Bimetallic Compounds Research Articles

Cooperative small molecule activation by apolar and weakly polar bonds through the lens of a suitable computational protocol.

Small molecule activation processes are central in chemical research and cooperativity is a valuable tool for the fine-tuning of the efficiency of these reactions. In this contribution, we discuss recent and remarkable examples in which activation processes are mediated by bimetallic compounds featuring apolar or weakly polar metal-metal bonds. Relevant experimental breakthroughs are thoroughly analyzed from a computational perspective. We highlight how the rational and non-trivial application of selected computational approaches not only allows rationalization of the observed reactivities but also inferring of general principles applicable to activation processes, such as the breakdown of the structure-reactivity relationship in carbon dioxide activation in a cooperative framework. We finally provide a simple yet unbiased computational protocol to study these reactions, which can support experimental advances aimed at expanding the range of applications of apolar and weakly polar bonds as catalysts for small molecule activation.

Thermodynamic phase control of Cu-Sn alloy electrocatalysts for selective CO2 reduction.

In the electrochemical CO2 reduction reaction (CO2RR), Cu alloy electrocatalysts can control the CO2RR selectivity by modulating the intermediate binding energy. Here, we report the thermodynamic-based Cu-Sn bimetallic phase control in heterogeneous catalysts for selective CO2 conversion. Starting from the thermodynamic understanding about Cu-Sn bimetallic compounds, we established the specific processing window for Cu-Sn bimetallic phase control. To modulate the Cu-Sn bimetallic phases, we controlled the oxygen partial pressure (pO2) during the calcination of electrospun Cu and Sn ions-incorporated nanofibers (NFs). This resulted in the formation of CuO-SnO2 NFs (full oxidation), Cu-SnO2 NFs (selective reduction), Cu3Sn/CNFs, Cu41Sn11/CNFs, and Cu6Sn5/CNFs (full reduction). In the CO2RR, CuO-SnO2 NFs exhibited formate (HCOO-) production and Cu-SnO2 NFs showed carbon monoxide (CO) production with the faradaic efficiency (FE) of 65.3% at -0.99 V (vs. RHE) and 59.1% at -0.89 V (vs. RHE) respectively. Cu-rich Cu41Sn11/CNFs and Cu3Sn/CNFs enhanced the methane (CH4) production with the FE of 39.1% at -1.36 V (vs. RHE) and 34.7% at -1.50 V (vs. RHE). However, Sn-rich Cu6Sn5/CNFs produced HCOO- with the FE of 58.6% at -2.31 V (vs. RHE). This study suggests the methodology for bimetallic catalyst design and steering the CO2RR pathway by controlling the active sites of Cu-Sn alloys.

Two bimetallic compounds with attractive structures and properties

Two new bimetallic lanthanide-mercury isonicotinic acid compounds were successfully synthesized through classical hydrothermal reactions using DyCl3·6H2O or LuCl3·6H2O, HgCl2, isonicotinic acid, and distilled water. The resulting compounds, [Dy2(IA)6(H2O)2(H3O)2(Hg2Cl5)2]n(3nHgCl2) (1; IA refers to isonicotinic acid anions) and [Lu(HIA)(IA)2(H2O)2Hg2Cl5]2n[3n(HgCl2)]·6nH2O (2; HIA refers to isonicotinic acid), exhibit intriguing crystal structures and photophysical properties. The crystal structures of compounds 1 and 2 were determined through single crystal X-ray diffraction, revealing their two-dimensional (2D) nature. Compound 1 displays upconversion yellow photoluminescence, attributed to the 4F9/2 → 6H13/2 electronic transition of the trivalent dysprosium ion. In contrast, compound 2 exhibits blue photoluminescent emission. The Commission Internationale de I'Éclairage (CIE) chromaticity coordinates of (0.4874, 0.5115) for 1 and (0.1225, 0.0678) for 2. The correlated color temperatures (CCT) are 2960 K and 5503 K for compounds 1 and 2, respectively. Furthermore, the semiconductor band gaps for compounds 1 and 2, determined by solid-state diffuse reflectance experiments, are 2.92 eV and 4.75 eV, respectively. Additional insights into their thermal stability are provided via thermogravimetric analysis (TG) results.

On-Surface Synthesis of Multiple Cu Atom-Bridged Organometallic Oligomers.

