Ni OH Research Articles

Unveiling the mechanistic synergy in Mn-doped NiO catalysts with atomic-burry structure: Enhanced CO oxidation via Ni-OH and Mn bifunctionality

The development of non-noble metal catalysts for low-temperature CO oxidation is a pivotal subject in various disciplines. In this study, an optimized Mn-doped NiO catalyst (Mn-NiO-0.5), prepared via aerosol pyrolysis with an equal molar ratio of Ni to Mn, demonstrates remarkable performance. It achieves an 82 % CO conversion at -20 °C and a 100 % conversion between 10 °C and 800 °C. The catalyst’s turnover frequency (TOF) for CO oxidation significantly surpasses that of previously reported noble-metal-based catalysts, underscoring its superior efficiency. Dynamic analyses suggest that the enhanced catalytic activity is a result of the unique atom burr structure, which presents an extensive surface area replete with abundant active sites. This structural feature is instrumental in maximizing the catalyst’s interaction with CO molecules. Experimental findings, corroborated by density functional theory (DFT) calculations, elucidate the mechanism of CO oxidation on the Mn-NiO-0.5 catalyst. The process is facilitated by the synergistic action of bimetallic sites, where the Ni–OH site acts as the primary adsorption point for CO. Subsequently, the CO is oxidized to bicarbonate through the interaction with the oxygen (O or O2) at adjacent Mn sites. This pioneering study introduces a paradigm-shifting insight: the effectiveness of non-noble metal oxide catalysts can now compete with, and in some cases, outperform their noble metal counterparts. This breakthrough is set to transform the industry, presenting a compelling alternative to conventional noble metal catalysts and propelling the evolution of state-of-the-art environmental conservation technologies.

Stable CO2 reduction under natural air on Ni–Sn hydroxide photocatalyst with dynamic renewable oxygen vacancies

Advanced photocatalysts are highly desired to activate the photocatalytic CO2 reduction reaction (CO2RR) with low concentration. Herein, the NiSn(OH)6 with rich surface lattice hydroxyls was synthesized to boost the activity directly under the natural air. Results showed that terminal Ni–OH could serve as donors to feed protons and generate oxygen vacancies (VO), thus beneficial to convert the activated CO2 (HCO3 −) mainly into CO (5.60 μmol g−1) in the atmosphere. It was flexible and widely applicable for a stable CO2RR from high pure to air level free of additionally adding H2O reactant, and higher than the traditional gas–liquid–solid (1.58 μmol g−1) and gas–solid (4.07 μmol g−1) reaction system both using high pure CO2 and plenty of H2O. The strong hydrophilia by the rich surface hydroxyls allowed robust H2O molecule adsorption and dissociation at VO sites to achieve the Ni–OH regeneration, leading to a stable CO yield (11.61 μmol g−1) with the enriched renewable VO regardless of the poor CO2 and H2O in air. This work opens up new possibilities for the practical application of natural photosynthesis.

Structural modification of nickel tetra(thiocyano)corroles during electrochemical water oxidation.

In this study, we present two fully characterized nickel tetrathiocyanocorroles, representing a novel class of 3d-metallocorroles. These nickel(II) ions form square planar complexes, exhibiting a d8-electronic configuration. These anionic complexes are stabilized by the electron-withdrawing SCN groups on the bipyrrole unit of the corrole. The reduced aromaticity in these anionic nickel(II) corrole complexes is evidenced by single crystal X-ray diffraction (XRD) data and a markedly altered absorption profile, with stronger Q bands compared to Soret bands. Notably, the UV-Vis and electrochemical data exhibit significant differences from previously reported nickel(II) corrole radical cation and nickel(II) porphyrin complexes. While these electrochemical data bear a resemblance to those of the anionic nickel(II) corrole by Gross et al., the UV-Vis data show substantial distinctions. Additionally, we explore the utilization of nickel(II)-corrole@CC (where CC denotes carbon cloth) as an electrocatalyst for the oxygen evolution reaction (OER) in an alkaline medium. During electrochemical water oxidation, the molecular catalyst is partially converted to nickel (oxy)hydroxide, Ni(O)OH. The structure reveals the coexistence of the molecular complex and Ni(O)OH in the active catalyst, achieving a turnover frequency (TOF) of 3.32 × 10-2 s-1. The synergy between the homogeneous and heterogeneous phases improves the OER activity, providing more active sites and edge sites and enhancing interfacial charge transfer.

