High-throughput Compositional Screening of PdxTi1-xHy and PdxNb1-xHy Hydrides for CO2 Reduction

Electrochemical experiments and theoretical calculations have shown that Pd-based metal hydrides can perform well for the CO2 reduction reaction (CO2RR). Our previous work on doped-PdH showed that doping Ti and Nb into PdH can improve the CO2RR activity, suggesting that the Pd alloy hydrides with better performance are likely to be found in the PdxTi1-xHy and PdxNb1-xHy phase space. However, the vast compositional and structural space with different alloy hydride compositions and surface adsorbates, makes it intractable to screen out the stable and active PdxM1-xHy catalysts using density functional theory calculations. Herein, an active learning cluster expansion (ALCE) surrogate model equipped with Monte Carlo simulated annealing (MCSA), a CO* binding energy filter and a kinetic model are used to identify promising PdxTi1-xHy and PdxNb1-xHy catalysts with high stability and superior activity. Using our approach, we identify 24 stable and active candidates of PdxTi1-xHy and 5 active candidates of PdxNb1-xHy. Among these candidates, the Pd0.23Ti0.77H, Pd0.19Ti0.81H0.94, and Pd0.17Nb0.83H0.25 are predicted to display current densities of approximately 5.1, 5.1 and 4.6 μA cm-2 at -0.5 V overpotential, respectively, which are significantly higher than that of PdH at 3.7 μA cm-2.

Graph Neural Network-Accelerated Multitasking Genetic Algorithm for Optimizing PdxTi1-xHy Surfaces under Various CO2 Reduction Reaction Conditions

Palladium (Pd) hydride-based catalysts have been reported to have excellent performance in the CO2 reduction reaction (CO2RR) and hydrogen evolution reaction (HER). Our previous work on doped PdH and Pd alloy hydrides showed that Ti-doped and Ti-alloyed Pd hydrides could improve the performance of the CO2 reduction reaction compared with pure Pd hydride. Compositions and chemical orderings of the surfaces with only one adsorbate under certain reaction conditions are linked to their stability, activity, and selectivity toward the CO2RR and HER, as shown in our previous work. In fact, various coverages, types, and mixtures of the adsorbates, as well as state variables such as temperature, pressure, applied potential, and chemical potential, could impact their stability, activity, and selectivity. However, these factors are usually fixed at common values to reduce the complexity of the structures and the complexity of the reaction conditions in most theoretical work. To address the complexities above and the huge search space, we apply a deep learning-assisted multitasking genetic algorithm to screen for PdxTi1-xHy surfaces containing multiple adsorbates for CO2RR under different reaction conditions. The ensemble deep learning model can greatly speed up the structure relaxations and retain a high accuracy and low uncertainty of the energy and forces. The multitasking genetic algorithm simultaneously finds globally stable surface structures under each reaction condition. Finally, 23 stable structures are screened out under different reaction conditions. Among these, Pd0.56Ti0.44H1.06 + 25%CO, Pd0.31Ti0.69H1.25 + 50%CO, Pd0.31Ti0.69H1.25 + 25%CO, and Pd0.88Ti0.12H1.06 + 25%CO are found to be very active for CO2RR and suitable to generate syngas consisting of CO and H2.

Metal-Doped PdH(111) Catalysts for CO2 Reduction

PdH-based catalysts hold promise for both CO₂ reduction to CO and the hydrogen evolution reaction. Density functional theory is used to systematically screen for stability, activity, and selectivity of transition metal dopants in PdH. The transition metal elements Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Ag, Cd, Hf, Ta, W, and Re are doped into PdH(111) surface with six different doping configurations: single, dimer, triangle, parallelogram, island, and overlayer. We find that several dopants, such as Ti and Nb, have excellent predicted catalytic activity and CO₂ selectivity compared to the pure PdH hydride. In addition, they display good stability due to their negative doping formation energy. The improved performance can be assigned to reaction intermediates forming two bonds consisting of one C-Metal and one O-Metal bond on the PdH surface, which break the scaling relations of intermediates, and thus have stronger HOCO* binding facilitating CO₂ activation.