A metal-metal bond between coordination complexes has the nature of a covalent bond in hydrocarbons. While bimetallic and trimetallic compounds usually have three-dimensional structures in solution, the high directionality and robustness of the bond can be applied for on-surface syntheses. Here, we present a systematic formation of complex organometallic oligomers on Cu(111) through sequential ring opening of 11,11,12,12-tetraphenyl-1,4,5,8-tetraazaanthraquinodimethane and bonding of phenanthroline derivatives by multiple Cu atoms. A detailed characterization with a combination of scanning tunneling microscopy and density functional theory calculations revealed the role of the Cu adatoms in both enantiomers of the chiral oligomers. Furthermore, we found sufficient strength of the bonds against sliding friction by manipulating the oligomers up to a hexamer. This finding may help to increase the variety of organometallic nanostructures on surfaces.

Ni‐Co‐based bimetal organic framework as superior electrode material for hydrogen evolution reaction and supercapacitors

AbstractMetal‐organic frameworks (MOFs) possess several desirable properties, including a homogeneous crystal structure, variable porosity, high surface area, and a notable adsorption affinity, making them highly promising contenders for deployment as electrode materials in supercapacitors (SCs) and water electrolyzers, which are acknowledged for the ever‐increasing demand for instantaneous energy. Herein, we report the rationally assembled Ni‐Co‐based bimetallic MOF compounds using a glutaric acid as an organic ligand and low‐temperature hydrothermal treatment that surmounts the electrocatalytic and electrochemical charge storage activity in an alkaline medium. The NiCo‐MOF surpassed the hydrogen evolution reaction (HER) among other as‐synthesized materials, exhibiting the least overpotential of 182 mV at 10 mA/cm2 of current density, showed splendid kinetics with a turnover frequency of 2.86 s−1, and higher stability after 1000 HER cycles in 1 M KOH. Furthermore, NiCo‐MOF impetuses were employed for SC application and displayed the highest specific capacitance of 978 F/g than Ni‐MOF (706 F/g) and Co‐MOF (91 F/g) at 1 A/g of current density. Theoretical studies exhibited that the optimal electronic coupling and synergistic effect due to Ni‐Co sites enhances the overall electronic properties of NiCo‐MOF. Therefore, enhancing its electrochemical performance concerning water‐splitting and charge storage. This study showcases a novel approach for producing ultrathin and flexible bimetallic MOF‐based electrode material to enrich the performance in electrocatalytic HER and SCs.

Design of NiCo2S4@ZnAl-LDH/TiO2@MXene synthesis as promising cathode catalyst for enhancing electrochemical performance in microbial fuel cell

In this work, a double-bimetallic compound (NiCo2S4@ZnAl-LDH/TiO2@MXene) was successfully prepared by a simple hydrothermal-coprecipitation method. NiCO2S4@ZnAl-LDH/TiO2@MXene was combined with two bimetallic compounds, NiCo2S4@ZnAl-LDH and TiO2@MXene, which formed a firm structure. This material showed superior catalytic oxygen reduction reaction (ORR) according to the large integral area and sharp slope. The maximum power density of NiCo2S4@ZnAl-LDH/TiO2@MXene-microbial fuel cell (MFC) was 565.81 mW/m2 and could be maintained for 10 d, which was 7.07 times of NiCo2S4/TiO2@ZnAl-LDH-MFC (80 mW/m2), 11.43 times of NiCo2S4@ZnAl-LDH (49.5 mW/m2), 14.15 times of TiO2@MXene (40 mW/m2), indicating the excellent electrical performance of NiCo2S4@ZnAl-LDH/TiO2@MXene. TiO2 and NiCo2S4 were introduced in ZnAl-LDH and MXene separately to avoid aggregation between layers, which provided more pathways for ions and accelerated the speed of the transportation of electrons. NiCO2S4@ZnAl-LDH/TiO2@MXene were coated tightly and firmly with the coprecipitation method which further enhanced the electrochemical performance of MFC. Therefore, this study would give a boarder horizon about the application of cathode materials of MFC.

