Molten-Salt Electrochemical Deoxidation Synthesis of Platinum-Neodymium Nanoalloy Catalysts for Oxygen Reduction Reaction

Platinum-rare earth metal (Pt-RE) nanoalloys are regarded as a potential high performance oxygen reduction reaction (ORR) catalyst. However, wet chemical synthesis of the nanoalloys is a crucial challenge because of the extremely high oxygen affinity of RE elements and the significantly different standard reduction potentials between Pt and RE. Here, this paper presents a molten-salt electrochemical synthetic strategy for the compositional-controlled preparation of platinum-neodymium (Pt-Nd) nanoalloy catalysts. Carbon-supported platinum-neodymium (Pt_xNd/C) nanoalloys, with distinct compositions of Pt₅Nd and Pt₂Nd, are obtained through molten-salt electrochemical deoxidation of platinum and neodymium oxide (Pt-Nd₂O₃) precursors supported on carbon. The Pt_xNd/C nanoalloys, especially the Pt₅Nd/C exhibit a mass activity of 0.40 A mg⁻¹_Pt and a specific activity of 1.41 mA cm⁻²_Pt at 0.9 V versus RHE, which are 3.1 and 7.1 times higher, respectively, than that of commercial Pt/C catalyst. More significantly, the Pt₅Nd/C catalyst is remarkably stable after undergoing 20 000 accelerated durability cycles. Furthermore, the density-functional-theory (DFT) calculations confirm that the ORR catalytic performance of Pt_xNd/C nanoalloys is enhanced by compressive strain effect of Pt overlayer, causing a suitable weakened binding energies of O^* $\mathrm{\Delta }{E}_{{\mathrm{O}}^{\ast }}$ and $\mathrm{\Delta }{E}_{{\mathrm{OH}}^{\ast }}$.     

Boosting the Methanol Oxidation Reaction Activity of Pt–Ru Clusters via Resonance Energy Transfer

The sluggish kinetics of the methanol oxidation reaction (MOR) with PtRu electrocatalyst severely hinder the commercialization of direct methanol fuel cells (DMFCs). The electronic structure of Pt is of significant importance for its catalytic activity. Herein, it is reported that low-cost fluorescent carbon dots (CDs) can regulate the behavior of the D-band center of Pt in PtRu clusters through resonance energy transfer (RET), resulting in a significant increase in the catalytic activity of the catalyst participating in methanol electrooxidation. For the first time, the bifunction of RET is used to provide unique strategy for fabrication of PtRu electrocatalysts, not only tunes the electronic structure of metals, but also provides an important role in anchoring metal clusters. Density functional theory calculations further prove that charge transfer between CDs and Pt promotes the dehydrogenation of methanol on PtRu catalysts and reduces the free energy barrier of the reaction associated with the oxidation of CO^* to CO₂. This helps to improve the catalytic activity of the systems participating in MOR. The performance of the best sample is 2.76 times higher than that of commercial PtRu/C (213.0 vs 76.99 ${\mathrm{mW}\mathrm{cm}}^{-2}{\mathrm{mg}}_{\mathrm{Pt}}^{-1}$). The fabricated system can be potentially used for the efficient fabrication of DMFCs.     

Hybrid Electrolyte Design for High-Performance Zinc–Sulfur Battery

Rechargeable aqueous Zn/S batteries exhibit high capacity and energy density. However, the long-term battery performance is bottlenecked by the sulfur side reactions and serious Zn anode dendritic growth in the aqueous electrolyte medium. This work addresses the problem of sulfur side reactions and zinc dendrite growth simultaneously by developing a unique hybrid aqueous electrolyte using ethylene glycol as a co-solvent. The designed hybrid electrolyte enables the fabricated Zn/S battery to deliver an unprecedented capacity of 1435 mAh g⁻¹ and an excellent energy density of 730 Wh kg⁻¹ at 0.1 Ag⁻¹. In addition, the battery exhibits capacity retention of 70% after 250 cycles even at 3 Ag⁻¹. Moreover, the cathode charge–discharge mechanism studies demonstrate a multi-step conversion reaction. During discharge, the elemental sulfur is sequentially reduced by Zn to S²⁻ (${\mathrm{S}}_8\to {\mathrm{S}}_{\mathrm{x}}^{2-}\to {\mathrm{S}}_2^{2-}+{\mathrm{S}}^{2-})$, forming ZnS. On charging, the ZnS and short-chain polysulfides will oxidize back to elemental sulfur. This electrolyte design strategy and unique multi-step electrochemistry of the Zn/S system provide a new pathway in tackling both key issues of Zn dendritic growth and sulfur side reactions, and also in designing better Zn/S batteries in the future.     

