Laser Precise Synthesis of Oxidation-Free High-Entropy Alloy Nanoparticle Libraries.

High-entropy alloy nanoparticles (HEA-NPs) show exceptional properties and great potential as a new generation of functional materials, yet a universal and facile synthetic strategy in air toward nonoxidized and precisely controlled composition remains a huge challenge. Here we provide a laser scribing method to prepare single-phase solid solution HEA-NPs libraries in air with tunable composition at the atomic level, taking advantage of the laser-induced metastable thermodynamics and substrate-assisted confinement effect. The three-dimensional porous graphene substrate functions as a microreactor during the fast heating/cooling process, which is conductive to the generation of the pure alloy phase by effectively blocking the binding of oxygen and metals, but is also beneficial for realizing accurate composition control via microstructure confinement-endowed favorable vapor pressure. Furthermore, by combining an active learning approach based on an adaptive design strategy, we discover an optimal composition of quinary HEA-NP catalysts with an ultralow overpotential for Li-CO2 batteries. This method provides a simple, fast, and universal in-air route toward the controllable synthesis of HEA-NPs, potentially integrated with machine learning to accelerate the research on HEAs.

Experimentally validated design principles of heteroatom-doped-graphene-supported calcium single-atom materials for non-dissociative chemisorption solid-state hydrogen storage.

Non-dissociative chemisorption solid-state storage of hydrogen molecules in host materials is promising to achieve both high hydrogen capacity and uptake rate, but there is the lack of non-dissociative hydrogen storage theories that can guide the rational design of the materials. Herein, we establish generalized design principle to design such materials via the first-principles calculations, theoretical analysis and focused experimental verifications of a series of heteroatom-doped-graphene-supported Ca single-atom carbon nanomaterials as efficient non-dissociative solid-state hydrogen storage materials. An intrinsic descriptor has been proposed to correlate the inherent properties of dopants with the hydrogen storage capability of the carbon-based host materials. The generalized design principle and the intrinsic descriptor have the predictive ability to screen out the best dual-doped-graphene-supported Ca single-atom hydrogen storage materials. The dual-doped materials have much higher hydrogen storage capability than the sole-doped ones, and exceed the current best carbon-based hydrogen storage materials.

Distinguished Roles of Nitrogen-Doped Sp2 and Sp3 Hybridized Carbon on Extraordinary Supercapacitance in Acidic Aqueous Electrolyte.

The acidic aqueous supercapacitors have been found to deliver appealing capacitive properties due to fast ion diffusion caused by the applied smallest size of hydrion. However, their practical applications are largely inhibited by the narrow electrochemical stability window of water (1.23 V). Herein, A nitrogen-enriched porous carbon materials (RNOPCs) is reported, consisting of varied nitrogen doping bonded on sp2 and sp3 carbon sites, which are capable of stimulating a wider potential window up to 1.4 V and thus resulting in a great enhancement of capacitive performance in aqueous acidic electrolytes. Together with the improved electrical conductivity and preferable hydrion diffusion, RNOPCs exhibit an ultrahigh volumetric capacitance (1084 F cm-3) in 0.5 M H2SO4. Besides, a fully packed RNOPCs-based symmetrical supercapacitor can deliver a high gravimetric and volumetric energy density of 31.8 Wh Kg-1 and 54.3 Wh L-1 respectively, approaching those of lead acid batteries (25-35 Wh Kg-1). The first-principles calculations reveal that the lone pair electrons of the doped nitrogen can be delocalized on its neighboring carbon atoms, improving charge uptakes and overpotentials. Such facile and scale-up production of carbon-based supercapacitors can bridge the gap of energy density between traditional supercapacitors and batteries in aqueous electrolytes.

Concurrent oxygen reduction and water oxidation at high ionic strength for scalable electrosynthesis of hydrogen peroxide.

