Incorporating Transition Metal Research Articles

Selective photothermal reduction of CO2 to CH4 via the synergistic effect of Ni-nanoparticle@NiO-nanosheet/V2C-MXene catalyst

Photothermal catalytic carbon dioxide (CO2) reduction has attracted increasing research attention as a promising method for recycling CO2 and producing renewable energy. However, it remains a challenge in the improvement of catalytic activity with regulated product selectivity in view of practical applications. Herein, we develop the two-dimensional layered V2C MXene (VC) supported Ni nanoparticle and NiO nanosheet (Ni@NiO/VC) composite as an efficient catalyst for selective photothermal reduction of CO2 to CH4. The optimal 0.8Ni@NiO/VC catalyst exhibits 48.1 % CO2 conversion with an evolution rate of 33.2 mmol/gcat/h and 99.2 % selectivity for CH4 production under a 300 W full-arc xenon lamp irradiation. Moreover, a long-term cyclic photothermal CO2 reduction reaction demonstrates the excellent stability of 0.8Ni@NiO/VC. The enhanced photothermal CO2 reduction activity with a high CH4 selectivity could be attributed to the large specific surface area and excellent photothermal effect of V2C MXene, and the synergistic effect of Ni and NiO on adsorption/activation of H2 and CO2 molecules. This work provides a feasible strategy for the construction of efficient photothermal CO2 reduction catalyst by properly incorporating transition metal nanoparticles and metal oxide with a suitable MXene.

Enhancing catalytic activity of zeolitic octahedral metal oxides through zinc incorporation for ethane oxidative dehydrogenation

Zeolitic octahedral metal oxides possess both redox properties and microporosity, making them highly active for catalysis. Tuning the property of micropore by incorporating transition metal ion in the pore improves the catalytic activity greatly. In this study, single Zn species was incorporated into a micropore of a zeolitic octahedral metal oxide based on vanadomolybdate. Structural characterization demonstrated that the crystalline structure remained unchanged, and the micropores remained unblocked in the presence of Zn. Furthermore, this incorporation of Zn improved the catalytic activity of ethane oxidative dehydrogenation, achieving a 50 % of ethane conversion and 90% of selectivity. The yield of ethylene remained consistently at 45 % over 35 h, demonstrating the high stability of the catalyst. Mechanism study revealed that the isolated Zn site not only activated both O2 and ethane, but also stabilized intermediates and transition states, leading to an increase in catalyst activity.

Modeling of the intrinsic softening of γ-carbides in cemented carbides

Cemented carbides are widely used materials in industrial applications due to their remarkable combination of hardness and toughness. However, they are exposed to high temperatures during service leading to a reduction of their hardness. A common practice to damp this softening is to incorporate transition metal carbides in cemented carbide compositions, which keeps the hardness relatively higher when temperature increases. Understanding the underlying mechanisms of this softening is crucial for the development of cemented carbides with optimal properties. In this work, atomic-scale mechanisms taking place during plastic deformation are analyzed and linked to the effect that they have on the intrinsic macro-scale softening of the most common TMC used in cemented carbides grades (TiC, ZrC, HfC, VC, NbC and TaC). The proposed model uses the generalized stacking fault energy obtained from density functional theory calculations as an input to Peierls-Nabarro analytical models to obtain the critically resolved shear stress needed for deformation to occur in different slip systems. Subsequently, this information is used to predict the hardness variation across the temperature service range experienced by cemented carbides in wear applications.In addition to the prediction of hot-hardness for TMC, the obtained results also offer valuable insights into the intrinsic mechanisms governing TMCs deformation. The results facilitate the identification of dominant dislocation types influencing plasticity within distinct temperature regimes, define energetically favorable slip systems, and predict the brittle-ductile transition temperature in these materials. For instance, for group IV carbides at low temperatures, the slip system with a lower GSFE is {110}<11̅0> and around 30% of their melting temperature, the GSFE of partial slip in {111}<12̅1> becomes lower, changing the dominant slip mechanism and characterizing the Brittle-Ductile transition.

