Nickel Sites Research Articles

P‐Doped NiFe Alloy‐Based Oxygen Evolution Electrocatalyst for Efficient and Stable Seawater Splitting and Organic Electrosynthesis at Neutral pH

AbstractDevelopment of high‐performance and inexpensive electrocatalysts for oxygen evolution reaction (OER) at neutral pH is important for direct seawater splitting and organic electrosynthesis but remains challenging due to the sluggish OER kinetics and diverse side reactions inherent to the constituents of working electrolytes. Herein, we report on a P:NiFe electrode, containing P‐doped NiFe alloy, as an excellent electrocatalyst for hydrogen evolution reaction (HER) and OER pre‐catalyst for efficient OER in both seawater and organic electrolyte for adiponitrile (ADN) electrosynthesis at neutral pH. Fe and P species modulate the coordination environment of nickel sites, which enables the simultaneous formation of OER‐active nickel species and FePOx passivation layer, thus transforming HER‐active P:NiFe to OER‐active a‐P:NiFe. Besides, the redox‐dependent interconversion between HER‐active P:NiFe and OER‐active a‐P:NiFe is fast and reversible. Finally, efficient and stable overall seawater‐splitting and ADN electrosynthesis at an industrially relevant current density (100 mA cm−2) in pH‐neutral media are also demonstrated.

Nickel model complexes to mimic carbon monoxide dehydrogenase reactions.

Biological CO2/CO interconversion catalyzed at the Ni/Fe heterobimetallic active site of anaerobic carbon monoxide dehydrogenases (CODHs) offers important insights for the design of efficient and selective synthetic catalysts for CO2 capture and utilization (CCU). Notably, this organometallic C1 interconversion process is mediated at a three-coordinate nickel site. Extensive research has been conducted to elucidate the redox and structural changes involved in substrate binding and conversion. The CO2-bound structure of CODH, in particular, has inspired many synthetic studies aimed at exploring key questions, concerning the choice of metal, the role of the unique iron (Feu), and the geometry and oxidation states of both Ni and Feu, as well as CO2/CO exchange mechanism. A better understanding of CODH chemistry promises to reveal and uncover fundamental principles for small molecule activation of first-row transition metal complexes. This mini-review focuses on three key aspects: (1) the coordination environment of the Ni centre in CODH, (2) bioinorganic Ni model systems that provide insight into the biological CO2/CO interconversion at the CODH active site, and (3) recent advances in CODH-inspired catalysis for selective CO2-to-CO conversion.

Dual Regulation of Sensitizers and Cluster Catalysts in Metal–Organic Frameworks to Boost H2 Evolution

Photocatalytic efficiency is closely correlated to visible‐light absorption ability, electron transfer efficiency and catalytic center activity of photocatalysts, nevertheless, the concurrent management of these factors to improve photocatalytic efficiency remains underexplored. Herein, we proposed a sensitizer/catalyst dual regulation strategy on the polyoxometalate@Metal−Organic Framework (POM@MOF) molecular platform to construct highly efficient photocatalysts. Impressively, Ni‐Sb9@UiO‐Ir‐C6, obtained by coupling strong sensitizing [Ir(coumarin 6)2(bpy)]+ with Ni‐Sb9 POM with extremely exposed nickel site [NiO3(H2O)3], can drive H2 evolution with a turnover number of 326923, representing a record value among all the POM@MOF composite photocatalysts. This performance is over 34 times higher than that of the typical Ni4P2@UiO‐Ir constructed from [Ir(ppy)2(bpy)]+ and Ni4P2 POM. systematical investigations revealed that dual regulation of sensitizing and catalytic centers endowed Ni‐Sb9@UiO‐Ir‐C6 with strong visible‐light absorption, efficient inter‐component electron transfer and high catalytic activity to concurrently promote H2 evolution. This work opens up a new avenue to develop highly active POM@MOF photocatalysts by dual regulation of sensitizing/catalytic centers at the molecular level.