Electrosynthesis of hydrogen peroxide via selective two-electron transfer oxygen reduction or water oxidation reactions offers a cleaner, cost-effective alternative to anthraquinone processes. However, it remains a challenge to achieve high Faradaic efficiencies at elevated current densities. Herein, we report that oxygen-deficient Pr1.0Sr1.0Fe0.75Zn0.25O4-δ perovskite oxides rich of oxygen vacancies can favorably bind the reaction intermediates to facilitate selective and efficient two-electron transfer pathways. These oxides exhibited superior Faradic efficiencies (~99%) for oxygen reduction over a wide potential range (0.05 to 0.45 V versus reversible hydrogen electrode) and current densities surpassing 50 mA cm-2 under high ionic strengths. We further found that the oxides perform a high selectivity (~80%) for two-electron transfer water oxidation reaction at a low overpotential (0.39 V). Lastly, we devised a membrane-free electrolyser employing bifunctional electrocatalysts, achieving a record-high Faradaic efficiency of 163.0% at 2.10 V and 50 mA cm-2. This marks the first report of the concurrent oxygen reduction and water oxidation catalysed by efficient bifunctional oxides in a novel membrane-free electrolyser for scalable hydrogen peroxide electrosynthesis.

Intrinsic Descriptor Guided Noble Metal Cathode Design for Li-CO2 Battery.

To date, the effect of noble metal (NM) electronic structures on CO2 reaction activity remains unknown, and explicit screening criteria are still lacking for designing highly efficient catalysts in CO2 -breathing batteries. Herein, by preferentially considering the decomposition of key intermediate Li2 CO3 , an intrinsic descriptor constituted of the d x 2 - y 2 ${{\rm{d}}}_{{x}^2 - {y}^2}$ orbital states and the electronegativity for predicting high-performance cathode material are discovered. As a demonstration, a series of graphene-supported noble metals (NM@G) as cathodes are fabricated via a fast laser scribing technique. Consistent with the preliminary prediction, Pd@G exhibits an ultralow overpotential (0.41 V), along with superior cycling performance up to 1400 h. Moreover, the overall thermodynamic reaction pathways on NM@G confirm the reliability of the established intrinsic descriptor. This basic finding of the relationship between the electronic properties of noble metal cathodes and the performance of Li-CO2 batteries provides a novel avenue for designing remarkably efficient cathode materials for metal-CO2 batteries.

Role of heteroatom-doping in enhancing catalytic activities and the stability of single-atom catalysts for oxygen reduction and oxygen evolution reactions.

Single-atom catalysts (SACs) are promising as efficient electrocatalysts for clean energy technologies such as fuel cells, water splitting, and metal-air batteries. Still, the unsatisfactory loading density and stability of the catalytic active centers limit their applications. Herein, a doping strategy is explored to achieve highly efficient and stable SACs for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The stability, electronic structures, and ORR/OER overpotentials of S-doped transition metal-nitrogen-carbon SAC structures were investigated using first-principles calculation methods. An intrinsic descriptor linking the intrinsic properties of catalysts and the catalytic activity was established for screening the best SACs. The theoretical predictions are well consistent with the experimental results, which provide a theoretical basis for understanding the catalytic mechanism and an approach for the rational design of SACs for clean energy conversion and storage.

Highly efficient and selective electrocatalytic hydrogen peroxide production on Co-O-C active centers on graphene oxide.

Electrochemical oxygen reduction provides an eco-friendly synthetic route to hydrogen peroxide (H2O2), a widely used green chemical. However, the kinetically sluggish and low-selectivity oxygen reduction reaction (ORR) is a key challenge to electrochemical production of H2O2 for practical applications. Herein, we demonstrate that single cobalt atoms anchored on oxygen functionalized graphene oxide form Co-O-C@GO active centres (abbreviated as Co1@GO for simplicity) that act as an efficient and durable electrocatalyst for H2O2 production. This Co1@GO electrocatalyst shows excellent electrochemical performance in O2-saturated 0.1 M KOH, exhibiting high reactivity with an onset potential of 0.91 V and H2O2 production of 1.0 mg cm-2 h-1 while affording high selectivity of 81.4% for H2O2. Our combined experimental observations and theoretical calculations indicate that the high reactivity and selectivity of Co1@GO for H2O2 electrogeneration arises from a synergistic effect between the O-bonded single Co atoms and adjacent oxygen functional groups (C-O bonds) of the GO present in the Co-O-C active centres.