Mesh‐Like Carbon Nanosheets with High‐Level Nitrogen Doping for High‐Energy Dual‐Carbon Lithium‐Ion Capacitors

Li‐ion capacitors (LICs) have demonstrated great potential for bridging the gap between lithium‐ion batteries and supercapacitors in electrochemical energy storage area. The main challenge for current LICs (contain a battery‐type anode as well as a capacitor‐type cathode) lies in circumventing the mismatched electrode kinetics and cycle degradation. Herein, a mesh‐like nitrogen (N)‐doped carbon nanosheets with multiscale pore structure is adopted as both cathode and anode for a dual‐carbon type of symmetric LICs to alleviate the above mentioned problems via a facile and green synthesis approach. With rational design, this dual‐carbon LICs exhibits a broad high working voltage window (0–4.5 V), an ultrahigh energy density of $218.4\mathrm{Wh}{\mathrm{kg}}^{–1}{}_{\mathrm{electrodes}}$ ( $229.8\mathrm{Wh}{\mathrm{L}}^{–1}{}_{\mathrm{electrodes}}$), the highest power density of $22.5\mathrm{kW}{\mathrm{kg}}^{–1}{}_{\mathrm{electrodes}}$ ( $23.7\mathrm{kW}{\mathrm{L}}^{–1}{}_{\mathrm{electrodes}}$) even under an ultrahigh energy density of $97.5\mathrm{Wh}{\mathrm{kg}}^{–1}{}_{\mathrm{electrodes}}$ ( $102.6\mathrm{Wh}{\mathrm{L}}^{–1}{}_{\mathrm{electrodes}}$), as well as reasonably good cycling stability with capacity retention of 84.5% (only 0.0016% capacity loss per cycle) within 10 000 cycles under a high current density of 5 A g^?1. This study provides an efficient method and option for the development of high performance LIC devices.     

Electronic Structure Engineering of Pt Species over Pt/WO3 toward Highly Efficient Electrocatalytic Hydrogen Evolution

Pt-based supported materials, a widely used electrocatalyst for hydrogen evolution reaction (HER), often experience unavoidable electron loss, resulting in a mismatching of electronic structure and HER behavior. Here, a Pt/WO₃ catalyst consisting of Pt species strongly coupled with defective WO₃ polycrystalline nanorods is rationally designed. The electronic structure engineering of Pt sites on WO₃ can be systematically regulated, and so that the optimal electron-rich Pt sites on Pt/WO₃-600 present an excellent HER activity with only 8 mV overpotential at 10 mA cm⁻². Particularly, the mass activity reaches 7015 mA mg⁻¹ at the overpotential of 50 mV, up to 26-fold higher than that of the commercial Pt/C. The combination of experimental and theoretical results demonstrates that the O vacancies of WO₃ effectively mitigate the tendency of electron transfer from Pt sites to WO₃, so that the d-band center could reach an appropriate level relative to Fermi level, endowing it with a suitable $\Delta G_{{\mathrm{H}}^{\ast }}$. This work identifies the influence of the electronic structure on catalytic activity.     

