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Metal matrix composites have attracted extensive attention from both the research and industrial perspective. In this study, we prepared aluminum-reduced graphene oxide (Al–rGO) composites with enhanced thermal conductivity in an easy single-step process. Pristine Al shows a thermal conductivity of 175 Wm−1K−1 (standard deviation

Development of metal dichalcogenides based air and water stable opto-electronic devices is a bottleneck in their commercial implementation. Here we address this issue by the direct catalyst-free deposition of fluorographene (FG) protective layer over monolayer MoS2 (MS), where such an atomic interface is found to be providing enormous photoresponse and chemical stability to the device. Electric field modulated (ionic liquid (IL) electrolyte based top-gated) photodetectors are developed with MS only and FG-MS heterostructure, where the MS photodetector has the responsivity of ~1.3 A/W (with VGS = 0 V while unstable with IL gating) while that of FG-MS is ~2000 A/W (with VGS = 0 V and ~8000 A/W with VGS = 1.5 V, and the detectivity ~1013). This giant photoresponse of the FG-MS is validated with the help of ultrafast transient absorption spectroscopy assisted charge carrier dynamics studies at different temperatures. The broad optical response (350–850 nm) of the FG-MS is found to be intact not only in IL based gating but also after exposing in water for a month or heat treated in air at 200 °C. Interfacing and capping with FG, developed via the direct growth method, are found to be ideal for realizing high shelf-life and good responsivity photodetectors and solar cells of several other monolayer TMDs too, while available for wafer-scale manufacture.

Tweaking the electrolyte of the anode compartment of zinc-air battery (ZAB) system is shown to be extending the charge-discharge cyclability of the cell. An alkaline zinc (Zn)-air cell working for ∼32 h (192 cycles) without failure is extended to >55 h (>330 cycles) by modifying the anode compartment with a mixture electrolyte of KOH and LiOH. The cell containing the mixture electrolyte has a low overpotential for charging along with high discharge capacity. The role of Li+ ions in tuning the electrode morphology and electrodics is studied both theoretically and experimentally. The synergistic effect of Li+ and K+ ions in the electrolyte on improved ZAB performance is proven. This study can pave new ways for the commercial implementation of ZAB, where it has already proven its potential in low-cost, high energy density, and mobility applications.

To counter the stress of a salt imbalance, the cell often produces low molecular weight osmolytes to resuscitate homeostasis. However, how zwitterionic osmolytes would tune the electrostatic interactions among charged biomacromolecular surfaces under salt stress has eluded mainstream investigations. Here, via combination of molecular simulation and experiment, we demonstrate that a set of zwitterionic osmolytes is able to restore the electrostatic interaction between two negatively charged surfaces that had been masked in the presence of salt. Interestingly, the mechanisms of resurrecting charge interaction under excess salt are revealed to be mutually divergent and osmolyte specific. In particular, glycine is found to competitively desorb the salt ions from the surface via its direct interaction with the surface. On the contrary, TMAO and betaine counteract salt stress by retaining adsorbed cations but partially neutralizing their charge density via ion-mediated interaction. These access to alternative modes of osmolytic actions would provide the cell the required flexibility in combating salt stress.

Protein assisted electrochemical hydrogen evolution catalyst development has been proposed here. The surfaces of carbon nanotubes (CNTs) and bulk MoS2 are modified with the metalloprotein cytochrome c, where the CNT–protein covalent functionalization is found to be attained via electrochemical cycling in acid medium. The hydrophobic interaction mediated surface modification of MoS2 is found to produce a highly active hydrogen evolution catalyst, much superior to bare MoS2 crystals while on par with CNT functionalized protein catalysts. Hence a strategy for active catalyst development which works both in bulk and nanomaterials is established.