A Tough Reversible Biomimetic Transparent Adhesive Tape with Pressure-Sensitive and Wet-Cleaning Properties.

Dry adhesives that combine strong adhesion, high transparency, and reusability are needed to support developments in emerging fields such as medical electrodes and the bonding of electronic optical devices. However, achieving all of these features in a single material remains challenging. Herein, we propose a pressure-responsive polyurethane (PU) adhesive inspired by the octopus sucker. This adhesive not only showcases reversible adhesion to both solid materials and biological tissues but also exhibits robust stability and high transparency (>90%). As the adhesive strength of the PU adhesive corresponds to the application force, adhesion could be adjusted by the preloading force and/or pressure. The adhesive exhibits high static adhesion (∼120 kPa) and 180° peeling force (∼500 N/m), which is far stronger than those of most existing artificial dry adhesives. Moreover, the adhesion strength is effectively maintained even after 100 bonding-peeling cycles. Because the adhesive tape relies on the combination of negative pressure and intermolecular forces, it overcomes the underlying problems caused by glue residue like that left by traditional glue tapes after removal. In addition, the PU adhesive also shows wet-cleaning performance; the contaminated tape can recover 90-95% of the lost adhesion strength after being cleaned with water. The results show that an adhesive with a microstructure designed to increase the contribution of negative pressure can combine high reversible adhesion and long fatigue life.

Unraveling the Structural Statistics and Its Relationship with Mechanical Properties in Metallic Glasses.

Metallic glasses exhibit excellent properties such as ultrahigh strength and excellent wear and corrosion resistance, but there is limited understanding on the relationship between their atomic structure and mechanical properties as a function of their structural state. In this paper, we bridge the processing-structure-property gap by utilizing molecular dynamics simulation for a model binary metallic glass, namely Ni80P20. The structural statistics including the fraction of Voronoi index, the distribution of Voronoi volume, and medium-range ordering are calculated to explain the observed changes in mechanical behavior and strain localization upon relaxation and rejuvenation. Our findings demonstrate that the evolution of mechanical properties can be linked to the atomic structure change in terms of short- and medium-range ordering. With the help of structural statistics, the mechanical properties are determined based on simple Voronoi analysis.

Designing Undercoordinated Ni-Nx and Fe-Nx on Holey Graphene for Electrochemical CO2 Conversion to Syngas.

In this study, we propose a top-down approach for the controlled preparation of undercoordinated Ni-Nx (Ni-hG) and Fe-Nx (Fe-hG) catalysts within a holey graphene framework, for the electrochemical CO2 reduction reaction (CO2RR) to synthesis gas (syngas). Through the heat treatment of commercial-grade nitrogen-doped graphene, we prepared a defective holey graphene, which was then used as a platform to incorporate undercoordinated single atoms via carbon defect restoration, confirmed by a range of characterization techniques. We reveal that these Ni-hG and Fe-hG catalysts can be combined in any proportion to produce a desired syngas ratio (1-10) across a wide potential range (-0.6 to -1.1 V vs RHE), required commercially for the Fischer-Tropsch (F-T) synthesis of liquid fuels and chemicals. These findings are in agreement with our density functional theory calculations, which reveal that CO selectivity increases with a reduction in N coordination with Ni, while unsaturated Fe-Nx sites favor the hydrogen evolution reaction (HER). The potential of these catalysts for scale up is further demonstrated by the unchanged selectivity at elevated temperature and stability in a high-throughput gas diffusion electrolyzer, displaying a high-mass-normalized activity of 275 mA mg-1 at a cell voltage of 2.5 V. Our results provide valuable insights into the implementation of a simple top-down approach for fabricating active undercoordinated single atom catalysts for decarbonized syngas generation.

Multiscale Manufacturing of Amorphous Alloys by a Facile Electrodeposition Approach and Their Property Dependence on the Local Atomic Order.