Giant Magnetocaloric Effect in Magnets Down to the Monolayer Limit

2D magnets can potentially revolutionize information technology, but their potential application to cooling technology and magnetocaloric effect (MCE) in a material down to the monolayer limit remain unexplored. Herein, it is revealed through multiscale calculations the existence of giant MCE and its strain tunability in monolayer magnets such as CrX₃ (X = F, Cl, Br, I), CrAX (A = O, S, Se; X = F, Cl, Br, I), and Fe₃GeTe₂. The maximum adiabatic temperature change ($\Delta T_{\text{ad}}^{\max }$), maximum isothermal magnetic entropy change, and specific cooling power in monolayer CrF₃ are found as high as 11 K, 35 µJ m⁻² K⁻¹, and 3.5 nW cm⁻² under a magnetic field of 5 T, respectively. A 2% biaxial and 5% a-axis uniaxial compressive strain can remarkably increase $\Delta T_{\text{ad}}^{\max }$ of CrCl₃ and CrOF by 230% and 37% (up to 15.3 and 6.0 K), respectively. It is found that large net magnetic moment per unit area favors improved MCE. These findings advocate the giant-MCE monolayer magnets, opening new opportunities for magnetic cooling at nanoscale.     

The Rule of Thirds: Controlling Junction Chirality and Polarity in 3D DNA Tiles

The successful self-assembly of tensegrity triangle DNA crystals heralded the ability to programmably construct macroscopic crystalline nanomaterials from rationally-designed, nanoscale components. This 3D DNA tile owes its “tensegrity” nature to its three rotationally stacked double helices locked together by the tensile winding of a center strand segmented into 7 base pair (bp) inter-junction regions, corresponding to two-thirds of a helical turn of DNA. All reported tensegrity triangles to date have employed $\left(Z+2/3\right)$ turn inter-junction segments, yielding right-handed, antiparallel, “J1” junctions. Here a minimal DNA triangle motif consisting of 3-bp inter-junction segments, or one-third of a helical turn is reported. It is found that the minimal motif exhibits a reversed morphology with a left-handed tertiary structure mediated by a locally-parallel Holliday junction—the “L1” junction. This parallel junction yields a predicted helical groove matching pattern that breaks the pseudosymmetry between tile faces, and the junction morphology further suggests a folding mechanism. A Rule of Thirds by which supramolecular chirality can be programmed through inter-junction DNA segment length is identified. These results underscore the role that global topological forces play in determining local DNA architecture and ultimately point to an under-explored class of self-assembling, chiral nanomaterials for topological processes in biological systems.     

Controlling the Facet of ZnO during Wet Chemical Etching Its (0001¯) O‐Terminated Surface

Special surface plays a crucial role in nature as well as in industry. Here, the surface morphology evolution of ZnO during wet etching is studied by in situ liquid cell transmission electron microscopy and ex situ wet chemical etching. Many hillocks are observed on the (000 $\overline{1}$) O‐terminated surface of ZnO nano/micro belts during in situ etching. Nanoparticles on the apex of the hillocks are observed to be essential for the formation of the hillocks, providing direct experimental evidence of the micromasking mechanism. The surfaces of the hillocks are identified to be {01 $\overline{1}\overline{3}$} crystal facets, which is different from the known fact that {01 $\overline{1}\overline{1}$} crystal facets appear on the (000 $\overline{1}$) O‐terminated surface of ZnO after wet chemical etching. O₂ plasma treatment is found to be the key factor for the appearance of {01 $\overline{1}\overline{3}$} instead of {01 $\overline{1}\overline{1}$} crystal facets after etching for both ZnO nano/micro belts and bulk materials. The synergistic effect of acidic etching and O‐rich surface caused by O₂ plasma treatment is proposed to be the cause of the appearance of {01 $\overline{1}\overline{3}$} crystal facets. This method can be extended to control the surface morphology of other materials during wet chemical etching.     

Scalable Synthesis of Holey Deficient 2D Co/NiO Single-Crystal Nanomeshes via Topological Transformation for Efficient Photocatalytic CO2 Reduction

