Single Ni Atom Research Articles

Powerful CO2 electroreduction performance with N–carbon doped with single Ni atoms

A single-atom dispersed Ni doping strategy to boost the performance of N–C materials for CO2RR by the pyrolysis of a metal–organic molecule complex was reported and revealed.

Dry Reforming of Methane on Single-Site Ni/MgO Catalysts: Importance of Site Confinement

Single-site catalysts (SSCs) have drawn considerable attention, because of their superior behaviors in catalysis. However, the origin of promoting the effect of a single site is not well understood. Here, we take the single-atom Ni1/Mg(100) and single-site Ni4/Mg(100) catalysts as a case study to elucidate their behaviors under the complex dry reforming of methane (DRM, CO2 + CH4→ 2CO + 2H2) reaction by combining theoretical modeling (density functional theory and kinetic Monte Carlo simulation) and experimental studies. The synergy between single Ni atom and MgO is found to improve the binding property of MgO; yet, it is not enough to dissociate CO2 and CH4. It can be achieved by the single-site Ni4/MgO(100) catalyst, enabling the formations of CO, H2, and H2O under the DRM conditions. During this process, coking, as observed for bulklike Ni particles, is eliminated. By confining the reaction to occur at the isolated Ni sites in the SSC, the Ni4/MgO(100) catalyst is able to balance the CO2 and CH4 activa...

Design of active nickel single-atom decorated MoS2 as a pH-universal catalyst for hydrogen evolution reaction

MoS2 has been considered as a potential alternative to Pt-based catalysts in the hydrogen evolution reaction (HER). However, the presence of the inactive in-plane domains limits their intrinsic electrocatalytic activity of the catalyst. Here, we demonstrate a new approach for activating these inactive sites and therefore dramatically enhancing the activity. We discover that decorating single Ni atom on MoS2 can increase the HER activity in both alkaline and acidic conditions. Experimental and theoretical results indicate that single Ni atom modifiers are inclined to single dispersion in the S-edge sites and H-basal sites of MoS2, resulting in a favorable change in the adsorption behavior of H atoms on their neighboring S atoms and subsequently the HER activity. Consequently, the single-Ni-atom decorated MoS2 (NiSA-MoS2) achieved cathodic current density of 10 mA cm−2 at overpotentials of 98 mV and 110 mV in 1 M KOH and 0.5 M H2SO4, respectively. The dispersion of the Ni single atoms in the NiSA-MoS2 is unaffected upon 2000 cycles in both acidic and alkaline conditions. This single atom decorating approach presents a facile and promising pathway for designing active electrocatalysts for energy conversion and storage.

Adjustable photocatalytic ability of monolayer g-C3N4 utilizing single–metal atom: Density functional theory

Single–atom catalysis is an effective method to improve the catalytic efficiency. With the aid of density functional theory calculations, we investigated the thermodynamic performances during water splitting besides the structural and electronic performances of monolayer g–C3N4 embedded with single Ni, Pd, Pt, Cu, Ag or Au atom. Based on the detailed analysis of the electronic redistributions and chemical bond relaxations, the ratio of ionic and covalent bonding parts of chemical bonds were adjusted by the single atoms, it changed the adsorption energy of intermediates, the free energy changes during reaction and then the overpotentials of oxidation evolution reaction (OER) and hydrogen evolution reaction (HER). Interestingly, the overpotentials of OER and HER reduce as the percentage of covalent bonding parts is close to a certain value, which are conductive to improve the OER and HER efficiency. In addition, the differences of redox potentials between catalysts and water oxidation/H+ reduction are larger than the corresponding overpotentials of OER and HER on Pd1/ and Pt1/g–C3N4, thus the OER and HER can happen on them.

Electronic and Magnetic Properties of Ni-Doped Zinc-Blende ZnO: A First-Principles Study.

