The σ+π dual aromaticity of typical bi-tetrazole ring molecule TKX-50.

Two complexes of dihydroxylammonium 5,5'-bistetrazole-1,1'-diolate (TKX-50) were employed to evaluate the aromaticity of their tetrazole rings via deep analysis such as the electronic structure, the ZZ component of the natural chemical shielding tensor (NICSZZ) and component orbitals, localized orbital locator purely contributed by σ-orbitals (LOL-σ) and localized orbital locator purely contributed by π-orbitals (LOL-π), the anisotropy of the induced current density (AICD) and the ZZ component of iso-chemical shielding surface (ICSSZZ) of these tetrazole rings thereof. The conclusion shows: that all tetrazole rings and bi-tetrazole rings in complexes have strong σ and a comparable strength π double aromaticity; all these magnetic shields almost symmetrically increase from the central axis to the tetrazole ring atoms; tetrazole rings in complex II show a little stronger dual aromaticity than that in complex I mainly due to the different orientation of the fragment 2 encompassing two hydroxylamine groups resulting in different effects on the contributions of σ orbitals and π orbitals to total aromaticity of tetrazole rings thereof; the difference in aromaticity is fundamentally caused by the atoms O with stronger electron-withdrawing than atom N in fragment 2 interact with bi-tetrazole ring through O in complex I but through N in complex II.

Fast Energy Storage of SnS2 Anode Nanoconfined in Hollow Porous Carbon Nanofibers for Lithium-Ion Batteries.

The development of conversion-typed anodes with ultrafast charging and large energy storage is quite challenging due to the sluggish ions/electrons transfer kinetics in bulk materials and fracture of the active materials. Herein, the design of porous carbon nanofibers/SnS2 composite (SnS2 @N-HPCNFs) for high-rate energy storage, where the ultrathin SnS2 nanosheets are nanoconfined in N-doped carbon nanofibers with tunable void spaces, is reported. The highly interconnected carbon nanofibers in three-dimensional (3D) architecture provide a fast electron transfer pathway and alleviate the volume expansion of SnS2 , while their hierarchical porous structure facilitates rapid ion diffusion. Specifically, the anode delivers a remarkable specific capacity of 1935.50 mAh g-1 at 0.1 C and excellent rate capability up to 30 C with a specific capacity of 289.60 mAh g-1 . Meanwhile, at a high rate of 20 C, the electrode displays a high capacity retention of 84% after 3000 cycles and a long cycle life of 10 000 cycles. This work provides a deep insight into the construction of electrodes with high ionic/electronic conductivity for fast-charging energy storage devices.

Metal-injection and interface density engineering induced nickel diselenide with rapid kinetics for high-energy sodium storage.

The key to the innovation of sodium-ion batteries (SIBs) is to find efficient sodium-storage electrode. Here, metal Mo doping of NiSe2 is proposed by modified electrospinning strategy followed by in situ conversion process. The Mo-NiSe2 anchoring on hollow carbon nanofibers (HCNFs) would make full use of the multi-channel HCNFs in the inner layer and the active sites of Mo-NiSe2 in the outer layer, which plays an important role in buffering the volume stress of Na+ (de)insertion and reducing the adsorption energy barrier of Na+. Innovatively, it is proposed to jointly regulate the SIBs performance of NiSe2 by both metal atom doping and interface effects, thereby adjusting the sodium ion adsorption barrier of NiSe2. The Mo-NiSe2@HCNFs exhibits remarkable performance in SIBs, demonstrating a high specific capacity of 396 mAh/g after 100 cycles at 1 A/g. Moreover, it maintains outstanding cycling stability, retaining 77.6 % of its capacity (211 mAh/g) even after 1000 cycles at 10 A/g. This comprehensive electrochemical performances are due to the structural stability and outstanding electronic conductance of the Mo-NiSe2@HCNFs, as evidenced by the diffusion analysis and ex situ charge-discharge process characterization. Furthermore, coupled with the Na3V2(PO4)2O2F cathodes, the full cell also achieves a high energy density of 123 Wh kg-1. The theoretical calculation of the hypervalent Mo doing further proves the benefit of its Na+ adsorption and denser conduction band distribution. This study provides a reference for the construction of transition metal selenide via doping and interface engineering in sodium storage.

Structural regulation enabled stable hollow molybdenum diselenide nanosheet anode for ultrahigh energy density sodium ion pouch cell.