Dual Regulation of Sensitizers and Cluster Catalysts in Metal-Organic Frameworks to Boost H2 Evolution.

Photocatalytic efficiency is closely correlated to visible-light absorption ability, electron transfer efficiency and catalytic center activity of photocatalysts, nevertheless, the concurrent management of these factors to improve photocatalytic efficiency remains underexplored. Herein, we proposed a sensitizer/catalyst dual regulation strategy on the polyoxometalate@Metal-Organic Framework (POM@MOF) molecular platform to construct highly efficient photocatalysts. Impressively, Ni-Sb9@UiO-Ir-C6, obtained by coupling strong sensitizing [Ir(coumarin 6)2(bpy)]+ with Ni-Sb9 POM with extremely exposed nickel site [NiO3(H2O)3], can drive H2 evolution with a turnover number of 326923, representing a record value among all the POM@MOF composite photocatalysts. This performance is over 34 times higher than that of the typical Ni4P2@UiO-Ir constructed from [Ir(ppy)2(bpy)]+ and Ni4P2 POM. Systematical investigations revealed that dual regulation of sensitizing and catalytic centers endowed Ni-Sb9@UiO-Ir-C6 with strong visible-light absorption, efficient inter-component electron transfer and high catalytic activity to concurrently promote H2 evolution. This work opens up a new avenue to develop highly active POM@MOF photocatalysts by dual regulation of sensitizing/catalytic centers at the molecular level.

Endophytic bacteria in Halogeton glomeratus from mining areas are mainly Sphingomonas pseudosanguinis, with a Cyanobacteria moving from roots to leaves to avoid heavy metals

In the cold and arid mining areas of Northwest China, Halogeton glomeratus C. Meyer (Amaranthaceae) is a promising plant for the remediation of heavy metal pollution. In this study, samples correspond to a gradient of nickel and copper pollution, and this study aims to analyze the characteristics of endophytic bacteria in H. glomeratus under such pollution gradients. Samples of the plant H. glomeratus and their corresponding rhizosphere soil were collected from a smelting area, a mining area, and a control area within the Jinchang mine. In mining and smelting areas, Ni in H. glomeratus rhizosphere soils was 95 and 6 times, and Cu was 40 and 94 times higher than control area. Ni in H. glomeratus from these areas was 27 and 4 times, and Cu was 4.2 and 4.6 times greater than control area. The endophytic bacteria predominantly found in H. glomeratus from nickel-copper mining regions was Sphingomonas pseudosanguinis. Our findings might corroborate the notion that heavy metal stress in the soil can markedly facilitate the migration of an unclassified second most abundant species of Cyanobacteria, residing within the roots of H. glomeratus, to aerial tissues, where the stress from heavy metals was diminished. RDA indicated that the migration and enrichment of nickel and copper into the tissues of H. glomeratus in smelting and mining areas influenced changes in the community structure of endophytic bacteria. Under varying levels of nickel and copper stress, endophytic bacteria underwent alterations in their metabolic characteristics, aiding H. glomeratus in withstanding heavy metal stress through processes such as lipid, nucleotide, and amino acid metabolism, xenobiotics biodegradation and metabolism, protein folding, sorting, and degradation, as well as replication and repair. The identification of plant growth-promoting traits, including the ability to release phosphorus, produce IAA and ACC deaminase, and exhibit tolerance to nickel and copper, among culturable dominant strains, had shown that Pseudomonas oryzihabitans K2l-2-LB and Pseudomonas putida K2r-3-R2A possess significant potential for application. These strains could be effectively utilized as microbial inoculants to promote plant growth during the restoration of vegetation in nickel and copper-contaminated mine sites.

