Ni-Fe Catalysts Research Articles

Influence of ZrO2 crystal structure on the catalytic performance of Fe-Ni catalysts for CO2-assisted ethane dehydrogenation reaction

The catalytic reaction of ethane with CO2 promotes the value-added conversion of natural gas and the resource utilization of greenhouse gases. In this work, the CO2-assisted ethane dehydrogenation reaction characteristics on Fe1.5Ni0.5/ZrO2(M, T, Mix) catalyst with different crystal plane structure were studied through catalyst activity test, catalytic reaction kinetics study and catalyst characterization analysis. It is found that the exposed crystal faces of the ZrO2-supported catalyst has a significant effect on the CO2-assisted ethane oxidative dehydrogenation reaction. The monoclinic phase Fe1.5Ni0.5/ZrO2-M catalyst exhibits the largest conversion of ethane (21.8%) and CO2 (25.2%) and the maximum selectivity to C2H4 (80.5%). Monoclinic phase of ZrO2 selectively exposes the (−111) and (111) low-index surfaces with higher oxygen vacancy (Ov) density and stronger metal-support interaction, which leads to the formation of more FexZr1-xO2 structures with high catalytic activity. The reductive oxygen vacancy Ov and Fe2+-O-Zr3+ sites promote the activation of CO2 through the cleavage of C=O bond to supplement O* species. The O* species on the oxidative Fe3+-O-Zr4+ site are captured and combined with H* species derived from the selective cleavage of ethane C–H bond to generate H2O.

Anion-Exchange Membrane Water Electrolyzers.

This Review provides an overview of the emerging concepts of catalysts, membranes, and membrane electrode assemblies (MEAs) for water electrolyzers with anion-exchange membranes (AEMs), also known as zero-gap alkaline water electrolyzers. Much of the recent progress is due to improvements in materials chemistry, MEA designs, and optimized operation conditions. Research on anion-exchange polymers (AEPs) has focused on the cationic head/backbone/side-chain structures and key properties such as ionic conductivity and alkaline stability. Several approaches, such as cross-linking, microphase, and organic/inorganic composites, have been proposed to improve the anion-exchange performance and the chemical and mechanical stability of AEMs. Numerous AEMs now exceed values of 0.1 S/cm (at 60–80 °C), although the stability specifically at temperatures exceeding 60 °C needs further enhancement. The oxygen evolution reaction (OER) is still a limiting factor. An analysis of thin-layer OER data suggests that NiFe-type catalysts have the highest activity. There is debate on the active-site mechanism of the NiFe catalysts, and their long-term stability needs to be understood. Addition of Co to NiFe increases the conductivity of these catalysts. The same analysis for the hydrogen evolution reaction (HER) shows carbon-supported Pt to be dominating, although PtNi alloys and clusters of Ni(OH)2 on Pt show competitive activities. Recent advances in forming and embedding well-dispersed Ru nanoparticles on functionalized high-surface-area carbon supports show promising HER activities. However, the stability of these catalysts under actual AEMWE operating conditions needs to be proven. The field is advancing rapidly but could benefit through the adaptation of new in situ techniques, standardized evaluation protocols for AEMWE conditions, and innovative catalyst-structure designs. Nevertheless, single AEM water electrolyzer cells have been operated for several thousand hours at temperatures and current densities as high as 60 °C and 1 A/cm2, respectively.

Fabrication of vertical graphene-loaded nickel-iron nanoparticles and their oxygen evolution reaction performance

