Transition Metal Hydroxides Research Articles

Pre-intercalation of phosphate into Ni(OH)2/NiOOH for efficient and stable electrocatalytic oxygen evolution reaction

Layered Ni(OH)2/NiOOH hydroxides are effective oxygen evolution reaction (OER) electrocatalysts, but their activities are still inferior to those of benchmark RuO2 and IrO2. Notably, the long-term stability becomes a significant challenge. Herein, we present a novel volume OER (VOER) strategy to solve the problems via pre-intercalation of phosphate. Phosphate-intercalated Ni-Ni(OH)2/NiOOH electrode was prepared by a two-step electrochemical method. The obtained porous electrode exhibits outstanding OER performance in the alkaline phosphate electrolyte with the overpotentials of 129 and 243 mV at 10 and 100 mA cm−2, respectively, and stability for 1000 h. The exceptional performance is mainly ascribed to effective VOER and elimination of the interlayer-produced protons, because the phosphate-intercalation enhances the interlayer water content, interlayer spacing and proton transport ability, endows the interlayers with proton buffering capacity, and alters the chemical environment of the interlayer Ni-O. The finding provides a strategy to develop highly efficient and stable OER materials and reaction systems for layered transition metal hydroxides.

Synergistic phosphorized NiFeCo and MXene interaction inspired the formation of high-valence metal sites for efficient oxygen evolution

Exploring low-cost, high-performance, and stable electrocatalysts toward the oxygen evolution reaction (OER) is highly desired but remains challenging. Transition metal hydroxide has been wildly utilized as a promising candidate, but practical implementation is impeded by insufficient catalytic activity, easy agglomeration, and poor conductivity. Here, we report that both phosphorization and combination with MXnene can improve the catalysts’ intrinsic activity and conductivity. Besides, MXene also prevents the agglomeration of the nanoparticles, resulting in the enhanced exposure of active sites. Experimental characterizing and density functional theory simulations revealed that P species can attract electrons to promote the formation of high-valence states of adjacent metal atoms, and coupling MXene support can effectively modulate the electronic structure and optimize the d-band center, which boosts the OER performance. Consequently, the optimized NiFeCoP/Mxene catalyst exhibits a low overpotential of 240 mV at a current density of 10 mA cm−2, a small Tafel slope of 55 mV dec−1, and superior long-term stability of 40 h in 1 M KOH electrolyte, which is superior to other counterparts.

Peculiar double-layered transition metal hydroxide nanosheets

Multi-layered nanosheets with controllable layer numbers may feature intrinsic physicochemical properties distinct from their single-layered counterparts. In this issue of <i>Chem Catalysis</i>, Ma and colleagues propose a new synthesis protocol to fabricate double-layered transition metal hydroxide nanosheets in bulk quantity, which exhibit intrinsically higher electrocatalytic activity than their single-layered counterparts for oxygen evolution reaction.

Atomically embedded Ag on transition metal hydroxides triggers the lattice oxygen towards sustained seawater electrolysis

Exploiting highly robust and active electrocatalysts for large-scale (sea)water electrolysis at industrial-level current densities (> 500 mA cm−2) is an increasingly appealing for developing renewable energy technologies. The current researches are limited by the complex synthetic procedures and poor stability of catalysts in practical application. Transition-metal (oxy)hydroxides are promising candidates for oxygen evolution reaction (OER) yet challenging approach to the clean energy by the low electrical conductivity. In this work, we pioneered an atomical-doping engineering strategy for achieving highly efficient and robust electrocatalyst towards large current density. Ag doped NiFe layered double hydroxide (LDH) was prepared by a one-step redox reaction on Ni foam without complex synthetic approach. Benefiting from the increased intrinsic conductivity, abundant active sites, and improved intrinsic surface area, Ag/NiFe LDH present a superior catalytic activity toward large-scale application, requiring low overpotentials of 240 and 276 mV at 100 and 1000 mA cm−2 in 1 M KOH, respectively. More importantly, a low overpotential of 303 mV at 1000 mA cm−2 in alkaline seawater-based electrolyte was attained, which remained 1000 h with long-term operation. Experimental and theoretical calculations demonstrated that the oxidation of Ag triggers the lattice oxygen redox and stabilizes the lattice oxygen, which does not induce significant material structure change and reconstruction during operation, ensuring the OER stability. This work remarkably advances the development of seawater electrolysis for large-scale clean energy.