Novel synthesis of nickel-based bimetallic compounds using ammonium tetrafluoroborate and ammonium bifluoride as structure directing agents for energy storage application

Nickel-based compounds are widely applied as the active material for energy storage devices, owing to high theoretical capacity and easy-fabricated process. Bimetallic compounds having multiple redox states can provide abundant redox reactions for charge storage. Structure directing agent (SDA) can promote the preferable growth of active materials and to enhance energy storage abilities. In this work, NH4BF4 and NH4HF2 are firstly used as SDA to synthesize nickel-based compounds along with 2-methylmidozole in the one-step solution process for energy storage applications. The bimetallic compounds are synthesized by incorporating Al, Mn, Co, Cu and Zn salts in the precursor solution including the Ni salt. The system with Al, Cu or Zn possesses single metal compound and barely nickel compound. Mn and Co-incorporated systems present clear bimetallic components with nickel hydroxide. The highest specific capacitance (CF) of 1336.3 F/g (297.0 mAh/g) are achieved at 20 mV/s for the NiCo-based electrode, owing to the bimetallic feature and favorable two-dimensional sheet-like structures. An energy storage device is assembled using the NiCo-based compound and reduced graphene oxide electrodes. The maximum energy density of 10.5 Wh/kg at 0.3 kW/kg, and the CF retention of 78.5% and Coulombic efficiency of 85.2% are achieved after 10,000 times charge/discharge cycles.

Cactus-like (Ni,Co)Se2 nanosheets with 3D structure decorated on the conductive substrate for efficient hydrogen evolution reaction

Transition metal selenides are a fascinating class of substitute for traditional noble metal electrocatalysts for hydrogen evolution reaction (HER). However, the monometallic selenides still have the disadvantages of low electroactive sites and electrical conductivity. To address such drawbacks, three-dimensional (3D) hierarchical nanostructures composed of bimetallic compounds have aroused great attention. In this study, cactus-like bimetallic nickel–cobalt nanosheets with a 3D nanostructure are successfully prepared on the surface of conductive substrate by a one-step hydrothermal reaction. Then a high-efficiency bimetallic catalyst ((Ni,Co)Se2/CFP) is obtained by a facile chemical vapor deposition. Benefiting from bimetallic components and the unique 3D structure, the cactus-like (Ni,Co)Se2/CFP only requires a low overpotential of 154 mV to reach the current density of 10 mA cm−2. The Tafel slope of (Ni,Co)Se2/CFP (67 mV dec−1) further shows that (Ni,Co)Se2/CFP has faster HER kinetics. Besides, the long-term stability test demonstrates the excellent durability of (Ni,Co)Se2/CFP in 0.5 M H2SO4. This research offers a useful technique and guide for improving the structure of bimetallic selenides based on transition metals to design high-efficient HER electrocatalysts.

Effects of metal ratios and post treatments on energy storage ability of cobalt manganese metal organic frameworks

Metal organic framework (MOF) with large surface area and pore tunability has been intensively applied on energy storage. Tubular structure is one of promising configurations due to abundant contacts to electrolyte at inner/outer surface and straight charge transfer paths. Bimetallic compounds with multiple redox states are favorable for generating redox reactions. Possible conversions to oxides or sulfides can also induce additional active sites and enhance conductivity. In this study, cobalt and manganese bimetallic MOF (CoMn-MOF) tubular structures are firstly synthesized using polypyrrole nanotubes as the template. Effects of metal ratio on energy storage is investigated to understand contributions from Co and Mn. The CoMn-MOF derived oxide and sulfide are further synthesized to enhance energy storage ability. A larger specific capacitance (CF) of 670.1 F/g is attained for CoMn-MOF derived sulfide (S-CoMn-MOF) electrode, respectively compared to those of 247.0 and 426.7 F/g for the CoMn-MOF and oxidized CoMn-MOF electrodes, because of surface connected tubular structure and balanced components of MOF and sulfides for S-CoMn-MOF. An energy storage device with S-CoMn-MOF and graphene electrodes shows a maximum energy density of 17.9 Wh/kg at 785.7 W/kg. The CF retention of 78% and Coulombic efficiency of 97% after 10,000 charge/discharge cycles are also obtained.

Electrodeposition Synthesis of Coral-like MnCo Selenide Binder-Free Electrodes for Aqueous Asymmetric Supercapacitors.

