Sheet Size Research Articles

Refining grain structure and improving elongation properties in AZ31 magnesium alloy sheets using hard plate accumulative roll bonding

Magnesium alloy sheet are an ideal choice for achieving material and structural light weighting. Traditional ARB technology can significantly reduce the size of magnesium alloy sheet, but it is faced with the challenge of strong plastic inversion. In addition, it is easy to produce edge cracking defects, and it is also difficult to control the quality of the sheet. In this study, we prepared AZ31 magnesium alloy sheet by HP-ARB process for the first time. The results show that compared to ARB, the HP-ARB sheet has remarkable improvements in and mechanical properties.After two passes, the average grain size of HP-ARB decreased from 6.19 μm to 4.58 μm, tensile strength reaches 291 MPa, and the elongation is 10.1%, which significantly increased to 55.4% compared with ARB. HP-ARB has the ability to transform part of shear stress into compressive stress, which improves the stress distribution on the sheet. On one hand, a large amount of energy stored in dislocations provides energy for DRX, which makes the process more complete, leading to microstructure refinement and grain orientation randomization. This leads to the deviation of texture orientation to TD direction, which leads to the decrease of pole density and weakening of the strong basal texture. On the other hand, dislocation density (ρD) of the sheet is relatively low. The average Schmidt factor of prismatic <a> slip and pyramidal <c+a> slip in the HP-ARB process is higher, which is beneficial to dislocation slip, thus promoting an increase of sheet elongation. This provides a new strategy for the forming and manufacture of high performance magnesium alloy sheet.

Effect of initial grain size on the microstructure and mechanical properties of vacuum solution treated Ti–6Al–4V alloy

Ti–6Al–4V alloy warm rolled sheets with different initial grain sizes were obtained by warm rolling with different reduction rates. In order to improve its strength-ductility matching, it was treated by vacuum solution treatment (ST). By means of OM, SEM, EBSD, TEM, EPMA and XRD, the effects of different initial grain sizes of warm rolled sheet on the microstructure and mechanical properties of vacuum ST. The findings indicate that the initial grain sizes significantly influence the grain size, morphological distribution, and mechanical properties following vacuum ST. By warm rolling 60% combined with subsequent solution treatment (ST-60%), the grain size of the primary α phase (αp) and the β transformed (βt) structure is minimized, predominantly fine and equiaxed, with a dense distribution. This results in an optimal strength-ductility balance, with ultimate tensile strength, yield strength, and total elongation measuring 1283 MPa, 1194 MPa, and 10.5%, respectively. The volume fraction, grain size, morphological distribution, and the acicular alpha phase (αs) of αp and βt structure are among the factors influencing their mechanical properties. Furthermore, the solution strengthening of Aluminum (Al) in αp during the ST significantly increases the nano-hardness of αs compared to βt structure. This disparity leads to a plastic strain distribution between αp and βt structure, activating a substantial amount of Geometrically Necessary Dislocations (GND) near the βt/αp interface. This provides additional Hetero-Deformation-Induced (HDI) strengthening, thereby maintaining high strength and good ductility.

Vibration and Small Scale Effects of Skew Graphene Sheets Using Nonlocal Elasticity Theory

Nonlocal elasticity theory is a popularly growing technique for the realistic analysis of nano structures. In the present work nonlocal elasticity plate theory has been employed and vibration analyses of skew graphene sheets are carried out. Relevant governing differential equations are reformulated using the nonlocal differential constitutive relations suggested by Eringen. The equations of motion including the nonlocal theory are derived. All edges of the skew graphene sheets are assumed to be simply supported. Naviers approach has been employed to solve the governing differential equations. Bauers skew plate analysis has been extended to include the nonlocal elasticity plate theory. Vibration response of the skew graphene sheets is studied. Effects of the (i) size of the graphene sheets (ii) modes of vibration (iii) nonlocal parameter and (iv) skew angle of graphene sheet on nonlocal vibration frequencies are investigated. It has been observed that the vibration response of the skew graphene sheets are influenced significantly by the nonlocal parameter.

Small Scale Effects and Vibration of Graphene Sheets with Various Boundry Conditions

Elastic theory of graphene sheets is reformulated using the nonlocal differential constitutive relations of Eringen. The equations of motion of the nonlocal theories are derived. Levy’s approach has been employed to solve the governing differential equations for various boundary conditions. Nonlocal theories are employed to bring out the small scale effect of the nonlocal parameter on the natural frequencies of the graphene sheets. Present vibration results associated with various boundary conditions are in good agreement with those available in literature. Further, effects of (i) nonlocal parameter, (ii) size of the graphene sheets and (iii) boundary conditions on nondimensional vibration frequencies are investigated. The theoretical development as well as numerical solutions presented here in should serve as reference for nonlocal theories of nanoplates and nanoshells.

