Single Ni Atom Research Articles

Effect of Ni-Doping on the Optical, Structural, and Electrochemical Properties of Ag29Nanoclusters.

Atomically precise metal nanoclusters (NCs) can be compositionally controlled at the single-atom level, but understanding structure-property correlations is required for tailoring specific optical properties. Here, the impact of Ni atom doping on the optical, structural, and electrochemical properties of atomically precise 1,3-benzene dithiol (BDT) protected Ag29 NCs is studied. The Ni-doped Ag29 (NiAg28(BDT)12) NCs, are synthesized using a co-reduction method and characterized using electrospray ionization mass spectrometry (ESI MS), ion mobility spectrometry (IMS), and X-ray photoelectron spectroscopy (XPS). Only a single Ni atom doping can be achieved despite changing the precursor concentration. Ni doping in Ag29 NCs exhibits enhanced thermal stability, and electrocatalytic oxygen evolution reaction (OER) compared to the parent NCs. Density functional theory (DFT) calculations predict the geometry and optical properties of the parent and NiAg28(BDT)12 NCs. DFT is also used to study the systematic single-atom doping effect of metals such as Au, Cu, and Pt into Ag29 NCs and suggests that with Ni and Pt, the d atomic orbitals contribute to creating superatomic orbitals, which is not seen with other dopants or the parent cluster. The emission mechanism is dominated by a charge transfer from the ligands into the Ag core cluster regardless of the dopant.

TM@MoSSe (TM = Ni, Fe) as novel electrocatalysts for reduction of CO2 to CO: A DFT study

It is crucial to develop highly efficient, selective and low-overpotential electrocatalysts for CO2 reduction. This paper proposes an efficient iron and nickel single-atom catalyst using Janus MoSSe as the substrate to reduce CO2 to CO by using DFT calculations. The adsorption of a single TM atom like Fe, Co, Ni, Ru, Rh, Pd, Os, Ir and Pt on Janus MoSSe monolayer results in a decrease in band gap, which may accelerate the catalytic CO2 reduction. The excellent catalytic activity of Fe@MoSSe and Ni@MoSSe is owing to the high d-band center and hence the strong TM-CO2 bonding. The asymmetric structure of Janus MoSSe creates the local built-in electric field, which further increases by about 8% or 0.8% after the adsorption of single Ni or Fe atom so as to afford the better electrocatalytic performances for reduction of CO2 to CO in both TM modified systems. So, this work proposes the catalysts Fe@MoSSe and Ni@MoSSe with good selectivity and activity for CO2 reduction by revealing their underlying mechanisms, and Janus MoSSe may be used as a potential substrate material for CO2 reduction catalysts.

Unveiling the Composition-Dependent Catalytic Mechanism of Pt-Ni Alloys for Oxygen Reduction: A First-Principles Study.

Unveiling the composition-dependent catalytic mechanism of Pt-based alloy cathodes for the oxygen reduction reaction (ORR) helps improve the proton exchange membrane fuel cells. Using density functional theory calculations, this study investigates the ORR catalytic performance of the Pt-Ni system with various compositions (1.00, ∼0.99, 0.75, 0.50, 0.25, ∼0.01, and 0.00). The ordered solid solution PtNi3(111) system shows activity comparable to Pt(111) and is cost-effective. The Ni1/Pt(111) system, featuring a single Ni atom on the Pt(111) surface as a surface single-atom alloy (SSAA), demonstrates the highest activity with an overpotential of only 0.28, which could be further reduced to 0.21 V by decreasing the surface Ni concentration to 1/16 monolayer coverage. The predicted high activity of Ni1/Pt(111) is confirmed when considering factors such as the implicit solution environment, constant potential conditions, and protonation capability. Moreover, surface-adsorbed oxygen species driven by reaction conditions stabilize these single Ni atoms of Ni1/Pt(111) by preventing segregation and dissolution processes, thereby exhibiting a dual functionality. This study reveals the composition dependence of Pt-based alloys and highlights the stability mechanisms of SSAA catalysts during the ORR.