<p indent="0mm">In recent years, the rapid consumption of traditional fossil fuels such as coal, oil and natural gas has caused inevitable harm to the environment. Hydrogen and other clean energy have attracted increasing attention. Electrolysis of water is one of the most promising technologies for hydrogen production compared with other techniques. However, due to the anode oxygen evolution reaction (OER) with slow dynamics, the catalysts such as RuO₂ and IrO₂ are not only expensive but also limited in reserve. Therefore, it is significant and urgent to develop OER catalysts with low cost and excellent catalytic activity and stability. As a representative transition metal, Ni is abundant on the earth and has excellent corrosion resistance. It is usually combined with Fe to prepare Ni-Fe oxides, hydroxides, sulfides, phosphating compounds and Ni-Fe alloys that can catalyze OER efficiently. From the view of catalytic kinetics, it is beneficial to construct the catalyst structure and reasonably design the specific morphology of nanomaterials. In other words, the activity of the electrocatalyst can be improved by increasing the number of active sites on a given electrode reasonably. In order to improve the catalytic activity of Ni-Fe catalytic system, a variety of processes have been developed to regulate the morphology and increase the number of active sites. Most of these processes focus on hydrothermal or calcination methods, which take a long time. Therefore, a simple and efficient method for preparing Ni-Fe catalysts with high catalytic activity for OER remains to be developed. Unlike the other three states (gas, liquid, and solid), plasma is composed of a mixture of electrons, ions, radicals and neutral particles. Compared with traditional methods, plasma-assisted modification (e.g., plasma etching, doping, and other surface treatments) and plasma-assisted synthesis (e.g., deposition, conversion, and decomposition) are becoming powerful tools for producing catalyst materials. Herein, vertical graphene nanosheets (VG) were prepared by plasma-enhanced chemical vapor deposition (PECVD). Then, Ni-Fe alloy nanoparticles were prepared by electrodeposition on the surface of VG as the active materials. The morphology and composition of the Ni-Fe electrocatalyst were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectrometry (EDS), Raman and X-ray photoelectron spectroscopy (XPS). Electrochemical workstation was used to characterize its electrocatalytic performance as OER catalyst. The overpotential of the catalyst for OER was obtained by linear sweep voltammetry (LSV), and the electrochemical active surface area (ECAS) was assessed by cyclic voltammetry (CV). The stability of the catalyst was also tested. The results show that the prepared nanocatalyst has excellent properties. In the solution of <sc>1 mol L^–1</sc> KOH, the overpotential is only 242 mV at <sc>10 mA cm^–2,</sc> the slope of Tafel is 43.13 mV dec^–1, and the stability is pretty good. This is mainly due to the open array structure of graphene nanosheets with small size of Ni-Fe nanoparticles, which is beneficial to mass transfer and gas diffusion. The synergistic structure has a large specific surface, so the catalyst exposes more active sites. The efficient method of preparation will provide an important technical basis for the preparation of transition metal-based OER nanocatalysts.

High-entropy metal carbide nanowires

The development of high-entropy ceramic nanomaterials has significant scientific and technological potential, yet studies on these materials are rare. Here, we successfully synthesize (Hf0.25Ta0.25Nb0.25Ti0.25)C high-entropy metal carbide (HEC-1) nanowires—a class of high-entropy ceramic nanomaterials—via a facile bamboo-based carbothermal method with an Fe-Ni catalyst. The growth of HEC-1 nanowires occurs through a classical vapor-liquid-solid mechanism based on the solubility of metal, carbon, and HEC-1 in the Fe-Ni alloy. After high-temperature treatment, HEC-1 nanowires show good thermal stability without morphological evolution below 1,600°C, while they evolve into “pearl-necklace”’-like nanostructures or particles above 1,600°C due to the Rayleigh instability mechanism. After high-pressure treatments, HEC-1 nanowires are broken into nanorods above 1 GPa, in which brittle fracture without any dislocations, slip bands, or amorphous shear bands is directly observed at nano and atomic scales.

From Nickel Foam to Highly Active NiFe‐based Oxygen Evolution Catalysts

AbstractA key challenge for the large‐scale application of the oxygen evolution reaction (OER) is the synthesis of active, cheap and robust catalysts. Here, a straightforward procedure to form novel porous and highly active multimetallic oxygen evolution catalysts was reported. They were derived from an original dendritic nickel foam (NiNF) using two strategies: i) Fe‐doping; and ii) Fe/Cr‐doping. A bimetallic NiFe catalyst, formed through controlled acid treatment followed by a simple galvanic exchange procedure proved remarkably active in 1 m KOH with a very low overpotential value of η200=276 mV at 200 mA cm−2 and a very low Tafel slope of 25 mV dec−1. A trimetallic FeNiCr catalyst, containing 11 % Cr, was also synthesised through electrodeposition and partial Cr leaching, to form a stable OER catalyst displaying a very low overpotential value of η200=279 mV at 200 mA cm−2 and a Tafel slope of 29 mV dec−1. These two novel catalysts are among the best performing OER catalysts reported so far.