Tuning Catalytic Activity of Ni–Co Nanoparticles Synthesized by Gamma‐Radiolytic Reduction of Acetate Aqueous Solutions

AbstractTransition metal‐based catalysts show great potential to replace Pt‐based material in energy conversion devices thanks to their low cost, reasonable intrinsic activity, thermodynamic stability, and corrosion resistance. The electrochemical performance of such catalysts is sensitive to their composition and structure. Here, it is demonstrated that homogeneous alloy nanoparticles with varying Ni‐to‐Co ratio and controlled structure can be synthesized from aqueous Ni(Co) acetate solutions using a facile γ‐radiolytic reduction method. The obtained samples are found to possess defects that are ordered to form polytypes structures. The concentration of these defects depends on the Ni‐to‐Co ratio, as supported by the results of ab initio calculations. It is found that structural defects may influence the activity of catalysts toward the oxygen evolution reaction, while this effect is less pronounced with respect to the oxygen reduction reaction. At the same time, the activity of Ni–Co catalysts in the hydrogen evolution reaction is affected by formation of NiOH bonds on the surface rather than by the presence of structural defects. This study demonstrates that the composition of NiCo nanoparticles is an essential factor affecting their structure, and both composition and structure can be tuned to optimize electrochemical performance with respect to various catalytic reactions.

Theoretical Assessment of the Mechanism and Active Sites in Alkene Dimerization on Ni Monomers Grafted onto Aluminosilicates: (Ni-OH)+ Centers and C-C Coupling Mediated by Lewis Acid-Base Pairs.

Ni-based solids are effective catalysts for alkene dimerization, but the nature of active centers and identity and kinetic relevance of bound species and elementary reactions remain speculative and based on organometallic chemistry. Ni centers grafted onto ordered MCM-41 mesopores lead to well-defined monomers that are rendered stable by the presence of an intrapore nonpolar liquid, thus enabling accurate experimental inquiries and indirect evidence for grafted (Ni-OH)+ monomers. Density functional theory (DFT) treatments presented here confirm the plausible involvement of pathways and active centers not previously considered as mediators of high turnover rates for C2-C4 alkenes at cryogenic temperatures. (Ni-OH)+ species act as Lewis acid-base pairs that stabilize C-C coupling transition states by polarizing two alkenes in opposite directions via concerted interactions with the O and H atoms in these pairs. DFT-derived activation barriers for ethene dimerization (59 kJ mol-1) are similar to measured values (46 ± 5 kJ mol-1) and the weak binding of ethene on (Ni-OH)+ is consistent with kinetic trends that require sites to remain essentially bare at subambient temperatures and high alkene pressures (1-15 bar). DFT treatments of classical metallacycle and Cossee-Arlman dimerization routes (Ni+ and Ni2+-H grafted onto Al-MCM-41, respectively) show that such sites bind ethene strongly and lead to saturation coverages, in contradiction with observed kinetic trends. These C-C coupling routes at acid-base pairs in (Ni-OH)+ differ from molecular catalysts in (i) the type of elementary steps; (ii) the nature of active centers; and (iii) their catalytic competence at subambient temperatures without requiring co-catalysts or activators.

Structural evolution of a water oxidation catalyst by incorporation of high-valent vanadium from the electrolyte solution

Electrochemical incorporation of high valent vanadium ions to obtain a V–Ni(OH)2–Ni(O)OH catalyst for water oxidation.

Multi-dimensional Ni(OH)2/(Ni(OH)2(NiOOH).167).857@Ni3S2 hierarchical structure for high-performance asymmetric supercapacitor

Multi-phase composite with multi-dimensional nano-structure is proved to have a more optimized electronic structure and abundant reactive active sites, which can effectively enhance the electrochemical behavior of the material. Herein, a three-phase hierarchical nanostructure electrode, Ni(OH)2/(Ni(OH)2(NiOOH).167).857@Ni3S2 (Ni(O)OH@Ni3S2), composed of 3-dimension (3D) Ni3S2 particles coated on the surface of the interlaced 1-dimension (1D) nanowires and 2-dimension (2D) nanosheets Ni(O)OH array, is successfully designed and constructed by a facile one-pot hydrothermal strategy. The formation mechanism is discussed by exploring the effect of S element content and hydrothermal time on the products. Benefiting from the synergistic effect between multi-dimensional nanomaterials, the Ni(O)OH@Ni3S2-1.0 composite electrode can deliver a high areal capacitance (11.74F cm−2 at 2 mA cm−2), displaying remarkable electrochemical behavior. In addition, the assembled Ni(O)OH@Ni3S2//AC asymmetric supercapacitor exhibits an areal energy density of 0.632 mWh cm−2 and an excellent cycling stability performance of 86.4 % after 6000 cycles at 100 mA cm−2. This work proposes the possibility and effectiveness of a one-step method to fabricate multi-dimensional and multi-phase composites for high-performance energy storage devices.