Structural features of early fuel cycle taggant incorporation for intentional nuclear forensics

To develop strategies for incorporating transition metal taggants (Fe, Cr, and Ni) into oxide fuels and to understand how these taggant candidates persist through early fuel cycle processes, synthetic procedures are modified from established production routes to yield intentionally tagged early fuel cycle intermediates including uranyl nitrate hexahydrate (UNH, UO2(NO3)2·6H2O), uranyl peroxide tetrahydrate (studtite, UO2O2·4H2O), and uranyl peroxide dihydrate (metastudtite, UO2O2·2H2O). First, Fe, Cr, and Ni nitrate solutions are introduced to an aqueous solution of UNH followed by precipitation to produce tagged UNH. Then, studtite is precipitated from UNH followed by dehydration to metastudtite. Structural influences of taggant incorporation within all synthesized phases are investigated using powder X-ray diffraction (PXRD) and Raman spectroscopy to provide insight into crystallographic modifications resulting from the addition of tags to these early fuel cycle materials and elucidate the chemical form of taggants introduced at these stages. The possibility of segregation of taggant species into discrete phases within U matrices was examined using scanning electron microscopy with energy dispersive X-ray spectroscopy. Taggant concentrations in solid-phase materials were determined using inductively coupled plasma-optical emission spectroscopy. Observations from Raman spectroscopy and PXRD indicate that introducing transition metal tags during uranyl nitrate precipitation results in potential impurity phase segregation in UNH, but transition metal incorporation is suggested by results for tagged uranyl peroxide materials. Results from this study will inform strategies for optimizing taggant incorporation in UO2.

Recent Progress in Spinel Ferrite (MFe2O4) Chemiresistive Based Gas Sensors.

Gas-sensing technology has gained significant attention in recent years due to the increasing concern for environmental safety and human health caused by reactive gases. In particular, spinel ferrite (MFe2O4), a metal oxide semiconductor with a spinel structure, has emerged as a promising material for gas-sensing applications. This review article aims to provide an overview of the latest developments in spinel-ferrite-based gas sensors. It begins by discussing the gas-sensing mechanism of spinel ferrite sensors, which involves the interaction between the target gas molecules and the surface of the sensor material. The unique properties of spinel ferrite, such as its high surface area, tunable bandgap, and excellent stability, contribute to its gas-sensing capabilities. The article then delves into recent advancements in gas sensors based on spinel ferrite, focusing on various aspects such as microstructures, element doping, and heterostructure materials. The microstructure of spinel ferrite can be tailored to enhance the gas-sensing performance by controlling factors such as the grain size, porosity, and surface area. Element doping, such as incorporating transition metal ions, can further enhance the gas-sensing properties by modifying the electronic structure and surface chemistry of the sensor material. Additionally, the integration of spinel ferrite with other semiconductors in heterostructure configurations has shown potential for improving the selectivity and overall sensing performance. Furthermore, the article suggests that the combination of spinel ferrite and semiconductors can enhance the selectivity, stability, and sensing performance of gas sensors at room or low temperatures. This is particularly important for practical applications where real-time and accurate gas detection is crucial. In conclusion, this review highlights the potential of spinel-ferrite-based gas sensors and provides insights into the latest advancements in this field. The combination of spinel ferrite with other materials and the optimization of sensor parameters offer opportunities for the development of highly efficient and reliable gas-sensing devices for early detection and warning systems.

Pt@Ni2P/C3N4 for charge acceleration to promote hydrogen evolution from ammonia-borane

Incorporating g-C3N4 with transition metal phosphides is emerging as a low-cost and robust co-catalyst for hydrogen evolution. The ammonia borane hydrolysis is an efficient method to release H2 at ambient conditions in the presence of a catalyst. An efficient and cheap catalyst is needed for practical application to achieve this benchmark. For this purpose, a catalyst Ni2P/C3N4 is synthesized by hydrothermal method and low-temperature phosphidation. The optimization reveals that the Ni2P/C3N4 with 6.5% Ni contents shows the best performance for H2 release. Furthermore, 2% Pt nanoparticles loading over Ni2P/C3N4 boosts the charge transfer and improves activity 5.7-fold compared to Ni2P/C3N4, and the Pt-loaded catalyst is depicted as Pt@Ni2P/C3N4. The reaction kinetics reveals that the hydrogen evolution rate accelerates by increasing the amount of Pt@Ni2P/C3N4 and AB concentration, and the loading of Pt nanoparticles loaded over Ni2P/C3N4 reduces the activation energy significantly. Moreover, the ionic interaction between Pt and Ni2P/C3N4 generates Ptᵟ+ and (Ni2P/C3N4)ᵟ− active sites which facilitates B–H cleavage and O–H bonds of ammonia borane and water, respectively. Incorporating transition metals phosphide and noble metals supported over g-C3N4 paves the pathway toward the efficient H2 evolution from ammonia borane, bringing cost-effective modifications to synthesize constructive catalysts.

