CoNi Alloy Nanoparticles Research Articles

Layered double hydroxides-derived CoNi alloy nanoparticles encapsulated by porous N-doped carbon nanofibers as efficient methanol electrocatalysts for alkaline direct methanol fuel cells

The exploration of inexpensive electrocatalysts possessing high activity and increased stability to replace precious metal catalysts in the methanol oxidation reaction (MOR) is highly desirable for alkaline direct methanol fuel cells (ADMFCs). This study presents a novel approach to synthesize layered double hydroxides (LDHs)-derived CoNi alloy nanoparticles confined within porous N-doped carbon nanofibers (CoNi@NCNFs) via facile electrospinning and pyrolysis for methanol electrooxidation.The one-dimensional N-doped carbon nanofibers could effectively prevent nanoparticle agglomeration during the pyrolysis of LDH precursors. The optimized CoNi@NCNF3-900 composite exhibits exceptional catalytic activity (80.3mAcm−2) for MOR in alkaline solution, attributed to its hierarchical porous structure, high surface area, and abundant accessible active sites. Furthermore, the catalyst demonstrates competitive electrocatalytic stability, retaining over 90% of its initial current density after 1000 consecutive cyclic voltammetry (CV) cycles. Notably, a single-cell ADMFC assembled with CoNi@NCNF3-900 as the anode catalyst achieves a promising maximum power density of 29.5mWcm−2, highlighting the potential of CoNi@NCNF3-900 for application in DMFC technology and clean energy sources.

Boosting Dry Reforming of Methane Over NiCo/CeO2 Catalysts Treated by Hydrogen Plasma

ABSTRACTNickel (Ni)‐based catalysts are prospective materials for dry reforming of methane (DRM) reaction, but suffer from coke formation and limited activity for CO2 conversion. To improve the reactivity of Ni‐based catalysts, a promising strategy is introducing cobalt (Co) metal. Here, we construct highly efficient NiCo sites on CeO2 support by H2 plasma, which enables the catalyst to obtain a remarkable increase in DRM reaction than the samples treated by conventional H2 reduction. H2 plasma treatment results in the formation of highly dispersed NiCo alloy nanoparticles and high‐concentration oxygen vacancy. These features create large numbers of highly active sites to boost the activation of CH4 and especially CO2 and their catalytic reactions, resulting in strong coke resistance in the DRM reaction.

Enhanced Methanol Electrooxidation and Supercapacitive Performance via Compositional Engineering of Colloidal Ni-Co Alloying Nanoparticles.

Among renewable energy technologies, particular attention is paid to electrochemically transforming methanol into valuable formate and storing energy into supercapacitors. In this study, we detailed a simple colloidal-based protocol for synthesizing a series of alloy nanoparticles with tuned Ni/Co atomic ratios, thereby optimizing their electrochemical performance. With the addition of 1 M methanol in 1 M KOH, the optimized composition was able to electrochemically produce formate at 0.149 mmol cm-2 h-1 with a Faradaic efficiency up to 95.1% at 0.6 V versus Hg/HgO within a 22-hour testing period. In 1 M KOH solution without methanol, the supercapacitive performance was achieved at a specific capacitance of over 1500 F g-1, and outstanding cycling stability with only approximately 20% decay after continuous 10000 charging-discharging cycles. These results underscore that the prepared Ni-Co alloy nanoparticles serve as multi-functional electrodes for electrochemical energy conversion and storage, particularly in the MOR and supercapacitors applications.

Gelation-pyrolysis strategy for fabrication of advanced carbon/sulfur cathodes for lithium-sulfur batteries

The development of high-performance carbon-based composite hosts play decisive roles in the electrochemistry of lithium sulfur batteries. Herein, a novel metal-ion induced gelation self-assembly technology is reported to construct sodium alginate carbon (SAC) based polar hierarchical carbon composites with cross-linked network architecture and in-situ co-grown cross-linked polar nanoparticles. Interestingly, it shows high versatility to an extensive array of materials including metals, alloys, and metallic oxides. As a representative, NiCo alloy nanoparticles are chosen to obtain the SAC/NiCo composite host for sulfur in LSBs, which possess superior physical/chemical adsorption capabilities and catalytic conversion kinetics to polysulfide in virtue of synergistic interaction between the hierarchical pore structures and NiCo catalyst. The designed SAC/NiCo-S cathode shows superior electrochemical performance with excellent rate capacity (2 C: 693.5 mAh/g) and enhanced cycling stability (764.3 mAh/g at 0.1 C after 240 cycles). This work provides a straightforward approach for fabricating multifunctional carbon composites with adjustable component for advanced energy storage system.