Bimetallic selenide compounds show great potential as supercapacitor electrode materials in energy storage and conversion applications. In this work, a coral-like MnCo selenide was grown on nickel foam using a facile electrodeposition method to prepare binder-free supercapacitor electrodes. The heating temperature was varied to tune the morphology and crystal phase of these electrodes. Excellent electrochemical performance was achieved due to the unique coral-like, dendritic- dispersed structure and a bimetallic synergistic effect, including high specific capacitance (509 C g-1 at 1 A g-1) and outstanding cycling stability (94.3% capacity retention after 5000 cycles). Furthermore, an asymmetric supercapacitor assembled with MnCo selenide as the anode and active carbon as the cathode achieved a high specific energy of 46.2 Wh kg-1 at 800 W kg-1. The work demonstrates that the prepared coral-like MnCo selenide is a highly promising energy storage material.

Novel combustion technique synthesis of ZnCo2O4 nanobeads/g-C3N4 nanosheet heterojunction photocatalyst in-effect of enhancing photocatalytic degradation for environmental remediation

An agglomerated nanobead ZnCo2O4 with g-C3N4 nanosheet composite was prepared through a novel combustion technique (tartaric acid as fuel). The heterojunction formation between the materials leads to a synergistic effect that enhances active sites and degradation efficiency. The prepared samples were further analyzed through various techniques like X-ray diffraction (XRD), high-resolution scanning electron microscopy (HRSEM), X-ray photoelectron spectroscopy (XPS), and UV–visible spectroscopy. The obtained 15% ZC/gCN achieved a higher percentage (95% and 80%) of degradation within 60 and 120 mins for RhB and CIP pollutants which were higher than pure gCN, with the rate kinetics of 0.0347 and 0.0102 x10−2 min−1. With respect to the photoluminescence and photoelectrochemical performance, the enhancement in the degradation was ascribed due to enhanced charge separation of photo-excited electrons and holes, which intend retarding the recombination of excited charges. The active reacting species during degradation, such as superoxide, was noted from scavenger analysis. The recyclability of the material confirms its good stability nature. Here a type-I heterojunction form was noticed by theoretical, empirical formula; through this, a reasonable position of conduction bands owing to a double reduction process was proposed. This work provided bimetallic oxide-based metal-free compound formation for environmental remediation.

Solvent-Free Mechanochemical Synthesis of Strongly Luminescent Eu(III) Hybrid Materials Using Tetramethylammonium Salts

Abstract A solvent-free mechanochemical treatment is used to synthesize an Eu(III) hybrid material containing Eu(D-facam)3 and tetramethylammonium acetate (TMAOAc), mechEu(D-facam)3-TMAOAc. The synthesis method is efficient and the reaction occurs within 10 s. Mechanochemically prepared mechEu(D-facam)3-TMAOAc is proven to be a bimetallic compound, in which TMAOAc functions as a bridging molecule between multiple Eu(III) complexes. Compared with Eu(D-facam)3, mechEu(D-facam)3-TMAOAc exhibits ultra-high luminescence, excellent circular polarization activity and thermal stability.

Facile Synthesis of Nitrogen-Rich Porous Carbon/NiMn Hybrids Using Efficient Water-Splitting Reaction.

Proper design of multifunctional electrocatalyst that are abundantly available on earth, cost-effective and possess excellent activity and electrochemical stability towards oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are required for effective hydrogen generation from water-splitting reaction. In this context, the work herein reports the fabrication of nitrogen-rich porous carbon (NRPC) along with the inclusion of non-noble metal-based catalyst, adopting a simple and scalable methodology. NRPC containing nitrogen and oxygen atoms were synthesized from polybenzoxazine (Pbz) source, and non-noble metal(s) are inserted into the porous carbon surface using hydrothermal process. The structure formation and electrocatalytic activity of neat NRPC and monometallic and bimetallic inclusions (NRPC/Mn, NRPC/Ni and NRPC/NiMn) were analyzed using XRD, Raman, XPS, BET, SEM, TEM and electrochemical measurements. The formation of hierarchical 3D flower-like morphology for NRPC/NiMn was observed in SEM and TEM analyses. Especially, NRPC/NiMn proves to be an efficient electrocatalyst providing an overpotential of 370 mV towards OER and an overpotential of 136 mV towards HER. Moreover, it also shows a lowest Tafel slope of 64 mV dec-1 and exhibits excellent electrochemical stability up to 20 h. The synergistic effect produced by NRPC and bimetallic compounds increases the number of active sites at the electrode/electrolyte interface and thus speeds up the OER process.