Probing the Local Electronic Structure in Metal Halide Perovskites through Cobalt Substitution.

Owing to the unique chemical and electronic properties arising from 3d-electrons, substitution with transition metal ions is one of the key routes for engineering new functionalities into materials. While this approach has been used extensively in complex metal oxide perovskites, metal halide perovskites have largely resisted facile isovalent substitution. In this work, it is demonstrated that the substitution of Co2+ into the lattice of methylammonium lead triiodide imparts magnetic behavior to the material while maintaining photovoltaic performance at low concentrations. In addition to comprehensively characterizing its magnetic properties, the Co2+ ions themselves areutilizedas probes to sense the local electronic environment of Pb in the perovskite, thereby revealing the nature of their incorporation into the material. A comprehensive understanding of the effect of transition metal incorporation is provided, thereby opening the substitution gateway for developing novel functional perovskite materials and devices for future technologies.

Comparison effect of thin microrod‐nanowhisker manganese oxide (MnO2) and spherical grain‐like cobalt oxide (Co3O4) as nanofiller for performance‐enhanced composite gel terpolymer electrolyte‐based dye‐sensitized solar cells

AbstractGel polymer electrolyte (GPE) are better replacement of liquid electrolyte for dye‐sensitized solar cell (DSSC) but they have low efficiency due to insufficient segmental motion within the electrolyte. By incorporating transition metal oxide nanofiller, it can improve the performance of DSSC due to the existence of cross‐linking center that provides interaction with polymer side chain and redox mediator. Two different transition metal oxides (namely, manganese oxide, MnO2 and cobalt oxide, Co3O4) were synthesized using sonochemical method and incorporated as nanofiller. Poly (vinyl butyral‐co‐vinyl alcohol‐co‐vinyl acetate) (P(VB‐co‐VA‐co‐VAc)) as a host terpolymer and sodium iodide (NaI) as a dopant salt were used to formulate the composite gel terpolymer electrolytes (CGPEs). The two different shapes of nanofiller have impacted the performance of CGPE proven by the structural analysis. It was found that both systems, the highest ionic conductivity achieved at 2.5 wt% of MnO2 and Co3O4 content with values of 6.40 and 5.2 mS cm−1, respectively. Surprisingly, the performance DSSC of Co3O4‐based CGPE was higher due to the strong Lewis's acidity of Co3O4, which absorb more iodide ions into the surface and facilitating the ions mobility. CGPE containing 2.5 wt% Co3O4 yield the highest efficiency, with value of 3.69%.

Chemoenzymatic Synthesis of Sterically Hindered Biaryls by Suzuki Coupling and Vanadium Chloroperoxidase Catalyzed Halogenations.

Halogenated biaryls are vital structural skeletons in bioactive products. In this study, an effective chemoenzymatic halogenation by vanadium-dependent chloroperoxidase from Camponotus inaequalis (CiVCPO) enabled the transformation of freely rotating biaryl bonds to sterically hindered axis. The yields were up to 84 % for the tribrominated biaryl products and up to 65 % when isolated. Furthermore, a one-pot, two-step chemoenzymatic strategy by incorporating transition metal catalyzed Suzuki coupling and the chemoenzymatic halogenation in aqueous phase were described. This strategy demonstrates a simplified one-pot reaction sequence with organometallic and biocatalytic procedures under economical and environmentally beneficial conditions that may inspire further research on synthesis of sterically hindered biaryls.

