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The electromechanical response of the group-IV monochalcogenide monolayers upon charge injection was investigated for applications in actuator devices and artificial muscles.

Detection of pollutant gases, such as formaldehyde (HCHO), in our homes and surrounding environment is of high importance for our health and safety. The effect of surface defects and specifically pre-adsorbed oxygen on the gas sensing reaction of HCHO with ZnO nanostructures is largely unknown. Using density functional theory, nonequilibrium Green's function method and

The ferroelectric material In2Se3 is currently of significant interest due to its built-in polarisation characteristics that can significantly modulate its electronic properties. Here we employ density functional theory to determine the transport characteristics at the metal-semiconductor interface of the two-dimensional multiferroic In2Se3/Fe3GeTe2 heterojunction. We show a significant tuning of the Schottky barrier height as a result of the change in the intrinsic polarisation state of In2Se3: the switching in the electric polarization of In2Se3 results in the switching of the nature of the Schottky barrier, from being n-type to p-type, and is accompanied by a change in the spin polarization of the electrons. This switchable Schottky barrier structure can form an essential component in a two-dimensional field effect transistor that can be operated by switching the ferroelectric polarization, rather than by the application of strain or electric field. The band structure and density of state calculations show that Fe3GeTe2 lends its magnetic and metallic characteristics to the In2Se3 layer, making the In2Se3/Fe3GeTe2 heterojunction a potentially viable multiferroic candidate in nanoelectronic devices like field-effect transistors. Moreover, our findings reveal a transfer of charge carriers from the In2Se3 layer to the Fe3GeTe2 layer, resulting in the formation of an in-built electric field at the metal-semiconductor interface. Our work can substantially broaden the device potential of the In2Se3/Fe3GeTe2 heterojunction in future low-energy electronic devices.

Systematic structural changes to the functional groups of sulfonimide anions can be used to improve the calculated oxidation potential, reductive stability, lithium binding energy and lithium-anion coordination for application in lithium-metal batteries.

We present a simple alternative pathway to transform carbon dioxide to perpetually stored solid carbon.

Nicotine, an addictive substance in tobacco products and electronic cigarettes (e-cigs), is recognized for increasing the risk of cardiovascular and respiratory disorders. Careful real-time monitoring of nicotine exposure is critical in alleviating the potential health impacts of not just smokers but also those exposed to second-hand and third-hand smoke. Monitoring of nicotine requires suitable sensing material to detect nicotine selectively and testing under free-living conditions in the standard environment. Here, we experimentally demonstrate a vanadium dioxide (VO

Boronium cation-based ionic liquids (ILs) have demonstrated high thermal stability and a >5.8 V electrochemical stability window. Additionally, IL-based electrolytes containing the salt LiTFSI have shown stable cycling against the Li metal anode, the “Holy grail” of rechargeable lithium batteries. However, the basic spectroscopic characterisation needed for further development and effective application is missing for these promising ILs and electrolytes. In this work, attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and density functional theory (DFT) calculations are used in combination to characterise four ILs and electrolytes based on the [NNBH2]+ and [(TMEDA)BH2]+ boronium cations and the [FSI]− and [TFSI]− anions. By using this combined experimental and computational approach, proper understanding of the role of different ion-ion interactions for the Li cation coordination environment in the electrolytes was achieved. Furthermore, the calculated vibrational frequencies assisted in the proper mode assignments for the ILs and in providing insights into the spectroscopic features expected at the interface created when they are adsorbed on a Li(001) surface. A reproducible synthesis procedure for [(TMEDA)BH2]+ is also reported. The fundamental findings presented in this work are beneficial for any future studies that utilise IL based electrolytes in next generation Li metal batteries.

Two-dimensional (2D) ferroelectric materials are providing promising platforms for creating future nano- and opto-electronics. Here we propose new hybrid van der Waals heterostructures, in which the 2D ferroelectric material CuInP

Narrow spectral sensitivity in materials is one of the crucial challenges to develop high-performance broadband photodetectors. Here, we design a heterostructure of two-dimensional molybdenum disul...