Rigidly Axial O Coordination-Induced Spin Polarization on Single Ni-N4-C Site by MXene Coupling for Boosting Electrochemical CO2 Reduction to CO.

Regulating the spin states in transition-metal (TM)-based single-atom catalysts (SACs), such as the TM-Nx-C configurations, is crucial for improving the catalytic activity. However, the role of spin in single Ni atoms facilitating the electrochemical CO2 reduction reaction (CO2RR) has been largely overlooked. Using first-principles simulations, we investigated the electrocatalytic performance of Ni-N4-C SACs vertically stacked on the O-terminated MXene nanosheets for the CO2RR. The terminated O atoms on MXene axially interact with the Ni atom due to significant charge transfer between them. Unlike the pure Ni-N4 site, which lacks spin polarization, the newly formed Ni-N4O configuration breaks the spin degeneracy of Ni d orbitals, dramatically lifting the energy level of spin-down d orbitals relative to that of spin-up d orbitals. As a result, the d electrons of Ni in the two spin channels are rearranged, leading to large net spin moments of 1.4 μB. Compared to the Ni-N4 site, the partially filled minority-spin dz2 orbitals of Ni on Ni-N4O weaken the occupied d-π* orbitals between Ni and *COOH, significantly stabilizing the key intermediate. The detailed reaction mechanisms and energetics show that four MXenes, namely, Hf3C2, Zr3C2, Hf2C, and Zr2C, can induce a large spin on the Ni site, thereby improving catalytic activity for CO2 reduction to CO, with a lower onset potential of about -0.75 V vs SHE compared to pure Ni SACs (-1.17 V) according to the potential-constant model with an explicit solvent environment.

Construction of Nickel Single Atoms by Using the Inherent Confined Space in Template-Occupied Mesoporous Silica.

Due to their maximum atomic use of metal sites, single-atom catalysts (SACs) exhibit excellent catalytic activity in a variety of reactions. Although many techniques have been reported for the production of SACs, the construction of single atoms through a convenient strategy is still challenging. Here, we provide a facile method to prepare nickel SACs by utilizing the inherent confined space between the template and silica walls in template-occupied mesoporous silica KIT-6 (TOK). After the introduction of nickel-containing precursors into the inherent confined space of the TOK by solid-phase grinding, Ni SACs can be produced promptly during calcination. Single Ni atoms create a covalent Ni-O-Si structure in the TOK, as indicated by density functional theory (DFT) calculations and experimental data. This synthetic approach is easy to scale up, and 10 g of sample can be effortlessly synthesized using ball milling. The resultant Ni SACs were applied to the oxygen evolution reaction and exhibited higher catalytic activity and stability than the comparative sample synthesized in the absence of confined space.

Boosting photocatalytic overall water splitting performance by dual-metallic single Ni and Pd atoms decoration of MoS2: A DFT study

Herein, we propose a novel MoS2 supported single Ni and Pb atoms catalyst (Ni/Pd@MoS2), on which the enhanced efficiency of water splitting is confirmed by quantitative density functional theory (DFT) calculations. The Bader charge, electron density difference (EDD) and projected density of state (PDOS) analysis demonstrates that the moderate electron transfer is reached by the synergy of the Ni atom and the Pd atom. As extra channel for excited carrier migration, the present of defect states obviously prolongs the carrier lifetime (143.45 ps). The unique electronic environment contributes to the electronic synergy and spatially separated of the effective active sites, leading the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) happen smoothly on the Pd and S site, respectively. Our research presents a novel idea for the development of highly efficient diatomic catalysts towards overall water splitting.

Complete Photooxidation of Formaldehyde to CO2 via Ni-Dual-Atom Decorated Crystalline Triazine Frameworks: A DFT Study.

