Stable Alloy Research Articles

High-Entropy Alloy with Mo-Coordination as Efficient Electrocatalyst for Oxygen Evolution Reaction

Electrochemical hydrolytic hydrogen production is the most promising method for renewable energy storage and conversion. However, the kinetic slow oxygen evolution reaction (OER) limits the development of water electrolysis at the anode. The state-of-the-art OER catalysts face a dilemma of high content of noble metals and low OER activities. Herein, a strategy for achieving efficient and stable high-entropy alloy (HEA) catalysts by Mo-coordination is reported. The earth-abundant FeCoNiMo HEA catalyst provides an overpotential as low as 250 mV at the current density of 10 mA cm–2 in alkaline medium, which is 89 mV lower than that of state-of-the-art IrO2. The turnover frequency of 0.051 s–1 at the overpotential of 300 mV of FeCoNiMo HEA is 3 times higher than that of commercial IrO2 catalyst and even 11 times higher than that of the FeCoNi alloy without Mo-coordination. Importantly, the FeCoNiMo HEA exhibits high OER stability at a high current density of 100 mA cm–2. Methanol molecular probe experiment and X-ray photoelectron spectroscopy analyses suggest that the electrons of Mo transfer to Fe, Co, and Ni in the FeCoNiMo HEA catalyst, which leads to a weakened OH* bonding and, as a result, enhanced OER performance of the FeCoNiMo HEA catalyst. Consistent with the methanol molecular probe analysis, the real-time OER kinetic simulation reveals that the coordination of Mo within FeCoNi can speed up the rate-determining OH* deprotonation step of OER. Our finding opens up a routine for designing efficient cost-effective electrocatalysts for OER, which could facilitate discoveries in OER catalysts.

A detailed review of the analysis of the different types of materials such as aluminum alloys and cast-iron piston by comparing the results we can say among these which one of the pistons had better results

A piston is a component of reciprocating engines, pumps and gas compressors. It is located in a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from expanding gas in the cylinder to the crankshaft via a piston rod and/or connecting rod. The alloy from which a piston is made not only determines its strength and wears characteristics, but also its thermal expansion characteristics. Hotter engines require more stable alloys to maintain close tolerances without scuffing. The normal temperature of gasoline engine exhaust is approximately 650ºC (923ºK). This is also approximately the melting point of most aluminum alloys and it is only the constant influx of ambient air that prevents the piston from deforming and failing. For this purpose testing different types of materials such as aluminum alloys and cast iron piston. In this project we design the three models of pistons flat head, concave head & convex heads by using Pro-Engineer 5.0 software, and imported them to make analysis in ANSYS 11.0 soft ware. And find out the vonmisses stresses, total deformation, heat distribution, and heat flux. By comparing the results we can say among these which one of the piston had better results.

Electronic and magnetic properties of iridium-based novel Heusler alloys

Half-metallicity and magnetism including exchange splitting are the most significant physical parameters to predict and design a candidate material for spintronic applications. We report here an ab-initio investigation on chemical formation and dynamical stability along with electronic structure and magnetic properties of Ir2Cr (Si, Ge) and IrRhCr (Si, Ge) Heusler alloys. The negative formation and cohesive energies with positive phonon dispersions confirm the stabilities of these alloys. Electronic structure calculations reveal that Ir2Cr (Si, Ge) and IrRhCrSi alloys are half-metallic ferromagnets with unprecedented exchange splitting. In addition, IrRhCrGe also shows semi-metallic nature. All of these materials follow Slater Pauling rule with large magnetic moments and 100% spin-polarization. With Cr bearing the majority of the local magnetic moment and exchange splitting, a ferromagnetic state is more stable than a nonmagnetic state. The electronic charge distribution and population analysis confirm mixed ionic and covalent bonding. The magnetocrystalline anisotropy energy, with the easy magnetization along the [1 1 1] direction, is significantly high in Ir2CrGe. Elastic constants such as shear (G), bulk (B), Young’s moduli, and Poisson’s ratio indicate that the IrRhCrSi and IrRhCrGe alloys are mechanically stable, and Ir2CrSi and Ir2CrGe are mechanically unstable. The Pugh’s (B/G) and Poisson’s ratios confirm that the stable alloys are ductile.

