High Rate, Dendrite Free Lithium Metal Batteries of Extended Cyclability via a Scalable Separator Modification Approach.

Owing to their great promise of high energy density, the development of safer lithium metal batteries (LMBs) has become the necessity of the hour. Herein, a scalable method based on conventional Celgard membrane (CM) separator modification is adopted to develop high-rate (10 mA cm-2 ) dendrite-free LMBs of extended cyclability (>1000 hours, >1500 cycles with 3 mA cm-2 , the bare fails within 50 cycles) with low over potential losses. The CM modification method entails the deposition of thin coatings of (≈6.6 µm) graphitic fluorocarbon (FG) via a large area electrophoretic deposition, where it helps for the formation of a stable LiF and carbon rich solid electrolyte interface (SEI) aiding a uniform lithium deposition even in higher fluxes. The FG@CM delivers a high transport number for Li ion (0.74) in comparison to the bare CM (0.31), indicating a facile Li ion transport through the membrane. A mechanistic insight into the role of artificial SEI formation with such membrane modification is provided here with a series of electrochemical as well as spectroscopic in situ/ex situ and postmortem analyses. The simplicity and scalability of the technique make this approach unique among other reported ones towards the advancement of safer LMBs of high energy and power density.

Photo-Rechargeable Li-Ion Batteries using TiS2 Cathode.

Photo-rechargeable (solar) battery can be considered as an energy harvesting cum storage system, where it can charge the conventional metal-ion battery using light instead of electricity, without having other parasitic reactions. Here a two-electrode lithium-ion solar battery with multifaceted TiS2 -TiO2 hybrid sheets as cathode. The choice of TiS2 -TiO2 electrode ensures the formation of a type II semiconductor heterostructure while the lateral heterostructure geometry ensures high mass/charge transfer and light interactions with the electrode. TiS2 has a higher lithium binding energy (1.6 eV) than TiO2 (1.03 eV), ensuring the possibilities of higher amount of Li-ion insertion to TiS2 and hence the maximum recovery with the photocharging, as further confirmed by the experiments. Apart from the demonstration of solar solid-state batteries, the charging of lithium-ion full cell with light indicates the formation of lithium intercalated graphite compounds, ensuring the charging of the battery without any other parasitic reactions at the electrolyte or electrode-electrolyte interfaces. Possible mechanisms proposed here for the charging and discharging processes of solar batteries, based on the experimental and theoretical results, indicate the potential of such systems in the forthcoming era of renewable energies.

A Synergistic View on Osmolyte's Role against Salt and Cold Stress in Biointerfaces.

We present our perspective on the role of osmolytes in mitigating abiotic stresses such as hypersalinity and sudden temperature changes. While the stabilizing effect of osmolytes on protein tertiary structures has been extensively studied, their direct impact on abiotic stress factors has eluded mainstream attention. Via highlighting a set of recent success stories of a joint venture of computer simulations and experimental measurements, we summarize the mechanistic insights into osmolytic action, particularly in the context of salt stress and combined cold-salt stress at the interface of biomolecular surfaces and saline environments. We stress the importance of chemical specificity in osmolytic activity, the interplay of differential osmolytic behaviors against heterogeneous salt stress, and the capability of osmolytes to adopt combined actions. Additionally, we discuss the potential of incorporating nanomaterial-based systems to enrich our understanding of osmolyte bioactions and facilitate their practical applications. We anticipate that this discourse will inspire interdisciplinary collaborations and motivate further investigations on osmolytes, ultimately broadening their applications in the fields of health and disease.

Two-Dimensional Iron Phosphorus Trisulfide as a High-Capacity Cathode for Lithium Primary Battery.

Metal phosphorus trichalcogenide (MPX3) materials have aroused substantial curiosity in the evolution of electrochemical storage devices due to their environment-friendliness and advantageous X-P synergic effects. The interesting intercalation properties generated due to the presence of wide van der Waals gaps along with high theoretical specific capacity pose MPX3 as a potential host electrode in lithium batteries. Herein, we synthesized two-dimensional iron thio-phosphate (FePS3) nanoflakes via a salt-template synthesis method, using low-temperature time synthesis conditions in single step. The electrochemical application of FePS3 has been explored through the construction of a high-capacity lithium primary battery (LPB) coin cell with FePS3 nanoflakes as the cathode. The galvanostatic discharge studies on the assembled LPB exhibit a high specific capacity of ~1791 mAh g-1 and high energy density of ~2500 Wh Kg-1 along with a power density of ~5226 W Kg-1, some of the highest reported values, indicating FePS3's potential in low-cost primary batteries. A mechanistic insight into the observed three-staged discharge mechanism of the FePS3-based primary cell resulting in the high capacity is provided, and the findings are supported via post-mortem analyses at the electrode scale, using both electrochemical- as well as photoelectron spectroscopy-based studies.