Transition-metal hydroxide nanosheets with peculiar double-layer structures as efficient electrocatalysts

Single- or few-layer nanosheets with a molecular-level thickness may provide an ideal model for the fundamental investigation of layer-number-dependent properties. Herein, we report a new strategy for a selective synthesis of transition-metal-containing Co-Fe and Co-Ni-Fe hydroxide nanosheets with peculiar double-layer structures. A unique second-stage phase was obtained from topochemical oxidative intercalation of brucite-type metal hydroxides, e.g., Co5/6Fe1/6(OH)2 and Co2/3Ni1/6Fe1/6(OH)2, with a molar ratio of Fe fixed at 1/6. After anion exchange, the second-stage phase was exfoliated into double-layer hydroxide nanosheets with an average thickness of ∼1.9 nm, which was approximately twice that of their single-layer counterparts (∼1.0 nm). Electrocatalytic measurements combined with theoretic calculations revealed that the double-layer hydroxide nanosheets exhibited excellent oxygen evolution reaction (OER) catalytic activity and kinetics, outperforming their single-layer counterparts, which validates the great potential of transition-metal hydroxide nanosheets with both tunable composition and layer numbers for efficient electrocatalysis.

Colloidal synthesis of flower-like Zn doped Ni(OH)2@CNTs at room-temperature for hybrid supercapacitor with high rate capability and energy density

Transition metal oxides and hydroxides are typically applied as electrode materials for supercapacitors, but it is often difficult to achieve both their high power density and energy density simultaneously. Herein, electrodes of flower-like Zn doped Ni(OH)2 combined with carbon nanotubes (i.e., Zn doped Ni(OH)2@CNTs) were in-situ synthesized using a colloidal synthesis method at room-temperature, assisted by cetyltrimethyl ammonium bromide (CTAB) and NaBH4. This electrode exhibits an excellent electrochemical performance, achieving a high specific capacity of 750.5 C g-1 at 0.5 A g-1 and maintaining 72.9% of its initial value when the current density is increased from 1 A g-1 to 10 A g-1. A hybrid supercapacitor (HSC) assembled using the Zn doped Ni(OH)2@CNTs as the positive electrode and an active carbon as the negative electrode exhibits a capacity of 201.7 C g−1 at 1 A g-1 and an energy density of 51.3 Wh kg-1 at a power density of 409.6 W kg-1. After running for 50,000 cycles at a current density of 6 A g-1, the capacity of the HSC becomes 115.8% of its initial value. Moreover, this HSC maintains a high energy density of 29.33 Wh kg-1 at a high power density of 16.5 kW kg-1 after cycling for 50,000 times, which indicates its suitability for energy storage applications.

Temperature-dependence of calcination processes of Ni-rich layered oxides

High-Ni layered lithium transition metal oxides, LiNi1−x−yMnxCoyO2 (1-x-y≥0.7), show great promise for application in next-generation lithium ion batteries because of their high energy density, low cost, and superior electrochemical properties. However, preparation of stoichiometric LiNi1−x−yMnxCoyO2 oxides with highly ordered layered structure is challenging, largely due to the Li/O loss during high-temperature calcinations. Thus, understanding the reaction mechanism is crucial for calcination design. Herein, X−ray diffraction in combination with nuclear magnetic resonance, are conducted to track the structural evolution in preparing LiNi1−x−yMnxCoyO2 below 500 °C. Our results reveal that a lithiated intermediate, Ni0.7Mn0.15Co0.15(OHy)2Lix, between the precursory transition metal hydroxide and the destination layered LiNi1−x−yMnxCoyO2 phase is generated, bypassing the formation of transition metal oxide phases. The unique reaction enables the calcination optimization at low temperature. Accordingly, high-ordered LiNi0.7Mn0.15Co0.15O2 is achieved via a developed two-step calcination at 500 °C, and it exhibits an excellent electrochemical performance, especially the high initial columbic efficiency.