Formaldehyde (CH2O) emerges as a significant air pollutant, necessitating effective strategies for its oxidation to mitigate adverse impacts on human health and the environment. Among various technologies, the photooxidation of CH2O stands out owing to its affordability, safety, and effectiveness. Nitrogen-rich crystalline triazine-based organic frameworks (CTFs) exhibit considerable potential in this domain. Nevertheless, the weak and unstable CH2O adsorption hinders the overall oxidation efficiency of CTF. To address this limitation, we incorporate single and dual Ni atoms into nitrogen-rich CTFs by density functional theory (DFT) calculations, resulting in CTF-Ni and CTF-2Ni. This strategic modification significantly enhances the adsorption capability of CH2O. Notably, this synergy between Ni dual atoms activates CH2O by strong chemical adsorption, thereby reducing the energy barrier of CH2O oxidation and achieving the complete oxidation of CH2O to CO2. Moreover, the introduction of dual-atom Ni over CTF ameliorates visible and near-infrared light absorption and facilitates photoexcited charge transfer and separation. Finally, the underlying mechanisms of complete CH2O oxidation over CTF-2Ni are proposed. This work offers novel insights into the rational design of photocatalysts for CH2O oxidation through the integration of Ni dual atoms into CTFs.

Plasmon assisted synthesis of TiN-supported single-atom nickel catalysts

We report the deposition of single atom nickel catalyst on refractory plasmonic titanium nitride (TiN) nanomaterials supports using the wet synthesis method under visible light irradiation. TiN nanoparticles efficiently absorb visible light to generate photoexcited electrons and holes. Photoexcited electrons reduce nickel precursor to deposit Ni atoms on TiN nanoparticles’ surface. The generated hot holes are scavenged by the methanol. We studied the Ni deposition on TiN nanoparticles by varying light intensity, light exposure time, and metal precursor concentration. These studies confirmed the photodeposition method is driven by hot electrons and helped us to find optimum synthesis conditions for single atoms deposition. We characterized the nanocatalysts using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), energy dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). We used density functional theory (DFT) calculations to predict favorable deposition sites and aggregation energy of Ni atoms on TiN. Surface defect sites of TiN are most favorable for single nickel atoms depositions. Interestingly, the oxygen sites on native surface oxide layer of TiN also exhibit strong binding with the single Ni atoms. Plasmon enhanced synthesis method can facilitate photodeposition of single atom catalysts on a wide class of metallic supports with plasmonic properties.

Unraveling Valence Electron Number Dependent Excitonic Effects over M1-N3C1 Sites in Single-Atom Catalysts.

Excitonic effects significantly influence the selective generation of reactive oxygen species and photothermal conversion efficiency in photocatalytic reactions; however, the intrinsic factors governing excitonic effects remain elusive. Herein, a series of single-atom catalysts with well-defined M1-N3C1 (M = Mn, Fe, Co, and Ni) active sites are designed and synthesized to investigate the structure-activity relationship between photocatalytic materials and excitonic effects. Comprehensive characterization and theoretical calculations unveil that excitonic effects are positively correlated with the number of valence electrons in single metal atoms. The single Mn atom with 5.93 valence electrons exhibits the weakest excitonic effects, which dominate superoxide radical (O2•-) generation through charge transfer and enhance photothermal conversion efficiency. Conversely, the single Ni atom with 9.27 valence electrons exhibits the strongest excitonic effects, dominating singlet oxygen (1O2) generation via energy transfer while suppressing photothermal conversion efficiency. Based on the valence electron number dependent excitonic effects, a reaction environment with hyperthermia and abundant cytotoxic O2•- is designed, achieving efficient and stable water disinfection. This work reveals single metal atom dependent excitonic effects and presents an atomic-level methodology for catalytic application targeted reaction environment tailoring.