Synergistic effect of nanocrystalline NiCo2S4 and NiCo alloy embedded in N-doped carbon fibers towards high-performance electrocatalysts for oxygen evolution reaction

Developing oxygen evolution reaction (OER) electrocatalysts with high efficiency, low cost and good stability for water splitting is significant to relieve the energy crisis and environmental pollution. Herein, NiCo alloy (NC) nanoparticles (NPs) embedded N-doped carbon fibers (NCF) were prepared by electrospinning and carbonization. The surfaces of the NC@NCF were anchored with nanocrystalline NiCo2S4 (NCS) in a following solvothermal process to form NCS-NC@NCF composite. Synergistic effect of the alloy (NC) and the semiconductor (NCS) was successfully stimulated, i.e., rapid charge separation and transfer was achieved during the OER process. In addition, the carbon fibers substrate is beneficial for good dispersion of the NC and NCS NPs as well as the conductivity improvement of the as-prepared NCS-NC@NCF catalyst. The prepared NCS-NC@NCF catalyst electrode owns good OER performances of a low overpotential of 291 mV, 342 mV and 376 mV to respectively deliver current densities of 10 mA cm−2, 50 mA cm−2 and 100 mA cm−2, which are respectively 19 mV, 82 mV and 116 mV lower than those of the RuO2 electrode (310 mV, 424 mV and 492 mV), indicating the great potential of the catalyst in water splitting. Moreover, good durability of current density retention of 90.7 % is observed after 60 h of continuous OER polarization for the catalyst. Additionally, a two-electrode system composed of commercial Pt/C and the NCS-NC@NCF electrodes only needs a driven voltage of 1.51 V to afford 10 mA cm−2 for water splitting, which is superior to that (1.69 V) of the Pt/C||RuO2 system.

Fabrication of CoM (M= Ni, Cu) alloys modified carbon electrocatalysts by pyrolysis of dual-metal-site metal-organic frameworks for efficient dye-sensitized solar cells

The regulation of interface properties of multi-component transition metals in carbon-based catalyst has been an effective method to boost the electrochemical performance of counter electrode (CE) catalysts for dye-sensitized solar cells (DSSCs). Herein, CoNi-metal-organic framework (MOF) and CoCu-MOF are fabricated through introducing Ni and Cu into the stable Co-MOF, and used as sacrificial precursor in the followed pyrolysis-alloying process. And then, the target product CoM (M=Ni, Cu)/N-doped polyhedron-like carbon (NC) are successfully obtained, in which CoNi and CoCu alloy nanoparticles are uniformly dispersed on the N-doped carbon skeleton. Such MOFs-derived carbon matrix can not only supply as conductive network, but also isolate the alloy nanoparticles to avoid agglomeration, ensuring more effective active sites. Meanwhile, the built-in electric field generated by the Mott-Schottky interface effect of CoM/NCs could regulate the electronic structure inside the catalysts, resulting in faster electron transfer ability. Significantly, the reduced work function due to the introduction of Cu atoms leads to stronger self-driven electron transfer at the heterogeneous interface of CoCu/NC, which helps to improve reaction activity and electrocatalytic efficiency. Among the tested catalysts, CoCu/NC displays a more satisfying power conversion efficiency (PCE) of 7.60 % when assembled into CE of DSSC, also superior to 7.19 % of Pt.