Turbulence, Particle Acceleration, and Heating Due To the Lower Hybrid Mode Near Magnetic Reconnection Regions in Magnetopause

AbstractMMS mission by NASA has observed lower hybrid waves (LHWs) and associated turbulence near the reconnection regions at Earth's magnetopause. The presented work studies LHWs (electromagnetic mode) and turbulence in the presence of magnetic islands (at the reconnection sites) in magnetopause. A nonlinear model representing electromagnetic 3D LHW has been developed. We have considered that nonlinear effects are due to the ponderomotive force. The dynamical equation, thus obtained, is solved using numerical methods and computer simulation. For spatial integration, we have used the pseudo‐spectral method and the finite difference method is used to study temporal evolution. The simulation results show the spatiotemporal development of the LHW localized structures and current sheets and confirm the presence of turbulence. Using a semi‐analytic model, we have determined the scale size of current sheets and localized structures and shown that these scale sizes depend upon the lower hybrid power. The turbulent power spectra have also been studied. The power scaling of k−2.8 (approximately) and k−2.1 (approximately) are observed along perpendicular and parallel directions, respectively. The power law scaling of turbulence generation has been used to study the formation of the thermal tail of energetic electrons. The fractional diffusion method has also been exploited to determine electron acceleration and plasma heating. We anticipate LHW may be responsible for the acceleration of the energetic electrons and anomalous heating in magnetopause.

Receiving a Response Image of a Solar Cell Efficiency by the Photo Scanning Method

The device for quality analysis of solar cells with different sensitive surface areas using radiation from a non-mechanical planar system is described. Current solutions for quality analysis of solar cells have disadvantages: work with analogy data, large dimensions of mechanical focusing system, interaction with small areas active zone of solar cells without possibility of identifying point pattern efficiency. Accordingly, a method is proposed for measuring the efficiency of solar cells at the production stage and during the operational period, which makes it possible to identify places of its insensitivity with the possibility of obtaining quantitative data on efficiency for the purpose of their mathematical processing. The developed photo scanning control device can be suitable for solar cells diagnostics with a sensitive zone area from 9 mm2 to A5 sheet size. The method makes it possible to measure local photocurrent and to find places of solar cell shunting. Process of diagnostics is controlled by one personal computer, which performs functions of controlling illumination of a monitor, setting diagnostic modes, obtaining data on the efficiency of the solar cells, storing and processing them. The device can be based on a laptop and is considered as mobile. Special software is used to manage, visualize and process the output data in a form of a rectangular matrix. An experiment was carried out on artificial darkening of the working areas of solar cells of different sensitivity. This confirmed effect of data changes and a visual display of obscuring zone on the output results. Tests were carried out on solar cells based on polycrystalline silicon. The results showed a high level of visibility and repeatability of the darkened area, and the quality of the data obtained made it possible to identify a small measurement error associated with external “noise”.

Graphene hydrogel improves S. putrefaciens' biological treatment of dye wastewater: Impacts of extracellular electron transfer and function of c-type cytochromes

Biocompatible materials and biocarriers have attracted great attention in biological wastewater treatment owing to their excellent performance in improving pollutant removal. Graphene-based material, a biocarrier candidate, with excellent adsorbability and conductivity was increasingly applied in anaerobic digestion due to its exceptional potential in the adsorption and electron transfer process. Nevertheless, the green approach for the formation of bio-graphene complexes and their mechanism in dye removal is limited. The aim of this study is to investigate and assess the performance of biological graphene hydrogel (BGH) formed by Shewanella putrefaciens CN32 on the removal of methyl orange (MO) and methylene blue (MB). The results showed that the formation of BGH is determined by the physicochemical characteristics of graphene oxide, including sheet size, oxidation degree, and interlayer distance. BGHs significantly increased the removal efficiency of dyes in comparison to non-graphene samples, with a 24-h removal rate of MO and MB reaching 92.9% and 91%, respectively. The synergetic mechanism of BGH on the enhanced removal rate of organic dye can be ascribed to GO's ability in accelerating extracellular electron transfer and stimulating biodegradation pathways relating to c-type cytochromes, including MtrA and MtrC. These findings provided an understanding of the relationship between graphene-based nanomaterials and Shewanella, which facilitated their future application in environmental biotechnology.