Preparation of holey, single-crystal, 2D nanomaterials containing in-plane nanosized pores is very appealing for the environment and energy-related applications. Herein, an in situ topological transformation is showcased of 2D layered double hydroxides (LDHs) allows scalable synthesis of holey, single-crystal 2D transition metal oxides (TMOs) nanomesh of ultrathin thickness. As-synthesized 2D Co/NiO-2 nanomesh delivers superior photocatalytic CO₂-syngas conversion efficiency (i.e., V_CO of 32460 µmol h⁻¹ g⁻¹ CO and $V_{{\mathrm{H}}_2}$ of 17840 µmol h⁻¹ g⁻¹ H₂), with V_CO about 7.08 and 2.53 times that of NiO and 2D Co/NiO-1 nanomesh containing larger pore size, respectively. As revealed in high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), the high performance of Co/NiO-2 nanomesh primarily originates from the edge sites of nanopores, which carry more defect structures (e.g., atomic steps or vacancies) than basal plane for CO₂ adsorption, and from its single-crystal structure adept at charge transport. Theoretical calculation shows the topological transformation from 2D hydroxide to holey 2D oxide can be achieved, probably since the trace Co dopant induces a lattice distortion and thus a sharp decrease of the dehydration energy of hydroxide precursor. The findings can advance the design of intriguing holey 2D materials with well-defined geometric and electronic properties.     

Fracture Toughness Characteristics of Stacked Bilayer Graphene via Far-Field Displacement Measurements

Mechanical properties of graphene, e.g., strength, modulus, and fracture toughness are extremely sensitive to flaws. Here the fracture properties of stacked bilayer graphene sheets (SBLG) are reported, obtained via stacking two individually grown graphene sheets. The SBLG is presented here as a building block for flaw-resilient nanomaterials. The fracture properties of freestanding SBLG sheets, suspended on transmission electron microscope (TEM) grids, are characterized by stretching the TEM grid inside an scanning electron microscope (SEM) chamber and monitoring the local displacements in real-time. The fracture toughness is measured and expressed as a function of the critical displacement required to propagate existing cracks in the experiment via computational models. This approach decouples force and displacements measurements, and utilizes the known elastic modulus along with the known displacement boundary conditions at the onset of crack growth to estimate the far field force and stress. This strategy represents a breakthrough in nanoscale fracture mechanics for statistical analysis and high throughput experimens on multiple samples at a time. Results demonstrate that the SBLG is markedly tougher than as-grown single or multilayer graphene, with a mode I fracture toughness of ≈28.06 ± 7.5 MPa$\sqrt{m}$. The mechanisms leading to a higher toughness of SBLG are also analyzed and discussed.     

Distributional and inferential properties of some new multivariate process capability indices for symmetric specification region

Statistical quality control is used to improve performance of processes. Since most of the processes are multivariate in nature, multivariate process capability indices (MPCIs) have been developed by many researchers depending on the context. However, it is generally difficult to understand and calculate MPCIs, compared to their univariate counterparts like $C_p$, $C_{pk}$, and so on. This paper discusses a relatively new development in MPCIs, namely, $C_G(u,v)$, which is a multivariate analogue of $C_p(u,v)$—the celebrated superstructure of univariate process capability indices . Some statistical properties of $C_G(u,v)$ are studied, particularly of $C_G(0,0)$, a member MPCI of the superstructure, which measures potential capability of a multivariate process. A threshold value of $C_G(0,0)$ is computed, and this can be considered as a logical cut-off for other member indices of $C_G(u,v)$ as well. The expression for the upper limit of the proportion of nonconformance is derived as a function of $C_G(0,0)$. Density plots of asymptotic distributions of four major member indices of $C_G(u,v)$, namely, $C_G(0,0)$, $C_G(1,0)$, $C_G(0,1)$, and $C_G(1,1)$, are made. Finally, a numerical example is discussed to supplement the theory developed in this paper.     

Comb and Bottlebrush Polymers with Superior Rheological and Mechanical Properties

Comb and bottlebrush polymers present a wide range of rheological and mechanical properties that can be controlled through their molecular characteristics, such as the backbone and side chain lengths as well as the number of branches per molecule or the grafting density. This review investigates the impact of these characteristics specifically on the zero shear viscosity, strain hardening behavior, and plateau shear modulus. It is shown that for a comb polymer with an entangled backbone and entangled side chains, a maximum in the strain hardening factor and minimum in the zero shear viscosity η₀ can be achieved through selection of an optimum number of branches q. Bottlebrush polymers with flexible filaments and extremely low plateau shear moduli relative to linear polymers open the door for a new class of solvent‐free supersoft elastomers, where their network modulus can be controlled through both the degree of polymerization between crosslinks, n_x, and the length of the side chains, n_sc, with $G_{BB}^0\approx \rho kT{n}_x^{?1}{(n_{sc}+1)}^{?1}$.     

