Amorphous NiFe Research Articles

In Situ Anodic Oxidation Tuning of NiFeV Diselenide to the Core-Shell Heterojunction for Boosting Oxygen Evolution.

Developing non-noble metal-based core-shell heterojunction electrocatalysts with high catalytic activity and long-lasting stability is crucial for the oxygen evolution reaction (OER). Here, we prepared novel core-shell Fe,V-NiSe2@NiFe(OH)x heterostructured nanoparticles on hydrophilic-treated carbon paper with high electronic transport and large surface area for accelerating the oxygen evolution rate via high-temperature selenization and electrochemical anodic oxidation procedures. Performance testing shows that Fe,V-NiSe2@NiFe(OH)x possesses the highest performance for OER compared to as-prepared diselenide core-derived heterojunctions, which only require an overpotential of 243 mV at 10 mA cm-2 and a low Tafel slope of 91.6 mV decade-1 under basic conditions. Furthermore, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) confirm the morphology and elementary stabilities of Fe,V-NiSe2@NiFe(OH)x after long-term chronopotentiometric testing. These advantages are largely because of the strong synergistic effect between the Fe,V-NiSe2 core with high conductivity and the amorphous NiFe(OH)x shell with enriched defects and vacancies. This study also presents a general approach to designing and synthesizing more active core-shell heterojunction electrocatalysts for OER.

Facile synthesis of amorphous bimetallic hydroxide on Fe-doped Ni3S2 as an active electrocatalyst for oxygen evolution reaction

The design and synthesis of efficient and earth-abundant nonprecious metal electrocatalyst for oxygen evolution reaction (OER) plays a vital role in electrocatalytic water splitting. Here, amorphous NiFe layered double hydroxide (LDH) nanosheets deposited on Fe doped Ni 3 S 2 nano-ridges (Fe-Ni 3 S 2 @NiFe LDH) are successfully synthesized through a simple hydrothermal-electrodeposition method and are applied as OER electrocatalysts. In addition, benefiting from the abundant electroactive sites, electronic effect induced by Fe-doping and synergistic effect between NiFe LDH and Fe-Ni 3 S 2 , the as-prepared Fe-Ni 3 S 2 @NiFe LDH heterogeneous catalyst can exhibit excellent OER performance in 1.0 M KOH solution. Fe-Ni 3 S 2 @NiFe LDH only reach an overpotential of 192 mV at the current density of 10 mA cm − 2 with a Tafel slope of 43.1 mV dec −1 . Notably, as-obtained Fe-Ni 3 S 2 @NiFe LDH electrocatalyst only requires a low overpotential of 217 mV to achieve a current density of 50 mA cm − 2 . And Fe-Ni 3 S 2 @NiFe LDH also exhibits excellent durability at 50 mA cm −2 in 1.0 M KOH at room temperature. This study provides a feasible approach for the design of highly efficient earth-abundant nonprecious metal electrocatalysts for OER. Three-dimensional architecture Fe-Ni 3 S 2 @NiFe LDH heterojunctions are successfully fabricated by hydrothermal and electrodeposition methods. Fe-Ni 3 S 2 @NiFe LDH heterojunctions can be used as high efficient and stable electrocatalysts for oxygen evolution reaction. • Three-dimensional Fe-Ni 3 S 2 @NiFe LDH heterojunctions were constructed by hydrothermal and electrodeposition methods. • Fe-Ni 3 S 2 @NiFe LDH exhibits remarkable OER activity and stability. • The Fe-Ni 3 S 2 @NiFe LDH is based on non-noble metals and shows better performance than RuO 2 .

Controlled direct electrodeposition of crystalline NiFe/amorphous NiFe-(oxy)hydroxide on NiMo alloy as a highly efficient bifunctional electrocatalyst for overall water splitting