Structural and Magnetization Dynamics of Borohydride-Bridged Rare-Earth Metallocenium Cations.

The structure and magnetic properties of the bimetallic borohydride-bridged dysprosocenium compound [{(η5-Cpttt)(η5-CpMe4t)Dy}2(μ:κ2:κ2-BH4)]+[B(C6F5)4]- ([3Dy][B(C6F5)4]) are reported along with the solution-phase dynamics of the isostructural yttrium and lutetium analogues (Cpttt is 1,2,4-tri(tert-butyl)cyclopentadienyl, CpMe4t is tetramethyl(tert-butyl)cyclopentadienyl). The synthesis of [3M][B(C6F5)4] was accomplished in the 2:1 stoichiometric reactions of [(η5-Cpttt)(η5-CpMe4t)Dy(BH4)] (2M) with [CPh3][B(C6F5)4], with the metallocenes 2M obtained from reactions of the half-sandwich complexes [(η5-Cpttt)M(BH4)2(THF)] (1M) (M = Y, Dy, Lu) with NaCpMe4t. Crystallographic studies show significant lengthening of the M···B distance on moving through the series 1M, 2M, and 3M, with essentially linear {M···B···M} bridges in 3M. Multinuclear NMR spectroscopy indicates restricted rotation of the Cpttt ligands in 3Y and 3Lu in solution. The single-molecule magnet (SMM) properties of [3M][B(C6F5)4] are characterized by Raman and Orbach processes, with an effective barrier of 533(18) cm-1 and relaxation via the second-excited Kramers doublet. Although quantum tunneling of the magnetization (QTM) was not observed for [3M][B(C6F5)4], it was, surprisingly, found in its magnetically dilute version, which has a very similar barrier of Ueff = 499(21) cm-1. Consistent with this observation, slightly wider openings of the magnetic hysteresis loop at 2 K are found for [3M][B(C6F5)4] but not for the diluted analogue. The dynamic magnetic properties of the dysprosium SMMs and the role of exchange interactions in 3Dy are interpreted with the aid of multireference ab initio calculations.

Playing with [{Mo6Bri6Sei2}(CN)a6]4− Cluster Building Blocks and Mn(salen)+ Nodes for the Crystal Engineering of Inorganic Coordination Polymers

AbstractWe present here the syntheses and structural characterizations of inorganic polymeric cluster compounds, Cs[Mn(salen)]3[{Mo6Br6Se2}(CN)6] (1) and (H3O)(TBA)[Mn(salen)]2[{Mo6Br6Se2}(CN)6] (2) (TBA=tetrabutylammonium ((n‐C4H9)4N+)), built‐up from [{Mo6Br6Se2}(CN)6]4− molecular building blocks and Mn(salen)+ complexes (salen = salen = N,N′‐bis(salicylidene)ethylenediamine). The nature of additional counter cations (i. e. Cs+ or TBA+) enables to control the interactions between the [{Mo6Br6Se2}(CN)6]4− building blocks and the Mn(salen)+ groups. Thus, 1 was obtained by slow diffusion of a methanol solution of K2Cs2[{Mo6Br6Se2}(CN)6] cluster compound into a methanol solution of Mn(salen)ClO4. 2 was obtained in a similar way but after the addition of tetrabutylammonium bromide into the solution of Mn(salen)ClO4. 1 is a bimetallic 3D coordination compound ( ) and 2 is a bimetallic 2D compound ( ). Structural correlations between 1 and 2 are discussed and compared with relevant examples found in the literature.