Metallic glasses are a unique class of materials combining ultrahigh strength together with plastic-like processing ability. However, the currently used melt quenching route to obtain amorphous alloys has a high cost basis in terms of manufacturing and expensive constituent elements often necessary to achieve the glassy state, thus hindering widespread adoption. In contrast, multimaterial electrodeposition offers a low-cost and versatile alternative to obtain amorphous alloys. Here, we demonstrate multiscale manufacturing of a model binary amorphous system by a facile and scalable pulsed electrodeposition approach. The structural and mechanical characteristics of electrodeposited Ni-P metallic glasses are investigated by a combination of experiments and molecular dynamics simulations. The property dependence on slight change in alloy chemistry is explained by the fraction of short-range-order clusters and geometrically unfavorable motifs. Bicapped square antiprism polyhedra clusters with two-atom connections result in more homogeneous deformation for Ni90P10 metallic glass, whereas a relatively higher fraction of three-atom connections in Ni85P15 metallic glass leads to higher strength, albeit localized and relatively brittle failure. The practicality of our approach is likely to stimulate the use of amorphous alloys in simple chemistries for multiscale use with systematic property optimization for specific applications.

A universal descriptor based on pz-orbitals for the catalytic activity of multi-doped carbon bifunctional catalysts for oxygen reduction and evolution.

Dual-/multi-heteroatom-doped carbon nanomaterials have been demonstrated to be effective bi-/multi-functional catalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), the critical reactions in fuel cells and metal-air batteries, respectively. However, trial-and-error routes are usually used to search for better catalysts from multi-doped complex material systems, and establishing design principles or intrinsic descriptors would accelerate the discovery of new efficient catalysts. Here, a descriptor based on pz-orbitals of active sites is proposed to describe the catalytic performance of dual-/tri-element-doped graphene catalysts for the ORR and the OER. In addition to multiple doping, the established descriptor is universal in nature and can also predict the contributions of defects and edges or their combinations. The prediction capacity of the descriptor is further enhanced by introducing a correction factor based on crystal orbital Hamilton population (COHP) analysis, which reveals the differences between the adsorption mechanism of edged C and graphitic C on graphene. The predictions are consistent with DFT calculations and experimental results. This work provides a powerful tool for rapidly screening multi-doped complex material systems for the desired ORR and OER bifunctional catalysts.

Hole-punching for enhancing electrocatalytic activities of 2D graphene electrodes: Less is more.

Using a polymer-masking approach, we have developed metal-free 2D carbon electrocatalysts based on single-layer graphene with and without punched holes and/or N-doping. A combined experimental and theoretical study on the resultant 2D graphene electrodes revealed that a single-layer graphene sheet exhibited a significantly higher electrocatalytic activity at its edge than that over the surface of its basal plane. Furthermore, the electrocatalytic activity of a single-layer 2D graphene sheet was significantly enhanced by simply punching microholes through the graphene electrode due to the increased edge population for the hole-punched graphene electrode. In a good consistency with the experimental observations, our density function theory calculations confirmed that the introduction of holes into a graphene sheet generated additional positive charge along the edge of the punched holes and hence the creation of more highly active sites for the oxygen reduction reaction. The demonstrated concept for less graphene material to be more electrocatalytically active shed light on the rational design of low-cost, but efficient electrocatalysts from 2D graphene for various potential applications ranging from electrochemical sensing to energy conversion and storage.

Self-Assembly of Metallo-Supramolecules under Kinetic or Thermodynamic Control: Characterization of Positional Isomers Using Scanning Tunneling Spectroscopy.