Efficient Co–Ni oxysulfide nanoarchitectured materials for long-lasting electrochemical cells: Biodegradable parafilm assisted pouch-type cells for portable electronic applications

An advance of highly efficient transition metal chalcogenides-based electroactive material for electrochemical cells (ECCs) is of high significance for endorsing large-scale sustainable fabrication of energy storage devices. Herein, the binary metal chalcogenide fish scales-like structures (FSSs) were directly grown on the conductive current collector (nickel foam) using a single-step sulfurization process. In this process, the reaction temperature plays a key role in generating the cobalt-nickel oxyhydroxide (Co–Ni)OH FSSs at a constant reaction time. As result, the as-designed (Co–Ni)OH-140 exhibited higher electrochemical performance than the other ones prepared at different reaction temperatures (i.e., 120 and 160 °C). Furthermore, the sulfur (S) dopant suggestively not only enhances the electrical conductivity but also improves the electrochemical performance of the electrode. The resulting Co–Ni oxysulfide ((Co–Ni)OS) FSS electrode exhibited significantly improved electrochemical activity with outstanding cycling retention of 116% even after 20000 cycles. Moreover, by utilizing the charge storage properties of the (Co–Ni)OS FSS electrode, an ECC was assembled, which is fabricated by using a biodegradable parafilm as the pouch. The as-fabricated ECC exhibited maximum areal/specific energy density (0.44 mWh cm −2 /65.9 Wh kg −1 ) and power density (51.5 mW cm −2 /7.6 kW kg −1 ) with a high rate capability of 59.1% even at a higher current density of 60 mA cm −2 . Furthermore, the self-powering work station with the wind turbine for energy conversion and the ECCs for charge storage was designed to drive portable electronic devices. The simple and cost-effective strategies of hierarchically connected nanomaterials provide a new path for the development of high-efficient ECCs. Synopsis: Binder-free metal chalcogenides-based nano active materials are designed using a single-step hydrothermal approach, followed by the sulfurization process. To assemble the electrochemical cell, biodegradable parafilm is used as the pouch-like bag to store energy, which can be stored from the wind energy to operate the real-time electronic appliances.

Activated Ni-OH Bonds in a Catalyst Facilitates the Nucleophile Oxidation Reaction.

The nucleophile oxidation reaction (NOR) is of enormous significance for organic electrosynthesis and coupling for hydrogen generation. However, the nonuniform NOR mechanism limits its development. For the NOR, involving electrocatalysis and organic chemistry, both the electrochemical step and non-electrochemical process should be taken into account. The NOR of nickel-based hydroxides includes the electrogenerated dehydrogenation of the Ni2+ -OH bond and a spontaneous non-electrochemical process; the former determines the electrochemical activity, and the nucleophile oxidation pathway depends on the latter. Herein, the space-confinement-induced synthesis of Ni3 Fe layered double hydroxide intercalated with single-atom-layer Pt nanosheets (Ni3 Fe LDH-Pt NS) is reported. The synergy of interlayer Pt nanosheets and multiple defects activates Ni-OH bonds, thus exhibiting an excellent NOR performance. The spontaneous non-electrochemical steps of the NOR are revealed, such as proton-coupled electron transfer (PCET; Ni3+ -O + X-H = Ni2+ -OH + X• ), hydration, and rearrangement. Hence, the reaction pathway of the NOR is deciphered, which not only helps to perfect the NOR mechanism, but also provides inspiration for organic electrosynthesis.

Cascading reconstruction to induce highly disordered Fe–Ni(O)OH toward enhanced oxygen evolution reaction

NiHCF nanocubes are in situ etched away and simultaneously induce the reconstruction of underneath Ni(OH)2 to form highly disordered Fe–Ni(O)OH.

Homoleptic Ni(II) dithiocarbamate complexes as pre-catalysts for the electrocatalytic oxygen evolution reaction.