Electrolytes that can enable the use of a Li metal anode at a vast 3860 mAh/g, in place of currently used graphite anodes (372 mAh/g), are required for the advancement of next-generation rechargeable Li batteries. Both quaternary ammonium and boronium (trimethylamine)(dimethylethylamine)dihydroborate [NNBH2](+) cation-based ionic liquids (ILs) show high electrochemical stability windows and thermal stability for use in Li batteries. Cyclization of the former cation shows improved electrolyte stability compared to the open-chain counterpart. However, it is not known whether this is the case for the cyclic derivative of [NNBH2](+), N,N,N',N'-tetramethylethylenediamine)dihydroborate [(TMEDA)BH2](+). Here, the details of the initial stages of solid-electrolyte interphase (SEI) layer formation on a lithium metal surface, Li(001), for the [(TMEDA)BH2](+) based ILs are revealed using density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations. These indicate that [(TMEDA)BH2](+) remains intact, displaying a similarly weak interaction with the Li metal surface as the open-chain analogue. The chemical stability shown by the boronium cation indicates spontaneous and unwanted side reactions with the Li anode are unlikely to occur, which could help to facilitate long-term cycling stability of the battery. Altogether, the findings suggest the [(TMEDA)BH2](+) ILs, like their [NNBH2](+) IL counterparts, are viable candidates for rechargeable Li metal batteries.

Antimicrobial resistance has rendered many conventional therapeutic measures, such as antibiotics, ineffective. This makes the treatment of infections from pathogenic micro-organisms a major growing health, social, and economic challenge. Recently, nanomaterials, including two-dimensional (2D) materials, have attracted scientific interest as potential antimicrobial agents. Many of these studies, however, rely on the input of activation energy and lack real-world utility. In this work, we present the broad-spectrum antimicrobial activity of few-layered black phosphorus (BP) at nanogram concentrations. This property arises from the unique ability of layered BP to produce reactive oxygen species, which we harness to create this unique functionality. BP is shown to be highly antimicrobial toward susceptible and resistant bacteria and fungal species. To establish cytotoxicity with mammalian cells, we showed that both L929 mouse and BJ-5TA human fibroblasts were metabolically unaffected by the presence of BP. Finally, we demonstrate the practical utility of this approach, whereby medically relevant surfaces are imparted with antimicrobial properties via functionalization with few-layer BP. Given the self-degrading properties of BP, this study demonstrates a viable and practical pathway for the deployment of novel low-dimensional materials as antimicrobial agents without compromising the composition or nature of the coated substrate.

Synthesizing two dimensional (2D) nanomaterials with controlled sub-nanometer thicknesses from non-layered crystals presents both significant challenges and vast opportunities. However, mechanical exfoliation techniques and physical/wet chemical deposition processes are widely disadvantageous for applicability to non-layered structures. Here we have utilized a simple self-limiting approach to prepare large sheets of 2D zinc oxide (ZnO) at the metal-melt/air interface. These ultra-thin sheets demonstrated highly crystalline hexagonal structures. The specific ZnO hexagonal sheet thickness and its interaction with the substrate were found to have a critical impact on d33. This unusual structure resulted in an exceptionally high out of plane piezoelectricity, yielding a giant value of 80 ± 0.8 pm/V at 2.5 unit-cell thickness for d33, which is 5 Zn-O layers in the wurtzite crystal. This out of plane piezoelectricity value is approximately 8 times larger than that of the value for bulk ZnO. Theoretical studies were carried out to elucidate the impact of the thickness and the substrate’s role on the polarization of the layers. The existence of a large piezoelectricity offered by the synergy of the substrate and specific thickness of ultrathin films offers the opportunity for other groups of potentially piezoelectric materials to be explored.

Surface paramagnetism of the ZnO(1010) facet is a well-known property of this surface and has been explained by the ionosorption of negatively charged oxygen species, which play a significant role...

The use of three-dimensional printing in chemistry education has expanded greatly in the past 10 years. The technique has been used to demonstrate a range of concepts including molecular structure,...