For the continued use of sodium-ion batteries (SIBs), which require matching anode materials, it is crucial to create high energy density energy storage devices. Here, hollow nanoboxes shaped carbon supported sulfur-doped MoSe2 nanosheets (S-MoSe2@NC) are fabricated by in situ growth and heterodoping strategy. This ensures that the MoSe2 nanosheets are tightly anchored to the nanoboxes carbon, and the structure can effectively buffer the volume stress caused by sodium ion (de)intercalation, as well as providing abundant ion/electron migration transportations. As anode for SIBs, the S-MoSe2@NC shows a higher rate capability and excellent cycling stability (431.1 mAh/g after 1100 cycles at 10 A/g). This excellent cycle life and high rate ability are due to the structural stability and outstanding electronic conductance with reduced band gap of the S-MoSe2@NC, as evidenced by the diffusion analysis and theoretical calculation. In order to promote the application of SIBs, the S-MoSe2@NC and NaNi1/3Fe1/3Mn1/3O2 were assembled into a pouch cell, and the test found that besides the excellent cycle rate performance, the ultrahigh energy density of 256 Wh kg-1 and flexible characteristics can be achieved. This study has proven that building a structure with a rock-steady foundation and quick ion migration may efficiently control sodium storage and pave the way for novel applications of high-performance transition metal dichalcogenides in sodium storage.

BTEX sensing potential of elemental-doped graphene: a DFT study.

Elementally-doped graphene demonstrates remarkable gas sensing capabilities as a novel 2D sensor material. In this study, we employed density functional theory calculations, we investigated the impact of various dopants on the BTEX (benzene, toluene, ethylbenzene, and xylene) sensing performance of graphene. Through the systematic analysis of electronic structures and sensitivity, we observed that both the doping method and dopant type significantly influence the interactions between graphene and BTEX molecules. Out of the 22 different elemental doped graphenes studied, N-, O-, and Pd-doped graphenes emerged as promising candidates for BTEX sensor materials. Graphene with N-doping exhibited relatively higher sensitivity towards toluene, ethylbenzene, and xylene compared to O- and Pd-doped graphenes. However, it demonstrated low sensitivity towards benzene. On the other hand, O-doped graphene displayed excellent selectivity for ethylbenzene over the other three gas molecules (benzene, toluene, and xylene). Similarly, Pd-doped graphene also exhibited significant selectivity for ethylbenzene and possessed higher sensitivity than the O-doped graphene. Their distinct characteristics and sensitivities make them potential candidates for future applications in gas sensing technology.

Theoretical study on intra-molecule interactions in TKX-50.

To fully and deeply understand the weak interactions in the gaseous structure of the TKX-50 molecule, two conformations I and II of the TKX-50 molecule confirmed in a crystal cell were optimized at the B3LYP/6-311g(d,p) level in the gas state, and the single point energy of the optimized structure was calculated at the M06-2X/ma-TZVPP level. Analyzing methods for weak interactions such as the interaction region indicator (IRI), topological basin analysis, and the extended transition state-natural orbitals for chemical valence (ETS-NOCV) theory with the help of Multiwfn code were employed to reveal the corresponding intramolecular weak interactions. The results showed that there were 5 kinds of intramolecular weak interaction in both conformations. They are two types of H bond, two types of intra-ring weak interaction, and one type of O-N bond within the molecular fragment containing the bis-tetrazole ring. The combined effect of all these weak interactions holds the bis-tetrazole ring of TKX-50 retaining an almost coplanar configuration. Meanwhile, the strength of these weak interactions is significantly different in conformation I and conformation II. The most obvious difference is that conformation II has a significant H transfer between intramolecular fragments due to the mirror rotation of almost 180° of cations (NH3OH)+ perpendicular to the N-O bond axis thereof as compared to the reference conformation I. This conformational difference not only makes the weak interaction between the two conformations very different but also forms a quasi-covalent bond in conformation II with much larger bonding energy than other H bonds, thus resulting in conformation II having lower electron energy and more stable geometry. In addition, the order of breaking various H bonds in the combustion decomposition process of TKX-50 is deduced by comparing various H bonds.

Aliovalent doping and structural design of MoSe2 with fast reaction kinetics for high-stable sodium-ion half/full batteries.