Realizing 1,1-Dehydration of Secondary Alcohols to Carbenes: Pyrrolidin-2-ols as a Source of Cyclic (Alkyl)(Amino)Carbenes.

Herein we report secondary pyrrolidin-2-ols as a source of cyclic (alkyl)(amino)carbenes (CAAC) for the synthesis of CAAC-CuI -complexes and cyclic thiones when reacted with CuI -salts and elemental sulfur, respectively, under reductive elimination of water from the carbon(IV)-center. This result demonstrates a convenient and facile access to CAAC-based CuI -salts, which are well known catalysts for different organic transformations. It further establishes secondary alcohols to be a viable source of carbenes-realizing after 185 years Dumas' dream who tried to prepare the parent carbene (CH2 ) by 1,1-dehydration of methanol. Addressed is also the reactivity of water towards CAACs, which proceeds through an oxidative addition of the O-H bond to the carbon(II)-center. This emphasizes the ability of carbon-compounds to mimic the reactivity of transition-metal complexes: reversible oxidative addition and reductive elimination of the O-H bond to/from the C(II)/C(IV)-centre.

Photo Rechargeable Li-Ion Batteries Using Nanorod Heterostructure Electrodes.

New ways of directly using solar energy to charge electrochemical energy storage devices such as batteries would lead to exciting developments in energy technologies. Here, a two-electrode photo rechargeable Li-ion battery is demonstrated using nanorod of type II semiconductor heterostructures with in-plane domains of crystalline MoS2 and amorphous MoOx . The staggered energy band alignment of MoS2 and MoOx limits the electron holes recombination and causes holes to be retained in the Li intercalated MoS2 electrode. The holes generated in the MoS2 pushes the intercalated Li-ions and hence charge the battery. Low band gap, high efficiency photo-conversion and efficient electron-hole separation help the battery to fully charge within a few hours using solar light. The proposed concept and materials can enable next generation stable photo-rechargeable battery electrodes, in contrast to the reported materials.

Lithium, sodium and magnesium ion conduction in solid state mixed polymer electrolytes.

Alkali and alkaline earth metal-ion batteries are currently among the most efficient electrochemical energy storage devices. However, their stability and safety performance are greatly limited when used with volatile organic liquid electrolytes. A solid state polymer electrolyte is a prospective solution even though poor ionic conductivity at room temperature remains a bottleneck. Here we propose the mixing of two similar polymer matrices, poly(dimethyl siloxane) and poly(ethylene oxide), to address this challenge. The resulting electrolyte matrix is denser and significantly improves room-temperature ionic conductivity. Ab initio analyses of the reaction between the cations and the polymers show that oxygen sites act as entrapment sites for the cations and that ionic conduction likely occurs through hopping between adjacent oxygen sites. Molecular dynamics simulations of the dynamics of both polymers and the dynamics of the polymer mix show that the more frequent and more pronounced molecular vibrations of the polymer mix are likely responsible for reducing the time between two consecutive oxygen entrapments, thereby speeding up the conduction process. This hypothesis is experimentally validated by the practically useful ionic conductivity (σ≈ 10-4 S cm-1 at 25 °C) and the improved safety parameters exhibited by a transparent flexible multi-cation (Li+, Na+ and Mg2+) conducting solid channel made up of the above mixed polymer system.

Graphene-hBN non-van der Waals vertical heterostructures for four- electron oxygen reduction reaction.