Development of chopped (non‐woven) carbon fiber reinforced composite sheet and its electrothermal performance for heating applications

AbstractNon‐woven carbon fiber sheet‐based heaters have been used for various thermal and material science applications, which possess rapid thermal heating at low input power. This work investigates the optimization of chopped carbon fiber composite sheet for heating applications. Here, different lengths of chopped carbon fiber have been used to fabricate the composite sheet. The parameters of composite sheets, such as morphology, porosity, electrical conductivity, mechanical property, and thermal stability, were studied. Besides, the electrothermal performance of prepared sheet heaters was investigated, and the results were compared at the input voltages of 10 and 12 V. The input power consumed by different sheet heaters was also investigated. The optimal chopped size of the carbon fiber composite sheet showed the highest surface thermal heating temperature of 245°C at 12 V.

Electrostatic lower hybrid turbulence due to magnetic islands and particle heating in magnetopause reconnection regions

This investigation presents a model to understand the magnetopause turbulence in the lower hybrid frequency range at reconnection regions as observed by the magnetospheric multiscale mission. We have modeled 3D electrostatic lower hybrid wave (LHW) in cold magnetized plasma in the presence of magnetic islands. In this model, we have developed the modified nonlinear Schrödinger equation, contemplating that nonlinear effects are due to ponderomotive force. The dynamical equation of the system thus obtained is solved using numerical simulation techniques. The simulation results illustrate the formation and evolution of localized structures and the current sheets. Due to the nonlinear effects and magnetic reconnection, the current sheets become turbulent with time. A semi-analytical model is also given to illustrate the scale size of current sheets. The turbulent power spectra have also been studied. The spectral index of the power spectrum is found to be −2.7 (approximately) in the perpendicular direction and −2.2 (approximately) in the parallel direction, indicating anisotropy. Using the Folker–Plank diffusion equation with the new velocity space diffusion coefficient, we find the distribution function of energetic electrons due to these turbulent structures. We propose that LHW may be responsible for plasma heating in magnetopause.

Linear relationship between lateral size of reduced graphene oxide (RGO) and water vapor barrier property in RGO/PEI composite membrane

The wide distribution of the lateral size of lab-prepared graphene oxide (GO) sheets often complicates the measurement of accurate average size. Herein, a series of reduced-GO/polyethyleneimine (RGO/PEI) composite membranes with compact brick-wall structures were successfully prepared. The large lateral size of RGO sheets in the membrane benefited gas barrier properties, including oxygen, nitrogen, and water vapor. The RGO sheets acted as impermeable inorganic filler to prolong the diffusion path, forcing gas molecules to wiggle through the permeable and tortuous channels of the PEI/water mixture. The water vapor transmission rate of RGO/PEI composite membranes was relatively high, and a linear correlation was established between the length of PEI/water channels and the water vapor barrier property. The length of PEI/water channels under the same membrane thickness was determined by the lateral size of RGO sheets. Therefore, the statistic averages of lateral size of RGO sheets (from 2.48μm to 44.35μm) showed a linear correlation with the water vapor barrier property, as confirmed by the positron annihilation technique and molecular dynamics simulations. In sum, the linear correlation could be used to practicably measure the statistic averages of lateral size of GO sheets according to water vapor permeability measurements.

Optimization of Asset and Liability Management of Banks with Minimum Possible Changes

Asset-Liability Management (ALM) of banks is defined as simultaneous planning of all bank assets and liabilities under different conditions and its purpose is to maximize profits and minimize the risks in banks by optimizing the parameters in the balance sheet. Most of the studies `and proposed models in the ALM field are based on an objective function that maximizes bank profit. It is not easy to apply changes in these models in order to reach the optimal values of the parameters in the balance sheet. In this article, an attempt has been made to propose a linear model using constraints to achieve optimal values of balance sheet parameters using ALM objectives and considering balance sheet, system and regulatory constraints. It has also been tried to design the model according to the most possible mode and with the least changes and to minimize the size of the balance sheet. The analysis of the model presented in this article has been conducted using the parameters of the balance sheet and income statement of one of the famous Iranian banks. The results obtained from the proposed model show that the values of cash and receivables from banks and other credit institutions have decreased by 30% and increased by 200%, respectively, compared to the actual values of these parameters. Also, Total Income, Operating Income and Non-Operating Income have grown by 30% compared to the actual values of these parameters. Also, the values of a number of parameters are estimated to be zero after optimization. According to the results, it is obvious that the performance of bank managers, especially in the management of bank assets, is significantly different from the optimal values of the balance sheet, and the results obtained from the proposed model can help the management of banks as much as possible.