Highly uniform Co-Cu bimetallic sulfides for rechargeable alkaline aqueous zinc batteries

Rechargeable alkaline aqueous zinc batteries (RAZBs) have attracted increasing attention. However, most RAZBs are hindered by the limited availability of cathode materials. The practical electrochemical performance of most cathode materials is lower than the theoretical value due to their poor electrical conductivity and low utilization capacity. In this work, we develop a facile hydrothermal procedure to prepare highly uniform bimetallic sulfides as novel cathode materials for RAZBs. Copper-cobalt binary metallic oxides materials possess higher conductivity and larger capacity compared with their mono-metal oxides compounds due to bimetallic synergistic effects and multiple oxidation states. Furthermore, bimetallic sulfide compounds have smaller bond energy and longer bond length than their oxides, leading to less structural damage, faster kinetics of electrochemical reactions, and better stability. The as-prepared Co-Cu bimetallic sulfides show enhanced electrochemical performance due to various valences of Co and Cu as well as the existence of S. As a result, aqueous Zn/CuCo2S4 battery shows a high specific capacity of 117.4 mAh/g at 4 A/g and a good cycle life of over 8000 cycles. Based on PANa hydrogel electrolytes, a flexible Zn/CuCo2S4 battery demonstrates excellent cycling stability. This battery can also meet the requirements of electronic devices with different shapes and performs well in extreme environments, such as freezing, drilling, and hammering. This work opens new avenues to obtain high-rate and long-life cathode materials for RAZBs by utilizing the synergistic effects of bimetallic sulfides and provides a new platform for flexible energy storage devices.

Tailoring Ni-Fe-Se film on Ni foam via electrodeposition optimization for efficient oxygen evolution reaction

The development of efficient non-precious metal electrocatalysts is essential for oxygen evolution reaction (OER) for water splitting. Among them, amorphous bimetallic NiFe-based compounds are recognized as one of the excellent candidates for efficient OER. Herein, the Ni-Fe-Se film is rationally designed via facile one-step electrodeposition with tailored active sites and thicknesses. Accordingly, the optimized sample, with an increased Fe-incorporation level and a thickness of ∼50 nm, shows a low overpotential of ∼290 mV at a current density of 40 mA cm−2 and long-term durability in 1 M KOH solution, representing its overall excellent OER performance. Furthermore, operando Raman and ex-situ XPS are used to identify the active sites for OER. This work provides some new insights into exploring earth-abundant free-standing catalysts for OER toward overall water-splitting applications.

Heterobimetallic NiFe Cooperative Molecular Water Oxidation Catalyst

AbstractWe reported herein the development of heterobimetallic NiFe molecular platform to understand NiFe synergistic effect in water oxidation catalysis. Compared to homonuclear bimetallic compounds (NiNi and FeFe), NiFe complex possesses more remarkable catalytic water oxidation performance. Mechanistic studies suggest that this remarkable difference is attributed to the fact that NiFe synergy can effectively promote O−O bond formation. The generated NiIII(μ‐O)FeIV=O is the key intermediate and O−O bond was formed via intramolecular oxyl‐oxo coupling between bridged O radical and terminal FeIV=O moiety.

Heterobimetallic NiFe Cooperative Molecular Water Oxidation Catalyst.

We reported herein the development of heterobimetallic NiFe molecular platform to understand NiFe synergistic effect in water oxidation catalysis. Compared to homonuclear bimetallic compounds (NiNi and FeFe), NiFe complex possesses more remarkable catalytic water oxidation performance. Mechanistic studies suggest that this remarkable difference is attributed to the fact that NiFe synergy can effectively promote O-O bond formation. The generated NiIII(μ-O)FeIV=O is the key intermediate and O-O bond was formed via intramolecular oxyl-oxo coupling between bridged O radical and terminal FeIV=O moiety.

Nickel-loaded red mud catalyst for steam gasification of bamboo sawdust to produce hydrogen-rich syngas

Ni/red mud (RM) catalysts were prepared by wet impregnation and used in the catalytic steam gasification of bamboo sawdust (BS) to produce hydrogen-rich syngas. The system was optimized in terms of the amount of added nickel (10%), reaction temperature (800 °C), and catalyst placement (separately behind the BS). The maximum H2 yield was 17.3% higher than that using pure RM catalyst and 43.8% higher than that of BS gasification alone, and the H2/CO ratio in the syngas reached 7.82. This Ni/RM catalyst also retained good activity after six cycles in a double-stage fixed bed reactor. Analysis using X-ray fluorescence, X-ray diffraction, scanning electron microscopy-energy dispersive spectroscopy, and other methods revealed that the interaction of Ni, Fe, and Mg in Ni/RM produced bimetallic compounds containing active sites, such as NiFe2O4, MgNiO2, and NiO. This explains the good catalytic performance in the tar conversion during the gasification process.