A novel vertical non-van der Waals (non-vdW) heterostructure of graphene and hexagonal boron nitride (G/hBN) is realized and its application in direct four-electron oxygen reduction reaction (ORR) in alkaline medium is established. The G/hBN differs from previously demonstrated vdW heterostructures, where it has a chemical bridging between graphene and hBN allowing a direct charge transfer - resulting in high ORR activity. The ORR efficacy of G/hBN is compared with that of graphene-hBN vdW structure and individual layers of graphene and hBN along with that of benchmark platinum/carbon (Pt/C). The ORR activity of G/hBN is found to be on par with Pt/C in terms of current density but with much higher electrochemical stability and methanol tolerance. The onset potential of the G/hBN is found to be improved from 780 mV at a glassy carbon electrode to 930 mV and 940 mV in gold and platinum electrodes, respectively, indicating its substrate-dependent catalytic activity. This opens possibilities of new benchmark catalysts of metals capped with G/hBN atomic layers, where the underneath metal is protected while keeping the activity similar to that of pristine metal. Density functional theory-based calculations are found to be supporting the observed augmented ORR performance of G/hBN.

On the hydrogen evolution reaction activity of graphene-hBN van der Waals heterostructures.

Although graphene technology has reached technology readiness level 9 and hydrogen fuel has been identified as a viable futuristic energy resource, pristine atomic layers such as graphene are found to be inactive towards the hydrogen evolution reaction (HER). Enhancing the intrinsic catalytic activity of a material and increasing its number of active sites by nanostructuring are two strategies in novel catalyst development. Here, electrocatalytically inert graphene (G) and hexagonal boron nitride (hBN) are made active for the HER by forming van der Waals (vdW) heterostructures via vertical stacking. The HER studies are conducted using defect free shear exfoliated graphite and hBN modified glassy carbon electrodes via layer by layer sequential stacking. The G/hBN stacking pattern (AA, AB, and AB') and stacking sequence (G/hBN or hBN/G) have been found to play important roles in the HER activity. Enhancement in the intrinsic activity of graphene by the formation of G/hBN vdW stacks has been further confirmed with thermally reduced graphene oxide and hBN based structures. Tunability in the HER performance of the G/hBN vdW stack is also confirmed via a three-dimensional rGO/hBN electrode. HER active sites in the G/hBN vdW structures are then mapped using density functional theory calculations, and an atomistic interpretation has been identified.

Stacking sequence dependent photo-electrocatalytic performance of CVD grown MoS2/graphene van der Waals solids.

New layered solids by the combinatorial stacking of different atomic layers are emanating as novel candidates for energy efficient devices. Here, sequentially stacked single layer graphene-molybdenum disulfide (MoS2) van der Waals (vdW) solids are demonstrated for their efficacy in the catalysis of hydrogen evolution reaction (HER), and importance of their stacking order in tuning the photo-electrocatalytic (PEC) efficiency is unraveled. Single layer graphene and a few layered MoS2 stacked vdW solids based transparent flexible electrodes were prepared, and a particular stacking sequence where top-graphene: bottom-MoS2/polydimethylsiloxane (PDMS) geometry (MSGR) exhibited the lowest onset and over potentials and a very high exchange current density (j 0 âˆ¼ 245 ± 1 µA cm-2) in acidic HER in comparison to the individual layers and other stacked configuration (MoS2 on top of graphene on PDMS, GRMS). The HER studies under dark and white light illuminations were conducted to explore the PEC responses of the devices. The augmented HER performance of MSGR is further confirmed from the charge transfer resistance measurements using electrochemical impedance spectroscopy. Role of graphene plasmonics and MoS2 to graphene electron transfer were studied, and this study unravels the importance of a new factor, stacking order of vdW layers, while designing novel devices from the layered solids.

On the development of multifunctional luminescent supramolecular hydrogel of gold and egg white.

Highly stable, luminescent, and printable/paintable supramolecular egg white hydrogel-based surface enhanced Raman scattering (SERS) matrix is created by an in situ synthesis of gold clusters inside a luminescent egg white hydrogel (Au-Gel). The synthesis of stable luminescent egg-white-based hydrogel, where the hydrogel can act as a three dimensional (3D) matrix, using a simple cross-linking chemistry, has promising application in the biomedical field including in 3D cell culturing. Furthermore, this functional hydrogel is demonstrated for micromolar-level detection of Rhodamine 6G using the SERS technique, where Au-Gel is painted over a flexible cellulose pad.

Single step, bulk synthesis of engineered MoS2 quantum dots for multifunctional electrocatalysis.

