NiFe Hydroxide Research Articles

Motivating high-valence Nb doping by fast molten salt method for NiFe hydroxides toward efficient oxygen evolution reaction

High-valence Nb has been proved to be promising to enhance oxygen evolution reaction (OER). However, how to realize the atomic doping of larger-radii Nb is challenging. Herein, an elaborate molten salt method is applied to rapidly incorporate Nb into NiFe-layered double hydroxides (Nb-NiFe-LDH). The fabricated Nb-NiFe-LDH is featured with nano pompons composed of cross-linked hollow nanotubes, which ensures maximum exposure of active sites. Meanwhile, the generated lattice defects can adjust electron density and absorption property of intermediates on the surface, facilitating oxygen evolution. As validation, the obtained Nb-NiFe-LDH exhibits motivated OER activity with overpotential of 242 mV at 50 mA cm−2 and small Tafel slope of 31.3 mV dec−1 as well as long-term stability of 73 h. DFT reveals that such superior OER performance benefits from the fine-tuned surface adsorption ability for reaction intermediates and electron transfer capability as well as optimized oxidation cycle of active metals by synergistic Nb and defects. This work is expected to provide deep insights into the advanced catalysts development via high-valence metal doping achieved by molten salt method.

Metamorphosis of Heterostructured Surface-Mounted Metal-Organic Frameworks Yielding Record Oxygen Evolution Mass Activities.

Materials derived from surface-mounted metal-organic frameworks (SURMOFs) are promising electrocatalysts for the oxygen evolution reaction (OER). A series of mixed-metal, heterostructured SURMOFs is fabricated by the facile layer-by-layer deposition method. The obtained materials reveal record-high electrocatalyst mass activities of ≈2.90 kA g-1 at an overpotential of 300mV in 0.1 m KOH, superior to the benchmarking precious and nonprecious metal electrocatalysts. This property is assigned to the particular in situ self-reconstruction and self-activation of the SURMOFs during the immersion and the electrochemical treatment in alkaline aqueous electrolytes, which allows for the generation of NiFe (oxy)hydroxide electrocatalyst materials of specific morphology and microstructure.

Unveiling Role of Sulfate Ion in Nickel‐Iron (oxy)Hydroxide with Enhanced Oxygen‐Evolving Performance

AbstractThe rational design of effective catalysts for sluggish oxygen evolution reactions (OERs) is desired but challenging. Nickel‐iron (NiFe) (oxy)hydroxides are promising pre‐electrocatalysts for alkaline OER. However, OER performances are limited by the slow reconstruction process to generate active species of high‐valance NiFe oxyhydroxides. In this work, a sulfate ion (SO42−) modulated strategy is developed to boost the OER activity of NiFe (oxy)hydroxide by accelerating the electrochemical reconstruction of pre‐catalyst and stabilizing the reaction intermediate of OOH* during OER. The SO42− decorated NiFe (oxy)hydroxide catalyst (NF‐S0.15) is fabricated via scalable anodization of NiFe foam in a thiourea‐dissolved electrolyte. The experimental and theoretical investigations demonstrate the dual effect of SO42− on improving OER performances. SO42− leaching is favorable for the electrochemical reconstruction to form active NiFeOOH under OER condition. Simultaneously, the residual SO42− adsorbed on surface can stabilize the intermediate of OOH*, and thus enhance the OER performances. As expected, NF‐S0.15 delivers an ultralow overpotential of 234 mV to reach the current density of 50 mA cm−2, a fast OER kinetics (27.7 mV dec−1), and a high stability for more than 100 h. This unique insights into anionic modification could inspire the development of advanced electrocatalysts for efficient OER.

Operando X-ray study of service behavior of catalytic materials based on synchrotron radiation