The development of high-quality anode materials is critical for the advancement of sodium-ion batteries (SIBs). MoSe2 is a candidate anode for SIBs, while its inherent limitations, such as the agglomeration of nanosheets, poor electron conductance and mechanical strain due to volume changes during cycling, which can lead to decreased performance and durability in SIBs. To overcome the challenges, a novel aliovalent doping and structural engineering was taken to prepare reduced graphene oxide (rGO) functionalized and phosphorus-doped MoSe2 flake (P-MoSe2@rGO) via in situ growth technique. The unique structural design of P-MoSe2@rGO addresses material limitations and optimizes performance by providing a high conductive grid for ion/electron transfer, a large surface area for full electrolyte penetration, and effective suppression of MoSe2 nanosheet agglomeration and mechanical strain due to volume change during charge/discharge in SIBs. The P-MoSe2@rGO inherits the enhanced electronic conductivity and enlarged layer spacing (from 0.652 to 0.668 nm), which boosts the reaction kinetics and facilitates the insertion/extraction of sodium ions. The P-MoSe2@rGO exhibits excellent long-cycle properties with a high reversible capacity of 384 mAh/g at 2 A/g and 338 mAh/g at 10 A/g after 1450 circulations. Detailed discussion of reaction kinetics is conducted. Theoretical calculations prove that doping of P atoms in MoSe2 reduces the forbidden band gap from 1.443 to 1.397 eV and accelerates ion and electron migration. Furthermore, the full cell P-MoSe2@rGO//Na3V2(PO4)3@C (NVP@C) demonstrates a remarkable cycling durability of 326 mAh/g after 200 cycles and a high energy density of 159.6 Wh kg-1. This process provides a reference for the adjustment and modification of MoSe2 to adapt to high performance SIBs anode.

In situ Cu doping of ultralarge CoSe nanosheets with accelerated electronic migration for superior sodium-ion storage.

The progress of sodium-ion batteries is currently confronted with a noteworthy obstacle, specifically the paucity of electrode materials that can store large quantities of Na+ in a reversible fashion while maintaining competitiveness. Herein, ultrafast and long-life sodium storage of metal selenides is rationally demonstrated by employing micron-sized nanosheets (Cu-CoSe@NC) through electron accumulation engineering. The nanosheet structure proves to be effective in reducing the transport distance of sodium ions. Furthermore, the addition of Cu ions enhances the electron conductivity of CoSe and accelerates charge delocalization. As an anode for sodium-ion batteries, Cu-CoSe@NC exhibits a noticeably enhanced specific capacity of 527.2 mA h g-1 at 1.0 A g-1 after 100 cycles. Additionally, Cu-CoSe@NC maintains a capacity of 428.5 mA h g-1 at 5.0 A g-1 after 800 cycles. It is possible to create sodium-ion full batteries with a high energy density of 101.1 W h kg-1. The superior sodium storage performance of Cu-CoSe@NC is attributed to the high pseudo-capacitance and diffusion control mechanisms, as evidenced by theoretical calculations and ex situ measurements.

Unexpected electro-catalytic activity of the CO reduction reaction on Cr-embedded poly-phthalocyanine realized by strain engineering: a computational study.

The electrochemical conversion of carbon monoxide (CO) into value-added products is highly promising for carbon utilization and CO removal. Based on previous theoretical studies, we computationally explored the effect of strain engineering on electrocatalysis of the CO reduction reaction (CORR) by two-dimensional (2D) transition metal embedded polyphthalocyanines (MPPcs). By calculating the adsorption energy of CO and the free energies of key intermediates on the MPPcs under uniaxial and biaxial strains, it was revealed that only CrPPc under biaxial strain has the potential to exhibit significant enhancement of the catalytic performance. The free energy diagrams of the CORR catalyzed by CrPPc were plotted under specific biaxial strains, where both the optimal reaction pathway and rate-determining step are found to be evidently changed. What's more, the 5% compressive strain imposed on CrPPc results in an ultra-low limiting potential (UL = -0.09 V) with high selectivity on CH4 as the final product, indicating unexpected electro-catalytic activity. Our study clearly elucidates that moderate strain could greatly enhance the electrocatalytic performance of 2D materials in the CORR.

Understanding Trends in Electrochemical Methanol Oxidation Reaction Activity on a Single Transition-Metal Atom Embedded in N-Coordinated Graphene Catalysts.