Bi- or tri- functional catalysts based on atomic layers are receiving tremendous scientific attention due to their importance in various energy technologies. Recent studies on molybdenum disulphide (MoS2) nanosheets revealed that controlling the edge states and doping/modifying with suitable elements are highly important in tuning the catalytic activities of MoS2. Here we report a bulk, single step method to synthesize metal modified MoS2 quantum dots (QDs). Three elements, namely Fe, Mg and Li, are chosen to study the effects of dopants in the catalytic activities of MoS2. Fe and Mg are found to act like dopants in the MoS2 lattice forming respective doped MoS2 QDs, while Li formed an intercalated MoS2 QD. The efficacy and tunability of these luminescent doped QDs towards various electrocatalytic activities (hydrogen evolution reaction, oxygen evolution reaction and oxygen reduction action) are reported here.

3D macroporous solids from chemically cross-linked carbon nanotubes.

Suzuki reaction for covalently interconnected 3D carbon nanotube (CNT) architectures is reported. The synthesis of 3D macroscopic solids made of CNTs covalently connected via Suzuki cross-coupling, a well-known carbon-carbon covalent bond forming reaction in organic chemistry, is scalable. The resulting solid has a highly porous, interconnected structure of chemically cross-linked CNTs. Its use for the removal of oil from contaminated water is demonstrated.

Probing the biocompatibility of MoS2 nanosheets by cytotoxicity assay and electrical impedance spectroscopy.

Transition metal dichalgogenides such as MoS2 have recently emerged as hot two-dimensional (2D) materials due to their superior electronic and catalytic properties. Recently, we have reported the usefulness of MoS2 nanosheets toward the electrochemical detection of neurotransmitters and glucose (Narayanan et al 2014 Nanotechnology 25 335702). Furthermore, there are reports available in the literature that demonstrate the usefulness of MoS2 nanosheets for biosensing and energy storage applications (Zhu et al 2013 J. Am. Chem. Soc. 135 5998-6001; Pumera and Loo 2014 Trends Anal. Chem. 61 49-53; Lee et al 2014 Sci. Rep. 4 7352; Stephenson et al 2014 Energy Environ. Sci. 7 209-31). Understanding the cytotoxic effect of any material is very important prior to employing them for any in vivo biological applications such as implantable sensors, chips, or carriers for drug delivery and cell imaging purposes. Herein, we report the cytotoxicity of the MoS2 nanosheets based on the cytotoxic assay results and electrical impedance analysis using rat pheochromocytoma cells (PC12) and rat adrenal medulla endothelial cells (RAMEC). Our results indicated that the MoS2 nanosheets synthesized in our work are safe 2D nanosheets for futuristic biomedical applications.

Selective and efficient electrochemical biosensing of ultrathin molybdenum disulfide sheets.

Atomically thin molybdenum disulfide (MoS2) sheets were synthesized and isolated via solvent-assisted chemical exfoliation. The charge-dependent electrochemical activities of these MoS2 sheets were studied using positively charged hexamine ruthenium (III) chloride and negatively charged ferricyanide/ferrocyanide redox probes. Ultrathin MoS2 sheet-based electrodes were employed for the electrochemical detection of an important neurotransmitter, namely dopamine (DA), in the presence of ascorbic acid (AA). MoS2 electrodes were identified as being capable of distinguishing the coexistence of the DA and the AA with an excellent stability. Moreover, the enzymatic detection of the glucose was studied by immobilizing glucose oxidase on the MoS2. This study opens enzymatic and non-enzymatic electrochemical biosensing applications of atomic MoS2 sheets, which will supplement their established electronic applications.

Understanding electrochemical interfaces through comparing experimental and computational charge density-potential curves.

Electrode-electrolyte interfaces play a decisive role in electrochemical charge accumulation and transfer processes. Theoretical modelling of these interfaces is critical to decipher the microscopic details of such phenomena. Different force field-based molecular dynamics protocols are compared here in a view to connect calculated and experimental charge density-potential relationships. Platinum-aqueous electrolyte interfaces are taken as a model. The potential of using experimental charge density-potential curves to transform cell voltage into electrode potential in force-field molecular dynamics simulations, and the need for that purpose of developing simulation protocols that can accurately calculate the double-layer capacitance, are discussed.

Ultra-Low-Loaded Platinum Bonded Hexagonal Boron Nitride as Stable Electrocatalyst for Hydrogen Generation.