Four new functionalized Ni(II) dithiocarbamate complexes of the formula [Ni(Lx)2] (1-4) (L1 = N-methylthiophene-N-3-pyridylmethyl dithiocarbamate, L2 = N-methylthiophene-N-4-pyridylmethyl dithiocarbamate, L3 = N-benzyl-N-3-pyridylmethyl dithiocarbamate, and L4 = N-benzyl-N-4-pyridylmethyl dithiocarbamate) have been synthesized and characterized by IR, UV-vis, and 1H and 13C{1H} NMR spectroscopic techniques. The solid-state structure of complex 1 has also been determined by single crystal X-ray crystallography. Single crystal X-ray analysis revealed a monomeric centrosymmetric structure for complex 1 in which two dithiocarbamate ligands are bonded to the Ni(II) metal ion in a S^S chelating mode resulting in a square planar geometry around the nickel center. These complexes are immobilized on activated carbon cloth (CC) and their electrocatalytic performances for the oxygen evolution reaction (OER) have been investigated in aqueous alkaline solution. All the complexes act as pre-catalysts for the OER and undergo electrochemical anodic activation to form Ni(O)OH active catalysts. Spectroscopic and electrochemical characterization revealed the existence of the interface of molecular complex/Ni(O)OH, which acts as the real catalyst for the OER. The active catalyst obtained from complex 2 showed the best OER activity achieving 10 mA cm-2 current density at an overpotential of 330 mV in 1.0 M aqueous KOH solution.

Theory-guided design of atomic Fe–Ni dual sites in N,P-co-doped C for boosting oxygen evolution reaction

The principle of how the active sites of catalysts match the reaction intermediates has long been sought after. Herein, we report a theory-guided atomic design and fabrication strategy of a C-based catalyst with diatomic Fe–Ni and N,P co-doping for the oxygen evolution reaction (OER). The configuration matching (with O∗ on the Ni site and OH∗ on the adjacent Fe site) and the local electron engineering by P doping significantly facilitate the rate-determining step of OOH∗ formation. Such diatomic Fe–Ni is demonstrated to be thermodynamically stable and is precisely constructed through the pyrolysis of Fe 3+ /Ni 2+ -adsorbed ZIF-8 under NaH 2 PO 2 co-feeding. The synergistic effects endow the catalyst with a low overpotential and high turnover frequency, exceeding all transition-metal N-based catalysts so far as we know, which provides a deep understanding of the OER mechanism on heteroatomic metal-based catalysts. This strategy will pave the way for novel catalyst design and the replacement of noble-metal-based catalysts. • Atomic Fe–Ni dual sites in N,P-co-doped C as efficient OER catalyst • The OER mechanism on Fe–Ni dual sites with P doping is explored by DFT calculation • The rational fabrication of Fe–Ni dual sites is confirmed by GC-MC simulation • A high-performance Zn-air battery with an Fe-Ni-N-P-C-based cathode is achieved The global warming caused by fossil fuels stimulates the development of clean-energy devices, such as metal-air batteries, water splitting, and fuel cells, in which the anodic reaction of the oxygen evolution reaction (OER) has attracted great attention. However, the intrinsic sluggish kinetics and costly noble-metal-based catalysts have vitally limited its flourishing. Great efforts have been devoted to developing cost-effective transition-metal-based catalysts, but the understanding of synergistic effects of multi-active sites and the controllable fabrication strategies are still in their infancy. We report a theory-guided atomic design and fabrication of diatomic Fe–Ni sites in N,P-co-doped C, which achieves geometric and local electron matching with OOH∗ intermediate, leading to superior OER performance. Our work provides deep insight into how active sites interact with intermediates at an atomic level and will pave the way for the development of electrocatalysts with multi-active sites. Pan et al. provide a theory-guided design and fabrication strategy of atomic Fe–Ni dual sites in N,P-co-doped C as catalysts for the oxygen evolution reaction (OER). The enhanced OER activity originates from the geometric and electron matching between Fe–Ni dual sites with P doping and OOH∗ intermediates. This strategy, considering configuration matching with local electron modulation, will pave the way for the rational design, fabrication, and mechanistic understanding of catalysts with dual-metallic active sites in various complex reaction systems.

Hydrosilylative reduction of primary amides to primary amines catalyzed by a terminal [Ni-OH] complex.

A terminal [Ni-OH] complex 1, supported by triflamide-functionalized NHC ligands, catalyzes the hydrosilylative reduction of a range of primary amides into primary amines in good to excellent yields under base-free conditions with key functional group tolerance. Catalyst 1 is also effective for the reduction of a variety of tertiary and secondary amides. In contrast to literature reports, the reactivity of 1 towards amide reduction follows an inverse trend, i.e., 1° amide > 3° amide > 2° amide. The reaction does not follow a usual dehydration pathway.