Effects of Mg content on microstructure, mechanical properties and fracture behavior of wrought Al–8Si–(

In this paper, the effects of the Mg content on the microstructure, mechanical properties and fracture behavior of wrought Al–8Si–(<0.01–1.32)Mg (mass fraction, %) alloy sheets in T6 temper were systematically studied by OM, SEM/EDS, EBSD, LSCM, DSC, TEM and tensile tests. The results show that the size of Si particles decreased slightly with the increase of Mg content, and the recrystallized grain size of experimental alloy sheets was refined from about 16 µm to about 11 µm. The size of β" phases did not change obviously, but its volume fraction increased gradually and then became stable. When Mg content was 1.32%, there were many associated aggregation areas of Mg2Si particles and Si particles in alloy sheet. In addition, the strength of experimental alloy sheets showed an initial increase followed by a slight decrease as the Mg content increased, while the elongation gradually decreased. The finite element model accurately predicted the yield strength of Al–8Si–(<0.01–1.32)Mg alloy sheets in T6 temper, and the model was able to quantify the contribution of various strengthening mechanisms to the yield strength of the alloy sheets. The predicted results were in good agreement with the actual measured results. The tensile fracture mode of Al–8Si alloy sheet was ductile fracture. When Mg content was greater than 0.51%, the fracture pattern of the sheets comprised a combination of ductile and brittle fractures. With the increase of Mg content, the number of dimples in experimental alloy sheets increased slightly, the depth gradually became shallow and the size slightly decreased. Meanwhile, most secondary cracks on the surface of the Al–8Si alloy sheets after tensile fracture bypassed the Si particles and a few sheared the Si particles. With the Mg content gradually increasing to 0.78%, the number of Si particles sheared by secondary cracks gradually increased. However, When Mg content was 1.32%, the intergranular fracture phenomenon of Al–8Si–1.32Mg in T6 temper was weakened or even disappeared. There were multiple particles embedded in the same dimples in the tensile fracture. The particles in the associated aggregation areas were more easily broken.

Molecular-level understanding of carbon materials by temperature-programmed desorption

A wide variety of surface functional groups, such as oxygen-containing ones and hydrogen, exist at the graphene edge sites of carbon materials. Because the presence of these functional groups greatly affects the chemical properties of carbon-based materials produced from them, knowledge of the edge site state is essential to understand carbon chemistry. This review describes the analyses of edge sites and carbon-material structures by temperature-programmed desorption (TPD). Deuterium labeling of the protonic hydrogen of oxygen-containing functional groups enables the precise identification of the chemical structure of edge sites. Furthermore, the spatial distribution of edge sites in the carbon structure can be determined by the kinetic analysis of H2 desorption spectra collected at temperatures above 1000 °C. The average size of graphene sheets forming the carbon can be estimated from the number of edge sites. The TPD-based analytical approaches described in this paper help provide a better understanding of the carbon structure at the molecular level.

New insight into the biocompatibility/toxicity of graphene oxides and their reduced forms on Chlamydomonas reinhardtii

Graphene oxides (GOs) and their reduced forms are often discussed both positively and negatively due to the lack of information about their chemistry and structure. This study utilized GOs with two sheet sizes that were further reduced by two reducing agents (sodium borohydride and hydrazine) to obtain two different degrees of reduction. The synthesized nanomaterials were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), elemental analysis (EA), Fourier transform infrared (FTIR) spectroscopy, and Raman spectroscopy (RA) to understand their chemistry and structure. The second focus of our investigation included in vitro testing of the biocompatibility/toxicity of these materials on a model organism, the freshwater microalga Chlamydomonas reinhardtii. The effects were studied on the basis of biological endpoints complemented by biomass investigation (FTIR spectroscopy, EA, and atomic absorption spectrometry (AAS)). The results showed that the biocompatibility/toxicity of GOs is dependent on their chemistry and structure and that it is impossible to generalize the toxicity of graphene-based nanomaterials.