The lack of efficient catalysts and research on the mechanism for the methanol oxidation reaction (MOR) impedes the development of direct methanol fuel cells. In this work, based on density functional theory calculations, we systematically investigated the activity trends of electrochemical MOR on a single transition-metal atom embedded in N-coordinated graphene (M@N4C). By calculating the free energy diagrams of MOR on M@N4C, Co@N4C was screened out to be the most effective MOR catalyst with a low limiting potential of 0.41 V due to the unique charge transfers and electronic structures. Importantly, one- and two-dimensional volcano relationships in MOR on M@N4C catalysts are established based on the d-band center and the Gibbs free energy of ΔG*CH3OH and ΔG*CO, respectively. In one word, this work provides theoretical guides toward the improved activity of MOR on M@N4C and hints for the design of active and efficient MOR electrocatalysts.

Accelerated Accumulation of γ-Aminobutyric Acid and Modifications on Its Metabolic Pathways in Black Rice Grains by Germination under Cold Stress.

Germination can increase γ-aminobutyric acid (GABA) accumulation in grains, but the combined effects of germination and other external stress on rice grains have been little studied. In this investigation, enhanced accumulation of GABA and modification of its metabolic pathways in black rice grains were investigated during germination under cold stress. The combination of cold stress and germination resulted in a greater accumulation of GABA than germination alone. The treatment of cold stress at 0 °C for 1 h and germination for 72 h induced a maximum GABA content of 195.64 mg/100 g, 51.54% higher compared to the control, which was superior to any other treatment. We modified the metabolism of the GABA shunt to the orientation of GABA synthesis, in which the activity of glutamic acid decarboxylase and protease were stimulated. The total content of free amino acid indicated an upward trend as germination prolonged. The degradation of polyamines was partly promoted due to elevated diamine oxidase and polyamine oxidase activity, but the activity of amino-aldehyde dehydrogenase for the direct synthesis of GABA in the pathway was suppressed. The result implied that the GABA shunt might play a major role in enhancing GABA accumulation induced by cold stress and germination rather than the polyamines degradation pathway. This investigation provides a practical reference for GABA accumulation by germination under cold stress and a theoretical basis for the possible mechanism underlying the accelerating action.

Mapping the Porous and Chemical Structure-Function Relationships of Trace CH3I Capture by Metal-Organic Frameworks using Machine Learning.

Large-scale computational screening has become an indispensable tool for functional materials discovery. It, however, remains a challenge to adequately interrogate the large amount of data generated by a screening study. Here, we computationally screened 1087 metal-organic frameworks (MOFs), from the CoRE MOF 2014 database, for capturing trace amounts (300 ppmv) of methyl iodide (CH3I); as a primary representative of organic iodides, CH3129I is one of the most difficult radioactive contaminants to separate. Furthermore, we demonstrate a simple and general approach for mapping and interrogating the high-dimensional structure-function data obtained by high-throughput screening; this involves learning two-dimensional embeddings of the high-dimensional data by applying unsupervised learning to encoded structural and chemical features of MOFs. The resulting various porous and chemical structure-function maps are human-interpretable, revealing not only top-performing MOFs but also complex structure-function correlations that are hidden when inspecting individual MOF features. These maps also alleviate the need of laborious visual inspection of a large number of MOFs by clustering similar MOFs, per the encoding features, into defined regions on the map. We also show that these structure-function maps are amenable to supervised classification of the performances of MOFs for trace CH3I capture. We further show that the machine-learning models trained on the 1087 CoRE MOFs can be used to predict an unseen set of 250 MOFs randomly selected from a different MOF database, achieving high prediction accuracies.

Computational Studies on Holey TMC6 (TM = Mo and W) Membranes for H2 Purification.

The purification of hydrogen (H2) has been a vital step in H2 production processes such as steam−methane reforming. By first-principle calculations, we revealed the potential applications of holey TMC6 (TM = Mo and W) membranes in H2 purification. The adsorption and diffusion behaviors of five gas molecules (including H2, N2, CO, CO2, and CH4) were compared on TMC6 membranes with different phases. Though the studied gas molecules show weak physisorption on the TMC6 membranes, the smaller pore size makes the gas molecules much more difficult to permeate into h-TMC6 rather than into s-TMC6. With suitable pore sizes, the s-TMC6 structures not only show an extremely low diffusion barrier (around 0.1 eV) and acceptable permeance capability for the H2 but also exhibit considerably high selectivity for both H2/CH4 and H2/CO2 (>1015), especially under relatively low temperature (150−250 K). Moreover, classical molecular dynamics simulations on the permeation process of a H2, CO2, and CH4 mixture also validated that s-TMC6 could effectively separate H2 from the gas mixture. Hence, the s-MoC6 and s-WC6 are predicted to be qualified H2 purification membranes, especially below room temperature.