Template ion-exchange synthesis of Co-Ni composite hydroxides nanosheets for supercapacitor with unprecedented rate capability

Because of the inherent poor conductivity, electrodes based on transition metal hydroxides (TMHs) for supercapacitors (SCs) usually suffer from inferior rate capability. Herein, we present a strategy for the improvement of rate capability of Co-Ni hydroxides by creating well-structured composites via a template ion-exchange method (TIEM). The derived binary hydroxides own nanosheet morphology with ultrathin thickness of 5–10 nm, and display well-composited structure, large specific surface area as well as homogenous element distribution. Importantly, the inherent conductivity of the composite is twice more than that of the individual hydroxides. Featuring with these unique advantages, the hydroxide composite with optimized Co/Ni ratio viz. Co0.52Ni0.48(OH)2, as electrode material for supercapacitor achieves performances superior to those of single hydroxides, including large capacitance (1608F/[email protected].0 A/g), high energy density (55.9 Wh/[email protected] W/kg), long cycling stability, and greatly enhanced rate capability. Notably, the optimized composite exhibits an unprecedented rate capability of 90.6% from 1.0 to 20 A/g, much superior to that of Ni(OH)2 (16%) and Co(OH)2 (75.3%) and the reported Co-Ni composite hydroxides, posing as a promising candidate for energy storage devices. Overall, the present template ion-exchange strategy provides a simple method for the fabrication of well-structured composite metal hydroxides and opens an avenue for the use of such materials in fields such as energy storage, catalysis, sensor, and so on.

Hydrazine Hydrate Induced Three-Dimensional Interconnected Porous Flower-like 3D-NiCo-SDBS-LDH Microspheres for High-Performance Supercapacitor.

Porous structure and surface defects are important to improve the performance of supercapacitors. In this study, a facile pathway was developed for high-performance supercapacitors, which can produce transition metal hydroxides (LDHs) with abundant porous structure and surface defects. The NiCo-SDBS-LDH was prepared by one-step hydrothermal reaction using sodium dodecylbenzene sulfonate (SDBS) as anionic surfactant. And then, three dimensional (3D) interconnected porous flower-like 3D-NiCo-SDBS-LDH microspheres were designed and synthesized using the gas-phase hydrazine hydrate reduction method. Results showed that the hydrazine hydrate reduction not only introduces a large number of pores into 3D-NiCo-SDBS-LDH microspheres and causes the formation of oxygen vacancies, but it also roughens the surface of the microspheres. All these changes contribute to the enhancement of electrochemical activity of 3D-NiCo-SDBS-LDH; the NiCo-SDBS-LDH electrode after hydrazine hydrate treatment (3D-NiCo-SDBS-LDH) exhibits a higher specific capacitance of 1148 F·g−1 at 1 A·g−1 (about 1.46 times larger than that of NiCo-SDBS-LDH) and excellent long cycle life with 94% retention after 4000 cycles. Moreover, the assembled 3D-NiCo-SDBS-LDH//AC (active carbon) asymmetric supercapacitor (ASC) achieves remarkable energy density of 73.14 W h·kg−1 at 800 W·kg−1 and long-term cycling stability of 95.5% retention for up to 10,000 cycles. The outstanding electrochemical performance can be attributed to the synergy between the rich porous structure and the roughened surface that has been created by the hydrazine hydrate treatment.

Formation of fringed carnation-like cobalt manganese fluoride hydroxide assisted by ammonium fluoride for supercapacitor applications