Insights into CO2 Adsorption in M–OH Functionalized MOFs

A series of benzotriazolate MOFs containing nucleophilic transition metal hydroxide (M–OH) groups has been synthesized to compare the effects of framework structure, metal composition, and method of postsynthetic ligand exchange (PSLE) on CO2 adsorption. Analogues of MFU-4 (1a/b-OH, [Zn5(OH)4(bbta)3], bbta2– = benzo-1,2,4,5-bistriazolate) and MFU-4l (2a/b-OH, [Zn5(OH)4(btdd)3], btdd2– = bis(1,2,3-triazolo)dibenzodioxin) were prepared by direct Cl–/OH– ligand exchange (a) or Cl–/HCO3– ligand exchange followed by thermal activation (b). A Ni/Zn heterobimetallic analogue of MFU-4l (2a/b-NiOH) was also synthesized to investigate the effect of metal identity. The products have been characterized by powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). All of the M–OH functionalized MOFs show steep CO2 adsorption at low partial pressures. However, materials synthesized using the direct Cl–/OH– ligand exchange method show greater low-pressure CO2 uptake than those prepared by Cl–/HCO3– PSLE. Notably, the small pore size in 1a/b-OH not only promotes stronger framework–CO2 interactions and higher CO2 uptake than 2a/b-OH but also results in slow adsorption kinetics. The Ni/Zn heterobimetallic analogue 2a-NiOH exhibits the greatest low-pressure CO2 capacity (1.70 mmol g–1 at 2.6 mbar) among the series. In situ DRIFTS studies reveal that both 2a-OH and 2a-NiOH contain weak Zn–OH binding sites that readily desorb CO2 at room temperature. However, 2a-NiOH also contains strong Ni–OH binding sites that are spectroscopically distinct and only desorb CO2 upon heating.

Autologous growth of Fe-doped Ni(OH)2 nanosheets with low overpotential for oxygen evolution reaction

Highly active and durable electrocatalysts for oxygen evolution reaction (OER) play a vital role in water splitting. Despite numerous efforts, the strategies to prepare durable and effective electrocatalysts via scalable methods still remain a great challenge. In this work, we fabricated Fe-doped Ni(OH)2 ultrathin nanosheets (Fe–Ni–OH/Ni) via autologous growing of Ni(OH)2 from Ni foam, and in situ electrochemical-assisted doping Fe into Ni(OH)2. Benefiting from the unique structure with large surface areas and strong coupling effects between Fe and Ni, the optimal Fe–Ni–OH electrodes exhibit remarkable catalytic performance toward OER, which requires an overpotential of 220 mV to achieve a current density of 10 mA cm−2 with a Tafel slope of 48.3 mV dec−1. The Fe–Ni–OH electrodes also possess high stability even under a high current density of 500 mA cm−2 for 600 h with an ultralow overpotential of 290 mV. Using Ni–Fe–OH electrodes as both anode and cathode for overall water splitting, only a small overpotential of 1.57 V is required to reach a current density of 10 mA cm−2. Moreover, the high catalytic performance and scalable preparation method can meet the emergency needs for the practical application.

Nickel Doping Enhances the Reactivity of Fe3O4(001) to Water

We studied how nickel doping affects water adsorption at the Fe3O4(001) surface to understand the enhanced performance of spinel ferrites for the water-gas shift and oxygen evolution reactions. Two different configurations were prepared: 2-fold-coordinated Ni adatoms on top of the surface and Ni atoms incorporated into the octahedral sites of the support. Using temperature-programmed desorption, X-ray photoemission spectroscopy, and scanning tunneling microscopy, we show that water is adsorbed and dissociated on the nickel adatoms at room temperature, resulting in Ni–OH species and surface hydroxyl groups. Nickel atoms incorporated into the support do not directly adsorb water but modify the electronic properties of the surface Fe, and water adsorbed on these sites has similar characteristics as that of water adsorbed on intrinsic surface defects. In both cases, the presence of Ni significantly alters the growth of the first water monolayer on Fe3O4(001).

New Transition Metal Oxo‐Thiostannate: Synthesis, Characterization, and Investigation of its Photocatalytic Properties

The new transition metal oxo‐thiostannate {[Ni(cyclen)]6[Sn6S12O2(OH)6]}·2(ClO4)·19H2O (1) was prepared under hydrothermal conditions using Na4SnS4·14H2O and [Ni(cyclen)](ClO4)2 as reactants. In the crystal structure the rare [Sn6S12O2(OH)6]10– anion is observed, which is composed of SnS2O(OH)3 and SnS4O2 octahedra, and SnS4 tetrahedra sharing edges and corners. The anion is expanded by six Ni2+ centered complexes via Ni–S and Ni–OH bonds. The photocatalytic properties for the visible light driven hydrogen evolution reaction shows that 26.6 mmol·g–1 H2 were evolved after 3 h.