Effect of Bi Doping on the Kinetics of Nickel Oxides-Based Electrocatalyst in Alkaline Oxygen Evolution Reaction

As a generation process of hydrogen fuel, an alkaline water electrolysis is considered as one of the most promising pathway. The water electrolysis is able to divide into two half-cell reaction: hydrogen evolution reaction (HER) in cathode and oxygen evolution reaction (OER) in anode. However, high activation energy of OER is regarded as a major bottleneck for utilization of water electrolysis, therefore it is necessary to use an electrocatalyst to improve the reaction rate. Currently, commercially used electrocatalysts of OER is precious metal such as platinum (Pt), ruthenium (Ru), and iridium (Ir) based compound which have critical drawback for high cost and low stability in alkaline electrolyte.As a substitute of platinum group materials for electrocatalyst of oxygen evolution reaction (OER), the development of cost-effective and high-active nickel oxide catalyst has attracted intense research interest. Alkaline OER is composed by five states: M, M-OH, M-O, M-OOH, and M + O2, and the gibbs free energy of final state is 4.92 eV higher than the first state. Thus, the free energy difference between each states equally becomes 1.23 eV to minimize the activation energy of rate determining step (RDS). In this point, nickel oxide shows a remarkable catalytic activity because a rapid and reversible electrochemical oxidation on the surface of nickel oxide triggers reconstructions to form hydroxide which is suitable structures for intermediate of OER. However, the nickel oxide still has high activation energy of reaction step from nickel(II) oxide to nickel(III) oxyhydroxide (3rd step of OER, Ni-O à Ni-OOH), which becomes RDS of OER. Because the catalytic activity seriously reduces without the balanced rate between each step of reaction, it is necessary to control the electric structure of nickel oxide to optimize adsorption energy of intermediates.In this context, bismuth doped nickel oxide is synthesized for electrocatalyst of OER. Because bismuth has higher electronegativity than nickel, the adsorption energy of positively charged nickel with proton decreases and the adsorption energy of positively charged nickel oxide with hydroxide ion increases. Therefore, the activation energy of RDS of OER is expected to reduce than the pristine nickel oxide.In practice, the bismuth doped nickel oxide is synthesized by hydrothermal process and the composition of bismuth is controlled by the concentration of precursors. The crystal structure of nickel oxide is maintained after the addition of bismuth, but the inter-planar spacing of overall plane of nickel oxide structure decreases according to selected area electron diffraction (SAED) pattern of transmission electron microscopy (TEM). In this context, the bismuth additive does not form the bi-metal oxide with nickel, but it substitutes the nickel site of nickel oxide structure. According to the nickel 2p3/2 spectra of x-ray photoelectron spectroscopy (XPS), a binding energy of nickel oxide peak positively shifts when the composition of bismuth additive increased due to the shifted electron from nickel to bismuth atom. As electrochemical measurement for evaluation of catalytic activity, the bismuth doped nickel oxide shows 59 mV lower overpotential at 20 mA cm-2 in alkaline OER, respectively, than the nickel oxide. In particular, the addition of bismuth is especially influenced to intrinsic activity, the bismuth doped nickel oxide catalyst shows higher turnover frequency than the pristine nickel oxide although it has similar active surface area. Figure 1

Study of the Mechanism and Charge-Transfer Processes in Water Oxidation Catalysis by Nickel Hydroxide and Silk Fibroin: A Spectroelectrochemical Approach