Ultrafine CoNi alloy nanoparticles anchored on surface-roughened halloysite nanotubes for highly efficient catalytic hydrogenation of 4-nitrophenol

The hydrogenation of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) is an effective and cost-competitive procedure to change waste into valuables. With the purpose of designing efficient and green catalysts to convert 4-NP, we adopt halloysite nanotubes (HNTs), a resource-rich and eco-friendly clay mineral material, as CoNi alloy nanoparticles support in this study. The HNTs used have been increased the surface roughness (defined as rHNTs) through the etching process. Thereafter, a series of ultrafine CoNi alloy nanoparticles (1.2 ∼ 1.4 nm) anchored onto rHNTs (CoxNi1-x/rHNTs, where x represents the molar percentage of Co to total metal elements) are successfully synthesized via a simple one-pot approach. Benefitting from the positive synergy of Co and Ni bimetals and the powerful metal-support interaction, Co0.7Ni0.3/rHNTs catalyst (8.55 wt% total actual metal loading) exhibits the best catalytic performance for 4-NP degradation with a conversion efficiency of 99 % within 4 min at 298 K, and meanwhile a high turnover frequency (TOF) of 1.16 × 10-2 mmol mg−1 min−1 is achieved with the rate constant of 1.09 min−1. Of note, Co0.7Ni0.3/rHNTs also show excellent degradation performance towards two other nitrophenol isomers (2-nitrophenol and 3-nitrophenol).

In-situ constructing ultrafine NiCo alloy confined in LDH nanoflower for efficient selective hydrogenation of furfural

Directional activation of oxygen-containing groups is a crucial challenge in the catalytic conversion of renewable biomass to high-value products. Herein, we fabricated uniform dispersed NiCo alloy nanoparticles by direct reduction flower-like layer double hydroxides (LDHs) precursors. The as-obtained Ni2Co1AlO exhibited outstanding yield (97.6 %) of tetrahydrofurfuryl alcohol (THFOL) in furfural hydrogenation, which is significantly superior to those of monometallic Ni-based (75 %) and Co-based (0 %) LDH catalysts and even higher than the most noble metal catalysts. The Ni2Co1AlO showed robust stability, e.g., the catalyst can be recycled up to 10 times without loss of its conversion and selectivity, which is attributed to the ultra-dispersed metal cations in layers and the confined effect of metal oxides. Characterizations and theoretical calculations demonstrate that alloying Ni with Co can downshift the d-band center of Ni in NiCo alloys, which facilitates the H* desorption to improve hydrogenation activity. The unique electronic interactions between Ni and Co facilitated the parallel adsorption of furfural while reduced the energy barriers of the furan ring hydrogenation, promoting the production of THFOL. This work provides a promising strategy of tailoring d-band center, which can shed light on the design of heterogeneous catalysts.

Coupling phyllosilicate and NiCo alloy nanoparticles on sepiolite to enhance stability for hydrogen production by ethanol steam reforming

For hydrogen production from ethanol steam reforming (ESR), The NiCo alloy immobilized on sepiolite (SEP) support by a phyllosilicate precursor was deemed as an effective strategy to improved catalyst stability. The Ni/Co ratio was regulated to optimized the ESR reactivity of the bi-metallic catalysts prepared by the NH4F assisted urea hydrothermal method. The synergy effect of NiCo alloy with a Ni-rich surface on ESR reactivity and anti-deactivation was investigated. The 5Ni10Co/SEP catalyst presented the highest conversion (99.4 %) and H2 yield (68.2 %) at 700 °C, which was benefited from the downsized nanoparticle size and strong metal-support interaction. The proposal structure-activity relationship suggested that the NiCo alloy was exsolved from the phyllosilicate precursor grafted on SEP framework, providing an excellent mitigation for metal sintering. In addition, the synergy of NiCo alloy was elaborated by a combination of enhanced ethanol adsorption/dissociation on Ni sites and restrained methanation on Co sites, offering a 50 h catalyst stability during ESR consisting of the ethanol dehydration route. The developed NiCo alloy catalyst based on SEP support with phyllosilicate precursor provided a prospect on the application to H2 production from ESR over the bimetallic catalysts with simple preparation, high economy and structure stability.

Enhancing oxygen reduction reaction performance through eco-friendly chitosan gel-assisted molten salt strategy: Small NiCo alloy nanoparticles decorated with high-loading single Fe-NX