Investigation of Nitrile Hydration Chemistry by Two Transition Metal Hydroxide Complexes: Mn–OH and Ni–OH Nitrile Insertion Chemistry

Herein we describe the synthesis of a series of nickel complexes, including the formation of [(iPrPNHP)Ni(PMe3)][BPh4] (iPrPNHP = HN(CH2CH2(PiPr2))2). The ability of this phosphine complex to perform the 1,2-addition of H2O to produce the Ni–OH species [(iPrPNHP)NiOH][BPh4] has been investigated. The nucleophilicity of the hydroxide moiety of both [(iPrPNHP)NiOH][BPh4] and the previously reported (iPrPNHP)MnOH(CO)2 was investigated through the hydration of aryl and alkyl nitriles, leading to the formation of a number of metal carboxamide (RC(O)NH–) bonds. This reactivity generated complexes with the general structures of [(iPrPNHP)Ni(NHC(O)R)][BPh4] for nickel and (iPrPNHP)Mn(NHC(O)R)(CO)2 for manganese. Under catalytic conditions, the hydration of nitriles using nickel complexes yielded only a single turnover. However, (iPrPNHP)MnOH(CO)2 produced several turnovers, and the reaction conditions were probed for optimization.

Terminal NiII−OH/−OH2 complexes in trigonal bipyramidal geometries derived from H2O

The preparation and characterization of two NiII complexes are described, a terminal NiII–OH complex with the tripodal ligand tris[(N)-tert-butylureaylato)-N-ethyl)]aminato ([H3buea]3−) and a terminal NiII–OH2 complex with the tripodal ligand N,N′,N″-[2,2′,2″-nitrilotris(ethane-2,1-diyl)]tris(2,4,6-trimethylbenzenesulfonamido) ([MST]3−). For both complexes, the source of the –OH and –OH2 ligand is water. The salts K2[NiIIH3buea(OH)] and NMe4[NiIIMST(OH2)] were characterized using perpendicular-mode X-band electronic paramagnetic resonance, Fourier transform infrared, UV–vis spectroscopies, and its electrochemical properties were evaluated using cyclic voltammetry. The solid state structures of these complexes determined by X-ray diffraction methods reveal that they adopt a distorted trigonal bipyramidal geometry, an unusual structure for 5-coordinate NiII complexes. Moreover, the NiII–OH and NiII–OH2 units form intramolecular hydrogen bonding networks with the [H3buea]3− and [MST]3− ligands. The oxidation chemistry of these complexes was explored by treating the high-spin NiII compounds with one-electron oxidants. Species were formed with S=1/2 spin ground states that are consistent with formation of monomeric NiIII species. While the formation of NiIII–OH complexes cannot be ruled out, the lack of observable O–H vibrations from the putative Ni–OH units suggest the possibility that other high valent Ni species are formed.

DFT study of the adsorption and dissociation of water on Ni(111), Ni(110) and Ni(100) surfaces

Water adsorption and dissociation on catalytic metal surfaces play a key role in a variety of industrial processes, and a detailed understanding of this process and how it is effected by the surface structure will assist in developing improved catalysts. Hence, a comparative study of the adsorption and dissociation of water on Ni(111), Ni(110) and Ni(100) surfaces, which is often used as catalyst, has been performed using density functional theory. The results show that the adsorption energies and dissociation rates depend on the surface structure. The adsorption energies for H2O and OH decrease in the order Ni(110)>Ni(100)>Ni(111), and for the O and H atoms the adsorption energies decrease in the order Ni(100)>Ni(111)>Ni(110). In addition, the splitting of water to OH and H has lower activation energies over less packed Ni(110) and Ni(100) surfaces compared to the highly packed Ni(111) surface. The subsequent splitting of the OH to O and H also has the lowest activation energy on the Ni(110) surface. At 463K, which is typical for industrial processes that include the water gas shift reaction, the H2O splitting is approximately 6000 and 10 times faster on the Ni(110) surface compared to the Ni(111) and Ni(100) surfaces, respectively, and OH splitting is 200 and 3000 times faster, respectively. The complete water dissociation reaction rate decreases in the order Ni(110)>Ni(100)>Ni(111).