Photodepositing CdS on the Active Cyano Groups Decorated g-C3 N4 in Z-Scheme Manner Promotes Visible-Light-Driven Hydrogen Evolution

g-C₃ N₄ /CdS heterojunctions are potential photocatalysts for hydrogen production but their traditional type-II configuration generally leads to weak oxidative and reductive activity. How to construct the novel Z-scheme g-C₃ N₄ /CdS counterparts to address this issue remains a great challenge in this field. In this work, a new direct Z-scheme heterojunction of defective g-C₃ N₄ /CdS is designed by introducing cyano groups (NC-) as the active bridge sites. Experimental observations in combination with density functional theory (DFT) calculations reveal that the unique electron-withdrawing feature of cyano groups in the defective g-C₃ N₄ /CdS heterostructure can endow this photocatalyst with numerous advantageous properties including high light absorption ability, strong redox performance, satisfactory charge separation efficiency, and long lifetime of charge carriers. Consequently, the resultant photocatalytic system exhibits more active performance than CdS and g-C₃ N₄ under visible light and reaches an excellent hydrogen evolution rate of 1809.07 µmol h^-1 g^-1 , which is 6.09 times higher than pristine g-C₃ N₄ . Moreover, the defective g-C₃ N₄ /CdS photocatalyst maintains good stability after 40 h continuous test. This work provides new insights into design and construction of Z-scheme heterojunctions for regulating the visible-light-induced photocatalytic activity for H₂ evolution.

Transforming Photocatalytic g-C3 N4 /MoSe2 into a Direct Z-Scheme System via Boron-Doping: A Hybrid DFT Study

Z-scheme photocatalytic systems are an ideal band alignment structure for photocatalysis because of the high separation efficiency of photo-induced carriers while simultaneously preserving the strong reduction activity of electrons and oxidation activity of holes. However, the design and construction of Z-scheme photocatalysts is challenging because of the need for appropriate energy band alignment and built-in electric field. Here, we propose a novel approach to a Z-scheme photocatalytic system using density functional theory calculations with the HSE06 hybrid functional. The undesirable type-I g-C₃ N₄ /MoSe₂ heterojunction is transformed into a direct Z-scheme system through boron doping of g-C₃ N₄ (B-doped C₃ N₄ /MoSe₂ ). Detailed analysis of the total and partial density of states, work functions and differential charge density distribution of the B-doped C₃ N₄ /MoSe₂ heterojunction shows the proper band alignment and existence of a built-in electric field at the interface, with the direction from g-C₃ N₄ to MoSe₂ , demonstrating a direct Z-scheme heterojunction. Further investigation on the absorption spectra reveals a large enhancement of the light absorption efficiency after boron doping. The results consistently confirm that electronic structures and photocatalytic performance can be effectively manipulated by a facile boron doping. Modulating the band alignment of heterojunctions in this way provides valuable insights for the rational design of highly efficient heterojunction-based photocatalytic systems.

Coupling a Sponge Metal Fibers Skeleton with In Situ Surface Engineering to Achieve Advanced Electrodes for Flexible Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) are regarded as promising next-generation energy storage systems, however, the uncontrollable dendrite formation and serious polysulfide shuttling severely hinder their commercial success. Herein, a powerful 3D sponge nickel (SN) skeleton plus in situ surface engineering strategy, to address these issues synergistically, is reported, and a high-performance flexible LSB device is constructed. Specifically, the rationally designed spray-quenched lithium metal on the SN matrix (solid electrolyte interface (SEI)@Li/SN), as dendrite inhibitor, combines the merits of the 3D lithiophilic SN skeleton and the in situ formed SEI layer derived from the spray-quenching process, and thereby exhibits a steady overpotential within 75 mV for 1500 h at 5 mA cm^-2 /10 mA h cm^-2 . Meanwhile, in situ surface sulfurization of the SN skeleton hybridizing with the carbon/sulfur composite (SC@Ni₃ S₂ /SN) serves as efficient lithium polysulfide adsorbent to catalyze the overall reaction kinetics. COMSOL Multiphysics simulations and density functional theory calculations are further conducted to explore the underlying mechanisms. As a proof of concept, the well-designed SEI@Li/SN||SC@Ni₃ S₂ /SN full cell shows excellent electrochemical performance with a negative/positive ratio in capacity of ≈2 and capacity retention of 99.82% at 1 C under mechanical deformation. The novel design principles of these materials and electrodes successfully shed new light on the development of flexible LSBs.