Ni-doped Co3O4 the influence of different exposed crystal facets and doping amount on the humidity sensitivity: Experiment and theory

Water vapor causes the baseline resistance, response, recovery time, and long-term stability of the metal oxide semiconductor (MOS) gas sensors to change in different humidity. Combining first-principle and experimental can provide an in-depth understanding of the sensing mechanism from the atomic and molecular scales. In this work, we examined the humidity sensitivity of different concentrations of Ni-doped Co3O4 in detail. Co48O64 (110) and Co48O64(111) were constructed by HR-TEM and doped with single, double, and treble Ni atoms on both surfaces. We calculated the adsorption of water and n-butanol molecule on these eight surfaces. The results show that Ni doping improves the moisture resistance properties of Co48O64 (110) and Co48O64(111), and the sensing properties of C3H9OH adsorbed on Ni2Co46O64 (110) and Ni2Co46O64(111) are higher than single and treble Ni atoms doping. To investigate the humidity sensitivity further, we synthesized nanorods Co3O4 with and without Ni doping. The experimental results showed that the humidity sensitivity of Ni-Co3O4 was significantly lower than that of Co3O4. The decrease in the response value for the C3H9OH may be attributed to the change in the concentration of the Ni doping or the difference in the primarily exposed crystal facet.

CO oxidation reactions on 3-d single metal atom catalysts/MgO(100).

The present work deals with a comprehensive computational theoretical study of the molecular CO and O2 adsorption on 3d single atoms (M/MgO(100)). The study is based on the chemical elements of the 3d row, as they represent an economic advantage compared with the so-called noble metals. The present study has been performed employing density functional theory calculations. Through the representation of the metastable states, we perform a synergetic analysis of the CO oxidation reaction to find trends that suggest the possible use of new candidates such as Ni/MgO(100) or Cu/MgO(100) single-atom catalysts, for this type of redox reaction. We found that Ni and Cu produce energetically viable CO to CO2 reactions. Ni and Cu atoms show the greatest diffusion barrier and are the best candidates due to their low sintering capability. The energetic and electronic properties of the single Cu and Ni atoms on MgO (100) give them the best characteristics to help in the CO oxidation process.

Isolated Ni-atom catalyst supported on Ti3C2Tx with an asymmetrical C-Ni-N structure for the hydrogen evolution reaction.

Single-atom catalysts (SACs), distinguished by their exceptional atomic efficiency and modifiable coordination structures, find wide-ranging applicability, notably in the context of the hydrogen evolution reaction (HER). Herein, we synthesized a Ti3C2Tx-based Ni single-atom catalyst (Ni SA@N-Ti3C2Tx) by immersing a single Ni atom into the Ti vacancies of Ti3C2Tx and using a N-doping strategy. X-Ray adsorption fine structure revealed the formation of local Ni-N1C1 and an unsaturated C-Ni-N bridge configuration for isolated Ni species. Moreover, Ni SA@N-Ti3C2Tx exhibited an excellent HER performance with an overpotential of 63 mV at 10 mV cm-2. This work could enable use of MXene-based SACs in the HER.

Activating iodine redox by enabling single-atom coordination to dormant nitrogen sites to realize durable zinc–iodine batteries

The introduction of a single Ni atom into an inactive N-doped carbon matrix, through its role as an electrocatalyst, awakens the dormant N sites, significantly suppressing the polyiodide shuttle effect and enhancing iodine redox kinetics.

Confinement Effect and 3D Design Endow Unsaturated Single Ni Atoms with Ultrahigh Stability and Selectivity toward CO2 Electroreduction.

Developing single-atomic catalysts with superior selectivity and outstanding stability for CO2 electroreduction is desperately required but still challenging. Herein, confinement strategy and three-dimensional (3D) nanoporous structure design strategy are combined to construct unsaturated single Ni sites (Ni-N3) stabilized by pyridinic N-rich interconnected carbon nanosheets. The confinement agent chitosan and its strong interaction with g-C3N4 nanosheet are effective for dispersing Ni and restraining their agglomeration during pyrolysis, resulting in ultrastable Ni single-atom catalyst. Due to the confinement effect and structure advantage, such designed catalyst exhibits a nearly 100% selectivity and remarkable stability for CO2 electroreduction to CO, exceeding most reported state-of-the-art catalysts. Specifically, the CO Faradaic efficiency (FECO) maintains above 90% over a broad potential range (-0.55 to -0.95V vs. RHE) and reaches a maximum value of 99.6% at a relatively low potential of -0.67V. More importantly, the FECO is kept above 95% within a long-term 100h electrolyzing. Density functional theory (DFT) calculations explain the high selectivity for CO generation is due to the high energy barrier required for hydrogen evolution on the unsaturated Ni-N3. This work provides a new designing strategy for the construction of ultrastable and highly selective single-atom catalysts for efficient CO2 conversion.