Bimetallic Ni-Fe catalysts for methanation of CO2: Effect of the support nature and reducibility

A series of Ni-Fe bimetallic catalysts supported on high surface area of Ce0.8Zr0.2O2 (CZ) and SiO2 (S) were prepared by impregnation (10 wt% of metal charge) with different Ni:Fe ratios (10:0, 9:1, 3:1 and 1:1) and the effect of Fe content on promotion of CO2 methanation was investigated. Hydrogen reduction favors Fe incorporation into the Ni structure, forming Ni1−xFex alloys, whereas some Fe-O species remain unreduced. Ni-Fe/CZ catalysts showed a promoted reducibility at low temperature as well as high density of weak and medium basic sites in comparison with Fe-Ni/S catalysts. Activity tests revealed that CO2 conversion and CH4 selectivity increases with the decrease of Fe content. In the bimetallic catalysts, the presence of unreduced Fe-O species restricts the contact between hydrogen supplied by Ni1−xFex and adsorbed CO2. Superior activity of Ni/CZ was associated to the close location of medium basic sites and Ni nanoparticles to activate hydrogen. Microstructural studies of Ni/CZ catalyst after prolonged operation demonstrated the absence of carbon deposition and good Ni availability on the CZ surface.

Zn constructs micro/nano porous structure to boost efficient oxygen evolution reaction for bulk NiFe alloy

Oxygen evolution reaction (OER) electrocatalysts play an important role in producing high purity hydrogen fuels in the water splitting reaction. However, developing bulk catalytic electrode with low-cost and efficient activity for OER is still a challenge. In this paper, the porous bulk NiFe alloys with nanosheet structure were fabricated by a facile microwave sintering powder metallurgy method coupled with Zn as space holder. The obtained porous bulk Ni0.75Fe0.25 alloy exhibits the high catalytic activity for OER with a low overpotential of 235 mV at 100 mA cm−2, a small Tafel slope of 26.1 mV dec−1 and superior stability in 1.0 M KOH. In addition, the residual Zn in the porous NiFe alloy can be dissolved to further improve the specific surface area, and a metal (oxy)hydroxide amorphous layer is formed through electrochemical self-reconstruction during the OER process. This Zn-doped porous bulk NiFe catalyst with high OER catalytic performance and outstanding stability can become a promising candidate for commercial water splitting.

Interfacial Atom‐Substitution Engineered Transition‐Metal Hydroxide Nanofibers with High‐Valence Fe for Efficient Electrochemical Water Oxidation

Developing low‐cost electrocatalysts for efficient and robust oxygen evolution reaction (OER) is the key for scalable water electrolysis, for instance, NiFe‐based materials. Decorating NiFe catalysts with other transition metals offers a new path to boost their catalytic activities but often suffers from the low controllability of the electronic structures of the NiFe catalytic centers. Here, we report an interfacial atom‐substitution strategy to synthesize an electrocatalytic oxygen‐evolving NiFeV nanofiber to boost the activity of NiFe centers. The electronic structure analyses suggest that the NiFeV nanofiber exhibits abundant high‐valence Fe via a charge transfer from Fe to V. The NiFeV nanofiber supported on a carbon cloth shows a low overpotential of 181 mV at 10 mA cm−2, along with long‐term stability (>20 h) at 100 mA cm−2. The reported substitutional growth strategy offers an effective and new pathway for the design of efficient and durable non‐noble metal‐based OER catalysts.

Interfacial Atom‐Substitution Engineered Transition‐Metal Hydroxide Nanofibers with High‐Valence Fe for Efficient Electrochemical Water Oxidation

AbstractDeveloping low‐cost electrocatalysts for efficient and robust oxygen evolution reaction (OER) is the key for scalable water electrolysis, for instance, NiFe‐based materials. Decorating NiFe catalysts with other transition metals offers a new path to boost their catalytic activities but often suffers from the low controllability of the electronic structures of the NiFe catalytic centers. Here, we report an interfacial atom‐substitution strategy to synthesize an electrocatalytic oxygen‐evolving NiFeV nanofiber to boost the activity of NiFe centers. The electronic structure analyses suggest that the NiFeV nanofiber exhibits abundant high‐valence Fe via a charge transfer from Fe to V. The NiFeV nanofiber supported on a carbon cloth shows a low overpotential of 181 mV at 10 mA cm−2, along with long‐term stability (&gt;20 h) at 100 mA cm−2. The reported substitutional growth strategy offers an effective and new pathway for the design of efficient and durable non‐noble metal‐based OER catalysts.