The binary transition metal oxides or hydroxides have received significant attention as potential materials in supercapacitor applications owing to their unique characteristics. In this study, a binary cobalt-manganese fluoride hydroxide-CoMn(OH)F is assembled successfully through the crucial assistance of an ammonium fluoride agent in an alkali source of hexamethylenetetramine (HMTA). At a rational design, the CoMn(OH)F with fringed carnation-like morphology obtains a specific capacitance of 541 F g −1 (at a current density of 1 A g −1 ) in a three-electrode system and cycling stability of 84% after 15,000 cycles. Furthermore, an asymmetric device CoMn(OH)F//activated carbon in a two-electrode system not only exhibits a remarkable specific capacitance of 135 F g −1 (at 0.4 A g −1 ), a high energy density of 39 Wh kg −1 , and a power density of 3.65 kW kg −1 but also maintains 91% of the initial capacitance after 10,000 cycling tests. These electrochemical performances demonstrate the considerable potential of the fluoride hydroxide CoMn(OH)F for supercapacitor applications. • CoMn(OH)F was formed via the key role of NH 4 F and the optimal precursor ratio. • CoMn(OH)F had a fringed carnation-like morphology. • Sample obtained synergistic effects of diffusion and capacitive-controlled process. • CoMn(OH)F//AC exhibited energy density 39 Wh kg −1 and power density 3.65 kW kg −1 .

Efficient CO2 reduction MOFs derivatives transformation mechanism revealed by in-situ liquid phase TEM

Materials derived from MOFs have great potentials in energy conversion. However, the nanoscale transformation processes of MOFs derivatives remain unknown. Herein, by using in-situ liquid phase TEM, we directly visualize the MOFs etching processes. For the first time, unexpected nanobubble stability controlled transformation mechanism of ZIF-67 to porous or layered cobalt transition metal hydroxide (Co-TMH) is identified. Voids in MOFs migrate and merge to form nanobubbles due to structural collapse. Under slow diffusion conditions, nanobubbles move slowly and Co-TMH clusters generate on the nanobubble interface, further favoring the formation of internal nanocages and porous structures. On the other hand, a fast diffusion leads to rapid nanobubbles generation, aggregation and reshaping, inducing layered structure formation. Inspired by in-situ observation, we further synthesize porous Co-TMH at − 80 ℃ under inhibited diffusion conditions, which exhibits excellent catalytic performance on CO2 reduction reaction.

Ultrathin 2D nanosheets of transition metal (hydro)oxides as prospective materials for energy storage devices: A short review

The ultrathin two-dimensional (2D) transition metal oxides and hydroxides (TMO and TMH) nanosheets are attractive for creating high-performance energy storage devices due to a set of unique physical and chemical properties. Flat 2D structure of such materials provides a sufficient number of active adsorption centers, and the ultra-small thickness, on the order of several nanometers, provides fast charge transfer, which significantly improves electronic conductivity. This brief review summarizes recent progress in the synthesis of materials based on ultrathin 2D nanosheets for energy storage applications, including pseudocapacitors, lithium-ion batteries, and other rechargeable devices. The review also presents examples of representative work on the synthesis of ultrathin 2D nanomaterials based on TMO and TMH for various power sources. In conclusion, the article discusses possible prospects and directions for further development of methods and routes for the synthesis of ultrathin two-dimensional transition metal oxides and hydroxides.

Bottom-up synthesis of 2D layered high-entropy transition metal hydroxides.

Low-dimensional high-entropy materials, such as nanoparticles and two-dimensional (2D) layers, have great potential for catalysis and energy applications. However, it is still challenging to synthesize 2D layered high-entropy materials through a bottom-up soft chemistry method, due to the difficulty of mixing and assembling multiple elements in 2D layers. Here, we report a simple polyol process for the synthesis of a series of 2D layered high-entropy transition metal (Co, Cr, Fe, Mn, Ni, and Zn) hydroxides (HEHs), involving the hydrolysis and inorganic polymerization of metal-containing species in ethylene glycol media. The as-synthesized HEHs demonstrate 2D layered structures with interlayer distances ranging from 0.860 to 0.987 nm and homogeneous elemental distribution of designed equimolar stoichiometry in the layers. These 2D HEHs exhibit a low overpotential of 275 mV at 10 mA cm−2 in a 0.1 M KOH electrolyte for the oxygen evolution reaction. Superparamagnetic spinel-type high-entropy nanoparticles can also be obtained by annealing these HEHs. Our polyol approach creates opportunities for synthesizing low-dimensional high-entropy materials with promising properties and applications.

Heterostructured FeNi hydroxide for effective electrocatalytic oxygen evolution.