Water electrolysis has emerged as a crucial electrochemical reaction on the generation of sustainable fuels, due to the ongoing climate crisis. To divert from expensive catalysts based on rare noble metals such as Ir and Ru, transition metal oxides seem to be promising candidates and several recent studies have deepened the investigation on the nickel oxide/hydroxide for water oxidation catalysis. It has been proposed that in the presence of elements such as iron and gold, a partial charge-transfer occurs between the nickel and the metal, facilitating the formation of superoxide species and nickel in higher oxidation states that enhance the oxygen evolution reaction (OER). 1–4 Rao et al (2022)5 developed a methodology combining UV-Vis spectroscopy and voltametric techniques to determine the number of these nickel species in higher oxidation levels during the OER for nickel oxides dopped with Zn, Fe, Co and Mn. From their results, they proposed a mechanism for the OER that involves two steps: 1) initial oxidation from NiII to NiIII and superoxide formation, which is limited by the potential and 2) coupling and desorption of the superoxide species, which is limited by rate. Next, they demonstrated that the different dopants modulated the bond strength between the nickel and the oxygen: too weak-bonding limited the ability to oxidize nickel and too strong-bonding limited the combination and desorption of the oxygen.In this work, monolayers of nickel hydroxide were electrodeposited, in the presence and the absence of silk fibroin (SF), on top of electrodes containing gold nanoparticles and used surface-enhanced Raman scattering (SERS)and UV-Vis spectroeletrochemical techniques to study the influence of the gold and SF on the catalytic performance of nickel hydroxide. Our previous results6 showed that the silk protein was able to stabilize the α-Ni(OH)2 nanoparticles and improved its electrochemical activity. Here, we followed the Rao et al’s methodology and found analogous results for the mechanisms of water oxidation. Figure 1A and B shows the number oxidized species and the calculated turnover frequency (TOF) as function of the potential for the samples with 1, 3, 6 and 9 monolayers, containing or not SF. While the number of oxidized species remains comparable across samples with the same number of monolayers, those containing fibroin generally exhibit higher TOFs. A volcano-like graph (Figure 1C) was obtained when the TOFs at an overpotential of 0.3 V is plotted against the NiII-NiIII redox potential, indicating a transition from potential-limited to rate-limited regions as monolayer thickness increases. We propose that this behavior is caused by the charge-transfer effect between nickel and gold, which is strongest for one monolayer and decreases as the number of nickel sites on the bulk moves away the gold surface. Notably, as monolayer thickness increases, samples containing SF show less susceptibility to decrease in TOFs, implying an additional charge-transfer effect between the protein and nickel, which contributes for the balance of the nickel bond strength with oxygen and facilitates its coupling and desorption.In summary, our study advances understanding of OER mechanisms and charge-transfer processes involving nickel hydroxide electrocatalysis, suggesting that proteins like SF can actively contribute to catalytic processes. However, further investigations are needed in order to elucidate the precise role of the protein and how to use them to optimize catalytic performance. REFERENCES 1. Diaz-Morales, O., Ferrus-Suspedra, D. & M. Koper, M. T. Chem. Sci. 7, 2639–2645 (2016).2. Yeo, B. S. & Bell, A. T. J. Phys. Chem. C 116, 8394–8400 (2012).3. Li, C.-F. et al. Angew. Chem. Int. Ed. 61, e202116934 (2022).4. Trotochaud, L., Young, S. L., Ranney, J. K. & Boettcher, S. W. J. Am. Chem. Soc. 136, 6744–6753 (2014).5. Rao, R. R. et al. J. Am. Chem. Soc. 144, 7622–7633 (2022). 6. do Nascimento, E. R. et al. ACS Appl. Electron. Mater. 4, 1214–1224 (2022). Figure 1

Enhancing Alloyed Nickel Sites via Heterogeneous CoP3–Ni2P Modification for Highly Efficient Urea Electrooxidation

Enhancing Alloyed Nickel Sites via Heterogeneous CoP₃–Ni₂P Modification for Highly Efficient Urea Electrooxidation

Iron and nickel based alloy nanoparticles anchored on phosphorus-modified carbon-nitrogen plane enhances electrochemical nitrate reduction to ammonia