The synthesis of an electrocatalyst with high activity, long lifetimes, low cost, bifunctional ability, and facile fabrication strategy simultaneously for overall water splitting is urgent and remains a grand challenge. Herein, a controlled direct electrodeposition strategy is developed to deposit the heterogeneous crystalline NiFe (cNF)/amorphous NiFe-(oxy)hydroxide (aNFO) standing nanosheets on the NiMo modified substrate (NM@cNF/aNFO) as a highly efficient bifunctional electrocatalyst for overall water splitting. The precise control of electrodeposition voltage can tune the component ratio of cNF and aNFO and the yield of cNF/aNFO nanosheets, and −3.5 V is the optimal voltage. The ultrafine NiFe nanocrystals with good electronic conductivity and abundant edges, the amorphous NiFe-(oxy)hydroxide support with rich nanosized pores and defects, and the firm grasp of the NiMo alloy toward the standing nanosheets generate complex synergistic effects, rendering abundant active sites, fast charge and mass transfer, and excellent electrochemical stability. NM@cNF/aNFO can achieve 20 mA cm−2 at a low overpotential of 133.2 mV with a small Tafel slope of 19.9 mV dec−1 for oxygen evolution reaction and 91.9 mV with 59.9 mV dec−1 for hydrogen evolution reaction. Accordingly, NM@cNF/aNFO as both anode and cathode delivers 10 mA cm−2 at a cell voltage of 1.45 V and prominent stability for over 100 h even at 100 mA cm−2. Our work demonstrates a facile voltage-controlled electrodeposition strategy for the design of highly active, cost-effective, stable, and bifunctional electrocatalysts for water splitting.

One-step fabrication of amorphous Ni-Fe phosphated alloys as efficient bifunctional electrocatalysts for overall water splitting

Herein, the amorphous Ni-Fe-P alloys with different phosphorus concentrations were fabricated by the one-step electrodeposition, and the electrocatalytic activities toward hydrogen and oxygen evolution reaction (HER and OER) were evaluated in alkaline solution. It was found that the doped phosphorus played an important role in the formation of amorphous structure and improving active sites. The Ni-Fe-P electrocatalysts with the optimized phosphorus concentration exhibited the simultaneously enhanced HER and OER performances. Furthermore, Ni-Fe-P electrocatalysts as the bifunctional electrodes displayed the excellent water splitting performance and durability with a cell potential of 1.71 V (on Cu sheet) and 1.59 V (on Ni foam) reaching 10 mA·cm−2 significantly better than that of as-synthesized Ni-Fe alloys. Additionally, the boosting electrocatalytic performance was discussed in detail. The simultaneous improving HER and OER performances of Ni-Fe-P electrocatalyst might broaden the horizon in designing the highly efficient and earth-abundant electrocatalyst to produce hydrogen by electrocatalytic water splitting.

Amorphous-Amorphous Coupling Enhancing the Oxygen Evolution Reaction Activity and Stability of the NiFe-Based Catalyst.

Efficient and stable electrocatalytic water splitting plays a critical role in energy storage and conversion but is strongly restricted by the low activity and stability of catalysts associated with the complicated oxygen evolution reaction (OER). This work provides a strategy to fabricate an advanced NiFe-based catalyst to steadily speed up the OER based on a strong amorphous-amorphous coupling effect generated through amorphous CuS that induces the formation of amorphous NiFe layered double hydroxide (LDH) nanosheets (A-NiFe NS/CuS). The presence of the strong coupling effect not only modifies the electronic structure of catalytic sites to accelerate the reaction kinetics but also enhances the binding between the catalyst and substrate to strengthen the durability. In comparison to well-grown core-shell crystalline NiFe LDH on CuO, the as-synthesized amorphous A-NiFe NS/CuS gives a low overpotential of 240 mV to achieve 100 mA cm-2 and shows robust stability under 100 h of operation at the same current density. Therefore, amorphous-amorphous coupling between catalyst-substrate by elaborate and rational engineering yields an opportunity to design efficient and robust NiFe-based OER catalysts.

Electrochemical deposited amorphous FeNi hydroxide electrode for oxygen evolution reaction

The electrodeposition approach is significant in electrode fabrication for practical application. Herein, the electrodeposited amorphous NiFe hydroxide species for oxygen evolution reaction (OER) in water splitting reaction is demonstrated by revealing the synergistic effect influenced by the support electrode of Fe and Ni foil and the contents of Fe and Ni in the electrolyte. All the electrodeposited samples have an amorphous structure and similar profiles of binding energy and chemical states for Fe and Ni as characterized by the spectroscopic techniques. While the support effect and Fe/Ni synergistic effect are indeed observed for the varied catalytic performances observed for the different electrodes; the Ni foil supported catalyst exhibits much higher performance than that of the Fe foil supported catalyst, and the different redox potentials of Ni species in the different Fe/Ni electrode resulting from the Fe–Ni synergism are observed in the cyclic voltammetry curve analysis. The surface roughness and the electrochemical surface area are also influenced by the support effect and the Fe/Ni ratio in the plating electrolyte. The optimal electrode shows a very low overpotential of ∼200 mV to reach 10 mA cm−2, and very high catalytic stability by the consecutive cyclic voltammetry measurements and 20 h stability test. Though it has the largest electrochemical surface area, the highest catalytic efficiency for these active sites is also indicated by the specific activity and turnover frequency polarization curves. The current work shows the effective experience for the electrodeposited Fe/Ni based catalysts in large-scale fabrication, which can be more practical for hydrogen generation in the alkaline water electrolysis.