Coordination-driven self-assembly has been extensively employed to construct a variety of discrete structures as a bottom-up strategy. However, mechanistic understanding regarding whether self-assembly is under kinetic or thermodynamic control is less explored. To date, such mechanistic investigation has been limited to distinct, assembled structures. It still remains a formidable challenge to study the kinetic and thermodynamic behavior of self-assembly systems with multiple assembled isomers due to the lack of characterization methods. Herein, we use a stepwise strategy which combined self-recognition and self-assembly processes to construct giant metallo-supramolecules with 8 positional isomers in solution. With the help of ultrahigh-vacuum, low-temperature scanning tunneling microscopy and scanning tunneling spectroscopy, we were able to unambiguously differentiate 14 isomers on the substrate which correspond to 8 isomers in solution. Through measurement of 162 structures, the experimental probability of each isomer was obtained and compared with the theoretical probability. Such a comparison along with density functional theory (DFT) calculation suggested that although both kinetic and thermodynamic control existed in this self-assembly, the increased experimental probabilities of isomers compared to theoretical probabilities should be attributed to thermodynamic control.

Preaddition of Cations to Electrolytes for Aqueous 2.2 V High Voltage Hybrid Supercapacitor with Superlong Cycling Life and Its Energy Storage Mechanism.

Electrolyte solutions and electrode active materials, as core components of energy storage devices, have a great impact on the overall performance. Currently, supercapacitors suffer from the drawbacks of low energy density and poor cyclic stability in typical alkaline aqueous electrolytes. Herein, the ultrathin Co3O4 anode material is synthesized by a facile electrodeposition, followed by postheat treatment process. It is found that the decomposition of active materials induces reduction of energy density and specific capacitance during electrochemical testing. Therefore, a new strategy of preadding Co2+ cations to achieve the dissolution equilibrium of cobalt in active materials is proposed, which can improve the cyclic lifetime of electrode materials and broaden the operation window of electrochemical devices. Co2+ and Li+ embedded in carbon electrode during charging can enhance H+ desorption energy barrier, further hampering the critical step of bulk water electrolysis. More importantly, the highly reversible chemical conversion mechanism between Co3O4 and protons is demonstrated to be the fact that a large amount of quantum dots and second-order flaky CoO layers were in situ formed in the electrochemical reaction process, which is first discovered and reported in neutral solutions. The as-assembled device achieves a high operation voltage (2.2 V), excellent cycling stability (capacitance retention of 168% after 10 000 cycles) and ultrahigh energy density (99 W h kg-1 at a power density of 1100 W kg-1). The as-prepared electrolytes and highly active electrode materials will open up new opportunities for aqueous supercapacitors with high safety, high voltage, high energy density, and long-lifespan.

Origins of Boosted Charge Storage on Heteroatom-Doped Carbons.

Although tremendous efforts have been devoted to understanding the origin of boosted charge storage on heteroatom-doped carbons, none of the present studies has shown a whole landscape. Herein, by both experimental evidence and theoretical simulation, it is demonstrated that heteroatom doping not only results in a broadened operating voltage, but also successfully promotes the specific capacitance in aqueous supercapacitors. In particular, the electrolyte cations adsorbed on heteroatom-doped carbon can effectively inhibit hydrogen evolution reaction, a key step of water decomposition during the charging process, which broadens the voltage window of aqueous electrolytes even beyond the thermodynamic limit of water (1.23 V). Furthermore, the reduced adsorption energy of heteroatom-doped carbon consequently leads to more stored cations on the heteroatom-doped carbon surface, thus yielding a boosted charge storage performance.

Controllable growth of two-dimensional iron carbide in steels under accumulation deformation.

Two dimensional (2D) materials such as metal carbides are attractive owing to their unique structures and various potential applications. Although various synthetic methods have been developed for fabrication of 2D materials, it is still challenging to directly synthesize 2D carbides. Herein, we propose a new approach to convert in-situ 3D iron carbide into defect free 2D one in conventional carbon steels by controlling the deformation accumulation to drive atomic rearrangement within the carbides. Density functional theory (DFT) calculation demonstrated that ring-like, helical and other morphological 2D iron carbides can be formed under 30 % compressive deformation. Experimentally, the strength of 2D hexagonal iron carbide is estimated to be 12 GPa-18 GPa, which is 4-5 times that of original orthorhombic iron carbide (3.0 GPa-3.5 GPa) and the in-situ grown 2D carbide results in 176 % increase in strength of the steels. The first principles simulations show that the 2D iron carbides can be converted through its multiple slip systems under both the compressive and tensile pressure. This approach may open a new door for in-situ controllable growth of various 2D materials owning to rich metallic bond variety, slip system multiplicity and deformation diversity in metallic alloys.