Thermally stable and corrosion resistant nanolaminated Al-Mn alloy with low angle boundary structures

Metals with nanometer-sized grains are strong but often suffer from poor thermal stability. Herein, nanolaminated (NL) structure with an average thickness of 110 nm and a low angle grain boundaries (LAGBs) fraction of 80% was obtained in an Al-1Mn (in wt%) alloy produced by high strain rate deformation at cryogenic temperature. The NL structures are thermally stable up to 523 K, which can effectively suppress GB precipitation during aging, thus improving the pitting corrosion resistance in 0.6 M NaCl solution. The high thermal stability of NL structures can be mainly attributed to the formation of a large fraction (80%) of LAGBs.

Designing nanoparticles-strengthened high-entropy alloys with simultaneously enhanced strength-ductility synergy at both room and elevated temperatures

Developing microstructurally stable alloys with the outstanding strength-ductility combination at both room temperature and elevated temperatures is highly desirable for advanced structural applications, which, however, still remains challenging despite years of efforts. In this study, leveraging on the computation-aided thermodynamic modeling, novel high-strength Ni39.9Co20Fe30-xCrxAl6Ti4B0.1 (x = 0, 10, 15, and 20 at.%) high-entropy alloys (HEAs) were rationally designed, which maintained a stable coherent precipitation microstructure when continually substitute Fe with Cr. The structural features, mechanical properties, and underlying deformation micro-mechanisms were systematically investigated. We found that Cr mostly partitions into the face-centered-cubic (FCC) matrix relative to the L12-type nanoparticles. The increased Cr concentration substantially decreases the stacking fault energy (SFE) of the matrix and results in the stacking-fault-prevailed deformation behaviors, thereby producing simultaneously enhanced strength and ductility at room temperature. By contrast, when tested at 600 °C, the Cr-free HEA suffers from an extremely brittle fracture along grain boundaries caused by environmental oxidation damages. Interestingly, with Cr doping up to 20 at.%, such a serve intergranular embrittlement can be completely eliminated due to the increased oxidation resistance, leading to a distinct brittle-to-ductile transition (from 3.4 to 25.2%) at a high strength level of ∼ 1136 MPa. These findings will give new insights into the controllable design of novel high-performance HEAs for achieving target microstructures and superior property combinations.

A dimensionally stable lithium alloy based composite electrode for lithium metal batteries

Lithium (Li) metal is regarded as the most promising anode material for next-generation secondary batteries due to its high theoretical specific capacity and low potential. However, the huge volume change and uncontrollable dendrites growth lead to its structural instability during charge/discharge processes. Herein, a lithium alloy-based composite (Li-Sn-Bi) is fabricated for the first time, by fusing Li metal and low melting Sn-Bi eutectic alloy to address the structural change of Li electrodes. In this composite electrode, Li3Bi alloy exhibits a skeleton structure that can alleviate dimensional change of the electrode, meanwhile Li-Sn alloys (Li22Sn5 and Li5Sn2) are embedded in the Li3Bi skeleton that uniform Li plating owing to their low lithium mass-transfer barriers. Thus, the Li-Sn-Bi electrode can preserve its structural integrity during the redox process by combining the respective role of each alloy. Notably, the lifespan of the symmetric battery with Li-Sn-Bi electrode exceeds 4000 h under a fixed capacity of 3 mAh cm−2 and sustains 2000 cycles at a high current density of 30 mA cm−2. This work provides a facile method to fabricate dimensionally stable Li composite electrodes for high-energy–density secondary lithium batteries.