Significance of density functional theory (DFT) calculations for electrocatalysis of N2 and CO2 reduction reactions.

Density functional theory (DFT) based computational methods have shown great significance in developing high-performance electrocatalysts. In this perspective, we briefly summarized the state-of-the-art research progress of electrocatalysts for the nitrogen reduction reaction (NRR) and CO2 reduction reaction (CO2RR), which are important processes for the conversion of common molecules into value-added products. With the help of DFT calculations, various modulation strategies are employed to improve the catalytic activity and performance of NRR and CO2RR electrocatalysts. DFT calculations are performed to confirm the surface catalytic sites, evaluate the catalytic activity, reveal the possible reaction mechanisms, and design novel structures with high catalytic performance. By discussing the currently applied computational methods and conditions during the calculations, we outlined our concerns on the prospects and future challenges of DFT calculations in electrocatalysis studies.

Effective Transport Tunnels Achieved by 1,2,4,5-Tetrazine-Induced Intermolecular C-H...N Interaction and Anion Radicals for Stable ReRAM Performance.

The D-A structured small-molecule-based resistive random-access memory (ReRAM) device has been well-researched in the last decade, and the switching mechanism was mainly induced by the intramolecular/intermolecular charge transfer processes from the donors to the acceptors. However, in the previous work, some small molecules with pristine electron acceptors in the backbone could still show the typical memory behaviors, of which the switching mechanism is still ambiguous. In this work, two 1,2,4,5-tetrazine based n-type small-molecular isomers, 2-DPTZ and 4-DPTZ, with the same electron acceptor, 1,2,4,5-tetrazine and pyridine, are chosen to investigate the isomeric effects on molecular packing, switching mechanism, and memory performance. Because of the abundant nitrogen atoms with a localized lone pair of electrons in the sp2 orbital, 2-DPTZ and 4-DPTZ compounds could self-assemble into a long-range ordered molecular packing through intermolecular C-H...N interactions, affording effective transporting tunnels for charge-carrier transport. As expected, the sandwich-structured ITO/2-DPTZ or 4-DPTZ/Al memory devices both showed binary memory characteristics, with 2-DPTZ based memory devices showing the write once read many times (WORM) memory behavior and 4-DPTZ based memory devices having the negative differential resistance (NDR) memory performance. These distinct ReRAM properties arose from the different morphologies of 2-DPTZ and 4-DPTZ films that were induced by the different packing styles between the adjacent molecules, as confirmed by X-ray diffraction (XRD) and tapping-mode atomic force microscopy (AFM) height images. Most importantly, the switching mechanism was thought to be attributed to the injected electrons that reduced the neutral molecules of 2-DPTZ and 4-DPTZ to their corresponding anion radicals. Thus, this present work helps us better understand the conducting mechanism of small molecules with pristine electron acceptors in the backbone and provides a supplementary guideline for designing multilevel small molecules to match the structure-stacking-property relationship.

Turning the structure of the Aß42 peptide by different functionalized carbon nanotubes: a molecular dynamics simulation study.

Functionalized carbon nanotubes (CNTs) can inhibit the self-assembly of amyloid-beta (Aß) peptides. Under abnormal conditions, the structure of the Aß peptides undergoes a fundamental transformation, and this transformation will induce conformational conversions of other polymerized Aß peptides. Here, we explore the interactions between different functionalized CNTs and Aß42 peptides by molecular dynamics simulations. Our results show that compared to the original CNTs, the highly functionalized CNTs induce different adsorption patterns of the peptides. This adsorption pattern destroys the α-helix structure and increases the ß-turn and random coil content significantly. The hydrogen bonds formed by the peptide and water molecules or CNTs further reveal the reasons for the structural transformation of the peptide. Due to electrostatic interactions and π-π stacking interactions, some amino acids (such as Phe4, Lys16, Phe20, and Lys28) are tightly fixed on the surfaces, and other amino acids move around these amino acids to accelerate the unfolding and denaturation of the peptide. Our research shows that functionalized CNTs have excellent potential to inhibit the abnormal aggregation of Aß42 peptides. Our research also provides theoretical guidance in the design and synthesis of carbon nanomedicines for protein conformation diseases.

Modulation of MoS2 interlayer dynamics by in situ N-doped carbon intercalation for high-rate sodium-ion half/full batteries.