Considering the energy and environmental issues faced by human society, hydrogen has become increasingly important, and electrocatalytic water splitting is considered to be an ideal way to solve these energy issues. However, although most electrocatalysts will undergo a structural evolution when in service conditions, our understanding of the service behavior of catalysts is limited. To design highly active catalysts, operando characterization techniques must be used to study their dynamic structural evolution. Today, the development of synchrotron radiation devices has reached an important stage. Synchrotron-radiation-based X-ray characterization, which has high energy, large flux, and excellent collimation compared with the ordinary laboratory X-ray source, can capture the precise structure of catalytic materials. In this review, we present the development status of synchrotron radiation devices and the basic principles of operando X-ray absorption spectroscopy, X-ray diffraction spectroscopy, and X-ray photoelectron spectroscopy based on synchrotron radiation. In addition, we highlight studies related to the dynamic service behavior of water-splitting catalysts under real conditions and list a variety of operando studies of typical water-splitting catalysts, including NiFe hydroxide/(oxy)hydroxides, perovskite oxides, spinel oxides, and noble-metal-based catalysts. The use of operando X-ray techniques deepens our understanding of the catalyst reaction mechanism and provides a basis for identifying the dynamic structure–performance correlation of catalysts. We summarize the problems and challenges of operando X-ray-based techniques in complex electrochemical environments and propose the prospect of an advanced synchrotron radiation facility for operando X-ray characterization. With the development of the next-generation synchrotron radiation facility, adequately using this advanced X-ray light source to study the dynamic structure–activity correlation of catalytic materials throughout their life cycle to achieve the precise design and synthesis of complex pre-catalysts will advance the development of this field by enabling greater refinement and control.

Trifle Pt coupled with NiFe hydroxide synthesized via corrosion engineering to boost the cleavage of water molecule for alkaline water-splitting

Developing cost-effective and highly efficient hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) electrocatalysts with small overpotentials and superior long-term stabilities is imperative for catalyzing water electrolysis. Herein, corrosion engineering is applied to synthesize NiFe-LDH incorporating noble metals on a 3D porous Ni foam at room temperature to afford the NF-Na-Fe-Pt electrocatalyst. The optimized balance adsorption of hydroxyl ions and atomic hydrogen that are manifested by the synergism between NiFe-LDH and trifle noble metals endow the nanomaterial with an excellent electrocatalytic performance and long-term durability for mediating the water-splitting process in 1 M KOH. Only 31 and 261 mV are required to drive 10 mA cm−2 of the prepared NF-Na-Fe-Pt electrocatalyst for HER and OER, respectively. DFT calculations demonstrate that Pt and NiFe-LDH synergistically accelerate the Volmer reaction and adsorption/desorption of atomic H to enhance alkaline HER. Moreover, the NF-Na-Fe-Pt electrocatalyst also exhibit remarkable catalytic activity for water splitting.

Promoting Bifunctional Water Splitting by Modification of the Electronic Structure at the Interface of NiFe Layered Double Hydroxide and Ag.

Electrochemical water splitting is a promising method for the renewable production of high-purity hydrogen via the hydrogen evolution reaction (HER). Ni-Fe layered double hydroxides (Ni-Fe LDHs) are highly efficient materials for mediating the oxygen evolution reaction (OER), a half-reaction for water splitting at the anode, but LDHs typically display poor HER performance. Here, we report the preparation of self-organized Ag@NiFe layered double hydroxide core-shell electrodes on Ni foam (Ag@NiFe/NF) prepared by galvanic etching for mediating both the HER and OER (bifunctional water-splitting electrocatalysis). This synthetic strategy allowed for the preparation of organized hierarchical architectures which displayed improved the electrochemical performance by tuning the electronic structure of the catalyst and increasing the surface area utilization. X-ray photoelectron spectroscopy (XPS) and theoretical calculations revealed that electron transfer from the Ni-Fe LDH to Ag influenced the adsorption of the reaction intermediates leading to enhanced catalytic activity. The Ag@NiFe/NF electrode displayed overpotentials as low as 180 and 80 mV for oxygen and hydrogen evolution, respectively, at a current density of 10 mA cm-2, and improvements in the specific activity by ∼5× and ∼1.5× for the oxygen and hydrogen evolution reaction, respectively, compared to benchmark NiFe hydroxide materials. Additionally, an integrated water-splitting electrolyzer electrode can be driven by an AA battery.