Metal-Based Nanocatalysts via a Universal Design on Cellular Structure

Metal-based nanocatalysts supported on carbon have significant prospect for industry. However, a straightforward method for efficient and stable nanocatalysts still remains extremely challenging. Inspired by the structure and comptosition of cell walls and membranes, an ion chemical bond anchoring, an in situ carbonization coreduction process, is designed to obtain composite catalysts on N-doped 2D carbon (C-N) loaded with various noble and non-noble metals (for example, Pt, Ru, Rh, Pd, Ag, Ir, Au, Co, and Ni) nanocatalysts. These 2 nm particles uniformly and stably bond with the C-N support since the agglomeration and growth are suppressed by anchoring the metal ions on the cell wall and membrane during the carbonization and reduction reactions. The Pt@C-N exhibits excellent catalytic activity and long-term stability for the hydrogen evolution reaction, and the relative overpotential at 100 mA cm-2 is only 77 mV, which is much lower than that of commercial Pt/C and Pt single-atom catalysts reported recently.

Defect Promoted Capacity and Durability of N-MnO2- x Branch Arrays via Low-Temperature NH3 Treatment for Advanced Aqueous Zinc Ion Batteries

Defect engineering (doping and vacancy) has emerged as a positive strategy to boost the intrinsic electrochemical reactivity and structural stability of MnO₂ -based cathodes of rechargeable aqueous zinc ion batteries (RAZIBs). Currently, there is no report on the nonmetal element doped MnO₂ cathode with concomitant oxygen vacancies, because of its low thermal stability with easy phase transformation from MnO₂ to Mn₃ O₄ (≥300 °C). Herein, for the first time, novel N-doped MnO_{2- x} (N-MnO_{2- x} ) branch arrays with abundant oxygen vacancies fabricated by a facile low-temperature (200 °C) NH₃ treatment technology are reported. Meanwhile, to further enhance the high-rate capability, highly conductive TiC/C nanorods are used as the core support for a N-MnO_{2- x} branch, forming high-quality N-MnO_{2- x} @TiC/C core/branch arrays. The introduced N dopants and oxygen vacancies in MnO₂ are demonstrated by synchrotron radiation technology. By virtue of an integrated conductive framework, enhanced electron density, and increased surface capacitive contribution, the designed N-MnO_{2- x} @TiC/C arrays are endowed with faster reaction kinetics, higher capacity (285 mAh g^-1 at 0.2 A g^-1 ) and better long-term cycles (85.7% retention after 1000 cycles at 1 A g^-1 ) than other MnO₂ -based counterparts (55.6%). The low-temperature defect engineering sheds light on construction of advanced cathodes for aqueous RAZIBs.

Coupled Biphase (1T-2H)-MoSe2 on Mold Spore Carbon for Advanced Hydrogen Evolution Reaction

Performance breakthrough of MoSe₂ -based hydrogen evolution reaction (HER) electrocatalysts largely relies on sophisticated phase modulation and judicious innovation on conductive matrix/support. In this work the controllable synthesis of phosphate ion (PO₄^3- ) intercalation induced-MoSe₂ (P-MoSe₂ ) nanosheets on N-doped mold spore carbon (N-MSC) forming P-MoSe₂ /N-MSC composite electrocatalysts is realized. Impressively, a novel conductive N-MSC matrix is constructed by a facile mold fermentation method. Furthermore, the phase of MoSe₂ can be modulated by a simple phosphorization strategy to realize the conversion from 2H-MoSe₂ to 1T-MoSe₂ to produce biphase-coexisted (1T-2H)-MoSe₂ by PO₄^3- intercalation (namely, P-MoSe₂ ), confirmed by synchrotron radiation technology and spherical aberration-corrected TEM (SACTEM). Notably, higher conductivity, lower bandgap and adsorption energy of H⁺ are verified for the P-MoSe₂ /N-MSC with the help of density functional theory (DFT) calculation. Benefiting from these unique advantages, the P-MoSe₂ /N-MSC composites show superior HER performance with a low Tafel slope (≈51 mV dec^-1 ) and overpotential (≈126 mV at 10 mA cm^-1 ) and excellent electrochemical stability, better than 2H-MoSe₂ /N-MSC and MoSe₂ /carbon nanosphere (MoSe₂ /CNS) counterparts. This work demonstrates a new kind of carbon material via biological cultivation, and simultaneously unravels the phase transformation mechanism of MoSe₂ by PO₄^3- intercalation.