Preparation and performance of graphene oxide-polyacrylamide based nanoscale microsphere emulsion for profile control

A new kind of in-depth profile control and displacement graphene oxide-polyacrylamide (GO-PAM) based nanoscale microsphere emulsion for enhancing oil recovery was designed by the inverse microemulsion polymerization technology, which simultaneously plays the multifunction roles of plugging pore throat, reducing water-oil interfacial tension and oil viscosity benefiting from the synergistic effect of nanoscale microsphere and GO sheets. The emulsion shows superior suspension properties, thermal stability, hydration swelling, and the excellent emulsifying ability for crude oil. The average particle size of PAM microspheres is about 40 nm, and the size of GO sheets is about 1–10 µm. Only 0.1% dispersion of GO-PAM emulsion reduces the water-oil interfacial tension by 63%, and reduces the viscosity of thick oil by 10%. And with increasing emulsion dosage to 5%, the viscosity can be reduced by more than 50%. For low permeability simulated cores, the plugging efficiency of the GO-PAM emulsion system increases from 80% to 88% compared with PAM emulsion. The microscopic oil displacement experiment shows that our designed emulsion enhanced oil recovery by 6–7%. The GO-PAM composite microsphere emulsion is expected to be a competitive candidate for in-depth profile control and heavy crude recovery.

An Experimental Study On Friction Stir Welding Of Aluminum-Magnesium Alloys For Improved Mechanical Properties Of Tailor Welded Blanks.

Tailor welded blanks (TWB) are used in automotive and aerospace industries as they offer weight saving followed by cost saving and improved fuel economy. Being light in weight and having low cost, Aluminum alloys have piqued the interest of scientists. Friction Stir Welding (FSW) is a well-known accepted technique used since 1991 worldwide for Aluminum and its alloys. Due to friction stir welding, mechanical changes occur due to stirring action at the joint. Also the inter-metallic compounds, kissing bond formation, onion ring formation etc. are defects encountered in the nugget zone of welding. Hence, a novel technique is suggested to carry out the friction stir welding using a blend of techniques viz. double sided friction stir welding and multi objective optimization of process parameters. For experimentation, AA 5182 and AA 5754-Aluminum Magnesium alloys of 5000 series are used with sheet size of 1.5 mm thickness. Experimentation was carried out on a vertical machining center, with circular, square, and triangular tool pin profiles with a tool rotational speed range between 1500 -1800 rpm and a welding speed range of 40 mm/min.-60 mm/min. For the analysis purpose, L9 orthogonal array was used and Grey Relational Analysis(GRA) was employed and ASTM standards were used for tensile testing. Base sample materials of AA 5182 and AA5754 are having ultimate tensile strengths of 289.58 N/mm2 and 220.75N/mm2respectively. The designed welded blank of the two materials recorded maximum ultimate tensile strength of 268.11N/mm2which was remarkable for FSW. Welded joint efficiency was found to be 92.73% and percentage elongation of TWB was found to be 44% as compared to the base metals.

Promoting the electrical conductivity of polyimide/in-situ reduced graphene oxide nanocomposites by controlling sheet size

Polyimide (PI)-based nanocomposite films have found promising applications in electronics. However, despite their superior thermomechanical properties, PI/graphene oxide (GO) nanocomposites have a lower electrical conductivity compared to the case when pre-reduced graphene oxide (rGO) is used. To address this gap, we aimed to increase the electrical conductivity of PI/GO nanocomposite films without sacrificing other properties by forming in-situ reduced GO (irGO) particles and enhancing their aspect ratio. We produced GO nanosheets with various sizes via the modified Hummer method and used them to prepare PI/irGO nanocomposites via in-situ polymerization. The in-situ reduction of GO particles occurred along with the thermal imidization. Analysis of IR spectroscopy, XRD patterns, DMTA, and SEM images suggested the formation of chemical bonds between GO particles and PI matrix, which fortified the interface compared to PI/rGO nanocomposites. Thermal analyses revealed that enhancing the sheet size led to a decrease in the degradation rate below 200 °C and an increase in the ash residual. More importantly, the electrical resistance of PI/irGO was significantly decreased, even below that of the PI/rGO nanocomposite, by increasing the size of the nanosheets. These results are promising for the application of PI/irGO nanocomposites in electronics, and they may even replace PI/rGO nanocomposites when higher thermomechanical properties are desired.