Synergy effect of the Niδ+-Nδ− atom pair for photocatalytic conversion of CO to ethanol: A computation study

By constructing a unique Niδ+–Nδ− atom pair, we designed a promising catalyst for the photocatalytic reduction of CO (pCOR), namely, anchoring a single Ni atom on a defective hexagonal boron nitride monolayer with a B-N divacancy (Ni/d-BN). The density functional theory (DFT) computations revealed that the synergy effect between the anchored Ni atom and its adjacent N atoms can capture multiple CO molecules, followed by their effective C–C coupling with a low kinetic barrier. Interestingly, these coupled CO species can be favorably reduced to ethanol (C2H5OH) product with a less negative limiting potential (–0.27 V), as compared with methane (CH4, –0.63 V), propanol (C3H7OH, –0.46 V), and the competitive hydrogen evolution reaction (HER, –0.84 V), suggesting the superior catalytic activity and the excellent selectivity of Ni/d-BN catalyst towards pCOR. Specially, this Ni/d-BN catalyst can significantly improve the visible light absorption with a suitable band position, enabling it ideal for solar-driven conversion of CO into C2H5OH. In particular, Ni/d-BN holds great potential for experimental synthesis due to its extremely high stability. Our findings not only open a new avenue to solve the problems of the high energy-consumption in FTS, but also offer a tandem strategy for CO2 conversion to multi-carbon products.

Changes in fundamental and catalytic properties of β-molybdenum carbide decorated by a single atom of Fe, Co, Ni and Cu

The interaction of single Fe, Co, Ni, and Cu atoms with polar terminations of orthorhombic Mo2C(001) surface has been investigated at low surface coverage by using density functional theory. Calculations indicate high stability of all considered adsorbates, regardless the surface termination. The presence of a single foreign atom has a localized impact on the properties of the surface, causing charge redistribution in the adsorbate/surface interface. As the result lowering of the work function is observed for both Mo2C(001) terminations. Another effect is shifting the position of d-band center further away from the Fermi level for surface Mo atoms of metal-terminated carbide, while no changes are seen for carbon’s near-Fermi level electronic states in the case of C-terminated modified surface. Results demonstrate a short-range effect on the stability of atomic hydrogen caused by the foreign adatom on both terminations. Specifically, the observed adsorption energy weakening would entail an enhancement in the catalytic activity of Mo2C toward hydrogen evolution reaction according to the Sabatier principle. Results evidence that molybdenum carbide modified by cobalt and iron is expected to be more active toward hydrogen evolution reaction than Mo2C modified by nickel and copper or than unmodified carbide.

Geometric and Electronic Structural Engineering of Isolated Ni Single Atoms for a Highly Efficient CO2 Electroreduction.

Tuning the coordination environment and geometric structures of single atom catalysts is an effective approach for regulating the reaction mechanism and maximize the catalytic efficiency of single-atom centers. Here, a template-based synthesis strategy is proposed for the synthesis of high-density NiNx sites anchored on the surface of hierarchically porous nitrogen-doped carbon nanofibers (Ni-HPNCFs) with different coordination environments. First-principles calculations and advanced characterization techniques demonstrate that the single Ni atom is strongly coordinated with both pyrrolic and pyridinic N dopants, and that the predominant sites are stabilized by NiN3 sites. This dual engineering strategy increases the number of active sites and utilization efficiency of each single atom as well as boosts the intrinsic activity of each active site on a single-atom scale. Notably, the Ni-HPNCF catalyst achieves a high CO Faradaic efficiency (FECO ) of 97% at a potential of -0.7V, a high CO partial current density (jCO ) of 49.6mA cm-2 (-1.0V), and a remarkable turnover frequency of 24900 h-1 (-1.0V) for CO2 reduction reactions (CO2 RR). Density functional theory calculations show that compared to pyridinic-type NiNx , the pyrrolic-type NiN3 moieties display a superior CO2 RR activity over hydrogen evolution reactions, resulting in their superior catalytic activity and selectivity.