Boosting overall water splitting by incorporating sulfur into NiFe (oxy)hydroxide

Developing highly active and cost-effective electrocatalysts for enhancing the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is a significant challenge for overall water splitting. Sulfur-incorporated nickel iron (oxy)hydroxide (S-NiFeOOH) nanosheets were directly grown on commercial nickel foam using a galvanic corrosion method and a hydrothermal method. The incorporation of sulfur into NiFeOOH enhanced the catalytic activity for the HER and OER in 1 M KOH electrolyte. The enhanced catalytic activity is attributed to the change in the local structure and chemical states due to the incorporation of sulfur. High performance for overall water splitting was achieved with an alkaline water electrolyzer. This was realized by employing S-NiFeOOH as a bifunctional electrocatalyst, thereby outperforming a water electrolyzer that requires the usage of precious metal electrocatalysts (i.e., Pt/C as the HER electrocatalyst and IrO2 as the OER electrocatalyst). Moreover, when driven by a commercial silicon solar cell, an alkaline water electrolyzer that uses S-NiFeOOH as a bifunctional electrocatalyst generated hydrogen under natural illumination. This study shows that S-NiFeOOH is a promising candidate for a large-scale industrial implementation of hydrogen production for overall water splitting because of its low cost, high activity, and durability. In addition, the solar-driven water electrolyzer using S-NiFeOOH as a bifunctional electrocatalyst affords the opportunity for developing effective and feasible solar power systems in the future.

Benchmarking of oxygen evolution catalysts on porous nickel supports

Summary Active and inexpensive oxygen evolution reaction (OER) electrocatalysts are needed for energy-efficient electrolysis applications. Objective comparison between OER catalysts has been blurred by the use of different supports and methods to evaluate performance. Here, we selected nine highly active transition-metal-based catalysts and described their synthesis, using a porous nickel foam and a new Ni-based dendritic material as the supports. We designed a standardized protocol to characterize and compare the catalysts in terms of structure, activity, density of active sites, and stability. NiFeSe- and CoFeSe-derived oxides showed the highest activities on our dendritic support, with low overpotentials of η100 ≈ 247 mV at 100 mA cm–2 in 1 M KOH. Stability evaluation showed no surface leaching for 8 h of electrolysis. This work highlights the most active anode materials and provides an easy way to increase the geometric current density of a catalyst by tuning the porosity of its support.

Constructing Ultrathin W-Doped NiFe Nanosheets via Facile Electrosynthesis as Bifunctional Electrocatalysts for Efficient Water Splitting.

Exploring cost-effective and efficient bifunctional electrocatalysts via simple fabrication strategies is strongly desired for practical water splitting. Herein, an easy and fast one-step electrodeposition process is developed to fabricate W-doped NiFe (NiFeW)-layered double hydroxides with ultrathin nanosheet features at room temperature and ambient pressure as bifunctional catalysts for water splitting. Notably, the NiFeW nanosheets require overpotentials of only 239 and 115 mV for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively, to reach a current density of 10 mA/cm2 in alkaline media. Their exceptional performance is further demonstrated in a full electrolyzer configuration with the NiFeW as both anode and cathode catalysts, which achieves a low cell voltage of 1.59 V at 10 mA/cm2, 110 mV lower than that of the commercial IrO2 (anode) and Pt (cathode) catalysts. Moreover, the NiFeW nanosheets are superior to various recently reported bifunctional electrocatalysts. Such remarkable performances mainly ascribe to W doping, which not only effectively modulates the electrocatalyst morphology but also engineers the electronic structure of NiFe hydroxides to boost charge-transfer kinetics for both the OER and HER. Hence, the ultrathin NiFeW nanosheets with an efficient fabrication strategy are promising as bifunctional electrodes for alkaline water electrolyzers.

Dual-ligand modulation approach for improving supercapacitive performance of hierarchical zinc–nickel–iron phosphide nanosheet-based electrode

Mixed nanostructured transition metal-based complex materials with hierarchical and porous architectures, built from interconnected nano-building blocks, are considered as high-performance positive electrode materials in supercapacitors (SCs). Herein, zinc–nickel–iron phosphide (ZnNiFe–P) and Zn–Ni–Fe–hydroxide precursors (ZnNiFe–OH) were combined in a 3D hierarchical and porous structure (ZnNiFe–(P/OH)) to improve their durability and electrochemical activity by incorporating a dual-ligand synergistic modulation strategy. The 3D ZnNiFe–(P/OH) architectures, comprising perfectly aligned nanosheet arrays (NSA), were successfully grown on Ni foam using a facile hydrothermal process followed by partial phosphorization. The dual-ligand ZnNiFe–(P/OH) electrode exhibited excellent specific capacitance/areal capacitance (1708Fg−1/5.64Fcm−2 for 1Ag−1), high rate performance (62% upto 15Ag−1) and good cycle life. Moreover, the ZnNiFe–(P/OH) NSA positive electrode was coupled with an activated carbon negative electrode to design an asymmetric supercapacitor device. The device delivered an excellent capacitance of ∼187Fg−1 at 0.8Ag−1, a superior energy density of ∼58.4Whkg−1 at 600Wkg−1, and an excellent power density of 11250Wkg−1 at 34.4Whkg−1 while maintaining good cycling performance (88% after 5000 cycles).