Chemical stability of hexagonal boron nitride (hBN) ultrathin layers in harsh electrolytes and the availability of nitrogen site in hBN to stabilize metals like Pt are used here to develop a high intrinsic activity hydrogen evolution reaction (HER) catalyst having low loaded Pt (5 weight% or <1 atomic%). A catalyst having a nonzero oxidation state for Pt (with a Pt-N bonding) is shown to be HER active even with low catalyst loadings (0.114 mgcm-2). Electronic modification of the shear exfoliated hBN sheets is achieved by Au nanoparticle-based surface decoration (hBN_Au), and further anchoring with Pt develops a catalyst (hBN_Au_Pt) with high turnover frequency for HER (∼15). The hBN_Au_Pt is shown to be a highly durable catalyst even after the accelerated durability test for 10000 cycles and temperature annealing at 100 °C. Density functional theory based calculations gave insights in to the electronic modifications of hBN with Au and the catalytic activity of the hBN_Au_Pt system, in line with the experimental studies, indicating the demonstration of a new class of catalyst system devoid of issues such as carbon corrosion and Pt leaching.

Polysaccharide Modified Cathodes for High-Capacity Rechargeable Nonaqueous Li-O2 Batteries.

Nonaqueous rechargeable Li-O2 batteries are recognized as possible alternatives to the currently established Li-ion battery technology for next-generation traction by virtue of their high specific energy. However, the technology is still far from commercial realization mainly due to the performance-limiting reactions at the cathode. The insulating discharge product, Li2O2, can passivate the cathode leading to issues such as low specific capacity and early cell death. Herein, the -OH functionalities at the cathode, incorporated by polysaccharide addition, are shown to enhance the discharge capacity and cyclability. The -OH functional group (high pKa) at the cathode helps to stabilize the intermediate, LiO2, via an energetically favorable pathway and delays the precipitation to Li2O2, without any parasitic reaction, unlike the other reported low pKa additives. The role of the functionalities is studied using various experimental techniques and first principles density functional theory based studies. This approach provides a rational design route for the cathodes that provide high capacities for the emergent Li-O2 batteries.

Osmolytes as Cryoprotectants under Salt Stress.

Cryoprotecting agent (CPA)-guided preservation is essential for effective protection of cells from cryoinjuries. However, current cryoprotecting technologies practiced to cryopreserve cells for biomedical applications are met with extreme challenges due to the associated toxicity of CPAs. Because of these limitations of present CPAs, the quest for nontoxic alternatives for useful application in cell-based biomedicines has been attracting growing interest. Toward this end, here, we investigate naturally occurring osmolytes' scope as biocompatible cryoprotectants under cold stress conditions in high-saline medium. Via a combination of the simulation and experiment on charged silica nanostructures, we render first-hand evidence that a pair of archetypal osmolytes, glycine and betaine, would act as a cryoprotectant by restoring the indigenous intersurface electrostatic interaction, which had been a priori screened due to the cold effect under salt stress. While these osmolytes' individual modes of action are sensitive to subtle chemical variation, a uniform augmentation in the extent of osmolytic activity is observed with an increase in temperature to counter the proportionately enhanced salt screening. The trend as noted in inorganic nanostructures is found to be recurrent and robustly transferable in a charged protein interface. In hindsight, our observation justifies the sufficiency of the reduced requirement of osmolytes in cells during critical cold conditions and encourages their direct usage and biomimicry for cryopreservation.

Soft pinning: Experimental validation of static correlations in supercooled molecular glass-forming liquids.

Enormous enhancement in the viscosity of a liquid near its glass transition is a hallmark of glass transition. Within a class of theoretical frameworks, it is connected to growing many-body static correlations near the transition, often called "amorphous ordering." At the same time, some theories do not invoke the existence of such a static length scale in the problem. Thus, proving the existence and possible estimation of the static length scales of amorphous order in different glass-forming liquids is very important to validate or falsify the predictions of these theories and unravel the true physics of glass formation. Experiments on molecular glass-forming liquids become pivotal in this scenario as the viscosity grows several folds (∼1014), and simulations or colloidal glass experiments fail to access these required long-time scales. Here we design an experiment to extract the static length scales in molecular liquids using dilute amounts of another large molecule as a pinning site. Results from dielectric relaxation experiments on supercooled Glycerol with different pinning concentrations of Sorbitol and Glucose, as well as the simulations on a few model glass-forming liquids with pinning sites, indicate the versatility of the proposed method, opening possible new avenues to study the physics of glass transition in other molecular liquids.