Hydrogen production technology by water splitting has been heralded as an effective means to alleviate the envisioned energy crisis. However, the overall efficiency of water splitting is limited by the effectiveness of the anodic oxygen evolution reaction (OER) due to the high energy barrier of the 4e− process. The key to addressing this challenge is the development of high-performing catalysts. Transition-metal hydroxides with high intrinsic activity and stability have been widely studied for this purpose. Herein, we report a gelatin-induced structure-directing strategy for the preparation of a butterfly-like FeNi/Ni heterostructure (FeNi/Ni HS) with excellent catalytic performance. The electronic interactions between Ni2+ and Fe3+ are evident both in the mixed-metal “torso” region and at the “torso/wing” interface with increasing Ni3+ as a result of electron transfer from Ni2+ to Fe3+ mediated by the oxo bridge. The amount of Ni3+ also increases in the “wings”, which is believed to be a consequence of charge balancing between Ni and O ions due to the presence of Ni vacancies upon formation of the heterostructure. The high-valence Ni3+ with enhanced Lewis acidity helps strengthen the binding with OH− to afford oxygen-containing intermediates, thus accelerating the OER process. Direct evidence of FeNi/Ni HS facilitating the formation of the Ni–OOH intermediate was provided by in situ Raman studies; the intermediate was produced at lower oxidation potentials than when Ni2(CO3)(OH)2 was used as the reference. The Co congener (FeCo/Co HS), prepared in a similar fashion, also showed excellent catalytic performance.

Introducing oxygen vacancies to NiFe LDH through electrochemical reduction to promote the oxygen evolution reaction.

The transition metal hydroxide NiFe LDH is a promising oxygen evolution reaction (OER) catalyst. Surface engineering, such as the introduction of oxygen vacancies into NiFe LDH, has been reported to further improve the OER performance; however, searching a facile approach remains an issue. In this work, we report a novel and efficient electrochemical reduction method for in situ introduction of oxygen vacancies into NiFe LDH laminates by applying a constant negative voltage. The results show that the reduced NiFe LDH (denoted as r-NiFe LDH) exhibits enhanced OER performance versus its counterpart NiFe due to the increase of oxygen vacancy density, the electrochemically active surface area, wetting ability, and the significant electron transfer rate. In 1 M KOH, the r-NiFe LDH shows a high current density of 110 mA cm-2 at 1.60 V (vs. RHE), which is 2.8 times the current density of NiFe LDH (40 mA cm-2), as well as the long-term stability of 100 h. This electroreduction method is also applicable to other LDH materials loaded by different current substrates or synthesized by various methods, demonstrating its universality for the enhancement of the OER activity of LDH electrocatalysts.

Template-assisted synthesis of accordion-like CoFe(OH) nanosheet clusters on GO sheets for electrocatalytic water oxidation

• Accordion-like CoFe(OH) x are prepared on GO sheets via a template-assisted route. • The CoFe(OH) x /GO composite displays superior electrocatalytic performance for OER. • The synergy effect of CoFe(OH) x and GO contributes to the enhanced OER performance. • The Fe content in CoFe(OH) x /GO has a significant effect on the OER performance. Developing highly efficient, low-cost and stable electrocatalysts for oxygen evolution reaction (OER) is momentous to achieve the conversion and storage of sustainable energy. Herein, the CoFe(OH) x / GO composites with accordion-like CoFe(OH) x nanosheets clusters dispersed on graphene oxide (GO) sheets are prepared via a template-assisted route. It is found that the OER performance of the CoFe(OH) x / GO composites strongly depends on the content of GO and the mole ratio of Co/Fe. The optimized CoFe(OH) x / GO composites exhibit remarkably enhanced OER electrocatalytic activity in 1 M KOH with a low overpotential of 294 mV at 10 mA cm −2 and a small Tafel slope of 63.4 mV dec −1 , which are far superior to the corresponding Co(OH) 2 / GO and bare CoFe(OH) x . The enhanced electrocatalytic activity can be ascribed to the regulated electronic structure surrounding the active metal sites by introducing Fe, the improved conductivity by GO for faster charge transfer, and the accordion-like hierarchical structure with increased accessible active sites. This work demonstrates a comprehensive strategy to improve the electrocatalytic performance of transition metal hydroxide based OER catalysts.