Tailoring Bandgap of Perovskite BaTiO₃ by Transition Metals Co-Doping for Visible-Light Photoelectrical Applications: A First-Principles Study

The physical and chemical properties of V-M″ and Nb-M″ (M″ is 3d or 4d transition metal) co-doped BaTiO₃ were studied by first-principles calculation based on density functional theory. Our calculation results show that V-M″ co-doping is more favorable than Nb-M″ co-doping in terms of narrowing the bandgap and increasing the visible-light absorption. In pure BaTiO₃, the bandgap depends on the energy levels of the Ti 3d and O 2p states. The appropriate co-doping can effectively manipulate the bandgap by introducing new energy levels interacting with those of the pure BaTiO₃. The optimal co-doping effect comes from the V-Cr co-doping system, which not only has smaller impurity formation energy, but also significantly reduces the bandgap. Detailed analysis of the density of states, band structure, and charge-density distribution in the doping systems demonstrates the synergistic effect induced by the V and Cr co-doping. The results can provide not only useful insights into the understanding of the bandgap engineering by element doping, but also beneficial guidance to the experimental study of BaTiO₃ for visible-light photoelectrical applications.

Variation in lipid composition of Chinese mitten-handed crab, Eriocheir sinensis during ovarian maturation

This experiment was conducted to investigate the variation in lipid composition during the ovarian maturation of the crab Eriocheir sinensis. The Chinese mitten-handed crab broodstock was divided into six different maturation periods according to the size and color of ovary. Ovary, hepatopancreas, muscle, and hemolymph of broodstock in different maturation periods were analyzed for total lipid and fatty acids using gas chromatography, and lipid classes by thin-layer chromatography. The ovarian lipid concentration (expressed as percent wet ovarian weight) increased steadily from stage II (5.4%) to stage IV (19.1%), and decreased to the lowest levels after spawning (stage V, 6.6%). The hepatopancreatic lipid concentration (expressed as percent wet hepatopancreatic weight) increased with maturity of the ovaries, reached a maximum at stage III(2) (29.9%), and decreased during the subsequent period to spawning (16.7%). The muscular and hemolymph lipid concentration did not change markedly during the ovarian development. These results suggest the possible movement of hepatopancreatic lipids to the ovaries during the ovarian maturation. Both triacylglycerol and phosphatidylcholine were responsible for the increase in ovarian lipid concentration during sexual maturation. The fatty acids of total lipid, triacylglycerol, and phosphatidylcholine of the ovaries did not vary systematically during the ovarian maturation, but the ratio between n-3PUFA (polyunsaturated fatty acid) and n-6PUFA did change regularly with the ovarian lipid. These suggest that enough PUFA, especially n-3PUFA, should be supplied to the crab during ovarian maturation.

Standard errors for the retransformation problem with heteroscedasticity

Economists often estimate models with a log-transformed dependent variable. The results from the log-transformed model are often retransformed back to the unlogged scale. Other studies have shown how to obtain consistent estimates on the original scale but have not provided variance equations for those estimates. In this paper, we derive the variance for three estimates--the conditional mean of y, the slope of y, and the average slope of y--on the retransformed scale. We then illustrate our proposed procedures with skewed health expenditure data from a sample of Medicaid eligible patients with severe mental illness.

Heterozygous loss of Six5 in mice is sufficient to cause ocular cataracts

Myotonic dystrophy (DM) is an autosomal dominant disorder characterized by skeletal muscle wasting, myotonia, cardiac arrhythmia, hyperinsulinaemia, mental retardation and ocular cataracts. The genetic defect in DM is a CTG repeat expansion located in the 3' untranslated region of DMPK and 5' of a homeodomain-encoding gene, SIX5 (formerly DMAHP; refs 2-5). There are three mechanisms by which CTG expansion can result in DM. First, repeat expansion may alter the processing or transport of the mutant DMPK mRNA and consequently reduce DMPK levels. Second, CTG expansion may establish a region of heterochromatin 3' of the repeat sequence and decrease SIX5 transcription. Third, toxic effects of the repeat expansion may be intrinsic to the repeated elements at the level of DNA or RNA (refs 10,11). Previous studies have demonstrated that a dose-dependent loss of Dm15 (the mouse DMPK homologue) in mice produces a partial DM phenotype characterized by decreased development of skeletal muscle force and cardiac conduction disorders. To test the role of Six5 loss in DM, we have analysed a strain of mice in which Six5 was deleted. Our results demonstrate that the rate and severity of cataract formation is inversely related to Six5 dosage and is temporally progressive. Six5+/- and Six5-/- mice show increased steady-state levels of the Na+/K+-ATPase alpha-1 subunit and decreased Dm15 mRNA levels. Thus, altered ion homeostasis within the lens may contribute to cataract formation. As ocular cataracts are a characteristic feature of DM, these results demonstrate that decreased SIX5 transcription is important in the aetiology of DM. Our data support the hypothesis that DM is a contiguous gene syndrome associated with the partial loss of both DMPK and SIX5.