The electronic structure, band structure, density of state, and magnetic properties of Ni-doped zinc-blende (ZB) ZnO are studied by using the first-principles method based on the spin-polarized density-functional theory. The calculated results show that Ni atoms can induce a stable ferromagnetic (FM) ground state in Ni-doped ZB ZnO. The magnetic moments mainly originate from the unpaired Ni 3d orbitals, and the O 2p orbitals contribute a little to the magnetic moments. The magnetic moment of a supercell including a single Ni atom is 0.79 μB. The electronic structure shows that Ni-doped ZB ZnO is a half-metallic FM material. The strong spin-orbit coupling appears near the Fermi level and shows obvious asymmetry for spin-up and spin-down density of state, which indicates a significant hybrid effects from the Ni 3d and O 2p states. However, the coupling of the anti-ferromagnetic (AFM) state show metallic characteristic, the spin-up and spin-down energy levels pass through the Fermi surface. The magnetic moment of a single Ni atom is 0.74 μB. Moreover, the results show that the Ni 3d and O 2p states have a strong p-d hybridization effect near the Fermi level and obtain a high stability. The above theoretical results demonstrate that Ni-doped zinc blende ZnO can be considered as a potential half-metal FM material and dilute magnetic semiconductors.

Ethanol synthesis catalyzed by single Ni atom supported on Mo6S8 support

Conversion of carbon monoxide (CO) into ethanol has attracted significant interest due to ethanol can be used as alternative energy sources to satisfy the rising global energy demands and to solve the serious environmental problems, although it suffers from slow kinetics and low selectivity. Metal single-atom catalyst of Ni single atom supported on Mo6S8 (Ni-SA/Mo6S8) catalyst was developed for the exclusive conversion of CO into ethanol. Herein, ethanol synthesis on Ni-SA/Mo6S8 was systematically investigated using density functional theory (DFT) and microkinetic modeling. The adsorption situations and the reaction routes for ethanol reactions on Ni-SA/Mo6S8 were clarified. Interestingly, the selectivity to ethanol is controlled by CH3 formation and CC bond formation between CH3 species and CHO. Our results indicated that Ni-SA/Mo6S8 increases the stability of the reaction intermediates, and CH3 is the most favorable formed by CH3OH dissociation. Then CHO insertion into CH3 to form CH3CHO* is spontaneous, which suggested that the formation of ethanol is the most favorable on the Ni-SA/Mo6S8 catalyst. The BEP relationships of five different types of bonds in ethanol synthesis identified CO bond scission does not readily occur compared to the other four types of bonds, the formation of CH, OH, and CC bonds are easy to occur. Microkinetic modeling also confirmed Ni-SA/Mo6S8 shows extremely activity and selectivity for ethanol formation. We hope our study can provide the basis to understand and develop single-atom catalysis for ethanol synthesis.

Direct imaging of a single Ni atom cutting graphene to form a graphene nanomesh

A large area graphene nanomesh (GNM) etched by Ni is synthesized by a facile one-step liquid arc discharge in a Ni-containing solution. Atomic-resolution scanning transmission electron microscopy (STEM) combined with electron energy loss spectroscopy (EELS) is applied to identify the atomic structures of the product. The results show that the GNM with a pore size of about 10-50 nm comprises single- or few layer graphene, and there are some small pores of size 1 nm and defects of five membered rings or seven membered rings in the positions of the skeletons. Also Ni atoms or nanoparticles are uniformly distributed in graphene or at the edges of the GNM. A dynamic study using a microscope shows that the Ni atom at the edge of graphene is active and can move along the edge, which facilitates the fracture of C-C bonds and the diffusion of carbon atoms greatly. DFT calculation results show that the diffusion of carbon atoms along the edge in the GNM containing Ni is easier than that in pristine graphene. The Ni atoms or particles act as an "atomic knife" to cut the graphene sheet to feed the formation of the GNM. These results represent a significant advancement in the growth mechanism study of GNMs and thus the precise structure control of graphene.