Facile Preparation of Amorphous Nife Hydroxide by Corrosion Engineering for Electrocatalytic Water and Urea Oxidation

Facile Preparation of Amorphous Nife Hydroxide by Corrosion Engineering for Electrocatalytic Water and Urea Oxidation

Amorphous–crystalline FeNi2S4@NiFe–LDH nanograsses with molten salt as an industrially promising electrocatalyst for oxygen evolution

The hydrolysis of S ion FeNi2S4 can promote the in-situ formation of ultrathin amorphous NiFe–LDH grown in situ on crystalline FeNi2S4, which can not only improve activity but also significantly enhance stability for oxygen evolution reaction.

Core-shell trimetallic NiFeV disulfides and amorphous high-valance NiFe hydroxide nanosheets enhancing oxygen evolution reaction

Developing highly efficient, stable, and earth-abundant heterogeneous electrocatalysts for the oxygen evolution reaction (OER) is a significant challenge. Herein, we designed and synthesized a novel core–shell trimetallic Ni0.70Fe0.10V0.20S2 @ amorphous NiFe hydroxide for enhancing OER kinetics using thermal sulfidation and in situ electrochemical tuning methods. Electrochemical testing of various as-prepared catalysts at the same mass loading demonstrated that the trimetallic Ni0.70Fe0.10V0.20S2 @ amorphous NiFe hydroxide possessed the highest intrinsic activity for the OER compared to other reference catalysts. Furthermore, the heterostructures are directly grown on a carbon paper with a high surface area and good conductivity to form an integrated 3D electrode with an overpotential of 204 mV at the current density of 10 mA cm-2 and a small Tafel slope of 39 mV dec-1 in 1.0 M KOH electrolyte. This is one of the most effective OER electrocatalysts. X-ray photoelectron spectroscopy and scanning electron microscopy indicated that the material structure and chemical composition of Ni0.70Fe0.10V0.20S2 @ amorphous NiFe hydroxide exhibited good stability under harsh OER conditions. These advantages could be mainly attributed to the synergistic effect between the core and shell, high electronic conductivity of the core, and more active sites on the surface of the amorphous shell. Additionally, this study provides novel insights for designing and synthesizing heterostructure multimetallic disulfides electrocatalysts for OER in the future.

Crystallinity Effect of NiFe LDH on the Growth of Pt Nanoparticles and Hydrogen Evolution Performance.

NiFe layered double hydroxides (LDHs) usually exhibit high water-dissociation ability in the alkaline media and also provide an ideal substrate for anchoring noble metals, such as platinum (Pt), due to the 2D microstructure. Appropriate regulation of the interaction between Pt and substrate could enhance the intrinsic activity of composite catalysts toward the hydrogen evolution reaction (HER) in the alkaline media. Herein, we electrodeposit Pt nanoparticles on amorphous NiFe LDH (Pt/NiFe-ED) or crystalline NiFe LDH (Pt/NiFe-HD) to regulate the interaction between Pt and NiFe LDH. Experimental results reveal that Pt nanoparticles on NiFe-ED are smaller than those on NiFe-HD and possess a narrower size distribution. Thus, Pt/NiFe-ED (300 μM) exhibits a much lower overpotential of 81 mV at 100 mA cm-2 than Pt/NiFe-HD. In contrast, Pt/NiFe-HD exhibits a higher intrinsic activity than Pt/NiFe-ED, which could be caused by the easily elongated Pt-O bond. These findings provide new opportunities to understand the relationship between activity and crystallinity of substrates in the composite electrocatalyst.

Lithium-induced amorphization of Ni–Fe layered-double-hydroxide for highly efficient oxygen evolution

Engineering structure is a promising pathway to adjust the physicochemical properties of materials to optimize the performance for various applications. Herein, we designed a highly efficient NiFe layered-double-hydroxide (NiFe LDH) nanosheets arrays catalyst for superior oxygen evolution reaction electrocatalysis by lithium-induced amorphization. Electrochemical lithium tuning of layered NiFe LDH crystal makes for the formation of amorphous NiFe intermediate with abundant active sites. It exhibits excellent electrocatalytic activity towards the oxygen evolution reaction with an overpotential of 259 mV at 50 mA cm−2, a Tafel slope of 56 mV dec−1 and prominent long-term stability, better than the RuO2 as benchmark catalysts. Experimental studies show that the electrochemical tuning contributes to the enhancement of NiFe LDH intrinsic activity due to crystallinity loss, morphology changes and formation of grain boundaries. This work enlightens a unique strategy to effectively design the advanced electrocatalysts by regulating the structure of material.