We developed an effective and eco-friendly strategy using chitosan gel-molten salt to achieve high loading (2.23 At. %) of single Fe-NX as assistive active sites. These sites were combined with small NiCo alloy NPs distributed on porous carbon aerogels to boost the ORR performance. The FeSAs-NiCo alloy@N-C sphere exhibits exceptional mass activity and specific activity of 3.705 A.mg−1 and 8.79 mA.cm−2(ECSA), respectively, at 0.85 V versus RHE. It has a superior onset potential of 1.08 V versus RHE, surpassing that of its nanoparticle Fe counterpart and NiCo alloy@N-C sphere. The significant improvement in ORR performance of the FeSAs-NiCo alloy@N-C sphere could be attributed to the positive effects of increased lattice strain due to the single atoms of Fe-NX hybridized with small NiCo alloy NPs. The chitosan gel-assisted molten salt strategy and assistive active sites of Fe-NX hybridized with NiCo alloy NPs regulate the electronic properties of the FeSAs-NiCo alloy@N-C sphere, both geometrically via lattice strain mismatch and electronically through shifting of the d-band center. This could influence the binding energies for oxygen and/or oxygen reduction intermediate adsorption/desorption. The additional improvement in the ORR performance of the FeSAs-NiCo alloy@N-C sphere also benefits from having a lower electrochemical activation energy.

Pt-on-CoNi alloy nanoparticles supported on N and P co-doped graphene catalyst for highly efficient hydrogen evolution by acidic water electrolysis

The multimetallic catalysts with adjustable electronic structures and synergy effect between various metals compared to monometallic catalysts are widely applied in electrocatalysis. Herein, graphene is doped with N and P to prepare rGNP support, then a trimetallic PtCoNi/rGNP catalyst is prepared via simple impregnation and galvanic replacement reaction methods. Pt is highly dispersed on the CoNi alloy nanoparticles (NPs) on rGNP for PtCoNi/rGNP. Based on various characterization techniques and electrochemical testing results such as ICP-OES, XRD, XPS, TEM, HRTEM, STEM, STEM-EDX elemental mapping and line-scanning, it confirms the nanostructure of PtCoNi/rGNP (Pt-on-CoNi alloy). The overpotential of PtCoNi/rGNP for hydrogen evolution (HER) via acidic water electrolysis at 100 mA cm−2 is 15 mV, lower than commercial Pt/C (Pt/C) (66 mV). The Tafel slope of PtCoNi/rGNP is 6.46 mV dec−1, smaller than that of Pt/C (17.15 mV dec−1). The overpotential at 10 mA cm−2 only increases with 3.2 mV (reaching 13.2 mV) after a long time stability testing of 72 h, still lower than Pt/C (20 mV), indicating that it has high catalytic activity and stability. This work not only reveals the synergistic effect mechanism of noble metal-on-non-noble metal for the HER, but also provides a new strategy to develop efficient and highly stable catalysts for the HER.

Nitrogen-doped mesoporous carbon spheres decorated with NiCo alloy nanoparticles for high-performance electrochemical supercapacitors

Nitrogen-doped mesoporous carbon spheres (NMCSs) decorated with NiCo alloy nanoparticles (NiCo/NMCS) were prepared and examined for their prospective role as high-performance electrode materials. The average size and BET surface of the NMCSs are 488.1 nm and 660.9 m2g−1. The N content of the NMCSs and NiCo/NMCS-50 (NMCSs with 50 wt% of NiCo alloy nanoparticles (NPs)) was 1.49 wt% and 2.9 wt%, respectively. The NiCo alloy NPs, with an average diameter of 9.6 nm, were evenly incorporated into NMCSs. The NiCo/NMCS-50 exhibited a specific capacitance of 585 F g−1 when tested in a 6 M KOH solution at a current density of 1 A/g. The superior electrochemical performance of NiCo/NMCS-50 is attributed to the synergistic effect of mesoporous carbon structure and NiCo alloy NPs by improving redox-related mass transport and electron transfer. Symmetric supercapacitor devices assembled using two NiCo/NMCS-50 electrodes had a maximum energy density of 30.0 Wh kg−1 at a power density of 187.5 W kg−1 with notable cycling stability, maintaining 60.1 % of capacitance, up to 5,000 cycles. These results suggest that NiCo/NMCS composites have significant potential for utilization in high-energy storage applications.

Juice Vesicles Bioreactors Technology for Constructing Advanced Carbon-Based Energy Storage.