The catalysts of iron and nickel nanoparticles anchored on carbon–nitrogen plane (FeNi-CN) are considered as the potential candidates for promising electrochemical nitrate reduction to ammonia (ENO3RR). However, the high d-orbital energy levels of iron and nickel sites coordinated with nitrogen atoms often lead to overly strong adsorption of reaction intermediates on active sites, severely limiting the improvement of catalytic performance. Herein, a catalyst FeNi3@P-NC consisting FeNi3 alloy nanoparticles confined in phosphorus (P)-modified carbon–nitrogen plane is successfully fabricated, where the electron withdrawal effect induced by P on the carbon–nitrogen plane decreases the d-orbital energy, and optimizes the d-band center of FeNi alloy, thus weakening the overly strong adsorption of intermediates at the metal-N sites and thereby improving NO3RR activity. The prepared FeNi3@P-NC catalyst exhibits exceptional NO3RR performance with a 93 ± 4.5 % Faradaic efficiency of NH3 production (FENH3) and a high NH3 yield rate (YNH3) of 9633 ± 227.3 μg h−1 cm−2 at −0.7 V versus Reversible Hydrogen Electrode (vs. RHE) under alkaline medium. Importantly, FeNi3@P-NC also demonstrates superior catalytic stability and durability, which maintains stability over twenty-five successive electrochemical cycles and for 50 h of continuous electrolysis at 100 mA cm−2.

Tailoring d‐Band Center of Single‐Atom Nickel Sites for Boosted Photocatalytic Reduction of Diluted CO2 from Flue Gas

AbstractPhotocatalytic reduction of diluted CO2 from anthropogenic sources holds tremendous potential for achieving carbon neutrality, while the huge barrier to forming *COOH key intermediate considerably limits catalytic effectiveness. Herein, via coordination engineering of atomically scattered Ni sites in conductive metal–organic frameworks (CMOFs), we propose a facile strategy for tailoring the d‐band center of metal active sites towards high‐efficiency photoreduction of diluted CO2. Under visible‐light irradiation in pure CO2, CMOFs with Ni‐O4 sites (Ni‐O4 CMOFs) exhibits an outstanding rate for CO generation of 13.3 μmol h−1 with a selectivity of 94.5 %, which is almost double that of its isostructural counterpart with traditional Ni‐N4 sites (Ni‐N4 CMOFs), outperforming most reported systems under comparable conditions. Interestingly, in simulated flue gas, the CO selectivity of Ni‐N4 CMOFs decreases significantly while that of Ni‐O4 CMOFs is mostly unchanged, signifying the supremacy for Ni‐O4 CMOFs in leveraging anthropogenic diluted CO2. In situ spectroscopy and density functional theory (DFT) investigations demonstrate that O coordination can move the center of the Ni sites′ d‐band closer to the Fermi level, benefiting the generation of *COOH key intermediate as well as the desorption of *CO and hence leading to significantly boosted activity and selectivity for CO2‐to‐CO photoreduction.

Tailoring d-Band Center of Single-Atom Nickel Sites for Boosted Photocatalytic Reduction of Diluted CO2 from Flue Gas.

Photocatalytic reduction of diluted CO2 from anthropogenic sources holds tremendous potential for achieving carbon neutrality, while the huge barrier to forming *COOH key intermediate considerably limits catalytic effectiveness. Herein, via coordination engineering of atomically scattered Ni sites in conductive metal-organic frameworks (CMOFs), we propose a facile strategy for tailoring the d-band center of metal active sites towards high-efficiency photoreduction of diluted CO2. Under visible-light irradiation in pure CO2, CMOFs with Ni-O4 sites (Ni-O4 CMOFs) exhibits an outstanding rate for CO generation of 13.3 μmol h-1 with a selectivity of 94.5 %, which is almost double that of its isostructural counterpart with traditional Ni-N4 sites (Ni-N4 CMOFs), outperforming most reported systems under comparable conditions. Interestingly, in simulated flue gas, the CO selectivity of Ni-N4 CMOFs decreases significantly while that of Ni-O4 CMOFs is mostly unchanged, signifying the supremacy for Ni-O4 CMOFs in leveraging anthropogenic diluted CO2. In situ spectroscopy and density functional theory (DFT) investigations demonstrate that O coordination can move the center of the Ni sites' d-band closer to the Fermi level, benefiting the generation of *COOH key intermediate as well as the desorption of *CO and hence leading to significantly boosted activity and selectivity for CO2-to-CO photoreduction.