Oxygen vacancy regulated selective hydrogenation of α,β-unsaturated aldehydes over LDH surface group coordinated transition metal photocatalysts

Oxygen vacancies enriched MgAl-LDH coordinated transition metal hydroxides M(OH)x photocatalysts perform excellent in the selective hydrogenation of α,β-unsaturated aldehydes to corresponding alcohols under visible light irradiation.

Core–Shell Nanostructured Hybrid of Nickel Hydroxide Supported on Copper Hydroxide Nanorod Arrays Used as Advanced Supercapacitors with High Efficiency and Ultraperformance

AbstractThe fascinating search for ultraefficient and high‐powered supercapacitors has stimulated continuous exploration of diverse energy storage materials like transition metal hydroxides with core–shell structure. Thus in this paper, a novel core–shell hybrid electrode material of nickel hydroxide (Ni(OH)2) supported on copper hydroxide nanorod arrays (Cu(OH)2 NAs), which is constructed on copper foam as the substrate by an in situ chemical oxidation reaction accompanied by chemical bath deposition, is reported. As a result, it is found that the pre‐fabricated Cu(OH)2@Ni(OH)2 electrode has a remarkable areal capacitance of 9.27 F cm−2 and good cycling performance (retains 92.38% after 6000 cycles) compared to its counterpart Cu(OH)2 nanorods (88.57%). Additionally, the Cu(OH)2@Ni(OH)2 material, as a positive electrode, can also be used to assemble a hybrid supercapacitor (HSC) while activated carbon is chosen as the negative electrode. As a result, the constructed HSC device with the desired working voltage of 0–1.5 V can light up the light‐emitting diode indicator, proving the potential practicability of the pre‐fabricated HSC device.

Performance of biochar assisted catalysts during hydroprocessing of non-edible vegetable oil: Effect of transition metal source on catalytic activity

Biochar-supported catalysts were developed from nickel (Ni) - and cobalt (Co)- nitrates and hydroxides and tested for the hydrotreatment of carinata oil. Nitrate-based (from water-soluble salts) and hydroxide-based (from water-insoluble salts) catalysts of Ni and Co were prepared via wetness impregnation and aqueous dispersion methods, respectively. The catalysts were characterized using various tools such as, confocal XRF, BET specific surface area analyzer, NH3-TPD, and SEM-EDS. Synchroton method showed nitrate-sourced metals were dispersed mostly in the pores while, the hydroxide-sourced metals were distributed mainly on the catalyst surface. C = C saturation and cracking of triglycerides, decarboxylation, and hydrogenation of aromatic structures appeared to be dominant on the hydroxides of transition metals, hence took place on catalyst surface. Methanation and dehydrogenation (thus aromatization), however, seemed to be a pore phenomenon, catalyzed more over nitrate-based catalysts. A reaction network was proposed based on chemical analysis of upgraded carinata oil and erucic acid model compound. Catalytic cracking followed by hydrotreatment performed better in terms of fuel properties than other approaches in this study.

Structure and Oxygen Evolution Activity of β-NiOOH: Where Are the Protons?

Ni oxides and oxyhydroxides (NiOx) have been studied for a long time as cathode materials for alkaline batteries and electrocatalysts for the oxygen evolution reaction (OER). Yet, understanding of the connection between their atomic and electronic structures and electrochemical performance or stability is still incomplete. In this work, we use first-principles density functional theory (DFT) calculations to revisit the structure, electronic properties, and OER activity of β-NiOOH, the catalytically active phase of NiOx. Following extensive DFT-based screening, we identify a hitherto overlooked structure characterized by a uniform distribution of H atoms on the NiO2 layers. All the Ni3+ cations in this structure exhibit an identical tg6eg1 electronic configuration with an occupied 3dz2 orbital. Comparison of the calculated bond lengths with extended X-ray absorption fine structure (EXAFS) data unequivocally supports this structure relative to all other low-energy configurations. Based on this structure, we uncover and detail defect-dominated OER mechanisms on the basal β-NiOOH (001) surface, with overpotentials as low as 0.39 V. The present results should provide a valuable contribution to ongoing efforts for understanding and developing enhanced transition-metal hydroxide catalysts for the OER.