing insights into the origins of non-genetic cellular variability and mechanisms of miRNA regulation.