Ionic liquids are versatile solvents that can be tailored through modification of the cation and anion species. Relatively little is known about the corrosive properties of protic ionic liquids. In this study, we have explored the corrosion of both zinc and copper within a series of protic ionic liquids consisting of alkylammonium or alkanolammonium cations paired with nitrate or carboxylate anions along with three aprotic imidazolium ionic liquids for comparison. Electrochemical studies revealed that the presence of either carboxylate anions or alkanolammonium cations tend to induce a cathodic shift in the corrosion potential. The effect in copper was similar in magnitude for both cations and anions, while the anion effect was slightly more pronounced than that of the cation in the case of zinc. For copper, the presence of carboxylate anions or alkanolammonium cations led to a notable decrease in corrosion current, whereas an increase was typically observed for zinc. The ionic liquid-metal surface interactions were further explored for select protic ionic liquids on copper using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) to characterize the interface. From these studies, the oxide species formed on the surface were identified, and copper speciation at the surface linked to ionic liquid and potential dependent surface passivation. Density functional theory and ab initio molecular dynamics simulations revealed that the ethanolammonium cation was more strongly bound to the copper surface than the ethylammonium counterpart. In addition, the nitrate anion was more tightly bound than the formate anion. These likely lead to competing effects on the process of corrosion: the tightly bound cations act as a source of passivation, whereas the tightly bound anions facilitate the electrodissolution of the copper.

Summary To keep up with the fast-paced transitioning of the global energy sector, which is constantly thriving to enable reliable, economic, and sustainable energy production, catalysis research has been required to continuously evolve in response. The challenges in the existing systems are predominantly due to dependencies on heterogeneous solid catalysts that are susceptible to coking. In this respect, liquid-metal (LM) catalysts have been demonstrated to have a critical advantage over conventional catalysts. Recently, LMs acquired a place in catalysis, with a reputation often synonymous with interesting properties and a remarkable ability to break trade-offs between homogeneous and heterogeneous catalysis. This review bridges the fundamental principles of LM research and the recent advances in LM-based thermal and electrochemical catalysis for energy applications. Moreover, emerging approaches for the improved utilization of LMs are outlined, and the concepts requiring greater research attention that could enable the development of exciting energy solutions are highlighted.

Monolayer black phosphorus (phosphorene) displays mechanical and electronic properties that make it attractive for applications in flexible electronic devices. In this work, the effects of adsorpti...

Two-dimensional transition-metal dichalcogenides possess inherent structural characteristics that can be harnessed for enhancement of tribological properties by making them dispersible in lube media. Here, we present a hydrothermal approach to preparing MoS2 nanosheets comprising 4-10 molecular lamellae. A structural-defect-mediated route for grafting of octadecylamine (ODA) on MoS2 nanosheets is outlined. The unsaturated d orbitals of Mo at the sulfur vacancies on the MoS2 surface are coupled with the electron-rich nitrogen center of ODA and yield ODA-functionalized MoS2 (MoS2-ODA). The MoS2-ODA nanosheets exhibit good dispersibility in lube base oil and are used as an additive (optimized dose: 0.1 mg·mL-1) to mineral oil. It is shown that even at low concentration, MoS2-ODA nanosheets significantly reduce the friction (48%) and wear (44%). Microscopy (field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM)) and spectroscopy (Raman and elemental mapping) analyses of worn scars revealed the formation of MoS2-based protective thin films for lowering of friction and wear. This work, therefore, presents a pathway for low-friction lubricants by deploying functionalized low-dimensional material systems.

Augmented cycling performance in lithium metal batteries is often attributed to the formation of a stable solid electrolyte interphase (SEI) layer that forms on the Li surface. Boronium cation-base...

Chromism-based optical filters is a niche field of research, due to there being only a handful of electrochromic materials. Typically, electrochromic transition metal oxides such as MoO3 and WO3 are utilized in applications such as smart windows and electrochromic devices (ECD). Herein, we report MoO3-x-based electrically activated ultraviolet (UV) filters. The MoO3-x grown on indium tin oxide (ITO) substrate is mechanically assembled onto an electrically activated proton exchange membrane. Reversible H+ injection/extraction in MoO3-x is employed to switch the optical transmittance, enabling an electrically activated optical filter. The devices exhibit broadband transmission modulation (325-800 nm), with a peak of ∼60% in the UV-A range (350-392 nm). Comparable switching times of 8 s and a coloration efficiency of up to 116 cm2 C-1 are achieved.