Recreating Fuel Cell Catalyst Degradation in Aqueous Environments for Identical-Location Scanning Transmission Electron Microscopy Studies

Proton exchange membrane fuel cells (PEMFCs) have long been studied for applications in sustainable transportation. The recent shift in focus from passenger vehicle to heavy duty applications places increased demand on the efficiency and durability of the components used in membrane electrode assemblies (MEAs).[1] Of particular interest are the oxygen reduction reaction electrocatalysts used in the fuel cell cathode. While the relaxed capital cost requirements for heavy duty applications allows for increased precious metal loadings, the four-fold increase in operating lifetime requires improved catalysts which can express their high activity not only at beginning-of-life, but also after 25k-hour equivalent accelerated stress tests (ASTs).This paradigm shift prioritizes efforts aimed at understanding and subsequently controlling catalyst degradation. In situ characterization methods can be instrumental in this effort, but it is critical that the operating conditions in these studies reliably replicate the type and degree of degradation observed in the operating fuel cell.[2,3] In this study, identical-location scanning transmission electron microscopy (IL-STEM) is used to compare catalyst degradation in an aqueous environment to degradation observed ex situ in MEAs following AST cycling.[4] For traditional catalysts, the aqueous environment appears to replicate the dissolution and coalescence mechanisms observed for Pt catalysts with small starting particle sizes (<3nm) supported primarily on the surfaces of graphitized carbon supports. In evaluating more stable alloy catalysts (4-5nm) supported on high surface area carbon supports, the large discrepancy between degradation in the aqueous and MEA environment was observed. In particular, the Ostwald ripening mechanism, which is more dominate in these high surface area carbons, seemed absent in the aqueous environment.[5]To better replicate the type and degree of degradation in the MEA environment, various experimental parameters such as temperature, acid type/concentration, and upper and lower potential limits were explored. By extending the cycling potential window from 0.6-0.95 Vvs . to 0.4-1.0 Vvs . RHE in an sulfuric acid electrolyte containing Pt ions, the Ostwald ripening mechanism was enhanced, resulting in an end-of-test particle size distribution and composition which better match MEA tests. These refined conditions can now be used to perform in situ and identical-location experiments that will play an important role in the development of robust catalysts for heavy-duty vehicle applications.[6]References[1] D. A. Cullen, et al. Nat. Energy 2021, 6 (5), 462–474.[2] J. A. Gilbert, et al. Electrochim. Acta 2015, 173, 223–234.[3] I. Martens, et al. ACS Energy Lett. 2021, 6 (8), 2742–2749.[4] S. Rasouli, et al. Nano Lett. 2019, 19 (1), 46–53.[5] E. Padgett, et al. J. Electrochem. Soc. 2019, 166 (4), F198–F207[6] This material is primarily based on work performed by the Million Mile Fuel Cell Truck (M2FCT) Consortium (https://millionmilefuelcelltruck.org), technology manager Greg Kleen, which is supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office. Electron microscopy was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.

Prediction of stable Li-Sn compounds: boosting ab initio searches with neural network potentials

The Li-Sn binary system has been the focus of extensive research because it features Li-rich alloys with potential applications as battery anodes. Our present re-examination of the binary system with a combination of machine learning and ab initio methods has allowed us to screen a vast configuration space and uncover a number of overlooked thermodynamically stable alloys. At ambient pressure, our evolutionary searches identified an additional stable Li3Sn phase with a large BCC-based hR48 structure and a possible high-T LiSn4 ground state. By building a simple model for the observed and predicted Li-Sn BCC alloys we constructed an even larger viable hR75 structure at an exotic 19:6 stoichiometry. At 20 GPa, low-symmetry 11:2, 5:1, and 9:2 phases found with our global searches destabilize previously proposed phases with high Li content. The findings showcase the appreciable promise machine-learning interatomic potentials hold for accelerating ab initio prediction of complex materials.