Multimode laser Fizeau interferometer for measuring the surface of a thin transparent plate

A Fizeau interferometer utilizes a multimode laser as a light source for testing thin transparent plate samples. As a result of multimode linear laser operation, interference fringes are obtained only when the optical path difference between two surfaces is equal to twice a multiple of the laser's effective cavity length. For three parallel surfaces, we can either adjust their separations or select a laser such that only two of the three surfaces meet the requirement of twice a multiple of the laser's effective cavity length.

Testing an optical window of a small wedge angle: effect of multiple reflections

Multiple reflections between two surfaces of a window introduce a fixed pattern error in optical measurements. One way to remove these spurious reflections is to use a reasonably large wedge so that the interference fringes formed by the two surfaces are too dense for the detector to resolve. However, this method does not work if the wedge angle is small, e.g., several arcseconds. By tilting both the window and the return mirror properly, it is possible to remove the effect of multiple reflections of a window. Theory and experimental results are presented.

Absolute testing of flats by using even and odd functions

We describe a modified three-flat method. In a Cartesian coordinate system, a flat can be expressed as the sum of even-odd, odd-even, even-even, and odd-odd functions. The even-odd and the odd-even functions of each flat are obtained first, and then the even-even function is calculated. All three functions are exact. The odd-odd function is difficult to obtain. In theory, this function can be solved by rotating the flat 90°, 45°, 22.5°, etc. The components of the Fourier series of this odd-odd function are derived and extracted from each rotation of the flat. A flat is approximated by the sum of the first three functions and the known components of the odd-odd function. In the experiments, the flats are oriented in six configurations by rotating the flats 180°, 90°, and 45° with respect to one another, and six measurements are performed. The exact profiles along every 45° diameter are obtained, and the profile in the area between two adjacent diameters of these diameters is also obtained with some approximation. The theoretical derivation, experiment results, and error analysis are presented.

Effect of retroreflection on a Fizeau phase-shifting interferometer

Phase errors in a Fizeau phase-shifting interferometer caused by multiple-reflected beams from a retroreflective optics, such as a corner cube and a right-angle prism, are studied. Single- and double-pass configurations are presented, and their measurement results are compared. An attenuator is not needed in a double-pass configuration because light is reflected by the retroreflective optics twice and the reference surface once and hence the intensities match. It is more accurate to test a corner cube or a right-angle prism in a double-pass configuration than in a single-pass configuration. Simulations and experimental results are presented.

Interferometric stress birefringence measurement

We describe a sensitive method for measuring the stress birefringence of an optical window that utilizes a phase-measuring Fizeau interferometer incorporating a variable retarder and a nonpolarizing beam splitter. When we test a material in an interferometer cavity, the wave front transmitted through the material is deviated by the surfaces, inhomogeneity, and birefringence of the material. Birefringence causes the transmitted wave front to have different optical path difference (OPD) profiles for the vertical and horizontal orientations of linear polarization. Subtracting these OPD profiles reveals the amount of phase difference between the fast and slow axes of the material. Hence, birefringence may be calculated. Phase-measurement techniques and a computer-controlled interferometer employing a variable liquid-crystal retarder provide a fully automated instrument for measuring stress birefringence. The theoretical derivation, discussion of the instrument, and experimental results are presented.

Accurate measurement of the dihedral angle of a corner cube

The alignment of a corner cube affects the measurement of its dihedral angle. For 5 deg of tilt, the error is up to 7%, depending on the orientation of the tilt. A vector model is devised to derive formulas that take misalignment into account for both solid and hollow corner cubes. When the wave-front tilt caused by the dihedral angle error is not much greater than that caused by the surface figure, because of vignetting for a tilting illumination, the surface figure of the cube facet makes varying contributions to the wave-front tilt for different incident angles. Simulations and experimental results are presented.

Effect of spurious reflection on phase shift interferometry

The phase errors caused by spurious reflection in Twyman-Green and Fizeau interferometers are studied. A practical algorithm effectively eliminating the error is presented. Two other algorithms are reviewed, and the results obtained using the three algorithms are compared.

Effect of piezoelectric transducer nonlinearity on phase shift interferometry

If the nonlinearity of the motion of a piezoelectric transducer (PZT) can be described as a quadratic function, the integrated intensity of one frame in phase shift interferometry can be calculated using the Fresnel integral. For a PZT with smaller nonlinearity, the rms phase error is almost linearly proportional to the quadratic coefficient The effects of PZT nonlinearity on the three- and the four-bucket algorithms are compared.