Comparative study of mineral with different structures supported Fe-Ni catalysts for steam reforming of toluene

Four abundant minerals with different structures including diatomite (De), montmorillonite (Mt), halloysite (Hal), and sepiolite (Sep), were used as the supports to prepare Fe-Ni based catalysts. The catalytic performances of these catalysts for steam reforming of toluene (SRT) were tested in a fixed-bed reactor under different conditions. The effects of S/C molar ratio, long-term stability and catalytic deactivation and regeneration were explored under the optimal condition, and the kinetic parameters were also determined. The fresh and spent catalysts were characterized using XRD, FT-IR, H2-TPR, BET, SEM, TEM, Raman spectroscopy and TG analyzer. The results showed that Fe3Ni8/De displayed the best catalytic activity with the highest toluene conversion and gas yields compared to those of Fe3Ni8/Hal, Fe3Ni8/Mt, and Fe3Ni8/Sep. The increase of the reaction temperature and S/C molar ratio apparently favored the catalytic activity and stability of the catalysts for SRT. The best catalytic performance of Fe3Ni8/De for SRT was achieved at the reaction temperature of 700 °C under the S/C molar ratio of 1.0. The apparent activation energy and pre-exponential factor for Fe3Ni8/De were determined to be 53.76 kJ⋅mol−1 and 2.72 × 105 m3⋅kg−1⋅h−1. The characterization of the spent catalysts indicated the high dispersion of Fe-Ni alloy and relatively low coke deposition of Fe3Ni8/De.

Pyrolysis of biomass Tar model compound with various Ni-based catalysts: Influence of promoters characteristics on hydrogen-rich gas formation

This paper studied the conditions and mechanism of hydrogen-rich gas produced from catalytic pyrolysis of toluene by various Ni-based catalysts in a fixed-bed reactor. We specifically focused on the effect of different promoters and promoter characteristics on the physicochemical properties of Ni/HZSM-5 -based catalyst. The results revealed that, a similar initial activity for Ni-catalysts modified different promoters was tested with toluene conversion higher than 85%. The Fe-modified Ni/HZSM-5 catalyst has the most effective catalyst for hydrogen-rich gas production with the gaseous efficiency of 63.4 wt%, mainly gas (H2, CH4) yield of 118.6 mL/g-toluene, H2 yield of 53.4 mL/g-toluene at 800 °C pyrolysis for 40 min. The smaller crystal particles (3.1 nm), high surface area (219.5 m2/g), and sufficient loading quality (4 wt%) for Ni–Fe catalysts provided efficient active sites and promoted the pyrolysis process of toluene. The activity and stability of catalysts were also improved by Ce-modified Ni/ZSM-5 catalyst with the highest gaseous efficiency of 68.0 wt%, but the H2 yield of 40.3 mL/g-toluene was lower. However, Ni–Mg/HZSM-5 catalyst has lowest activity and stability. The catalyst deactivation is associated with nickel sintering and coke formation. After the Ni–Fe/HZ5 catalyst was regenerated twice, it still maintained high catalytic activity.

Fluoride mediated conversion of FeOOH into NiFeOOH for outstanding oxygen evolution reaction

By the use of different concentrations of F, we modulate the structure of NiFe catalysts to have a hybrid structure composed of different phases involved in Oxygen Evolution Reaction (OER) process. For the first time, in-situ Raman spectroscopy was used to study the structural change of the NiFe catalyst, associated with the effects of the concentration of F during the OER process. At a moderate concentration of F, it was found that; (1) the catalysts have a well-conductive hybrid structure composed of NiFeOOH (474 cm−1 and 544 cm−1), FeOOH (715 cm−1) and NiF2 (310 cm−1) phases, and (2) F promotes an optimum mass ratio between Ni and Fe, which helps in the collaborative operation between Ni and Fe. This led to generation of catalysts with an optimum structure portraying excellent OER performance. Specifically, the synthesized catalysts required explicit low overpotential of 259 mV to generate current density of 100 mAcm−2, Tafel slope of 60.3 mVdec−1, high charge transfer rate signified by low resistance of 1.46 Ω, and high number of active OER sites implied by large double layer capacitance of 2.90 mF. This study shades light to the understanding of the involved vital phases of F-NiFe catalysts and how F mediates the active phases during the OER process, hence contributing to the knowledge required for the designing of better catalysts for future electrodes.