Quantum dots (QDs), owing to their single atom-like electronic structure due to quantum confinement, are often referred to as artificial atoms. This unique physical property results in the diverse functions exhibited by QDs. A wide array of applications have been achieved by the surface functionalization of QDs, resulting in exceptional optical, antimicrobial, catalytic, cytotoxic and enzyme inhibition properties. Ordinarily, traditionally prepared QDs are subjected to post synthesis functionalization via a variety of methods, such as ligand exchange or covalent and non-covalent conjugation. Nevertheless, solvent toxicity, combined with the high temperature and pressure conditions during the preparation of QDs and the low product yield due to multiple steps in the functionalization, limit their overall use. This has driven scientists to investigate the development of greener, environmental friendly and cost-effective methods that can circumvent the complexity and strenuousness associated with traditional processes of bio-functionalization. In this review, a detailed analysis of the methods to bio-prepare pre-functionalized QDs, with elucidated mechanisms, and their application in the areas of catalysis and biomedical applications has been conducted. The environmental and health and safety aspects of the bio-derived QDs have been briefly discussed to unveil the future of nano-commercialization.

Rational design of a catalyst using earth abundant transition metals that can facilitate the smooth O–O bond formation is crucial for developing efficient water oxidation catalysts. The coordination environment around the metal ion of the catalyst plays a pivotal role in this context. We have chosen dinuclear mixed-valence CoIIICoII complexes of the general formula of [CoIIICoII(LH2)2(X)(H2O)] (X = OAc or Cl) which bear a coordinated water molecule in the primary coordination sphere. We anticipated that the water molecule in the primary sphere can take part in the proton coupled electron transfer (PCET) mechanism which can accelerate the facile formation of the O–O bond under strong alkaline conditions (1 M NaOH). To understand the role of the coordinated water molecule we have generated an analogous complex, [CoIIICoII(LH2)2(o-vanillin)] (o-vanillin = 2-hydroxy-3-methoxybenzaldehyde), without coordinated water. Interestingly, we have found that the water coordinated complexes show better oxygen evolution reaction (OER) activity and stability.

Herein we report secondary pyrrolidin-2-ols as a source of cyclic (alkyl)(amino)carbenes (CAAC) for the synthesis of CAAC-Cu-I-complexes and cyclic thiones when reacted with Cu-I-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 Cu-I-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.

Magnetic/non-magnetic/heterostructured ultra-thin films' characterisation is highly demanding due to the emerging diverse applications of such films. Diverse measurements are usually performed on such systems to infer their electrical, optical and magnetic properties. We demonstrate that MOKE-based spin-Hall effect of light (SHEL) is a versatile surface characterization tool for studying materials' magnetic and dielectric ordering. Using this technique, we measure magnetic field dependent complex Kerr angle and the coercivity in ultra-thin films of permalloy (Py) and at molybdenum disulphide (MoS$_2$) - permalloy (MSPy) hetero-structure interfaces. The measurements are compared with standard magneto-optic Kerr effect (MOKE) studies to demonstrate that SHEL-MOKE is a practical alternative to the conventional MOKE method, with competitive sensitivity. A comprehensive theoretical model and simulation data are provided to further strengthen the potential of this simple non-invasive optical method. The theoretical model is applied to extract the optical conductivity and susceptibility of non-magnetic ultra-thin layers such as MoS$_2$ ., 15 pages, 7 figure, one supplementary document

Atomic layers are sought after for molecular sensing due to their available high surface interaction area, and different types of monolayers are attempted for sensing in the recent past. However, their chemical stability towards these molecules is questioned in recent times and alternate methods need to be developed to circumvent such issues, while maintaining high sensitivity. Here, the van der Waals (vdWs) stacks of molybdenum disulfide (MoS2) and graphene are shown for their stable electrochemical sensing towards ascorbic acid (AA) and dopamine (DA)—two important biomolecules. AA is known to chemically react with MoS2 leading to unstable sensing platform, while here the graphene coverage is shown to protect the MoS2 even from low-energy plasma exposure while keeping the same high sensitivity. Upon proving the graphene-based protection of the sensor, such a sensing platform is shown for its applicability in DA sensing, where it is found to give a linear response in a wide range of concentrations (2.5 to 600 µmol·L−1) and even selective sensing in the presence of AA. Such a stack is found to be not merely giving protection to the beneath MoS2 layer but also the inter-layer charge transfer due to work function differences being beneficial in bringing fast and high sensitivity to the next-generation sensors and point-of-care devices.