Nickel–iron hydroxide oxygen evolution electrocatalysts prepared by a simple chemical bath deposition method

The oxygen evolution reaction (OER), which is an important process in water electrolysis, requires a high overpotential. There is a need for cheaper and more efficient catalysts for this process. Ni hydroxide-based OER catalysts are promising, but further research is required. This paper describes the use of a simple chemical bath deposition method for the preparation and characterization of three-dimensional microstructured Ni–Fe hydroxide electrochemical OER catalysts on nickel plates. The influences of the Fe ion content and pH of the chemical bath on the performance of the catalysts are addressed, allowing the preparation of an efficient and highly active catalyst. Thus, this study represents a stepping stone toward further developments in the field of water electrolysis.

Electrodeposited Trimetallic NiFeW Hydroxide Electrocatalysts for Efficient Water Oxidation

Tungsten-doped Ni-Fe hydroxides fabricated on a three-dimensional nickel foam through cathodic electrodeposition are proposed as effective oxygen evolution reaction (OER) catalysts for alkaline water oxidation. Incorporating an adequate amount of W into Ni-Fe hydroxides modulates the electronic structure by changing the local environment of Ni and Fe and create oxygen vacancies, resulting in abundant active sites for the OER. The optimized electrocatalyst, with a substantial number of catalytic sites, is found to outperform the well-established 20 wt% Ir/C electrocatalyst. The catalyst only requires small overpotentials of 224 mV and 251 mV to generate current densities of 10 mA cm-2 and 50 mA cm-2 , respectively, at an extremely low Tafel slope. Surface study after long-term chronopotentiometry (ca. 30 h) reveals that the tungsten dopant undergoes reduction to stabilize the Ni and Fe active sites for predominant water oxidation. This research provides new insight to apply optimum amounts of tungsten doping to enable more significant electronic coupling within Ni-Fe for the chemisorption of hydroxy and oxygen intermediates and greatly improved OER activity.

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.

Densely vertical-grown NiFe hydroxide nanosheets on a 3D nickel skeleton as a dendrite-free lithium anode.

Densely vertical-grown NiFe hydroxide nanosheets on a nickel foam (DVS-NFOH@NF) were designed and synthesized for a dendrite-free lithium anode. As a result, the Li dendrite was significantly suppressed. The invented Li anode presented a uniform morphology and great cycle performance in a symmetric cell.

Hollow nanocapsules of NiFe hydroxides to enable doxorubicin delivery and combinational tumour therapy.

In this study, fine hollow nanocapsules, consisting of NiFe hydroxides (denoted as H-NiFe(OH)x), are designed and synthesized for the delivery of an anticancer drug (Doxorubicin, DOX) and tumour depletion. Owing to its fascinating characteristics of "Fe2+ preservation and regeneration", H-NiFe(OH)x presents considerable Fenton activity for hydroxyl radical (˙OH) induction. Efficient delivery of DOX is ensured due to its hollow microstructure, and a typical pH-responsive drug release is enabled. More importantly, the intracellular DOX, in addition to its intrinsic antitumour properties, induces extra exogenous H2O2 which favors the production of ˙OH by H-NiFe(OH)x in tumour cells. In consequence, remarkable in vitro and in vivo antitumour properties are successfully achieved. This drug delivery system is particularly inspirational to further studies in the exploration of intelligent therapeutic platforms for combinational tumour therapy.

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...