The construction of high-quality carbon-based energy materials through biotechnology has always been an eager goal of the scientific community. Herein, juice vesicles bioreactors (JVBs) bio-technology based on hesperidium (e.g., pomelo, waxberry, oranges) is first reported for preparation of carbon-based composites with controllable components, adjustable morphologies, and sizes. JVBs serve as miniature reaction vessels that enable sophisticated confined chemical reactions to take place, ultimately resulting in the formations of complex carbon composites. The newly developed approach is highly versatile and can be compatible with a wide range of materials including metals, alloys, and metal compounds. The growth and self-assembly mechanisms of carbon composites via JVBs are explained. For illustration, NiCo alloy nanoparticles are successfully in situ implanted into pomelo vesicles crosslinked carbon (PCC) by JVBs, and their applications as sulfur/carbon cathodes for lithium-sulfur batteries are explored. The well-designed PCC/NiCo-S electrode exhibits superior high-rate properties and enhanced long-term stability. Synergistic reinforcement mechanisms on transportation of ions/electrons of interface reactions and catalytic conversion of lithium polysulfides arising from metal alloy and carbon architecture are proposed with the aid of DFT calculations. The research provides a novel biosynthetic route to rational design and fabrication of carbon composites for advanced energy storage.

Nitrogen-doped hollow carbon spheres decorated with NiCo alloy nanoparticles for high-performance supercapacitor electrode

Nitrogen-doped hollow carbon spheres (NHCSs) decorated with NiCo alloy nanoparticles (NPs) were prepared and examined for their prospective role as high-performance electrode materials. The NHCSs were synthesized through a silica-assisted synthesis method, followed by the decoration of NiCo alloy NPs onto the NHCSs using a simple wet impregnation method, employing a 1:1 M ratio of Co to Ni elements. The NiCo/NHCS-23, composed of NHCSs with 23 wt% of NiCo alloy NPs, exhibited a specific capacitance (Csp) of 536 F g−1 when tested in a 6 M KOH solution at a current density of 1 A g−1. This high Csp is attributed to the synergistic effect of the faradaic charge storage provided by NiCo alloy NPs and the N-doped hollow carbon structure. The N content of the NHCSs and NiCo/NHCS-23 was found to be 1.9 % and 2.2 %, respectively. Symmetric supercapacitor (SSC) devices were assembled using two NiCo/NHCS-23 electrodes and a 0.5 M tetraethylammonium tetrafluoroborate/propylene carbonate electrolyte. The resulting SSC device operated within a potential window of 3.5 V and exhibited an energy density of 16.1 Wh kg−1 at the power density of 250 W kg−1. The SSC device demonstrated impressive cycling stability, maintaining 90.0 % capacitance and 83.1 % Coulombic efficiency after 5000 cycles. These results suggest that NiCo/NHCS nanocomposites have significant potential for utilization in high-energy storage applications.

Noble-Metal-Free Carbon Encapsulated CoNi Alloy Catalyst for the Hydrogenation of 5-(Hydroxymethyl) Furfural to Tetrahydrofurandiol in Aqueous Media.

The selective hydrogenation of 5-(hydroxymethyl)furfural (HMF) into 2,5-bis-(hydroxymethyl)tetrahydrofuran (BHMTHF) in flow reactor using water as a green solvent, has been achieved on a non-noble metal catalyst based on monodispersed CoNi alloy nanoparticles covered by a thin carbon layer. The alloyed catalyst containing CoNi (molar ratio 1 : 1) was prepared in a one-step synthesis following a hydrothermal method. Total conversion of HMF with 91 % selectivity to BHMTHF was achieved. The reaction network has been stablished, in which the carbonyl group of HMF is first reduced to alcohol giving the 2,5-bis-(hydroxymethyl)furan (BHMF) with an apparent activation energy of 25 KJ/mol, and then the double bonds of the furan ring are hydrogenated (apparent Ea=31 KJ/mol). Formation of byproducts, mainly proceed from furan ring opening and ring rearrangement processes of BHMF, promoted by water. BHMTHF resulted a compound highly stable under reaction conditions. The fixed bed flow reactor was maintained operational for 65 h without observing any loss of catalytic activity and selectivity.