Modifying Hybrid Plasmonic Nanocatalysts Via Femtosecond Pulsed Laser for Solar-Fuel-Based Applications

Harvesting solar energy for chemical transformations is gaining a rising interest in promoting the clean and modular chemical synthesis approach and addressing conventional thermocatalytic systems’ limitations. Under light irradiation, noble metal nanoparticles, particularly those characterized by localized surface plasmon resonance, commonly known as plasmonic nanoparticles, generate a strong electromagnetic field, excited hot carriers, and photothermal heating. The catalytic activity of Plasmonic nanoparticles can be enhanced by incorporating transition metal catalysts as co-catalysts, promoters or stabilizers. In this talk, we demonstrate that by modifying the atomic structure of hybrid plasmonic nanocatalysts via femtosecond pulsed laser we are able to not only enhance the optoelectronic and catalytic properties of the resulting nanoparticles, but also to improve the mechanical stability of these hybrid nanostructures, which are of paramount importance for industrial applications. We also investigate the trade-off between the effect of light absorption, catalytic activity, and mechanical stability by optimizing the structure and composition of hybrid plasmonic nanoparticles. This work provides insight into the design of hybrid plasmonic-catalytic nanostructures with improved performance and stability for solar-fuel-based applications.

High areal capacitance and long cycling stability in asymmetric supercapacitors using binder-free, hierarchical nanostructured Ni3S2/MnO2 hybrid electrodes

Supercapacitors have become inevitable energy storage devices for portable electronics and electric vehicles. Among the various material choices, transition metal sulfides with high pseudocapacitive nature commands attention as supercapacitor electrode materials. Nevertheless, transition metal sulfides suffer from poor electrochemical cycling stability, which hinders their use in practical applications. Incorporating transition metal oxides into these materials to form hybrids can effectively rectify these stability issues. Here, we report a two-step hydrothermal synthesis of nanocrystalline Ni3S2/MnO2 hybrids and use them as electrodes to fabricate supercapacitors. The incorporation of MnO2 improves the surface area of the electrode, and the synergistic effect of the Ni3S2/MnO2 nanostructured hybrid helps achieve the best electrochemical performance. The Ni3S2/MnO2 hybrid electrode exhibits a high gravimetric capacitance of 806.6 F g−1 (2892 mF cm−2) at a current density of 1 A g−1 in 1 M KOH aqueous electrolyte. Along with the enhanced pseudocapacitance, the hybrid electrode exhibits exceptional cycling stability of 96.8 % even after 25,000 charge/discharge cycles performed at a current density of 5 A g−1. An asymmetric supercapacitor fabricated using activated carbon (AC) (Ni3S2/MnO2//AC) exhibits a cell capacitance of 34.8 F g−1 (139.9 mF cm−2) at a current density of 1 A g−1.

Intermetallic Copper-Based Electride Catalyst with High Activity for C-H Oxidation and Cycloaddition of CO2 into Epoxides.

Inorganic electrides have been proved to be efficient hosts for incorporating transition metals, which can effectively act as active sites giving an outstanding catalytic performance. Here, it is demonstrated that a reusable and recyclable (for more than 7 times) copper-based intermetallic electride catalyst (LaCu0.67 Si1.33 ), in which the Cu sites activated by anionic electrons with low-work function are uniformly dispersed in the lattice framework, shows vast potential for the selective C-H oxidation of industrially important hydrocarbons and cycloaddition of CO2 with epoxide. This leads to the production of value-added cyclic carbonates under mild reaction conditions. Importantly, the LaCu0.67 Si1.33 catalyst enables much higher turnover frequencies for the C-H oxidation (up to 25 276 h-1 ) and cycloaddition of CO2 into epoxide (up to 800 000 h-1 ), thus exceeding most nonnoble as well as noble metal catalysts. Density functional theory investigations have revealed that the LaCu0.67 Si1.33 catalyst is involved in the conversion of N-hydroxyphthalimide (NHPI) into the phthalimido-N-oxyl (PINO), which then triggers selective abstraction of an H atom from ethylbenzene for the generation of a radical susceptible to further oxygenation in the presence of O2 .