Optimized identification of earlywood and latewood stiffnesses in loblolly pine in simulated experiments

Knowledge of local mechanical behaviour of wood is especially important as silvicultural practices are modified to allow wood to compete as a relevant material in high technology applications. Challenges associated with identification of local mechanical behaviour have resulted in simplified test geometries designed to determine one or two constitutive parameters. The objective of this work was to design and simulate an entire experiment developed to simultaneously identify the earlywood and latewood orthotropic stiffnesses in loblolly pine in a single specimen and load geometry. The virtual experiment was capable of evaluating optimal orthotropy orientation for reduced identification errors and indicating most favourable choices for data smoothing filters and identification methodology. Additionally, certain ring spacing and latewood percentages were shown to produce large errors, but those combinations are unlikely to occur naturally. The simulation was able to identify $Q_{11},Q_{22}$, and $Q_{66}$ with approximately $\pm 10\%$ error; the $Q_{12}$ error was larger with more scatter. The methodology presented here contributes to the best practices available for heterogeneous stiffness identification.     

Wafer‐Scale Synthesis of Graphene on Sapphire: Toward Fab‐Compatible Graphene

The adoption of graphene in electronics, optoelectronics, and photonics is hindered by the difficulty in obtaining high‐quality material on technologically relevant substrates, over wafer‐scale sizes, and with metal contamination levels compatible with industrial requirements. To date, the direct growth of graphene on insulating substrates has proved to be challenging, usually requiring metal‐catalysts or yielding defective graphene. In this work, a metal‐free approach implemented in commercially available reactors to obtain high‐quality monolayer graphene on c‐plane sapphire substrates via chemical vapor deposition is demonstrated. Low energy electron diffraction, low energy electron microscopy, and scanning tunneling microscopy measurements identify the Al‐rich reconstruction $\left(\sqrt{31}\times \sqrt{31}\right)R\pm 9$° of sapphire to be crucial for obtaining epitaxial graphene. Raman spectroscopy and electrical transport measurements reveal high‐quality graphene with mobilities consistently above 2000 cm² V^?1 s^?1. The process is scaled up to 4 and 6 in. wafers sizes and metal contamination levels are retrieved to be within the limits for back‐end‐of‐line integration. The growth process introduced here establishes a method for the synthesis of wafer‐scale graphene films on a technologically viable basis.     

Efficient monitoring of coefficient of variation with an application to chemical reactor process

Control chart is a useful tool to monitor the performance of the industrial or production processes. Control charts are mostly adopted to detect unfavorable variations in process location (mean) and dispersion (standard deviation) parameters. In the literature, many control charts are designed for the monitoring of process variability under the assumption that the process mean is constant over time and the standard deviation is independent of the mean. However, for many real-life processes, the standard deviation may be proportional to mean, and hence it is more appropriate to monitor the process coefficient of variation (CV). In this study, we are proposing a design structure of the Shewhart type CV control chart under neoteric ranked set sampling with an aim to improve the detection ability of the usual CV chart. A comprehensive simulation study is conducted to evaluate the performance of the proposed $C{V}_{[\mathrm{NRSS}]}$ chart in terms of $ARL$, $MDRL,$ and $SDRL$ measures. Moreover, the comparison of $C{V}_{[\mathrm{NRSS}]}$ chart is made with the existing competitive charts, based on simple random sampling, ranked set sampling (RSS), median RSS, and extreme RSS schemes. The results revealed that the proposed chart has better detection ability as compared to all existing competitive charts. Finally, a real-life example is presented to illustrate the working of the newly proposed CV chart.     