Exsoluble Ni–Co alloy nanoparticles anchored on a layered perovskite for direct CO2 electrolysis

It has never been more important to develop new technologies that can reduce CO2 emissions or convert them into useful chemical products. As solid-state electrochemical devices, solid oxide electrolysis cell (SOEC) is capable of converting CO2 efficiently and selectively into CO or, when combined with water electrolysis, producing syngas (CO and H2). Herein, we demonstrate a novel layered perovskite oxide, reduced (La4Sr4)0.9Ti7.2Ni0.4Co0.4O26 (LSTNC-r), decorated by exsolved Ni-Co alloy nanoparticles for high-efficiency CO2 electrolysis. The cell renders a higher activity for electrolysis of CO2 with a current density of 1.53 A cm−2 @2.0 V and 850 °C. Faradic efficiency measurement and stability test suggest that LSTNC-r are promising fuel electrodes for high-efficient CO2 electrolysis.

Selective Reduction of Multivariate Metal-Organic Frameworks for Advanced Electrocatalytic Cathodes in High Areal Capacity and Long-Life Lithium-Sulfur Batteries.

Lithium-sulfur batteries hold great promise as next-generation high-energy-density batteries. However, their performance has been limited by the low cycling stability and sulfur utilization. Herein, we demonstrate that a selective reduction of the multivariate metal-organic framework, MTV-MOF-74 (Co, Ni, Fe), transforms the framework into a porous carbon decorated with bimetallic CoNi alloy and Fe3O4 nanoparticles capable of entrapping soluble lithium polysulfides while synergistically facilitating their rapid conversion into Li2S. Electrochemical studies on coin cells containing 89 wt % sulfur loading revealed a reversible capacity of 1439.8 mA h g-1 at 0.05 C and prolonged cycling stability for 1000 cycles at 1 C/1060.2 mA h g-1 with a decay rate of 0.018% per cycle. At a high areal sulfur loading of 6.9 mg cm-2 and lean electrolyte/sulfur ratio (4.5 μL:1.0 mg), the battery based on the 89S@CoNiFe3O4/PC cathode provides a high areal capacity of 6.7 mA h cm-2. The battery exhibits an outstanding power density of 849 W kg-1 at 5 C and delivers a specific energy of 216 W h kg-1 at 2 C, corresponding to a specific power of 433 W kg-1. Density functional theory shows that the observed results are due to the strong interaction between the CoNi alloy and Fe3O4, facilitated by charge transfer between the polysulfides and the substrate.

Substrate-Free Growth of N-Doped Bamboo Tube Morphology on CoNi Alloy Nanoparticles as an Electrocatalyst for Anion Exchange Membrane Fuel Cells

In the realm of fuel cell technology, the quest for durable and economical electrocatalysts persists as a critical endeavour. Herein, we introduce a durable electrocatalyst boasting a resilient knotted bamboo...

Carbon nanotubes with CoNi alloy nanoparticles growing on porous carbon substrate as cathode for Li-CO2 batteries

The over-exploitation of fossil fuels and rapid industrialization has released a large number of carbon dioxide. As a major greenhouse gas, it can induce the increasing global temperature and result in environmental issues. It is an urgent necessity to reduce carbon dioxide emission and increase carbon capture, utilization and storage. Li-CO2 battery can be used for the fixation and conversion of carbon dioxide to electrochemical energy. However, it is necessary to explore and design efficient catalysts, due to the low electronic conductivity and sluggish decomposition kinetics for lithium carbonate as the discharge product. Herein, carbon nanotubes with CoNi alloy nanoparticles growing on porous carbon substrate (PC/CoNi-CNTs) is designed by immersing porous melamine formaldehyde sponge into cobalt nitrate and nickel chloride solution with the subsequent carbonization. The porous structure of carbon substrate facilitates the electrolyte infiltration and carbon dioxide diffusion. The carbon nanotubes and CoNi alloy catalysts can efficiently enhance the reversible deposition and decomposition of lithium carbonate and carbon, taking advantage of their synergistic effect. At a current density of 0.05 mA cm−2, the terminal discharge and charge voltages are 2.76 and 4.23 V with a limited specific capacity of 0.2 mA h cm−2, respectively. These results demonstrat that the design of carbon nanotubes with alloy nanoparticles on porous carbon substrate as cathode can enhance the electrochemical performances of Li-CO2 battery.

Convenient Synthesis of NiCo Alloy Nanoparticles Encapsulated by N-Doped Porous Carbon for the Oxygen Evolution Reaction

Convenient Synthesis of NiCo Alloy Nanoparticles Encapsulated by N-Doped Porous Carbon for the Oxygen Evolution Reaction