In situ synthesis of highly stable FeCo alloy encapsulated in carbon from ethanol

– FeCo alloy nanoparticles encapsulated in carbon were synthesized in situ via chemical vapor decomposition using ethanol as carbon precursor at temperatures of 400, 500, 600 and 700 °C. The study was carried out in order to obtain a material with high chemical and thermal resistance. The materials were characterized by X-Ray Diffractometry (XRD), Magnetometry, Mössbauer Spectroscopy (ME), Raman Spectroscopy, Thermogravimetric Analysis (TGA), Temperature Programmed Reduction (TPR-H2), Temperature Programmed Desorption (TPD-NH3 and TPD-CO2), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Gas Chromatography (GC). The results indicated that an increase in the synthesis temperature directly influences the amount of carbon deposited on the alloy and, consequently, on its encapsulation. The increase in the synthesis temperature also provided chemical stability against pH variations between 3 and 11, greater resistance against oxidation, greater thermal stability, as well as an increase in the graphitization degree. SEM and TEM images confirmed the presence of carbon nanotubes whose organization is greater for the sample synthesized at higher temperature; the tip of nanotubes showed the encapsulated FeCo alloy nanoparticle. Methylene blue (MB) adsorption was performed as a model to evaluate the encapsulation degree for the alloy, which is favored at higher temperatures.

Versatile Asymmetric Separator with Dendrite-Free Alloy Anode Enables High-Performance Li-S Batteries.

Lithium–sulfur batteries (LSBs) with extremely‐high theoretical energy density (2600 Wh kg−1) are deemed to be the most likely energy storage system to be commercialized. However, the polysulfides shuttling and lithium (Li) metal anode failure in LSBs limit its further commercialization. Herein, a versatile asymmetric separator and a Li‐rich lithium–magnesium (Li–Mg) alloy anode are applied in LSBs. The asymmetric separator is consisted of lithiated‐sulfonated porous organic polymer (SPOP‐Li) and Li6.75La3Zr1.75Nb0.25O12 (LLZNO) layers toward the cathode and anode, respectively. SPOP‐Li serves as a polysulfides barrier and Li‐ion conductor, while the LLZNO functions as an “ion redistributor”. Combining with a stable Li–Mg alloy anode, the symmetric cell achieves 5300 h of Li stripping/plating and the modified LSBs exhibit a long lifespan with an ultralow fading rate of 0.03% per cycle for over 1000 cycles at 5 C. Impressively, even under a high‐sulfur‐loading (6.1 mg cm−2), an area capacity of 4.34 mAh cm−2 after 100 cycles can still be maintained, demonstrating high potential for practical application.

Critical assessment of the extreme mechanical behavior of a stable nanocrystalline alloy under shock loading

A material's spall-strength and Hugoniot elastic limit (HEL), are measures of its ability to resist failure and plastic deformation under shock loading. An ideal single-crystal, i.e., a defect-free material, offers perfect lattice rectification, and therefore, provides an upper bound, or expected limit, which has yet to be exceeded by their polycrystalline counterparts. Toward this, we used a nanocrystalline (NC) copper-tantalum alloy, a model system, to probe the HEL and the spall strength of a stable NC alloy and the pertaining microstructural features that control failure. The results reveal significant increases in the HEL to about 2.0 GPa and spall strength of 1.19–1.67 GPa compared to polycrystalline Cu along with negligible changes in the residual hardness and microstructure of the shock recovered samples. The observed spall strength is approximately 2-times that of polycrystalline Cu. Further, advanced microstructural characterization using transmission electron microscopy (TEM) found no increase in dislocation density and/or mechanical twinning between the as-received and shock recovered samples, i.e., stabilized NC-alloys exhibit an unprecedented ability to resist high defect (such as dislocation) accumulation and damage. This anomalous behavior in stable NC-alloys is attributed to the elimination/limitation of defects formed under shock conditions coupled with a divergent strain-rate-insensitive behavior of its main microstructural features. The present work highlights, if designed properly, that some critical lower length-scale features including grain and phase boundaries may not contribute to the failure process. However, more fundamental research is needed to address the role processing parameters have on the resultant material that could result in spall strengths comparable to those attained for single crystals.