Investigating the Influences of Metal-Support Interaction in Ni-Fe Catalysts on the Quality of Carbon Nanomaterials from Waste Polypropylene

Investigating the Influences of Metal-Support Interaction in Ni-Fe Catalysts on the Quality of Carbon Nanomaterials from Waste Polypropylene

High-performance and stable BiVO4 photoanodes for solar water splitting via phosphorus–oxygen bonded FeNi catalysts

The phosphorus–oxygen bonded FeNi catalysts on BiVO4 photoanodes significantly promote the PEC water oxidation activity and stability, achieving a photocurrent density of 6.73 mA cm−2 (1.23 VRHE, AM 1.5G).

Biomass-Derived Bimetallic Ni-Fe Catalyst with Enhanced Tar Removal Performance

Biomass-Derived Bimetallic Ni-Fe Catalyst with Enhanced Tar Removal Performance

Deep eutectic solvent-induced synthesis of Ni–Fe catalyst with excellent mass activity and stability for water oxidation

Ni–Fe bimetallic electrodes are currently recognized as a kind of benchmark transition metal-based oxygen evolution reaction (OER) electrocatalysts. Facile synthesis of Ni–Fe bimetallic electrode materials with excellent catalytic activity and satisfied stability by a simple and low-cost route is still a big challenge. Herein, well-defined Ni–Fe nanoparticles in-situ developed on a planar Fe substrate (Ni–Fe NPs/Fe) is fabricated via a facile one-step galvanic replacement reaction (GRR) carried out in an Ethaline-based deep eutectic solvent (DES). The prepared Ni–Fe NPs/Fe exhibits outstanding OER performance, which needs an overpotential of only 319 mV to drive a current density of 10 mA cm−2, with a small Tafel slope of 41.2 mV dec−1 in 1.0 mol L−1 KOH, high mass activity (up to 319.78 A g−1 at an overpotential of 300 mV) and robust durability for 200 h. Impressively, the Ni–Fe bimetallic oxygen-evolution electrode obtained from the Ethaline-based DES is catalytically more active and durable than that of its counterpart derived from the 4.2 mol L−1 NaCl aqueous solution. The reason for this is mainly related to the different morphology and surface state of the Ni–Fe catalysts obtained from these different solvent environments, particularly for the differences in phy–chemical properties, active species formed and deposition kinetics, offered by the Ethaline-based DES.

Plasma-catalytic carbon dioxide conversion by reverse water–gas shift over La0.9Ce0.1B0.5B’0.5O3-δ perovskite-derived bimetallic catalysts

Reverse water–gas shift (RWGS) reaction is one of the most promising and feasible CO2 utilization strategy to generate CO, which together with renewable H2 could be employed for Fischer-Tropsch synthesis. In this study, RWGS over La0.9Ce0.1B0.5B’0.5O3-δ perovskite-derived bimetallic (Ni-Cu, Ni-Fe and Fe-Cu) catalysts as well as the corresponding Cu-, Ni- and Fe-based monometallic catalyst were investigated in a dielectric barrier discharge (DBD) plasma-catalysis system. The result demonstrated that the plasma-catalysis system is of great potential in promoting RWGS reaction at low temperature and atmospheric pressure. Among different catalysts, La0.9Ce0.1Ni0.5Cu0.5O3-δ (LCNCO) and La0.9Ce0.1Ni0.5Fe0.5O3-δ (LCNFO) exhibited higher catalytic performance in terms of CO2 conversion (27.3–53.7% for LCNCO and 26.8–51.4% for LCNFO) and CO selectivity (59.4–94.9% for LCNCO and 58.0–91.8% for LCNFO). Their superior performance should be attributed to the formation of Ni-(Cu, Fe) alloy with smaller particle size, which facilitated the activation of H2 and its spillover to nearby oxygen vacancies. In addition, the abundant oxygen vacancies of LCNCO and LCNFO provided sufficient active sites for CO2 adsorption, promoting the selective dissociation of CO2 to CO.