Enhanced Piezoelectric,Ferroelectric, and Electrostrictive Properties of Lead-Free (1-x)BCZT-(x)BCST Electroceramics with Energy Harvesting Capability

Next-generation electronics and energy technologies can now be developed as a result of the design, discovery, and development of novel, environmental friendly lead (Pb)-free ferroelectric materials with improved characteristics and performance. However, there have only been a few reports of such complex materials’ design with multi-phase interfacial chemistry, which can facilitate enhanced properties and performance. In this context, herein, novel lead-free piezoelectric materials (1-x)Ba_0.95Ca_0.05Ti_0.95Zr_0.05O₃-(x)Ba_0.95Ca_0.05Ti_0.95Sn_0.05O₃, are reported, which are represented as (1-x)BCZT-(x)BCST, with demonstrated excellent properties and energy harvesting performance. The (1-x)BCZT-(x)BCST materials are synthesized by high-temperature solid-state ceramic reaction method by varying x in the full range (x = 0.00–1.00). In-depth exploration research is performed on the structural, dielectric, ferroelectric, and electro-mechanical properties of (1-x)BCZT-(x)BCST ceramics. The formation of perovskite structure for all ceramics without the presence of any impurity phases is confirmed by X-ray diffraction (XRD) analyses, which also reveals that the Ca²⁺, Zr⁴⁺, and Sn⁴⁺ are well dispersed within the BaTiO₃ lattice. For all (1-x)BCZT-(x)BCST ceramics, thorough investigation of phase formation and phase-stability using XRD, Rietveld refinement, Raman spectroscopy, high-resolution transmission electron microscopy (HRTEM), and temperature-dependent dielectric measurements provide conclusive evidence for the coexistence of orthorhombic + tetragonal (Amm2 + P4mm) phases at room temperature. The steady transition of Amm2 crystal symmetry to P4mm crystal symmetry with increasing x content is also demonstrated by Rietveld refinement data and related analyses. The phase transition temperatures, rhombohedral-orthorhombic (T_R-O), orthorhombic- tetragonal (T_O-T), and tetragonal-cubic (T_C), gradually shift toward lower temperature with increasing x content. For (1-x)BCZT-(x)BCST ceramics, significantly improved dielectric and ferroelectric properties are observed, including relatively high dielectric constant ε_r ≈ 1900–3300 (near room temperature), ε_r ≈ 8800–12 900 (near Curie temperature), dielectric loss, tan δ ≈ 0.01–0.02, remanent polarization P_r ≈ 9.4–14 µC cm⁻², coercive electric field E_c ≈ 2.5–3.6 kV cm⁻¹. Further, high electric field-induced strain S ≈ 0.12–0.175%, piezoelectric charge coefficient d₃₃ ≈ 296–360 pC N⁻¹, converse piezoelectric coefficient ${(d_{33}^{\ast })}_{\mathrm{ave}}$≈ 240–340 pm V⁻¹, planar electromechanical coupling coefficient k_p ≈ 0.34–0.45, and electrostrictive coefficient (Q₃₃)_avg ≈ 0.026–0.038 m⁴ C⁻² are attained. Output performance with respect to mechanical energy demonstrates that the (0.6)BCZT-(0.4)BCST composition (x = 0.4) displays better efficiency for generating electrical energy and, thus, the synthesized lead-free piezoelectric (1-x)BCZT-(x)BCST samples are suitable for energy harvesting applications. The results and analyses point to the outcome that the (1-x)BCZT-(x)BCST ceramics as a potentially strong contender within the family of Pb-free piezoelectric materials for future electronics and energy harvesting device technologies.     

Atomistic Understanding of the Competition between Dislocation and Twinning in Silver under Nanoindentation

In this study, the competition mechanisms between dislocation slip and twinning in silver with a low stacking fault energy using molecular dynamics (MD) simulation from an atomistic point of view are reported. Herein, three crystallographic surface orientations of $(001)$, $(011)$, and $(111)$ are considered and compared. The indentation stress–strain curves are successfully obtained from the load–displacement curves of nanoindentation. The stress of $(001)$, $(011)$, and $(111)$ orientations drops at the strains of 0.140, 0.133, and 0.136, which corresponds to the yield stress of 3.83, 4.33, and 4.99 GPa, respectively. Dislocation slip and twinning simultaneously form in silver as indicated by the total potential energy of the system. Furthermore, the typical four-, two-, and sixfold symmetries of the out-of-plane displacement as in copper are not observed for $(001)$, $(011)$, and $(111)$ orientations in silver. Hence, this observation can be supported by the simultaneous occurrence of dislocation slip and twinning in silver.