Single Ni atoms and Ni4 clusters have similar catalytic activity for ethylene dimerization

Atomic layer deposition (ALD) of Ni on the metal–organic framework NU-1000 has been shown to generate a material that serves as a catalyst for ethylene dimerization. However, the precise nature of the active catalytic site or sites remains uncertain. Here we employ periodic density functional calculations to characterize the structure and reactivity of the deposited species. Optimized lattice constants for a sequence of structures incorporating successively more Ni4-hydroxo clusters in the c pore of NU-1000 show good agreement with experimental trends involving multiple ALD cycles; therefore we study the catalytic cycle for this cluster in detail, and we compare it to that for a site with only a single Ni atom. We find that both the atomic Ni catalyst and the Ni4-hydroxo cluster have higher catalytic activity in the singlet state than in the triplet state. We also find that the two catalysts have very similar activity. Thus, precise size control of the active catalytic species is not essential for ethylene dimerization in this system.

Single Ni atom incorporated with pyridinic nitrogen graphene as an efficient catalyst for CO oxidation: first-principles investigation

We have investigated the potential catalytic activity of a single Ni atom incorporated with pyridinic nitrogen graphene (Ni-3N-G) in CO oxidation with first-principles calculations.

Adsorption Properties of Typical Lung Cancer Breath Gases on Ni-SWCNTs through Density Functional Theory

A lot of useful information is contained in the human breath gases, which makes it an effective way to diagnose diseases by detecting the typical breath gases. This work investigated the adsorption of typical lung cancer breath gases: benzene, styrene, isoprene, and 1-hexene onto the surface of intrinsic and Ni-doped single wall carbon nanotubes through density functional theory. Calculation results show that the typical lung cancer breath gases adsorb on intrinsic single wall carbon nanotubes surface by weak physisorption. Besides, the density of states changes little before and after typical lung cancer breath gases adsorption. Compared with single wall carbon nanotubes adsorption, single Ni atom doping significantly improves its adsorption properties to typical lung cancer breath gases by decreasing adsorption distance and increasing adsorption energy and charge transfer. The density of states presents different degrees of variation during the typical lung cancer breath gases adsorption, resulting in the specific change of conductivity of gas sensing material. Based on the different adsorption properties of Ni-SWCNTs to typical lung cancer breath gases, it provides an effective way to build a portable noninvasive portable device used to evaluate and diagnose lung cancer at early stage in time.

Single Ni sites distributed on N-doped carbon for selective hydrogenation of acetylene.

We prepared single Ni atoms embedded in an N-doped carbon catalyst with the assistance of metal organic frameworks. The dispersion of Ni atoms was verified by taking X-ray absorption fine structure measurements. Under the typical conditions for hydrogenation of acetylene, this single-site heterogeneous catalyst showed great potential as an alternative to Pd-based materials.

First-principles study of single transition metal atoms on ZnO for the water gas shift reaction

A single Ni atom substituted on a ZnO surface is a promising catalyst for the water gas shift reaction.

The adsorption of mercury species and catalytic oxidation of Hg0 on the metal-loaded activated carbon

The adsorption of mercury species (Hg0, HgCl and HgCl2) and catalytic oxidation of Hg0 on the metal-loaded activated carbon (AC) with single Fe, Co, Ni, Cu and Zn atom have been studied using the periodic density functional theory (DFT) method. The results indicate that Hg0 interacts with metal-loaded AC surfaces via a physical adsorption mechanism, while chemisorptions are likely adsorption mechanisms for HgCl and HgCl2. The existence forms of HgCl and HgCl2 on metal-loaded AC surfaces are dissociated or molecular, which greatly depend on initial interaction modes between mercury species and surfaces. Besides, in the presence of Cl2, Hg0 is oxidized to be HgCl2 molecule on the Fe/AC surface, while dissociatively adsorbed HgCl2 is predominant on Ni/AC, Cu/AC and Zn/AC surfaces, but both molecular and dissociated HgCl2 exist on the Co/AC surface. What’s more, the kinetic results show that the oxidation energy barrier of Hg0 on the Fe/AC surface is the lowest, implying that Fe-loaded AC is a favorable heterogeneous catalyst for Hg0 oxidation from the point of view of efficiency and cost.

Spin-polarized transport in hydrogen-passivated graphene and silicene nanoribbons with magnetic transition-metal substituents.