Impact of transition metal incorporation on the photocatalytic CO2 reduction activity of polymeric carbon nitride

Incorporation of transition metals in polymeric carbon nitride (CN) is an effective strategy to enhance its photocatalytic CO2 reduction activity, however, the difference of activity enhancement by incorporating different metals is not well understood. Herein, CN is modified with different transition metals by pyrolyzing the mixtures of urea and metal-organic frameworks (MOFs) to obtain MCN (M = Cu, Co, Ti or Fe). For each given type of metal-modified CN, the photocatalytic CO2 reduction activity is optimized by controlling the content of MOF precursor during pyrolysis. The optimized MCN delivers significantly enhanced CO evolution rate than pure CN, in the order of CN (83 μmol g−1 h−1) < CuCN (246 μmol g−1 h−1) < CoCN (326 μmol g−1 h−1) < TiCN (454 μmol g−1 h−1) < FeCN (490 μmol g−1 h−1). It is revealed that for CuCN and CoCN, Cu and Co are doped in CN. In contrast, for TiCN and FeCN, Ti and Fe exist as TiO2 and Fe2O3 forming Z-scheme heterojunctions with CN. The progressively improved photocatalytic activity corresponds to the increased specific surface area, CO2 adsorption capacity, visible light absorption as well as charge separation and transfer efficiency. Furthermore, we design and prepare bimetal incorporated CN through combining metal doping with heterojunction construction strategies, i.e., Cu doped CN/TiO2 and Co doped CN/Fe2O3, which exhibit further enhanced CO2 photoreduction performance with CO evolution rates of 613 and 718 μmol g−1 h−1, respectively. This work provides insight into the design and preparation of highly efficient CN-based photocatalytic materials.

A silk sericin-confined in-situ synthesis strategy: Fe7S8 inserted N,S co-doped carbon nano-aggregates for high-performance sodium storage

Owing to the low cost and renewability, biomass-derived hard carbons (B-HCs) are attractive anode candidates for sodium-ion batteries (SIBs). Although the specific capacity of B-HCs can be further improved by incorporating transition metal sulfides, it also brings out other issues, including the sluggish kinetics, “shuttle effect” of sodium polysulfides and voltage failure. Herein, a facile in-situ synthesis strategy for Fe 7 S 8 inserted N,S co-doped carbon nano-aggregates (Fe 7 S 8 -NS/C) is developed. The strong adsorption of sericin to Fe 3+ ensures the dispersive distribution of Fe 7 S 8 nanoparticles in carbon matrix, contributing to fast Na + transport kinetics. The first principles calculations demonstrate the self-doped pyridine N (3.45 at%) and pyrrolic N (7.91 at%) is conducive to Na adsorption, which promotes sodium storage. More importantly, the polar C-S and C-N bonds in the carbon matrix can effectively immobilize sodium polysulfides and inhibit abnormal voltage failure. As an anode material for SIBs, the elaborate Fe 7 S 8 -NS/C composite offers high reversible capacity (477 mAh g −1 at 1 A g −1 over 500 cycles) and excellent rate capability (326 mAh g −1 at 5 A g −1 ). The simple synthesis method and outstanding electrochemical performances make the Fe 7 S 8 -NS/C an attractive candidate for SIBs. • Nano-sized Fe 7 S 8 is uniformly distributed within the sericin-derived carbon matrix. • Fe 7 S 8 -NS/C nano-aggregates possess accelerated Na + transport kinetics. • DFT calculations confirm the strong Na adsorption ability of self N-doped carbon. • The polar C-N/C-S bonds inhibit the “shuttle effect” and abnormal capacity failure. • Fe 7 S 8 -NS/C with rational component and structure is a promising material for SIBs.

New Zinc-Based Active Chitosan Films: Physicochemical Characterization, Antioxidant, and Antimicrobial Properties.

The improvement of the antioxidant and antimicrobial activities of chitosan (CS) films can be realized by incorporating transition metal complexes as active components. In this context, bioactive films were prepared by embedding a newly synthesized acylpyrazolonate Zn(II) complex, [Zn(QPhtBu)2(MeOH)2], into the eco-friendly biopolymer CS matrix. Homogeneous, amorphous, flexible, and transparent CS@Znn films were obtained through the solvent casting method in dilute acidic solution, using different weight ratios of the Zn(II) complex to CS and characterized by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared (FT-IR), Raman, and scanning electron microscopy (SEM) techniques. The X-ray single-crystal analysis of [Zn(QPhtBu)2(MeOH)2] and the evaluation of its intermolecular interactions with a protonated glucosamine fragment through hydrogen bond propensity (HBP) calculations are reported. The effects of the different contents of the [Zn(QPhtBu)2(MeOH)2] complex on the CS biological proprieties have been evaluated, proving that the new CS@Znn films show an improved antioxidant activity, tested according to the DPPH method, with respect to pure CS, related to the concentration of the incorporated Zn(II) complex. Finally, the CS@Znn films were tried out as antimicrobial agents, showing an increase in antimicrobial activity against Gram-positive bacteria (Staphylococcus aureus) with respect to pure CS, when detected by the agar disk-diffusion method.