In recent years, there has been an increasing interest in designing economically viable metal-free carbon-supported catalysts for hydrogen-based energy technologies. Here we propose carbon nanotubes (CNTs) covalently functionalized with peptides or proteins as effective catalysts for electrochemical hydrogen evolution reaction (HER). We demonstrate that the HER activity of pristine CNTs can be greatly enhanced via simple functionalization by electrically insulating macromolecules. The roles of the conductive residues and the nitrogen content of the proteins, as well as the importance of their covalent connectivity with the CNTs, have been established. Moreover, we have observed a multifold enhancement in the HER current density due to electrochemical protein denaturation induced by the acidic medium used for HER. We have provided mechanistic insights into the HER activity of different metal-free peptides and proteins. Our work opens up new avenues in carbon-based metal-free HER catalysis, where, by careful selection of natural proteins, both the onset potential and the current density of the HER can be augmented.

Fluorographene (FG) ultra-thin films are directly grown on flexible and non-flexible insulating silicate substrates and are characterized in terms of their structural and electronic properties. FG ...

On-site peroxide generation via electrochemical reduction is gaining tremendous attention due to its importance in many fields, including water treatment technologies. Oxidized graphitic carbon-based materials have been recently proposed as an alternative to metal-based catalysts in the electrochemical oxygen reduction reaction (ORR), and in this work we unravel the role of C=O groups in graphene towards sustainable peroxide formation. We demonstrate a versatile single-step electrochemical exfoliation of graphite to graphene with a controllable degree of oxygen functionalities and thickness, leading to the formation of large quantities of functionalized graphene with tunable rate parameters, such as the rate constant and exchange current density. Higher oxygen-containing exfoliated graphene is known to undergo a two-electron reduction path in ORR having an efficiency of about 80 ± 2% even at high overpotential. Bulk production of H2O2 via electrolysis was also demonstrated at low potential (0.358 mV vs RHE), yielding ≈34 mg/L peroxide with highly functionalized (≈23 atom %) graphene and ≈16 g/L with low functionalized (≈13 atom %) graphene, which is on par with the peroxide production using state-of-the-art precious-metal-based catalysts. Hence this method opens a new scheme for the single-step large-scale production of functionalized carbon-based catalysts (yield ≈45% by weight) that have varying functionalities and can deliver peroxide via the electrochemical ORR process.

The boron–carbon–nitrogen (B–C–N) ternary phase diagram is rich with several stable phases. But experimentally exploring the vast array of plausible phases in atomically thin layers is quite challenging. BCN structures vary in nature with the method of preparation, which contributes to differences in their physical properties, particularly while studying photo/electrocatalytic applications. Here, we present a molecular dynamics (MD) approach to study the structural evolution of BCN systems, using the reactive force field (ReaxFF). ReaxFF-based MD simulations allow observation of bond breaking/making in BCN systems, in real time. This helps unravel physically stable structures for B,N-singly and co-doped GO. These predicted structures are subsequently realized in experiments, and characterised via various spectroscopic techniques. We further study the electrochemical activity of these structures for the hydrogen evolution reaction. Specifically, in B,N co-doped systems, we find that the electrocatalytic activity changes considerably if we consider separated doping or domain doping. Together, by combining simulation and experiments, this work shows a structure–property relationship of BCN structures, which ultimately governs their electrocatalytic activity towards the hydrogen evolution reaction.