Boron nitride nanotubes (BNNTs) represent a relatively new class of materials that provides alternative electrical and thermal properties to the carbon analogue. The high chemical and thermal stability and large band gap combined with high electrical resistance make BNNTs desirable in several thin-film applications. In this study, stable BNNT and hexagonal boron nitride (hBN) particle dispersions have been developed using environmentally friendly advanced oxidation processing (AOP) that can be further modified for electrophoretic deposition (EPD) to produce thin films. The characterization of the dispersions has revealed how the hydroxyl radicals produced in AOP react with BNNT/hBN and contaminant boron nanoparticles (BNPs). While the radicals remove the carbon contaminant present on BNNT/hBN and increase dispersion stability, they also oxidize the BNPs and the boron oxide produced, which, conversely, reduces the dispersion stability. The use of high- or low-powered ultrasonication in combination with the AOP affects the rate of the competing reactions, with low-powered sonication and AOP providing the best combination for producing stable dispersions with high concentrations. BNNT/hBN dispersions were functionalized with polyethyleneimine to facilitate EPD, where films of several micrometer thickness were readily deposited onto stainless steel and glass-fiber fabrics. BNNT/hBN films produced on glass fabrics by EPD exhibited a consistent through-thickness macroporosity that was facilitated by platelet and nanotube stacking. The film macroporosity present on the coated fabrics was suitable for use as separator layers in supercapacitors and provided improved device robustness with a minimal impact on electrochemical performance.

Metal chalcogenides are important members of the two-dimensional (2D) materials family and have been extensively investigated for high-performance electronic device applications. However, when they are produced on a large-scale, their carrier mobilities are strongly influenced by the surface conditions. Here, we print indium sulphide (In2S3) with the thickness down to the single unit cell limit on wafer-scale out of metallic indium liquid, in which structural indium vacancies are formed in an orderly fashion. First principles investigations reveal that the unique ordered-vacancy structure results in a highly dispersive conduction band with low effective electron mass, forming multiple band-like electronic transport channels sandwiched within the crystal structure which are less influenced by the surface conditions. Back-gated field effect transistors are fabricated, and the measured mobility is up to 58 cm2 V-1 s-1 with a high degree of reproducibility, which is amongst one of the highest reported for wafer-scale-grown ultra-thin metal chalcogenides. This establishes ordered-vacancy-enabled semiconductors in the 2D geometry as suitable alternatives for new generation high-performance electronic devices.

The ferroelectric material In

Lithium metal batteries (LMBs) require an electrolyte with high ionic conductivity as well as high thermal and electrochemical stability that can maintain a stable solid electrolyte interphase (SEI) layer on the lithium metal anode surface. The borate anions tetrakis(trifluoromethyl)borate ([B(CF3)4]−), pentafluoroethyltrifluoroborate ([(C2F5)BF3]−), and pentafluoroethyldifluorocyanoborate ([(C2F5)BF2(CN)]−) have shown excellent physicochemical properties and electrochemical stability windows, however, the suitability of these anions as high-voltage LMB electrolytes components that can stabilise the Li anode is yet to be determined. In this work, density functional theory calculations show high reductive stability limits and low anion–cation interaction strengths for Li[B(CF3)4], Li[(C2F5)BF3], and Li[(C2F5)BF2(CN)] that surpass popular sulfonamide salts. Specifically, Li[B(CF3)4] has a calculated oxidative stability limit of 7.12 V vs. Li+/Li0 which is significantly higher than the other borate and sulfonamide salts (≤6.41 V vs. Li+/Li0). Using ab initio molecular dynamics simulations, this study is the first to show that these borate anions can form an advantageous LiF-rich SEI layer on the Li anode at room (298 K) and elevated (358 K) temperatures. The interaction of the borate anions, particularly [B(CF3)4]−, with the Li+ and Li anode, suggests they are suitable inclusions in high-voltage LMB electrolytes that can stabilise the Li anode surface and provide enhanced ionic conductivity.