Entropy stabilization of two-dimensional transition metal dichalcogenide alloys: A density functional theory study

As high-entropy alloying provides an increasingly important avenue for widening the set of functional materials for a variety of applications, it is useful to uncover synthesis routes that do not rely on large temperatures for achieving entropic stabilization. Focusing on transition-metal dichalcogenides, we present direct computational evidence from density functional theory calculations that high-entropy disulfide (HES) alloys with five cations from groups 4–6 are thermodynamically stable at temperatures routinely achievable in conventional deposition systems. While all 126 sulfide combinations with five group 4–6 transition metals are thermodynamically favorable at low (&amp;lt;800 K) or medium (&amp;lt;1200 K) temperatures, we show that electronegativities, valence electron concentrations, and atomic radii of cations can help predict whether an HES alloy is stable in the 1-H or the 1-T structure. Furthermore, replacing one of the five cations with another, from outside groups 4–6, can still yield HES alloys with nearly planar layer morphologies and stabilization temperatures below 1200 K, albeit with some localized defects. These results demonstrate that a wide range of stable HES alloys can be synthesized experimentally as 2D layers, thereby providing facile ways for expanding the materials’ space with potential applications in electrochemical devices, catalysis, energy storage, or sensing.

Development of Ni-doped Fe/Ca catalyst to be used for hydrogen-rich syngas production during medicine residue pyrolysis

In this work, the catalytic pyrolysis of herbal residues (HR) by Ni–Fe/Ca catalysts and the effects of intrinsic ash and heating rate on the activity of Ni–Fe/Ca catalysts were investigated in a fixed-bed reactor. The results showed that the strong interaction of Fe and Ca formed Ca2Fe2O5, which inhibited the formation of CaCO3, shifted the weakly and moderately acidic sites to high temperatures, promoted the conversion of tar and char, and inhibited the formation of CO2. The H2 yield increased to 54.6 mL/g at 5% Fe/Ca catalyst. The addition of Ni to Fe/Ca improved the catalyst dispersion and promoted the adsorption of alkaline sites, while Ni formed a stable Fe3Ni2 alloy with Fe. The yields of H2 and CO increased from 54.6 mL/g and 63.4 mL/g (0.5% Fe/Ca) to 95.5 mL/g and 70.0 mL/g (0.5% Ni–Fe/Ca), respectively. The CO2 generation was suppressed at high temperatures and the calorific value of pyrolysis gas was significantly increased. Moreover, the acid wash pretreatment improved the tar yield, the alkaline sites in the Ni–Fe/Ca catalyst contributed to the conversion of aromatics and the reforming of CO2, and the presence of AAEMs promoted the redox reaction between gas and solid. The increase in the heating rate (100 °C/min) was beneficial to improve the activity of the Ni–Fe/Ca catalyst. The yields of H2 and CO reached 121.7 mL/g and 71.9 mL/g, respectively.

Li plating on alloy with superior electro-mechanical stability for high energy density anode-free batteries

Anode-free batteries possess high energy density and avoid the use of reactive Li during battery fabrication, and thus are highly desirable for high energy density batteries. However, they encounter fast failure due to the inferior electrochemical reversibility. One main reason is the fast inactive Li accumulation caused by the coupling of side reactions and mechanics during complicated Li plating/stripping processes, among which, mechanical stability of plated Li on current collector is crucial but often ignored. To achieve good electro-mechanical stability, we construct a stable lithium-metal alloy interphase for Li plating, which sharps the Li deposition morphology and enhances the connection with deposited Li. The Li-metal alloy possesses reduced Li nucleation energy barrier and strong bonding with metallic Li, which enables dense and chunky Li deposits with firm connection with the substrate in sharp contrast the fully peeling off of metallic Li for bare Cu after 50 Li plating/stripping cycles. A Li-Sn alloy-modified Cu anode displays stable Li plating/stripping cycling with average Coulombic efficiency of 94.1% for 400 cycles at 1 mA cm–2 and 1 mAh cm–2, significantly outperforming the bare Cu electrode. As a demonstration, in an anode-free cell with Li rich Mn-based cathode, 16.7% increase in capacity and 14.1% increase in capacity retention for 20 cycles are achieved using alloy-modified anode. This sheds new insights on the improvement of dynamic mechanical stability between Li deposits and current collector by regulating Li plating and its connection with the current collector and guides the design of high-performance initial-Li-free anode.