Though the role of supporting ions such as Li ions (Li+) in the electrochemical hydrogen evolution reaction (HER) has been extensively studied in the recent past, the fundamental mechanism influencing the HER kinetics of different metals under varied electrolyte conditions is still not known. Here we unveil the mechanism leading to a tunable HER on different metals under varying pH conditions, and it is established that despite the nominal role of counter anions, Li+ alone can tune both the HER thermodynamics and kinetics of metals. Different metals, namely Pt, Ir, Pd, Au, Fe, and Ni, are studied here to ensure the representation from both the sides of the Sabatier HER plot, under different pH conditions towards their HER efficacy at varying Li+ concentrations. Pt, Pd, and Ir showed suppression in their HER properties with increasing Li+ concentration, while the reverse phenomenon was observed on the rest of the metals. The metal–hydrogen (M–H) binding energy variation with Li+ is theoretically proven, and the Pt–H and Pd–H binding energy variations with Li+ containing electrolytes are experimentally demonstrated. Studies show that the tunability of the HER properties of both noble and non-noble metals can be achieved irrespective of the pH (0 and 13) and counter ions (TFSI−, Cl−, ClO4−, NO3− and OH−) by tuning the M–H bond energy using Li+, where this will be helpful in designing better electro-catalysts not only for the HER but also for other important reactions such as carbon dioxide reduction, nitrogen reduction, etc., where the HER is their competitor in aqueous medium.

Single phasic magnetite samples co-substituted with cobalt and nickel, with the formula CoxNi(0.4−x)FeII0.6FeIII2O4 (x = 0, 0.1, 0.2, 0.3, and 0.4) were synthesized in the nanoregime via a co-precipitation technique. Being an inverse spinel, magnetite will preferentially expose the octahedral sites and make metal cations available on the surface, which will play a conducive role in both hydrogen evolution (HER) and oxygen evolution (OER) reactions. We demonstrate that the partial substitution of Fe2+ (either by Ni2+ or Co2+ ions) on the octahedral sites of the inverse spinel structure of CoxNi(0.4−x)FeII0.6FeIII2O4 significantly enhance the bifunctional electrocatalytic activity of the magnetite samples in an alkaline medium. The spinel ferrite with the formula Co0.2Ni0.2FeII0.6FeIII2O4 exhibits outstanding bifunctional electrocatalytic activity in 1 M KOH with the lowest onset overpotential (ƞOER = 190 and ƞHER = 200 mV), small overpotential at η10 (OER = 270 mV and HER = 275 mV), excellent kinetics (Tafel slopes, bOER = 44 mV dec−1 and bHER = 99 mV dec−1), and high durability (>10 h). Furthermore, Co0.2Ni0.2FeII0.6FeIII2O4 can serve as both cathode and anode for the overall water-splitting reaction, and delivered a current density of 10 mA cm−2 at a very low cell voltage of 1.72 V with excellent stability (>10 h at 10 mA cm−2). Thus, this work provides a lucid approach to engineer a highly efficient non-noble transition metal-based electrocatalyst for renewable energy applications via simple micro-structural and surface engineering.

Naturally occurring biofilms are sought after for tremendous applications. Here eggshell membranes, biofilms separated from eggshells – a bio-waste – having a thickness of ∼50 μm, are shown for their potential in alkaline and acidic water electrolysis. Chemical modification by quaternization leads to an enhanced anion exchange performance of the eggshell membrane, which is on par with a commercial anion exchange membrane (Fumasep FAS-50). Morphological studies show a dense network of interconnected porous fibers in the eggshell membrane, providing considerable mechanical strength and flexibility (stress and strain at failure ∼2 MPa and ∼60%, respectively) to the membrane. The anion (OH−) and cation (H+) exchange capacities of the functionalized eggshell membranes are compared with those of the commercial membrane using chronoamperometry studies conducted with a homemade water electrolysis cell as well as with a membrane electrode assembly set-up. Studies show the potential of this low cost membrane in commercial anion and/or cation exchange membrane-based energy technologies.