Local Charge Modulation Induced the Formation of High‐Valent Nickel Sites for Enhanced Urea Electrolysis (Adv. Energy Mater. 41/2024)

Local Charge Modulation Induced the Formation of High‐Valent Nickel Sites for Enhanced Urea Electrolysis (Adv. Energy Mater. 41/2024)

Polyoxometalate‐Based Single‐Atom Catalyst with Precise Structure and Extremely Exposed Active Site for Efficient H2 Evolution

AbstractSingle‐atom catalysts with precise structure and extremely high catalytic efficiency remain a fervent focus in the fields of materials chemistry and catalytic science. Herein, a nickel‐substituted polyoxometalate (POM) {NiSb6O4(H2O)3[β‐Ni(hmta)SbW8O31]3}15− (NiPOM) with one extremely exposed nickel site [NiO3(H2O)3] was synthesized using the conventional aqueous method. The uniform dispersion of single nickel center with well‐defined structure was facilely achieved by anchoring nanosized NiPOM on graphene oxide (GO). The resulting NiPOM/GO can couple with CdS photoabsorber for the construction of low‐cost and ultra‐efficient hydrogen evolution system. The H2 yield can reach to 2753.27 mmol gPOM−1 h−1, which represents a record value among all the POM‐based photocatalytic systems. Remarkablely, an extremely high hydrogen yield of 3647.28 mmol gPOM−1 h−1 was achieved with simultaneous photooxidation of commercial waste plastic, representing the first POM‐based photocatalytic system for H2 evolution and waste plastic conversion. This work highlights a straightforward strategy for constructing extremely exposed single‐metal site with precise microenvironment by facilely manipulating nanosized molecular cluster to control individual atom.

Polyoxometalate-Based Single-Atom Catalyst with Precise Structure and Extremely Exposed Active Site for Efficient H2 Evolution.

Single-atom catalysts with precise structure and extremely high catalytic efficiency remain a fervent focus in the fields of materials chemistry and catalytic science. Herein, a nickel-substituted polyoxometalate (POM) {NiSb6O4(H2O)3[β-Ni(hmta)SbW8O31]3}15- (NiPOM) with one extremely exposed nickel site [NiO3(H2O)3] was synthesized using the conventional aqueous method. The uniform dispersion of single nickel center with well-defined structure was facilely achieved by anchoring nanosized NiPOM on graphene oxide (GO). The resulting NiPOM/GO can couple with CdS photoabsorber for the construction of low-cost and ultra-efficient hydrogen evolution system. The H2 yield can reach to 2753.27 mmol gPOM -1 h-1, which represents a record value among all the POM-based photocatalytic systems. Remarkablely, an extremely high hydrogen yield of 3647.28 mmol gPOM -1 h-1 was achieved with simultaneous photooxidation of commercial waste plastic, representing the first POM-based photocatalytic system for H2 evolution and waste plastic conversion. This work highlights a straightforward strategy for constructing extremely exposed single-metal site with precise microenvironment by facilely manipulating nanosized molecular cluster to control individual atom.

In Situ Carbon Thermal Reduction to Enrich Sulfur-Vacancy in Nickel Disulfide Cathode for Efficient Synthesizing Hydrogen Peroxide.