High-Performance, Long-Life, Rechargeable Li-CO2 Batteries based on a 3D Holey Graphene Cathode Implanted with Single Iron Atoms.

A highly efficient cathode catalyst for rechargeable Li-CO2 batteries is successfully synthesized by implanting single iron atoms into 3D porous carbon architectures, consisting of interconnected N,S-codoped holey graphene (HG) sheets. The unique porous 3D hierarchical architecture of the catalyst with a large surface area and sufficient space within the interconnected HG framework can not only facilitate electron transport and CO2 /Li+ diffusion, but also allow for a high uptake of Li2 CO3 to ensure a high capacity. Consequently, the resultant rechargeable Li-CO2 batteries exhibit a low potential gap of ≈1.17 V at 100 mA g-1 and can be repeatedly charged and discharged for over 200 cycles with a cut-off capacity of 1000 mAh g-1 at a high current density of 1 A g-1 . Density functional theory calculations are performed and the observed appealing catalytic performance is correlated with the hierarchical structure of the carbon catalyst. This work provides an effective approach to the development of highly efficient cathode catalysts for metal-CO2 batteries and beyond.

Deformation mechanism in Al0.1CoCrFeNi Σ3(111)[11̄0] high entropy alloys - molecular dynamics simulations.

High entropy alloys (HEAs), composed of multiple components with equal or near atomic proportions, have extraordinary mechanical properties and are expected to bear the impact of high-speed forces in armor protection structure materials. In order to understand the deformation behaviour of HEAs under tensile and compressive loading, molecular dynamics simulations were performed to reveal the deformation mechanism and mechanical properties of three crystal structures: Al0.1CoCrFeNi HEAs without grain boundaries (perfect HEAs), Al0.1CoCrFeNi HEAs with grain boundaries of Σ3(111)[11̄0] (GBs HEAs) and grain boundaries of Σ3(111)[11̄0] with chemical cluster HEAs (cluster-GBs HEAs). The mechanical properties of the three models at the same strain rate were discussed. Then, the mechanical properties at different strain rates were analyzed. The movement and direction of internal dislocations during the deformation process were investigated. The simulation results show that the GBs HEAs and the cluster-GBs both play an important role in the deformation and failure of the HEAs. Under tensile loading, three behaviour stages of deformation were observed. Cluster-GBs HEAs have a larger yield strength and Young's modulus than that of GBs and perfect HEAs. The higher the strain rate is, the greater the stress reduction rate. Under compressive loading, there are only two behaviour stages of deformation. Cluster-GBs HEAs also have the largest yield strength. Under tensile and compressive deformation, Shockley partial dislocations of 1/6 <112> are dominant and their moving direction and effect on mechanical properties are discussed.

Atomistic simulations on nanoimprinting of copper by aligned carbon nanotube arrays under a high-frequency mechanical vibration.

Nanoimprinting behaviors of copper substrates and double-walled carbon nanotubes with interwall sp 3 bonds are investigated using molecular dynamics simulations. A high-frequency mechanical vibration with various amplitudes is applied on the carbon nanotube (CNT) mold and copper substrate in different directions. Results show that exciting mechanical resonances both on the CNT and substrate drastically decrease the maximum imprint force and interfacial friction up to 50% under certain amplitudes. Meanwhile, it is demonstrated that defects occur in the {111} plane in the copper substrate during nanoimprinting. For different CNT array densities, a higher grafting density needs more imprint force to transfer patterns. The maximum imprint force for a large range of CNT array densities can be reduced by vibrational perturbations, while reduction rates depend on the CNT grafting density. This work sheds deep insights into the nanoimprint process at the atomic level, suggesting that vibration perturbation is an effective approach for improving the nanoimprinting accuracy and preventing the fracture of nanopatterns.