In comparison with lithium-ion batteries, sodium-ion batteries (SIBs) have been proposed as an alternative for large-scale energy storage. However, finding an anode material that can overcome the sluggish electrochemical reaction kinetics and fast capacity fading caused by large volume expansion during cycling is problematic. In this study, the intercalation technique for nitrogen-doped carbon layers is implemented for the molybdenum disulfide (MoS2/NC) structure to improve the rate and cycling stability of SIBs by increasing the diffusion rate of sodium ions and mitigating excessive volume structural expansion. The as-synthesized MoS2/NC anode has a high discharge specific capacity of 546 mA h g-1 at 1 A g-1 after 160 cycles, as well as a high rate and stable cycle performance of 406 mA h g-1 at 10 A g-1 after 1000 cycles. Upon coupling with a high-voltage Na3V2(PO4)2O2F cathode, the sodium-ion full battery displays high specific energies of 78.57 W h kg-1 and 49.70 W h kg-1 at specific powers of 193.76 W kg-1 and 3756.80 W kg-1, respectively, with commercialization potential demonstrated.

Suppressing vanadium dissolution of V2O5via in situ polyethylene glycol intercalation towards ultralong lifetime room/low-temperature zinc-ion batteries.

Zinc-ion batteries (ZIBs) are a main focus worldwide for their potential use in large-scale energy storage due to their abundant resources, environmental friendliness, and high safety. However, the cathode materials of ZIBs are limited, requiring a stable host structure and fast Zn2+ channel diffusion. Here, we develop a strategy for the intercalation of polyethylene glycol (PEG) to facilitate Zn2+ intercalation and to suppress the dissolution of vanadium in V2O5. In particular, PEG-V2O5 shows a high capacity of 430 mA h g-1 at a current density of 0.1 A g-1 as well as excellent 100 mA h g-1 specific capacity after 5000 cycles, with a high current density of 10.0 A g-1. A reversible capacity of 81 mA h g-1 can even be achieved with a low temperature of -20 °C at a current density of 2.0 A g-1 after 3500 cycles. The superior electrochemical performance comes from the intercalation of PEG molecules, which can improve kinetic transport and structural stability during the cycling process. The Zn2+ storage mechanism, which provides essential guidelines for the development of high-performance ZIBs, can be found through various ex situ characterization technologies and density functional density calculations.

Molecular-Scale Insights into Electrochemical Reduction of CO2 on Hydrophobically Modified Cu Surfaces.

Depressing the competitive hydrogen evolution reaction (HER) to promote current efficiency toward carbon-based chemicals in the electrocatalytic CO2 reduction reaction (CO2RR) is desirable. A strategy is to apply the hydrophobically molecular-modified electrodes. However, the molecular-scale catalytic process remains poorly understood. Using alkanethiol-modified hydrophobic Cu as an electrode and CO2-saturated KHCO3 as an electrolyte, we reveal that H2O, rather than HCO3-, is the major H+ source for the HER, determined by differential electrochemical mass spectrometry with isotopic labeling. As a result, using in situ Raman, we find that the hydrophobic molecules screen the cathodic electric field effect on the reorientation of interfacial H2O to a "H-down" configuration toward Cu surfaces that corresponds to the decreased content of H-bonding-free water, leading to unfavorable H2O dissociation and thus decreased H+ source for the HER. Further, density functional theory calculations suggest that the absorbed alkanethiol molecules alter the electronic structure of Cu sites, thus decreasing the formation energy barrier of CO2RR intermediates, which consequently increases the CO2RR selectivity. This work provides a molecular-level understanding of improved CO2RR on hydrophobically molecule-modified catalysts and presents general references for catalytic systems having H2O-involved competitive HER.

Single-side functionalized graphene as promising cathode catalysts in nonaqueous lithium-oxygen batteries.

High-performance cathode catalysts are always desirable for nonaqueous lithium-oxygen (Li-O2) batteries. Using density functional theory calculations, the structural, electronic, and magnetic properties of SSX-Gr with different C/X ratios (X = H or F) are systematically studied. Then, a detailed mechanism on the dissociation of O2 and the migration of Li on the SSX-Gr is revealed, based on which C6X and C8X are confirmed as the potential candidates as cathode catalysts. The studies on reaction pathways suggest that the four-electron pathway is the more possible catalytic pathway for the selected SSX-Gr. The free energy diagrams for discharging and charging processes catalyzed by SSX-Gr reveal that C6F exhibits the highest application potential due to its considerably low oxygen reduction overpotential (0.83 V) and oxygen evolution overpotential (1.47 V). The extra spins induced by single-side functionalization endow graphene with the electrocatalytic activity.