The discharge of liquid petroleum hydrocarbons into the environment is coined as an oil spill and is identified as a major form of ‘ocean pollution’. There are seven major proposed techniques to selectively remove spilled oil from water surfaces, and the choice of technique depends on the type of crude oil, temperature of the water, and other environmental conditions. After the proposal by Nicolaides et al. that the magnetic nanocomposite-based oil recovery method can be 30% less costly than other available methods, high surface area magnetic materials have received tremendous attention. Many interesting laboratory scale approaches have been reported so far on magnetic nanomaterial-based oil recovery. Most of the techniques use synergistic activities of engineered superhydrophobic scaffolds which are functionalized with magnetic particles either inherently or by external means. In this review article, the advancements in magnetic material-based oil spill clean-up are discussed by reviewing the literature from the last ten years. This review ends with the plausible future direction of this field and also discusses the commercial viability of some of these techniques.

Achieving room-temperature valley polarization in two-dimensional (2D) atomic layers (2D materials) by substitutional doping opens new avenues of applications. Here, monolayer MoS2, when doped with vanadium at low (0.1 atomic %) concentrations, is shown to exhibit high spin-valley coupling, and hence a high degree of valley polarization at room-temperature. The atomic layers of MoS2 (MS) and V-doped MoS2 (VMS) are grown via the chemical vapor deposition-assisted method. The formation of new energy states near the valence band is confirmed from band gap calculations and also from the density functional theory–based band structure analyses. Time-reversal symmetry broken energy shift in the equivalent valleys is predicted in VMS, and the room-temperature chirality-controlled photoluminescent (PL) excitation measurements indicate such a shift in valley exciton energies (∼35 meV). An enhanced valley polarization in VMS (∼42%) is observed in comparison to that in MS (, Authors from Tata Institute of Fundamental Research appreciate the support of the Department of Atomic Energy, Government of India (Project Identification No. RTI 4007). T.N.N. and G.R. acknowledge the financial support from DST-SERB, Government of India SUPRA scheme (Grant No. SPR/2020/000220). The TEM and XPS studies were performed in the Laboratorio de Microscopias Avanzadas (LMA), Universidad de Zaragoza, Spain. The authors thank G. Antorrena (LMA) for the XPS measurements. R.A. acknowledges support from Spanish MICINN (Grant No. PID2019-104739GB-100/AEI/10.13039/501100011033), the Government of Aragon (projects DGA E13-20R; FEDER, EU), and from the European Union H2020 programs “ESTEEM3” (Grant No. 823717) and Graphene Flagship (Grant No. 881603).

Platinum (Pt) is a benchmarked catalyst for several electro-catalytic processes, although the complex nature of heterogeneous charge transfer processes at the Pt–electrolyte interface hinders an atomistic-level understanding of the electrodics. In this study, we aim to capture the chemical changes of Pt surfaces brought on by an applied potential, which can probe the catalytic efficacy under varying applied bias. Through a combined experimental and reactive molecular dynamics (MD) simulation approach, we uncover the effect of charge buildup on the surface of the Pt electrode, which can be directed toward capacitive and faradaic processes. In the case of a moderately acidic pH shown here, the potential dependence of simulated electrodic processes aligns well with the experimental results from electrochemistry and in situ surface-enhanced Raman spectroscopy (SERS). Using reactive MD- and SERS-based studies, we are able to probe into the interfacial water structure and the formation of the Helmholtz layer. At reductive potentials of ∼0.3–0.0 V vs. RHE, we simulate phenomena such as under potential hydrogen adsorption and hydrogen evolution/oxidation reaction. Together, the investigation establishes a framework for quantitative exploration of catalytic processes in electrolytes at very high spatial and temporal resolution.

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 cause 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 cell. Low band gap, high efficiency photo-conversion and efficient electron-hole separation help the battery to fully charge within a few hours with a low power light. The proposed concept and materials could enable next generation stable solar chargeable battery electrodes, in contrast to the reported materials.