Planktonic foraminifera response to orbital and millennial-scale climate variability at the southern Iberian Margin (IODP Site U1385) during Marine Isotope Stages 20 and 19

The orbital configuration of Marine Isotope Stage (MIS) 19 provides a good analogue to our present interglacial, and it is marked by millennial-scale climate variability. To evaluate how orbital and millennial-scale climate changes interact during this interglacial we have conducted a high-resolution study of planktonic foraminifera assemblages at International Ocean Discovery Program (IODP) Site U1385, SW Iberian Margin, encompassing late MIS 20 and MIS 19. Estimates of sea surface temperature (SST), using transfer-functions, are compared with geochemical, XRF elemental data, biomarker and pollen records from the same site. These results are then compared with SST and ice-rafted debris records from North Atlantic IODP Site U1314 to reconstruct basin-wide palaeoceanographic conditions. During MIS 20, the large size of the ice sheets imparted a strong cooling in the subpolar gyre whereas the Iberian Margin remained under the influence of the subtropical gyre with the development of a high meridional thermal gradient in the North Atlantic. During MIS 20 terminal stadial (794–789 ka) and MIS 19b-a stadial events, the meltwater discharges related to the instability of ice sheets affected both the North Atlantic and the Iberian Margin leading to a weaker thermal gradient. Our data indicate that Termination IX (TIX, ∼795–788 ka) was punctuated by short-term warming/cooling phases in the ocean coupled with warming/cooling events on land. A short-term cooling episode, recognized in the ocean and on land, occurred on Termination IX and preceded the beginning of MIS 19c. During MIS 19c, the planktonic foraminifera SST indicates warm and almost stable conditions in the sea decoupling the cool and dry millennial-scale events on land inferred by pollen assemblages. Starting from 780 ka towards MIS 18, the planktonic foraminifera assemblages and SSTs indicate a cooling trend along the Iberian Margin related to a progressive southward migration of the polar front.

Chlorambucil-Loaded Graphene-Oxide-Based Nano-Vesicles for Cancer Therapy.

In this study, the authors have designed biocompatible nano-vesicles using graphene oxide (GO) for the release of chlorambucil (CHL) drugs targeting cancerous cells. The GO sheets were first sulfonated and conjugated with folic acid (FA) molecules for controlled release and high loading efficiency of CHL. The chlorambucil (CHL) drug loading onto the functionalized GO surface was performed through π-π stacking and hydrophobic interactions with the aromatic planes of GO. The drug loading and "in vitro" release from the nano-vesicles at different pH were studied. The average particle size, absorption, and loading efficiency (%) of FA-conjugated GO sheets (CHL-GO) were observed to be 300 nm, 58%, and 77%, respectively. The drug release study at different pH (i.e., 7.4 and 5.5) showed a slight deceleration at pH 7.4 over pH 5.5. The amount of drug released was very small at pH 7.4 in the first hour which progressively increased to 24% after 8 h. The rate of drug release was faster at pH 5.5; initially, 16% to 27% in the first 3 h, and finally it reached 73% after 9 h. These observations indicate that the drug is released more rapidly at acidic pH with a larger amount of drug-loading ability. The rate of drug release from the CHL-loaded GO was 25% and 75% after 24 h. The biotoxicity study in terms of % cell viability of CHL-free and CHL-loaded GO against human cervical adenocarcinoma cell line was found to have lower cytotoxicity of CHL-loaded nano-vesicles (IC50 = 18 μM) as compared to CHL-free (IC50 = 8 μM). It is concluded that a high drug-loading efficiency and controlled release with excellent biotoxicity of CHL-GO offers an excellent application in the biomedical field.

Nitrogen-Doped Porous Nickel Molybdenum Phosphide Sheets for Efficient Seawater Splitting.

Hydrogen is emerging as an alternative clean fuel; however, its dependency on freshwater will be a threat to a sustainable environment. Seawater, an unlimited source, can be an alternative, but its salt-rich nature causes corrosion and introduces several competing reactions, hindering its use. To overcome these, a unique catalyst composed of porous sheets of nitrogen-doped NiMo3 P (N-NiMo3 P) having a sheet size of several microns is designed. The presence of large homogenous pores in the basal plane of these sheets makes them catalytically more active and ensures faster mass transfer. The introduction of N and Ni into MoP significantly tunes the electronic density of Mo, surface chemistry, and metal-non-metal bond lengths, optimizing surface energies, creating new active sites, and increasing electrical conductivity. The presence of metal-nitrogen bonds and surface polyanions increases the stability and improves anti-corrosive properties against chlorine chemistry. Ultimately, the N-NiMo3 P sheets show remarkable performance as it only requires overpotentials of 23 and 35mV for hydrogen evolution reaction, and it catalyzes full water splitting at 1.52 and 1.55V to achieve 10mA cm-2 in 1m KOH and seawater, respectively. Hence, structural and compositional control can make catalysts effective in realizing low-cost hydrogen directly from seawater.