Catalytic advancements in carbonaceous materials for bio-energy generation in microbial fuel cells: a review.

Microbial fuel cells (MFCs) are a sustainable alternative for wastewater treatment and clean energy generation. The efficiency of the technology is dependent on the cathodic oxygen reduction reaction, where the sluggish reaction kinetics hampers its propensity. Carbonaceous materials with high electrical conductivity have been widely explored for oxygen reduction reaction (ORR) catalysts. Here, incorporating transition metal (TM) and heteroatom into carbon could further enhance the ORR activity and power generation in MFCs. Nitrogen (N)-doped carbons have also been a popular research hotspot due to abundant active sites formed, resulting in superior conductivity, stability, and catalytic activity over carbons. This review summarizes the progress in the carbon-based materials (primary focus on the cathode) for ORR and their utilization in MFCs. Furthermore, we discussed the conceptualization of MFCs and carbonaceous materials to instigate the ORR kinetics and power generation in MFC. Furthermore, prospects of carbon-based materials for actual application in bio-energy generation have been discussed. Carbonaceous catalysts and biomass-derived carbons exhibit good potential to replace precious Pt catalysts for ORR. M-N-C catalysts were found to be the most suitable catalysts. Electrocatalysts with MNx sites are able to achieve excellent activity and high-power output by taking advantage of the active site exposure and rapid mass transfer rate. Moreover, the use of biomass-derived carbons/self-doped carbons could further reduce the overall cost of catalysts. It is anticipated that the research gaps and future perspectives discussed will show new avenues to develop excellent electrocatalysts for better performance and transformation of technology to industrial applications.

The effect of transition metal and heavy metal incorporation on the structural, optical and electrical properties of zinc-phosphate ternary glassy system: A comparative study

The present communication reports the effect of the addition of different dopant elements in the zinc-phosphate host glass network having chemical composition 0.30A–(0.55ZnO–0.15P2O5) (A = V2O5, MoO3, and TeO2) that have been prepared through melt quenching technique. The X-ray diffraction patterns reveal the formation of nanocrystallites superimposing over the amorphous glass matrix of all the studied glassy systems, which is also verified by TEM micrographs. The physical characteristics like density and molar volume are examined and discussed in relation to their structural modifications. The FTIR spectra reveal a significant number of distinct characteristic absorption bands owing to different phosphate, molybdate, and vanadate groups. Depending on the different dopant elements, the variations in optical bandgap energies are observed and analyzed. The variations in the bandgap energies from 4.8 eV to 5.79 eV have been measured from the extrapolation of Tauc's plot. Various optical parameters like refractive index, optical density, optical conductivity, dissipation factor, skin depth, and optical basicity have been studied for all glassy systems. The DC and AC conductivity analyses conspicuously reveal that the V2O5 doped sample possesses the highest conductivity among all the investigated glassy systems.

One Decade of Computational Studies on Single-Atom Alloys: Is In Silico Design within Reach?