Transition metal catalysts are widely used in the 2e- ORR due to their cost-effectiveness. However, they often encounter issues related to low activity. Defect engineering are used on developing highly active catalysts, which can effectively modify active sites and promote electron transfer. Here, carbon-coated Ni3S2 (Ni3S2@C), where the additional sulfur vacancies (VS) is prepared induced by the carbon layer is coupled with active nickel sites. Through in situ and ex situ experiments combined with DFT calculations, it is demonstrated that the carbon layer can regulate the quantity of VS in Ni3S2. Materials with a higher concentration of VS exhibit enhanced 2e- ORR activity and higher H2O2 selectivity. In situ Raman spectroscopy confirms that Ni serves as the key active site in this catalyst. DFT calculations indicate that the OOH binding energy (ΔG) decreases with an increase in the number of VS, favoring the protonation of *OOH to generate H2O2. Upon performance testing, the average H2O2 selectivity is 92.3%, with the highest yield reaching up to 3860mmolgcat-1h-1. It is noteworthy that Ni3S2@C exhibits high stability, with only a slight decrease in 2e- pathway selectivity after 5000 cycles of ADT.

Small Molecule Activation at the acriPNP Pincer-Supported Nickel Sites.

ConspectusNickel pincer systems have recently attracted much attention for applications in various organometallic reactions and catalysis involving small molecule activation. Their exploration is in part motivated by the presence of nickel in natural systems for efficient catalysis. Among such systems, the nickel-containing metalloenzyme carbon monoxide dehydrogenase (CODH) efficiently and reversibly converts CO2 to CO at its active site. The generated CO moves through a channel from the CODH active site and is transported to a dinuclear nickel site of acetyl-coenzyme A synthase (ACS), which catalyzes organometallic C-S and C-C bond forming reactions. An analogous C-S bond activation process is also mediated by the nickel containing enzyme methyl-coenzyme M reductase (MCR). The nickel centers in these systems feature sulfur- and nitrogen-rich environments, and in the particular case of lactate racemase, an organometallic nickel pincer motif revealing a Ni-C bond is observed. These bioinorganic systems inspired the development of several nickel pincer scaffolds not only to mimic enzyme active sites and their reactivity but also to further extend low-valent organonickel chemistry. In this Account, we detail our continuing efforts in the chemistry of nickel complexes supported by acridane-based PNP pincer ligands focusing on our long-standing interest in biomimetic small molecule activation. We have employed a series of diphosphinoamide pincer ligands to prepare various nickel(II/I/0) complexes and to study the conversion of C1 chemicals such as CO and CO2 to value-added products. In the transformation of C1 chemicals, the key C-O bond cleavage and C-E bond (E = C, N, O, or S, etc.) formation steps typically require overcoming high activation barriers. Interestingly, enzymatic systems overcome such difficulties for C1 conversion and operate efficiently under ambient conditions with the use of nickel organometallic chemistry. Furthermore, we have extended our efforts to the conversion of NOx anions to NO via the sequential deoxygenation by nickel mediated carbonylation, which was applied to catalytic C-N coupling to produce industrially important organonitrogen compound oximes as a strategy for NOx conversion and utilization (NCU). Notably, the rigidified acriPNP pincer backbone that enforces a planar geometry at nickel was found to be an important factor for diversifying organometallic transformations including (a) homolysis of various σ-bonds mediated by T-shaped nickel(I) metalloradical species, (b) C-H bond activation mediated by a nickel(0) dinitrogen species, (c) selective CO2 reactivity of nickel(0)-CO species, (d) C-C bond formation at low-valent nickel(I or 0)-CO sites with iodoalkanes, and (e) catalytic deoxygenation of NOx anions and subsequent C-N coupling of a nickel-NO species with alkyl halides for oxime production. Broadly, our results highlight the importance of molecular design and the rich chemistry of organonickel species for diverse small molecule transformations.