In Situ Synthesis of Superhydrophilic Amorphous NiFe Prussian Blue Analogues for the Oxygen Evolution Reaction at a High Current Density

Synthesis of efficient and low-cost catalysts for the oxygen evolution reaction (OER) is a pivotal process for large-scale electrocatalytic water splitting to produce hydrogen. Prussian blue analog...

Self-supported three-dimensional macroporous amorphous NiFe bimetallic-organic frameworks for enhanced water oxidation

Amorphous materials are attractive for their “dangling bonds” and more active than the crystalline counterparts in many applications. Metal-organic frameworks (MOFs) have emerged as an exciting class of porous materials that received considerable interest in many research fields including electrocatalysis. However, amorphous MOFs have been rarely investigated directly as electrocatalysts compared with crystalline ones. In this study, amorphous bimetallic NiFe-MOF with a three-dimensional (3D) macroporous structure was successfully prepared on nickel foam via one-step bottom-up solvothermal reactions and exhibited the potential as efficient OER (oxygen evolution reaction) electrocatalysts. The prepared self-supporting electrode can provide a 10 mA cm−2 current density at an overpotential of 211 mV, as well as remarkable operational stability and nearly 100% Faraday efficiency. This performance is superior to most previously reported MOF electrocatalysts and well exceeds the corresponding crystalline NiFe-MOF. The greatly enhanced activity of amorphous NiFe-MOF was originated from the abundant active metal sites and improved charge transfer due to unsaturated coordination as well as increased contact area with the electrolyte and good mass transfer benefitting from the unique 3D macroporous structure. This work will stimulate widespread interest in the study of amorphous MOF nanostructures with abundant active sites for improved electrocatalysts and beyond.

Engineering Bimetallic NiFe-Based Hydroxides/Selenides Heterostructure Nanosheet Arrays for Highly-Efficient Oxygen Evolution Reaction.

Developing cost-effective and high-efficiency electrocatalysts toward alkaline oxygen evolution reaction (OER) is crucial for water splitting. Amorphous bimetallic NiFe-based (oxy)hydroxides have excellent OER activity under alkaline media, but their poorly electrical conductivity impedes the further improvement of their catalytic performance. Herein, a bimetallic NiFe-based heterostructure electrocatalyst that is composed of amorphous NiFe(OH)x and crystalline pyrite (Ni, Fe)Se2 nanosheet arrays is designed and constructed. The catalyst exhibits an outstanding OER performance, only requiring low overpotentials of 180, 220, and 230mV at the current density of 10, 100, and 300mA cm-2 and a low Tafel slope of 42mV dec-1 in 1 m KOH, which is among the state-of-the-art OER catalysts. Based on the experimental and theoretical results, the electronic coupling at the interface that leads to the increased electrical conductivity and the optimized adsorption free energies of the oxygen-contained intermediates plays a crucial role in enhancing the OER activities. This work focusing on improving the OER performance via engineering amorphous-crystalline bimetallic heterostructure may provide some inspiration for reasonably designing advanced electrocatalysts.

2D amorphous bi-metallic NiFe nitrides for a high-efficiency oxygen evolution reaction.

Two-dimensional bi-metallic NiFe nitrides (2D NiFe-N) are successfully synthesized in the designed ternary deep eutectic solvents under the guidance of DFT calculations. Taking advantage of the unique properties of large-size, ultrathin amorphous 2D structure and modulable electronic structure, the NiFe0.05-N exhibits extraordinary OER performance with relatively low overpotential of 238 mV at 10 mA cm-2 and durable stability.

Electrochemical integration of amorphous NiFe (oxy)hydroxides on surface-activated carbon fibers for high-efficiency oxygen evolution in alkaline anion exchange membrane water electrolysis

Designing a high-efficiency and low-cost three-dimensional (3D) OER electrode via electrochemical integration of amorphous NiFeOOH on surface activated carbon fibers.

In Situ Growth of Amorphous NiFe Hydroxides on Spinel NiFe2O4 via Ultrasonic-Assisted Reduction for an Enhanced Oxygen Evolution Reaction

Amorphous Ni–Fe hydroxides (NiFe(OH)x) are considered to possess promising potential as oxygen evolution reaction (OER) electrocatalysts, but amorphous NiFe(OH)x is hard to synthesize due to the co...