Summary Incorporation of as prepared single-walled carbon nanotubes (SWCNTs) into the electron transporting layer (ETL) is an effective strategy to enhance the photovoltaic performance of perovskite solar cells (PSCs). However, the fundamental role of the SWCNT electrical types in the PSCs is not well understood. Herein, we prepared semiconducting (s-) and metallic (m-) SWCNT families and integrated them into TiO2 photoelectrodes of the PSCs. Based on experimental and theoretical studies, we found that the electrical type of the nanotubes plays an important role in the devices. In particular, the mixture of s-SWCNTs and m-SWCNTs (2:1 w/w)-based PSCs exhibited a remarkable efficiency of up to 19.35%, which was significantly higher than that of the best control cell (17.04%). In this class of PSCs, semiconducting properties of s-SWCNTs play a critical role in extracting and transporting electrons, whereas m-SWCNTs provide high conductance throughout the electrode., Graphical Abstract, Highlights • PSCs based on ETLs containing separated families of SWCNTs are fabricated • Nanotube compositions are precisely tuned to enable the highest PCE • By optimizing the nanotube ratio, an efficiency of 19.35% is obtained • Elucidation of the optimal ratio of s-SWCNTs vs. m-SWCNTs for charge transport electrodes, Separation Science; Nanotechnology Fabrication; Materials Science; Energy Materials

This paper outlines a protocol, which combines quantum mechanics calculations and experimental synthesis, to enable systematic selection of suitable chromophores based on their stability of fluorescence and efficiency of the chemical reaction. The experimental conditions were optimised for the esterification of fatty acids with the most effective chromophore, 5-(4-(diphenylamine)phenylthiopheny-2-yl)methanol.

Silicene, the silicon analog of graphene, is an atomically thin two-dimensional material with promising applications in gas sensing, storage and as components in modern electronic devices. Silicene epitaxially grown on the Ag(111) surface can expand the utility of the silver surface by enabling the tuning of its work function through the functionalisation of silicene. Here we examine the electronic and structural properties and the thermodynamic stability of functionalised silicene/4 × 4 Ag(111) using density functional theory calculations coupled with ab initio molecular dynamics (AIMD) simulations. We focus on 11 functional groups, namely phenyl, methyl, hydroxyl, cyano, methoxyl, amino and ethylmethylamine, in addition to 4 halogen atoms. These functional groups are shown to endow the Si/Ag(111) surface with a large variation in the work function. Our AIMD simulations confirm the thermodynamic stability of these 11 functionalised structures. This work shows the possibility of tuning the electronic structure of silicene by functionalisation, which could then be utilized in polymer solar cells and nanoelectronic circuit components.

Imprinting vision as memory is a core attribute of human cognitive learning. Fundamental to artificial intelligence systems are bioinspired neuromorphic vision components for the visible and invisible segments of the electromagnetic spectrum. Realization of a single imaging unit with a combination of in-built memory and signal processing capability is imperative to deploy efficient brain-like vision systems. However, the lack of a platform that can be fully controlled by light without the need to apply alternating polarity electric signals has hampered this technological advance. Here, a neuromorphic imaging element based on a fully light-modulated 2D semiconductor in a simple reconfigurable phototransistor structure is presented. This standalone device exhibits inherent characteristics that enable neuromorphic image pre-processing and recognition. Fundamentally, the unique photoresponse induced by oxidation-related defects in 2D black phosphorus (BP) is exploited to achieve visual memory, wavelength-selective multibit programming, and erasing functions, which allow in-pixel image pre-processing. Furthermore, all-optically driven neuromorphic computation is demonstrated by machine learning to classify numbers and recognize images with an accuracy of over 90%. The devices provide a promising approach toward neurorobotics, human-machine interaction technologies, and scalable bionic systems with visual data storage/buffering and processing.