Ultra-strong and thermally stable nanocrystalline CrCoNi alloy

Grain refinement to the nanocrystalline regime is the most effective way to strengthen materials but this often deteriorates the grain-size thermal stability and plasticity. Here we manufactured a nanocrystalline face centred cubic CrCoNi medium entropy alloy with columnar grains via magnetron sputtering. Compression of CrCoNi pillars with diameters of ∼ 1 µm revealed a record high yield strength of ∼5 GPa for pillars with face centred cubic structures and engineering plastic strain of > 30%. The alloy possessed an outstanding grain-size thermal stability even at 1073 K. Both nanocrystalline grain size and a high density of nanotwins/stacking faults are critical to the exceptional yield strength. Deformation twinning, grains refinement during deformation, grain boundary sliding and random grain orientation all contribute to the large plasticity. The outstanding thermal stability is attributed to the sluggish diffusion effect and the low energy of twin boundaries.

Stable hexagonal ternary alloy phase in Fe-Si-H at 28.6–42.2 GPa and 3000 K

Hydrogen (H) and silicon (Si) are considered as important light elements for the planetary cores. A large amount of H is able to alloy with pure Fe metal at high pressures. Si can also alloy well with Fe. However, it remains uncertain how much H can alloy with iron silicides and if it alloys how H can alter the crystal structures of Fe-Si alloys at high pressures-temperatures ($P\text{\ensuremath{-}}T$). We performed experiments on Fe-9Si and Fe-16Si alloys (9 and 16 wt % Si, respectively) in a H medium up to 42.2 GPa and 3000 K in diamond-anvil cells coupled with pulsed laser heating and gated synchrotron x-ray diffraction techniques. We found conversion of the Fe-Si alloys into Fe-rich (fcc and dhcp $\mathrm{Fe}{\mathrm{H}}_{x}$), Si-rich (B20 and B2 FeSi), and intermediate (${\mathrm{Fe}}_{5}{\mathrm{Si}}_{3}{\mathrm{H}}_{x}$) phases. The new ${\mathrm{Fe}}_{5}{\mathrm{Si}}_{3}{\mathrm{H}}_{x}$ phase has a structure similar to the hexagonal ${\mathrm{Fe}}_{5}{\mathrm{Si}}_{3}$ phase but with expanded volumes, and thus, possible H incorporation. Both the observed volume expansion and the H content estimated by density-functional theory calculations support a significant amount of H with H/Fe \ensuremath{\approx} 0.6 in the crystal structure. Because ${\mathrm{Fe}}_{5}{\mathrm{Si}}_{3}$ is known to break down above \ensuremath{\sim}1300 K at \ensuremath{\sim}18 GPa, our results suggest that hydrogen stabilizes the hexagonal structure at high $P\text{\ensuremath{-}}T$. These results have implications for the crystallization of Fe-rich liquid at the solid-to-liquid boundary of planetary cores and possible existence of chemical heterogeneities in the solid cores.

Self-Organization of Binary Colloidal Mixtures via Diffusiophoresis.

Catalytic activity of the colloids and chemotactic response to gradients of the chemicals in the solution leads to effective interaction between catalytic colloids. In this paper, we simulate mixtures of active and passive colloids via a Brownian dynamics algorithm. These particles interact via phoretic interactions, which are determined by two independent parameters, surface activity and surface mobility. We find rich dynamic structures by tuning passive colloids’ surface mobility, size, and area fractions, which include schools of active colloids with exclusion zone, yolk/shell cluster, and stable active–passive alloys to motile clusters. Dynamical cluster can also be formed due to the nonreciprocity of the phoretic interaction. Increasing the size ratio of passive colloids to active colloids favors the phase separation of active and passive colloids, resulting in yolk/shell structure. Increasing the area fraction of active colloids tends to transfer from dynamical clusters into stable alloys. The simulated binary active colloid systems exhibit intriguing nonequilibrium phenomena that mimic the dynamic organizations of active/passive systems.