Amorphous NiFe–OH/Ni–Cu–P supported on self-supporting expanded graphite sheet as efficient bifunctional electrocatalysts for overall water splitting

With the serious intensification of energy shortage and greenhouse effect, people begin to look for the sustainable energy sources to replace fossil energy sources. Herein, self-supporting expanded graphite sheet (SSEGS) was developed as an ideal catalyst support through electrochemically intercalating flexible graphite sheet in alkaline solution. Electroless deposition was employed to synthesize Ni–Cu–P alloy on SSEGS and then an amorphous NiFe hydroxide/Ni–Cu–P/SSEGS (NiFe–OH/Ni–Cu–P/SSEGS) composite catalyst was further constructed through electrodeposition. Benefitting from the unique structural advantage of SSEGS and the synergistic effect between two amorphous Ni-based materials (Ni–Cu–P alloy and NiFe–OH), the resulting electrode exhibited superior bifunctional electrocatalytic performance in 1 M KOH. For H2 evolution reaction and O2 evolution reaction, the NiFe–OH/Ni–Cu–P/SSEGS composite catalyst could reach 10 mA cm−2 at low overpotentials of 75 and 240 mV, respectively. Remarkably, the two-electrode system driven by NiFe–OH/Ni–Cu–P/SSEGS as the anode and cathode could afford 10 mA cm−2 at a low cell voltage of 1.56 V vs. RHE. And after the 12 h stability test, the cell voltage at 10 mA cm−2 increased by only 7 mV, indicating that the two-electrode system had excellent stability. The preparation of NiFe–OH/Ni–Cu–P/SSEGS material with superior bifunctional electrocatalytic performance has a significance influence to the development and expansion of hydrogen production technology.

Amorphous NiFe phosphides supported on nanoarray-structured nitrogen-doped carbon paper for high-performance overall water splitting

The exploration of high-performance and low-cost electrocatalysts for catalyzing both hydrogen and oxygen evolution reaction (HER and OER) at high current density is of vital significance for the commercialization of water splitting. Herein, amorphous NiFe phosphides are electrodeposited on 3D nanoarray-structured nitrogen-doped carbon paper (NCP) for direct use as a hybrid electrode toward overall water splitting. The as-prepared NiFe-P/NCP electrode requires only an overpotential of 0.226 and 0.125 V at 50 mA cm–2 for OER and HER, respectively. In addition, NiFe-P/NCP electrodes are further measured as a catalytic cathode and anode couple (NiFe-P/NCP||NiFe-P/NCP) for overall water splitting, exhibiting a low cell voltage of 1.547 to reach 10 mA cm–2 as well as a long-term durability. Our work reveals the significance of introducing well-designed substrate and bimetallic active species for enhanced electrochemical performance towards overall water splitting.

Oxygen vacancy-rich amorphous porous NiFe(OH)x derived from Ni(OH)x/Prussian blue as highly efficient oxygen evolution electrocatalysts.

Oxygen vacancies or defects play a significant role in improving the intrinsic activities of bimetallic hydroxides towards the oxygen evolution reaction (OER); however, their rational design and preparation remain a great challenge. In this study, oxygen vacancy-rich amorphous porous nickel iron hydroxide nanolayers supported on carbon paper (NiFe(OH)x/CP) are rationally prepared through a facile approach involving the sequential electrochemical deposition of a Prussian blue (PB) nanocrystal layer and Ni(OH)x layer on carbon paper followed by an alkaline etching process, where PB nanocrystals act as an Fe source and template for the formation of an amorphous porous NiFe(OH)x layer. NiFe(OH)x/CP with an ultralow loading of 0.8 mg cm-2 exhibits outstanding OER activities, showing a low overpotential of 303 mV at 100 mA cm-2 and a small Tafel slope of 33.8 mV dec-1 in an alkaline electrolyte, which are superior to the state-of-the-art IrO2 catalysts, and among the best results compared to the reported bimetallic compounds. Moreover, NiFe(OH)x/CP exhibits excellent long-term stability with negligible degradation after water splitting for 50 h. Its superior electrocatalytic OER performance benefits from the massive oxygen vacancies derived from the amorphous and distorted structures, the synergistic effect between Ni and Fe species with an optimized Ni/Fe ratio, and the efficient electron and mass transfer of carbon paper. This work paves a new avenue for the rational design and preparation of amorphous porous structures with abundant oxygen vacancies to improve the intrinsic activities for energy storage and conversion applications.