We present a systematic theoretical study of the electronic transport in hydrogen passivated zigzag graphene and silicene nanoribbons with between zero and four neighboring H atoms on one edge replaced by magnetic transition metals (Fe, Co, and Ni). The calculations were performed using equilibrium transport and density-functional theory with the generalized gradient approximation to exchange and correlation. We considered the magnetic moments of the two edges aligned both ferromagnetically (Ferro-F form) and antiferromagnetically (Ferro-A form). The Ferro-A graphene-based ribbons were all semiconducting and would support moderate spin-polarized currents of either sign by applying positive or negative gate voltages. The Ferro-F graphene-based ribbons were all metallic; the most interesting for possible spintronic applications being that with a single Ni atom, in which strong spin-filtering at low bias resulted from a deep trough in the transmission of one spin component around the Fermi level. By contrast, in the Si-based analog this trough was split, partially eliminating the polarization of the current. This splitting was found to be related to the buckled structure of the Si-based nanoribbon, which has its origin in its preference for sp(3)-like hybridization.

The first-principles study on the interaction of Ni with the yttria-stabilized zirconia and the activity of the interface

Solid oxide fuel cell (SOFC) is expected to be a crucial technology in future power generation due to its advantages of high efficiency, fuel adaptability, all-solid state, modular assembly, and low pollution. The Ni/YSZ (yttrium-stabilized zirconia) cermet is the most popular anode material in SOFCs. However, a major problem is that it can be easily oxidized, thus resulting in the decline of long-term stability and activity as an anode catalyst. A better performance of the Ni/YSZ cermet can be obtained by improving its microstructure as well as the Ni distribution in it. Interactions between Ni and the yttria-stabilized zirconia (YSZ) (111) or oxygen-enriched YSZ(111) (YSZ+O) surface are studied in terms of the first-principles method based on the density functional theory with particular focus put on the activity of the Ni atom at the interface. The geometric and electronic structures of CO and O2 on the Ni1 (the single Ni atom)/YSZ and Ni1/YSZ+O surfaces are also studied. It is found that the Ni atom tends to be adsorbed to O sites and away from the Y atoms on both the surfaces. The most favorable adsorption site is the oxygen vacancy, which has an adsorption energy of 2.85 eV. Compared with YSZ, the single Ni atom loses 1.06 electrons and is oxidized as Ni+ on YSZ+O, which produces a strong interaction between the Ni atom and YSZ+O. Strong adsorption is mainly attributed to the interaction between Ni 3d and Ou 2p orbitals. And the oxidation of Ni can lead to the decrease of electrocatalytic activity of the Ni catalyst. The d-band DOS (density of states) peaks of the Ni1/YSZ+O are lower than that of the Ni1/YSZ, and the corresponding d-band centers are shifted away from the Fermi level to lower energy with the d value of -3.69 eV; therefore the CO and O2 adsorption is weakened. While the adsorption energy for CO on the Ni1/YSZ+O (0.42 eV) is much lower than that on the Ni1/YSZ surface (1.78 eV). In addition, the adsorbed CO gains 0.07 electrons, less than those on the Ni1/YSZ surface (0.34 e). The adsorption energy of O2 on Ni1/YSZ+O also decreases (0.34 eV) and gains fewer electrons (0.24 e) as compared with the corresponding values (2.57 eV, 1.15 eV) on Ni1/YSZ. Results would improve our understanding on the mechanism of oxidation of Ni on the Ni/YSZ anode of SOFCs and would be of great importance for designing highly active catalysts used for fuel cells.

Site-dependent magnetism of Ni adatoms on MgO/Ag(001)

We examine the adsorption of a single Ni atom on a monolayer of MgO on a Ag substrate using DFT and $\mathrm{DFT}+U$ computational approaches. We find that the electronic and magnetic properties vary considerably across the three binding sites of the surface. Two of the binding sites are competitive in energy, and the preferred site depends on the strength of the on-site Coulomb interaction $U$. These results can be understood in terms of the competition between bonding and magnetism for surface adsorbed transition metal atoms. Comparisons are made with a recent experimental and theoretical study of Co on MgO/Ag, and implications for scanning tunneling microscopy experiments on the Ni system are discussed.