ConspectusSingle-Atom alloys (SAAs) are an emerging class of materials consisting of a coinage metal (Cu, Ag, and Au) doped, at the single-atom limit, with another metal. As catalysts, coinage metals are rarely very active on their own, but when they are, they exhibit high selectivity. On the other hand, transition metals are usually very active but not as selective. Incorporating transition metals (guest elements) into coinage metals (host material) is therefore appealing for combining the activity and selectivity of each constituent in a balanced way. Additionally, first-principles calculations have shown that single atoms embedded in the surface of a coinage metal can exhibit emergent properties. Here, we describe how computational studies based on density functional theory (DFT) and kinetic Monte Carlo (KMC) simulations, often undertaken in close collaboration with experimental research groups, have shaped, over the past decade, the way we understand SAA catalysis.This Account reviews our contributions in elucidating the stability of SAAs, their electronic structure, and the way adsorbates interact and react on SAA catalytic surfaces. By studying in detail the processes that affect the stability of the SAA phase, we have shown that out of several bimetallic combinations of coinage metals with prominent Pt-group metals only PtCu and PdCu are stable surface alloys under vacuum. However, more surface alloy structures are possible in the presence of adsorbates because the latter can stabilize, via strong binding, dopants in the surface of the material. More interestingly, a large number of these surface alloys are resistant to the aggregation of dopant atoms into clusters, thereby favoring the SAA structure. These major results from DFT calculations serve as a guide for experimentalists to explore new SAA catalysts. Further analysis has shown that SAAs have a unique electronic structure with a very sharp d-band feature close to the Fermi level, analogous to the electronic structure of molecular entities. This is one of the reasons that SAAs are particularly sought after: although they are metallic nanoparticles, they have properties akin to those of homogeneous catalysts. In this context, we have contributed extensive screening studies, focusing on molecular fragments of catalytic relevance on a range of SAAs, which have driven the identification of new catalysts. We have also explored the rich chemistry of two-adsorbate systems via kinetic modeling, demonstrating how a spectator species with greater affinity for the dopant can modulate the reactivity of the catalyst via the so-called (punctured) molecular cork effect.Since the first experimental characterization of SAAs about a decade ago, theoretical models have been able to support and explain various experimental observations. These models have served as benchmarks for assessing the predictive capability of the underlying theoretical methods. In turn, the predictions that have been delivered have guided and continue to guide the experimental research efforts in the field. These advancements show that the in silico design of new SAA catalysts is now within reach.

CoNi nano-alloy anchored on biomass-derived N-doped carbon frameworks for enhanced oxygen reduction and evolution reactions

Bifunctional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are important for energy conversion systems such as fuel cells, water splitting, and metal-air battery devices. In this work, an earthly abundant and cheap biomass of tobacco-stem was used to prepare a novel porous carbon framework (NiCo@NC) by incorporating transition metal alloy and nitrogen-rich small molecules. The resultant catalyst affords an onset potential of 0.92 V and a half-wave potential of 0.86 V for oxygen reduction reaction in alkaline media, which is better than commercial Pt/C. Besides, the catalyst also exhibits good oxygen evolution reaction performance with a low overpotential of 280 mV @ 10 mA cm−2, and the potential gap between ORR and OER is only 0.65 V. The incorporation of NiCo alloy and N heteroatom modulates the electronic structure of the prepared carbon frameworks, creates abundant active sites, and improves charge redistribution, thus resulting in faster ORR and OER reaction kinetics. The applicability of the prepared NiCo@NC is fully harnessed for use as an air-cathode in a Zn-air battery. This work creates a platform for developing efficient porous and functionalized biomass-derived oxygen electrocatalysts for energy applications.

G-C3N4 templated synthesis of the tubular CoFe/N doped carbon composite as advanced bifunctional oxygen electrocatalysts for zinc-air batteries

Rational incorporating transition metal into porous heteroatom-doped carbon is intensively investigated as an effective strategy to achieve high-performance and bifunctional requirements. Herein, we fabricated the hollow composite that CoFe alloy nanoparticles decorated on the tubular N-doped carbon (denoted as T-CoFe/NC) by soft-templating strategy. In order to effectively incorporate the CoFe alloy into nitrogen doped hollow carbon matrix, g-C3N4 nanotubes were selected as the template to attain high contents of nitrogen doping for tubular carbon matrix. Meanwhile, the coordination effect between tannic acid and metal ions is utilized to limit the metal agglomeration in the process of pyrolysis. Consequently, the resultant catalyst shows an outstanding ORR activity with the half-wave potential of 0.86 V and outstanding stability with only a 2 mV decay after 10,000 cycles. T-CoFe/NC also displays comparable overpotential to the RuO2 at 10 mA cm−2. The high bifunctional electrocatalytic activity is attributed to the unique tubular structure and the combination of Co with Fe can optimize the interaction between the oxygenic species and metal surfaces, enhancing the catalytic activity. And T-CoFe/NC based zinc-air battery exhibits excellent power density, large capacity and good cycling stability.