Assessing the impact of textural properties in Ni–Fe catalysts for CO2 methanation performance

In heterogeneous catalysis, the benefits of employing adequate textural properties on the catalytic performances are usually stated. Nevertheless, the quantification of the extent of improvement is not an easy task since variations on the catalysts' specific areas and pore structures might involve modifications on a number of other surface catalytic features. This study establishes the impact of the catalyst textural properties on the CO2 methanation performance by investigating bimetallic Ni–Fe catalysts supported over carbon supports with different textural properties regarding surface area and pore structure. The comparable metal loading and dispersions attained for all systems enabled establishing forthright relationships between the catalyst textural properties and CO2 methanation rate. Once the influence of the external mass diffusions on the catalysts’ performance was experimentally discarded, the estimated Thiele modulus and internal effectiveness (φ and ηEff) values showed that the catalyst performance was majorly governed by the surface reaction rate whilst the pore size affected in no significant manner within the examined range (Dpore = 10.2 to 5.8 nm). Therefore, the rapport between the catalyst performance and surface area was quantified for the CO2 methanation reaction over Ni–Fe catalysts: increasing the surface area from 572 to 802 m2/g permit obtaining ca. 10% higher CO2 conversions.

Exploration of electrocatalytic water oxidation properties of NiFe catalysts doped with nonmetallic elements (P, S, Se)

The introduction of non-metallic atoms (P, S, Se) has emerged as an effective way to improve the catalytic activity of transition metal based layered double hydroxides (LDHs) for oxygen evolution reaction. However, objective comparisons of the performance of heteroelement-doped catalysts are complicated by the lack of standardization both in the electrochemical tests and physicochemical analysis. Herein, we use a unified protocol for evaluating the catalytic activities of heteroelement-doped NiFe-LDHs and explore the reasons for the differences in their catalytic performance. Some regular results are found from comparing the properties of the heteroelement-doped catalysts: (1) the introduction of P/S/Se can optimize the redox behaviors of Ni species, which is conducive to regulating adsorption energy of intermediates and the formation of high-valent active sites; (2) the specific area of catalysts was expanded after heteroelements doping, ensuring a more favorable structure for heterogeneous catalysis; (3) All P/S/Se-doped catalysts showed better activities when compared to the original NiFe LDHs in alkaline solutions, and the catalysts doped with S showed the best performance (Se < P < S).

Advanced Rechargeable Zinc-Air Batteries with Precious Metal Free Catalysts

Rechargeable zinc-air batteries (ZABs) could be promising energy storage devices with high energy and power density, enabling safe and cost-effective operation. ZABs have higher practical specific energy compared to traditional aqueous and lithium-ion batteries [1]. The schematic of rechargeable of ZAB is shown in Figure 1a. The main challenge of the electrically rechargeable ZABs in alkaline electrolytes is the limitation during recharging [2, 3]. The performance of ZAB largely depends on oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Figure 1a shows that the cell rechargeability is realized by the OER and design of the Zn electrode. Hence, advances of the air electrode enabled by bifunctional catalysts as well as the development of the Zn electrode are important.In this presentation, we will discuss rechargeable ZAB with novel NiCo and NiFe catalysts, as well as an advanced Zn electrode that is created with a hybrid method using electrodeposition and powder coating. These catalysts were pre-scanned by using rotating disk electrode (RDE) in the alkaline solution, as shown in Figure 1b. NiCo and NiFe exhibited high catalytic activity towards OER but not towards ORR. These catalysts were applied and tested in the in-house designed ZAB cell. The Zn electrode was made by coating the Zn power on the CuZn mesh that was prepared by electrodeposition. The ZAB in a two-electrode configuration exhibited a discharge cell voltage of ~0.8 V at 20 mA/cm2 (3 hours cycle time), as shown in Figure 1c. To determine which electrode is limiting the efficiency, an additional Zn reference electrode was introduced into the cell to setup a four-electrode configuration. The additional reference is inserted into the cathode compartment enable measurement of the overpotential in solution and for the oxygen electrode. Test results, for different types of catalyst and Zn electrodes will be shown and discussed.