High Capacity Hydrogen Storage in Ni Decorated Carbon Nanocone: A First-Principles Study

Hydrogen adsorption and storage on Ni-decorated CNC has been investigated by using DFT. A single Ni atom decorated CNC adsorbs up to six H2 with a binding energy of 0.316 eV/H2. The interaction of 3H2 with Ni-CNC is irreversible at 603 K. In contrast, the interaction of 4H2 with Ni-CNC is reversible at 456 K. Further characterizations of the two reactions are considered in terms of the projected densities of states, electrophilicity, and statistical thermodynamic stability. The free energy of the reaction between 4H2 and Ni-CNC, surface coverage and rate constants ratio meet the ultimate targets of DOE at 11.843 atm, 0.925 and 1.041 respectively. The Ni-CNC complexes can serve as high-capacity hydrogen storage materials with capacities of up to 11.323 wt.%. It is illustrated that unless the access of oxygen to the surface is restricted, its strong bond to the decorated systems will preclude any practical use for hydrogen storage.

First-principle study of methanol adsorption on Ni (Pd)-decorated graphene

Ab initio first-principle calculations, including dispersion correction, were carried out to investigate Ni (Pd)-decorated graphene for its application as methanol storage materials. Structural optimization showed that the CH3OH molecule is physisorbed on the pristine sheet via van der Waals forces with the adsorption energy of −11.7 kcal/mol. It was found that unlike the pristine graphene, metal-decorated sheet can effectively interact with the CH3OH molecule, so that single Ni and Pd atoms prefer to bind strongly on the top of the bridge site of graphene, and each metal atom bound on the sheet may adsorb up to four CH3OHs. Furthermore, no bond dissociation was observed for the adsorption of CH3OH on Ni (Pd)-decorated graphene, which means that decorated sheet can act as a storage device for methanol safety storage. The results also indicated that decoration of the Ni and Pd atoms on the surface of graphene induces some changes in the electronic properties of the sheet and its E g remained unchanged after the adsorption of CH3OH molecules.

A DFT study of formaldehyde adsorption on functionalized graphene nanoribbons

Density functional theory (DFT) based ab initio calculations were done to monitor the formaldehyde (CHOH) adsorptive behavior on pristine and Ni-decorated graphene sheet. Structural optimization indicates that the formaldehyde molecule is physisorbed on the pristine sheet via partly weak van der Waals attraction having the adsorption energy of about −15.7kcal/mol. Metal decorated sheet is able to interact with the CHOH molecule, so that single Ni atoms prefer to bind strongly at the bridge site of graphene and each metal atom bound on sheet may adsorb up to four CHOH. The findings also show that the Ni decoration on graphene surface results in some changes in electronic properties of the sheet and its Eg is remained unchanged after adsorption of CHOH molecules. It is noteworthy to say that no bond cleavage was observed for the adsorption of CHOH on Ni-decorated graphene.

Theoretical characterisation of irreversible and reversible hydrogen storage reactions on Ni-doped C60 fullerene

An attempt has been made to characterise the irreversible and reversible hydrogen storage reactions on Ni-doped C60 fullerene by using the state of the art density functional theory calculations. The single Ni atom prefers to bind at the bridge site between two hexagonal rings of C60 fullerene, and can bind up to four hydrogen molecules with average adsorption energies of −0.85, −0.83, −0.58, and −0.31 eV per hydrogen molecule. No evidence for metal clustering in the ideal circumstances and the hydrogen storage capacity is expected to be as large as 8.9 wt%. While the desorption activation barriers of the complexes nH2NiC60 (n = 1, 2) are outside the desirable energy window recommended by the department of energy for practical applications (–0.2 to –0.6 eV), the desorption activation barriers of the complexes nH2NiC60 (n = 3, 4) are inside this window. The irreversible 2H2 + NiC60 and reversible 3H2 + NiC60 interactions are characterised in terms of several theoretical parameters such as: (1) densities of states and projected densities of states, (2) pairwise and non-pairwise additivity, (3) infrared, Raman, and proton magnetic resonance spectra, (4) electrophilicity, and (5) statistical thermodynamic stability.