Two-dimensional transition-metal dichalcogenides possess inherent structural characteristics that can be harnessed for enhancement of tribological properties by making them dispersible in lube media. Here, we present a hydrothermal approach to preparing MoS

Chromism-based optical filters is a niche field of research, due to there being only a handful of electrochromic materials. Typically, electrochromic transition metal oxides such as MoO

Multifunctional electronic memories capable of demonstrating both analog and digital switching on-demand are extremely attractive for miniaturization of electronics without significant drain on energy consumption. Simultaneously translating functionality onto mechanically conformable platforms will further enhance their suitability. Here, we demonstrate the ability to engineer multifunctionality in strontium titanate (STO)-based resistive random-access memories (ReRAM) on a flexible polyimide platform. By utilizing different bottom electrodes of various work functions while the top electrode is fixed, differential work functions are induced in STO, to induce bipolar or complementary switching behaviors whenever required. This work-function difference-induced bifunctional switching on the flexible platform reveals a streamlined route for achieving flexible artificial neural networks, high density integration, and logic operation using a single ReRAM.

New structures of bilayer GaN displaying buckling are revealed, and their structural and electronic properties are studied using first-principles calculations. Layered GaN is a promising two-dimens...

Mobile technology is increasingly prevalent in higher education. Chemistry-related software applications (apps) on touchscreen computers are emerging as a popular platform in many areas, including in the chemistry classroom. In this work, a new game-based app designed for hand-held and portable touch-controlled devices is presented. Chirality-2 covers multiple aspects of introductory undergraduate organic chemistry. The app allows users to earn chemistry-type medals related to his or her score for each stage, track progress, and post scores and compete with peers on social media. The app is free to download on both the iOS and Android operating systems and aims to help reinforce important chemical concepts necessary for introductory undergraduate chemistry courses worldwide. The target audience includes teachers and students at the final year of high school and introductory undergraduate level.

Graphitic nanoplatelets (GNPs) have been treated using an ultrasonicated ozonolysis procedure to produce stable aqueous dispersions that facilitate deposition of thin films using electrophoretic deposition. The thin GNP films were then coated with zero valence (ZV) iron nanocubes using a pulsed electrodeposition technique. Characterization of the ZV-iron coating with deposition time revealed that the changing magnetic character of the ferromagnetic-graphitic hybrid material was related to the nucleation density and growth of the ZV-iron nanocubes. Density functional theory calculations show a preference for ZV-iron adsorption at the oxygen sites of the GNPs, with ZV-iron displacement of oxygen groups favored in some configurations. Transmission electron microscopy studies confirm ZV-iron growth nucleates preferentially at the graphite nanoplatelet edges and the hybrid material magnetism is affected by the convergent crystalline grain boundaries formed between adjacent ZV-iron nanocubes.

Black phosphorus (BP) has emerged as an exciting 2D material for optics, photonics, and electronics. However, there are few studies on BP in terms of modulation and enhancement of their electronic and optical properties and their concurrent reactivity and hence reduction after exposure to the ambient environment. To resolve such challenges, creating inorganic–organic hybrid materials is a suitable approach that offers significant opportunities to enhance the utility of BP by combining them with an organic material which has a complementary set of properties. Herein, a hybrid‐layered BP material coupled with a low bandgap donor–acceptor organic semiconducting polymer, selenophene‐flanked diketopyrrolopyrrole with thienyl‐vinylene‐thienyl (PDPPSe–TVT) is reported, to broaden the optical absorption and tune the ambipolar field effect transistor characteristics. A highly sensitive, nongated broadband photodetection capability of the hybrid device with a detection range from UV–vis to near‐IR (280–1050 nm) and responsivities of up to 4.22 × 103 A W−1 in ambient conditions. In addition to improved photodetection, simultaneous enhancement in both hole (71%) and electron (91%) mobilities is achieved while protecting the sensitive BP material from rapid environmental degradation. The findings therefore report a breakthrough in enhancing the utility of BP as a light‐active material for versatile photonics and electronics applications without operating in an inert environment.

Using tangible models to help students visualize chemical structures in three dimensions has been a mainstay of chemistry education for many years. Conventional chemistry modeling kits are, however, limited in the types and accuracy of the molecules, bonds and structures they can be used to build. The recent development of 3D printing technology has allowed a much wider variety of molecules to be created for teaching but is not simple to do. Creating the files needed to print molecular structures is often technically difficult and requires the use of multiple software programs, which are not always user-friendly. Not all educators or students have the resources or technical skill to create such files and so are put off trying to use 3D printing in the classroom. Here we demonstrate a simple method to easily generate the files needed for the 3D printing of almost any molecule using the National Institutes of Health Print Exchange server (or simple alternatives). The basic molecule structure may be created ...