Controlling the metal work function through atomic-scale surface engineering

Adsorbate induced work function modification of Ni have been investigated by means of first-principles calculations. More specifically, the adsorption of Li, Na, Si, Zr, Pd, Pt, or Sn at various coverages on Ni low-index surface models have been considered. In the case of Sn, a more thorough investigation was performed comparing the adsorption as an overlayer structure with the case of surface alloy formation. Our calculations suggest that the most stable Sn@Ni configuration corresponds to a surface alloy, and here the Ni(100)c(2 × 2)-Sn, Ni(110)c(2 × 2)-Sn, and Ni(111)(3×3)R30∘-Sn surface alloys were found to display similar stability. Concerning the induced work function change, a different behaviour as a function of coverage was observed depending on the nature of the Sn@Ni surface model. Both overlayer adsorption and surface alloying were found to induce a work function decrease already at relatively low coverages (≈ 0.05 atom Å −2), regardless of the underlying surface orientation. However, while the work function obtained for stable surface alloys was found to monotonously decrease as the coverage increases, the work function for the stable overlayer structures goes through a minimum. For all investigated surface modifications, the change in work function was found to be consistent with the orientation of the charge transfer at the adsorbate–surface interface. The computed data in this work may serve as handles for experimental endeavours aiming to optimize properties of active materials through atomic-scale surface engineering.

Efficient synthesis of Pt3Co/NC alloy catalysts with enhanced durability and activity for the oxygen reduction reaction

Lack of catalytic performance, short life, and high cost are three main problems related to JM-Pt/C catalysts for proton exchange membrane fuel cells. The introduction of cheap transition metals improves catalytic performance while significantly reducing the cost of the catalysts. Here, we report the synthesis of Pt3Co/NC alloy catalysts via coating and pyrolysis treatment. The agglomeration of nanoparticles during the high-temperature alloying process is significantly inhibited by coating with PANI. Remarkably, the obtained Pt3Co/NC alloy catalysts exhibit excellent ORR catalytic performance and structural stability in 0.1 mol/L HClO4. After 30,000 potential cycles, the mass activity and area-specific activity of Pt3Co/NC alloy catalysts are 1.949 and 3.936 times higher, respectively, than that of JM-Pt/C with negligible performance loss. The strong metal-support interaction between N and Pt and the Pt-rich surface restrict the dissolution of Pt and Co, resulting in excellent stability. This synthesis approach provides an effective way to develop active and stable Pt alloy catalysts.

Electronic properties and stability of M2O3 (M = Al, Ga, In) and alloy (MxGa1‐x)2O3 in α and β phases: A theoretical study

AbstractGa2O3 is clearly emerging as an important wide band‐gap semiconductor. Band‐gap engineering is now highly demanded for expanding its applications. Alloying with the same group of metal oxides is a straightforward and effective way. In this work, by using hybrid density functional theory calculations, the structural, electronic properties, and phase stability of group IIIA (Al, Ga, In) metal oxides and their ternary alloys (MxGa1‐x)2O3 (M = Al, In) in the corundum and monoclinic phases are systematically investigated. The lattice constants, elastic constants, modulus, formation energies, band‐gaps, band‐gap deformation potentials, band‐edge alignments, band‐gap bowing, and ternary alloy formation energies are obtained. The basic relations between the geometric structure and electronic properties are discussed. It is found that the cation ordered structure is the most stable alloy structure in the monoclinic phase, rather than the random alloy structure as is commonly thought. A phase stability diagram of the (MxGa1‐x)2O3 alloys is established, showing that the stable phase of the alloy changes from the monoclinic phase to the corundum phase when the incorporation of Al2O3 (In2O3) is greater than 69% (76%). These results can be used to understand the relative experimental data and shed some light on the synthesis and device design efforts of Ga2O3.