Rational design of a catalyst using earth abundant transition metals that can facilitate the smooth O-O bond formation is crucial for developing efficient water oxidation catalysts. The coordination environment around the metal ion of the catalyst plays a pivotal role in this context. We have chosen dinuclear mixed-valence Co

Development of atomic layers and their heterostructures opened new avenues in developing novel photocatalysts for enhanced light–matter interaction. Graphene–hexagonal boron nitride (G/hBN) van der...

A single-atom site catalyst for direct four electron oxygen reduction reaction (ORR) is identified where selenium (ultrasmall amount of Se, ≲1 at. % ) is the active center that couples reduced graphene oxide (rGO) sheets. This metal-free catalyst is found to be undergoing ORR through the direct four-electron pathway in alkaline medium, similar to platinum, whereas rGO prefers a two-electron path, and the experimental observation is correlated with theoretical study. The role of Se-like elements in graphene, which have similar electronegativity as carbon, is unraveled with a detailed density functional theory-based analyses.

Boron-doped graphene quantum dots (B-GQDs) have been synthesized via a microwave reactor assisted process from bulk boron carbide (B4C) crystals and they are shown to exhibit enhanced photoactivity. The B-GQDs are found to have an average lateral width of ∼6 ± 2 nm, and thickness of ∼0.2–0.3 nm. Nano ZnO is incorporated into these B-GQDs to prepare a B-GQDs-ZnO composite based high-performance photo-anode for Dye-Sensitized Solar Cells (DSSCs). The results showed the highest power conversion efficiency of ∼3.7% with these new composite based DSSCs, showing the potential of this composite in real cell applications.

The hydrogen evolution reaction (HER) plays a key role in hydrogen production for clean energy harvesting. Designing novel efficient and robust electrocatalysts with sufficient active sites and excellent conductivity is one of the key parameters for hydrogen production using water splitting devices. Recently, low-dimensional carbon materials have gained attention as metal-free catalysts for hydrogen production. Such nanostructures need to be engineered to improve their catalytic activity. Here, we designed and synthesized a B and N doped carbon nanostructure (CNS)-hBN heterostructure as an improved HER catalyst. The hBN layers on CNS could provide exposed defects and edges that act as active sites for proton adsorption and reduction. The composition, structure and chemical properties of the B and N doped CNS-hBN heterostructure were tuned to obtain excellent HER activity. Detailed morphological, structural and electrochemical characterization demonstrated that the synergistic effect rising from the interaction between B and N doped CNS and hBN structures contributes to enhance the electrocatalytic performances. To get more insight into the role of defects and doping, we performed density functional theory (DFT) calculations on the CNS-hBN heterostructure.

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.

Polymer based solid electrolytes (SEs) are envisaged as futuristic components of safer solid state energy devices. But the semi-crystalline nature and slow dynamics of the host polymer matrix are found to hamper the ion transport through the solid polymer network and hence solid state devices are still far beyond the scope of practical application. In this study, we unravel the synergistic roles of Li salt (LiClO4) and two different polymers – polyethylene oxide (PEO) and polydimethyl siloxane (PDMS), in the Li ion transport through their solid blend based electrolyte. A detailed study using dielectric spectroscopy and thermo-mechanical analysis is conducted to understand the tunability of the PEO chain dynamics with LiClO4 and the mechanism of hopping of Li ions by forming ion pairs with oxygen dipoles on the PEO backbone is established. Despite the lack of PDMS's capability to solvate ions and promote ion transport directly, its proper mixing within the PEO host matrix is demonstrated to enhance ion transport due to the influence of PDMS on the segmental dynamics of PEO. A detailed molecular dynamics study supported by experimental validation suggests that even inert polymers can affect the dynamics of the active host matrix and increase ion transport, leading to next generation high ionic conductivity solid matrices, and opens new avenues in designing polymer based transparent electrolytes.