Controlling the formation of the solid electrolyte interphase (SEI) layer of the future generation of lithium metal batteries is critical in optimising both their safety and performance. Unfortunately, lithium and lithiated anode materials are inherently susceptible to unwanted side-reactions including lithium metal dendrite formation, which compromises cell safety. This aberrant lithium re-deposition process ocurring on the lithium anode originates at the electrode surface, with few considering the initial adsorption of electrolyte components onto lithium metal, and the effect this has on the formative stages of SEI layer development. In this work, density functional theory calculations and ab initio molecular dynamics simulations are used to determine the preferred adsorption sites and orientations of two common battery electrolytes, ethylene carbonate (EC) and propylene carbonate (PC) on a Li(001) surface. Three types of orientations were found for both EC and PC each consisting of O atoms ionically bonded to surface Li atoms. Both molecules were found to weakly chemisorb with a similar stability to each other. Ab initio molecular dynamics simulations were used to determine the dissociation mechanism of both molecules on the surface. EC was shown to decompose within 7 ps of simulation time by first accepting an electron from the Li surface and breaking the bond between the carbonyl C and ring O. It then accepted another electron from the Li surface and the bond between the carbonyl C and the other ring O breaks. PC decomposition proceeded via a similar pathway over a longer timescale by accepting an electron from the Li surface and breaking the bond between the carbonyl C and a ring O atom. In contrast to EC, the breaking of the other carbonyl C ring O bond was not seen for PC within the 20 ps simulation, which has been ascribed to the greater stability provided by the methyl group.

The adsorption of formaldehyde (HCHO) gas on different one-dimensional ZnO nanostructures is examined using density functional theory calculations. The effects of nanostructure shape and gas concentration are investigated to determine how these factors may influence the surface reaction of HCHO for sensing applications. The binding energies, vibrational frequencies, charge transfer and density of states were determined. We show that HCHO associatively chemisorbs in multiple sites and orientations on the ZnO nanowire and facetted-nanotube. The facetted-nanotube offers a greater number of adsorption sites due to its larger surface area and hollow centre where HCHO can also adsorb. HCHO is able to form one or two bonds to the surface, where structures in the latter configuration show greater stability, with HCHO behaving as a charge acceptor. Conversely, HCHO acts as a charge donor in the singly coordinated structures. As the adsorption mechanism of HCHO gas on the surface of ZnO nanostructure is not well understood, this study provides useful insights into the gas-surface reaction that may assist future experimental development of ZnO nanostructures for gas sensing of formaldehyde.

Nitrogen dioxide (NO2) is a toxic gas that contributes to photochemical pollution and can cause adverse effects to human and environmental health. Monitoring this gas is therefore important to warn of potential exposure. Nanostructures of zinc oxide (ZnO) have been studied for the sensing of NO2 gas, however, the effect of nanostructure morphology on the gas-sensor reaction mechanism is not understood. We examine the NO2 sensing mechanism for three different ZnO nanostructures, namely a nanowire, a facetted nanotube and a single walled (8,0) nanotube using density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations. The effect of gas concentration and oxygen vacancies is also determined. It was shown that NO2 adsorbs on all nanostructures in multiple configurations, with the bonding being strongest on the nanowire and weakest on the single walled nanotube. NO2 behaves as a charge acceptor, consistent with adsorption on the thin film and desorbs intact from the nanostructures at simulation temperatures of 300 K and 700 K, providing new surface sites for detection of other molecules. The presence of surface oxygen vacancies was found to enhance the binding, with NO2 chemisorbing on all 3 nanostructures via two bonds to the surface. The AIMD simulations showed that at a simulation temperature of 500 K, NO2 dissociates on the nanowire and facetted nanotube defect surfaces resulting in a surface bound oxygen atom which fills the defect site, with the remaining NO desorbing from the surface. The single walled nanotube was shown to be unstable at these simulation temperatures. These findings provide important information for the experimental development of ZnO nanostructure-based gas sensors.