NiFe hydroxide pillared by metaborate for efficient oxygen evolution reaction

Water-splitting by electrolysis is one of the most important approaches to produce hydrogen as renewable clean energy with superior advantages of high-purity and good operability. But the key issue limiting the large-scale application is that it demands a much higher overpotential than the theoretical oxygen evolution potential. Herein, we report an efficient electrochemical catalyst of NiFeBO synthesized via a facile one-step process, presenting remarkable catalytic activity and long-term stability. In this work, we discussed the effects of the doping of Fe and the insertion of BO2− in the as-synthesized NiFeBO. According to the experimental results, NiFeBO shows a very low overpotential of 256 mV and a Tafel slope of 53 mV dec−1 with remarkable stability over 60 h of chronopotentiometry test. The inserted anion of BO2− can adsorb OH− in electrolyte around the catalyst to increase the concentration of OH− around the active sites, thereby improving the effectivity of oxygen evolution reaction. In addition, diffused micro-crystalline with different lattice formed during the oxidation of the as-synthesized catalyst, providing more active sites than the pristine amorphous.

Sulfide@hydroxide core–shell nanostructure via a facile heating-electrodeposition method for enhanced electrochemical and photoelectrochemical water oxidation

Designing low-cost, easy-fabricated, highly stable and active electrocatalysts for oxygen evolution reaction (OER) is crucial for electrochemical (EC) and solar-driven photoelectrochemical (PEC) water splitting. By using a facile heating-electrodeposition method, here we fabricated a porous but crystalline Fe-doped Ni3S2. A thin porous surface NiFe hydroxide layer (~10 nm) is then formed through OER-running. By virtue of the core Fe-doped Ni3S2 with good conductivity and the shell NiFe hydroxide surface with good electrocatalytic activity, the core–shell nanostructure on Ni foam exhibits excellent OER activity in 1 M NaOH, needing only 195 and 230 mV to deliver 10 and 100 mA/cm2, respectively, much more superior to those of 216 and 259 mV for the sample deposited under normal temperature. The enhanced photo-response of the [email protected] core–shell structure was also demonstrated, due to the efficient transfer of photo-generated carriers on the core/shell interface. More interestingly, it shows a good compatibility with Si based photoanode, which exhibits an excellent PEC performance with an onset potential of 0.86 V vs. reversible hydrogen electrode, an applied bias photon-to-current efficiency of 5.5% and a durability for over 120 h under AM 1.5 G 1 sun illumination, outperforming the state-of-the-art Si based photoanodes.

NiFe hydroxide nanosheet synthesized by in-situ chelation for highly efficient oxygen evolution reaction

Designing efficient and non-precious electrocatalysts for the oxygen evolution reaction (OER) was essential for renewable energy field, and the catalyst with composition gradient has emerged as a new dimension in improving the catalytic performance. Herein, a simple construction strategy was adopted to design the NiFe hydroxide nanosheet arrays with composition gradient for efficient oxygen evolution. The continuous gradient changes constructed efficient electron transmission channels and modified the NiOOH local electronic environment which optimized binding strength to oxygen evolution intermediates. Subsequently, the gradient varying NiFe hydroxide nanosheets array exhibited a low overpotential of 270 mV at a current density of 50 mA cm−2 and a small Tafel slope of 63.6 mV·dec−1 in alkaline media. In the meantime, it showed remarkable long-term stability and maintained the nanosheet arrays morphology with no significant degeneration of electrochemical performance.

Topotactically constructed nickel–iron (oxy)hydroxide with abundant in-situ produced high-valent iron species for efficient water oxidation

Exploring the relationship between high-valent iron content and current intensity of NiFe 0.2 -O x H y during oxygen evolution reaction by operando 57 Fe Mössbauer spectroscopy. The low efficiency of oxygen evolution reaction (OER) is regarded as one of the major roadblocks for metal-air batteries and water electrolysis. Herein, a high-performance OER catalyst of NiFe 0.2 (oxy)hydroxide (NiFe 0.2 -O x H y ) was developed through topotactic transformation of a Prussian blue analogue in an alkaline solution, which exhibits a low overpotential of only 263 mV to reach a current density of 10 mA cm −2 and a small Tafel slope of 35 mV dec −1 . Ex-situ / operando Raman spectroscopy results indicated that the phase structure of NiFe 0.2 -O x H y was irreversibly transformed from the type of α -Ni(OH) 2 to γ -NiOOH with applying an anodic potential, while ex-situ / operando 57 Fe Mössbauer spectroscopic studies evidenced the in-situ production of abundant high-valent iron species under OER conditions, which effectively promoted the OER catalysis. Our work elucidates that the amount of high-valent iron species in-situ produced in the NiFe (oxy)hydroxide has a positive correlation with its water oxidation reaction performance, which further deepens the understanding of the mechanism of NiFe-based electrocatalysts.