Ternary gallide Zr7Pd7–xGa3+x (0 ≤ x ≤ 1.8): Synthesis, crystal and electronic structures

The new ternary compound Zr7Pd7-xGa3+x (0 ≤ x ≤ 1.8) was synthesized by arc melting the elements under argon and subsequent annealing the ingots at 870 K for 720 h. The polycrystalline samples were characterized by powder X-ray diffraction (XRD) and the crystal structure of the compound was determined from single crystal X-ray diffraction data. Zr7Pd7Ga3 crystallizes with a ternary version of the Zr7Ni10 type of structure exhibiting statistical mixtures of palladium and gallium atoms on three crystallographically independent nickel sites (oS68, Cmce, a = 12.997(3), b = 9.623(2), c = 9.630(2) Ǻ, Z = 4, R1 = 0.033, wR2 = 0.067 for 719 unique reflections with Io> 2σ(Io) and 48 refined parameters). The crystal structure of Zr7Pd7Ga3 is represented by a 3D Pd–Ga framework built of sinusoidal layers of Pd and Ga stacking along the b axis sandwiching the Zr atoms. The homogeneity range of the compound Zr7Pd7–xGa3+x has been refined from powder XRD and EDX data: 0 ≤ x ≤ 1.8; variation of the lattice parameters is the following: a = 13.0174(8)–12.904(3), b = 9.6306(8)–9.559(8), c = 9.6348(8)–9.700(5) Å. Electronic structure calculations have been performed for an idealized model Zr7Pd10 as well as a model compound Zr7Pd6.5Ga3.5 revealing that the Ga-free Zr7Pd10 is significantly destabilized by strong Pd–Pd anti-bonding interactions. Substitution of Pd by Ga reduces those, stabilizing Zr7(Pd,Ga)10 which features strong heteroatomic bonding between Zr and the Pd/Ga substructure, putting it into the class of polar intermetallics.

Synergistic Engineering of Electron‐Enriched Nickel Sites for Highly Efficient Photocatalytic CO2 Reduction to C2H6

Synergistic Engineering of Electron‐Enriched Nickel Sites for Highly Efficient Photocatalytic CO₂ Reduction to C₂H₆

Influence of the Interaction of Nickel and Copper with Ceria on Ethanol Steam Reforming over Ni-Cu-CeO2 Catalysts

Catalysts of nickel-ceria, nickel-copper-ceria, and copper-ceria were explored with respect to their properties for hydrogen production through ethanol steam reforming (ESR). They were prepared by coprecipitation of the components within inverse microemulsions to achieve intimate contact between them, and the catalysts were characterized by N2 adsorption measurements, XRD, Raman spectroscopy, TPR, and XPS. The catalysts were tested for the ESR reaction, and they were regenerated with oxygen when significant deactivation took place, as occurred for the copper-containing systems. In contrast, the nickel–ceria catalyst exhibits a high activity and stability despite the formation of an important amount of carbon deposits during the course of the ESR test. The presence of nickel sites, which strongly interact with the ceria support, and which are affected by the presence of copper, and the limitation of copper for C-C bond breaking are invoked to explain the results obtained on the whole.

Local Charge Modulation Induced the Formation of High‐Valent Nickel Sites for Enhanced Urea Electrolysis

AbstractNi‐based electrocatalysts are considered to be significantly promising candidates for electrocatalytic urea oxidation reaction (UOR). However, their UOR activity and stability are severely enslaved by the inevitable Ni group self‐oxidation phenomenon. In this study, the glassy state NiFe LDH with uniform Cu dopant (Cu‐NiFe LDH) by a simple sol–gel strategy is successfully synthesized. When served as the UOR catalyst, Cu‐NiFe LDH required a 123 mV lower potential for UOR at both 10 and 100 mA cm−2 in comparison with the conventional anodic OER. It can also operate steadily for more than 300 h at 10 mA cm−2. The in‐depth investigation reveals that Cu incorporation can optimize the local electronic structure of Ni species to induce high‐valent Ni sites. The high‐valent Ni sites would act as the active center during the proposed energetically favorable UOR route, which directly reacts on the high‐valent Ni sites without self‐oxidation inducing the formation of NiOOH species, resulting in a boosted electrocatalytic UOR activity and stability.