Electrocatalytic reduction of carbon dioxide in confined microspace utilizing single nickel atom decorated nitrogen-doped carbon nanospheres

Carbon dioxide electroreduction reaction (CO2RR), as a rational regulation of CO2 resource utilization, demands effectively selective catalysts for converting CO2 into high-value-added chemicals. Carbon-based nanoreactors featuring rationally designed porous framework structures might provide a unique chemical environment for confining and stabilizing the active metal species, consequently improving the CO2RR activity. Herein, nitrogen-doped porous carbon nanospheres decorated by single Ni atom (Ni-NCN) featuring a Ni-N4 structure were synthesized using the modified sol-gel method for the reduction of CO2 to CO. The synergistic effect of the Ni-N4 active sites homogenously distributed in the interconnected pore structure and the favorable chemical confined microspace of carbon nanospheres endows it with excellent CO2RR activity. In the H- type cell, Ni-NCN displays a CO Faradaic efficiency up to 96.6 % and a CO current density of 9.8 mA cm−2 at − 0.83 V (vs. RHE), as well as a high turnover frequency (TOF) of 10658 h−1 at − 1.33 V (vs. RHE). In the flow cell, the mass transfer can be further facilitated by the formation of three-phase interface. The Faradaic efficiency and current density of CO2RR catalyzed by Ni-NCN is enhanced to 97.9 % and 102.4 mA cm−2 at − 1.13 V (vs. RHE), and the wide potential window ranges from − 0.53 V to − 1.33 V (vs. RHE) with the Faradaic efficiency more than 95 %. Density functional theory (DFT) calculations reveal that the high selectivity of Ni-N4 sites is mainly ascribed to the high energy barrier that restrains the hydrogen evolution reaction (HER). Meanwhile, the lower CO binding energy on Ni-N4 site helps the escape of CO to increase the TOF of active sites. The in-situ Fourier transform infrared (FTIR) spectroscopy verifies that the intermediate *COOH can be more stable in the confined environment of Ni-NCN to promote the selectivity of CO2RR. The strategy of constructing confined microspace paves a new path for the rational design of high-efficient single atom catalysts for CO2 reduction.

Metal–Organic Framework-Derived Mn/Ni Dual-Metal Single-Atom Catalyst for Efficient Oxygen Reduction Reaction

Non-precious-metal-based oxygen reduction reaction (ORR) catalysts hold great prospects for rechargeable metal–air batteries and reversible electrolyzer/fuel cell systems. Among the various earth-abundant and noble-metal-free catalysts, Mn- and Ni-based single-atom catalysts (SACs) are attracting attention for ORRs. Herein, we designed a facile and efficient strategy to obtain Mn/Ni dual-metal single-atom catalysts, in which atomic Mn and Ni sites were dispersed on nitrogen-doped porous carbon. The optimized Mn/Ni catalysts showed excellent ORR electrocatalytic performance with a half-wave potential of 0.803 V, comparable to that of commercial Pt/C catalysts. Meanwhile, the electron transfer number was determined to be 3.9, indicating a good four-electron reaction process. The excellent electrocatalytic performance was attributed to the N-doped porous carbon structure with a large specific surface area, which afforded abundant active sites to anchor the single Mn and Ni atoms.

Pyrrolic N anchored atomic Ni–N3–C catalyst for highly effective electroreduction of CO2 into CO

Herein, atomically dispersed Ni–N3–C materials are facilely synthesized by the pyrolysis of Ni-doped ZIF-8. Each single Ni atom is proved to be bonded with three N atoms to form Ni–N3 sites by X-ray absorption spectroscopy. During the pyrolysis at high temperature, the increasing of relative contents and blue-shift binding energy of pyrrolic N can be observed, indicating the Ni might be bonded with pyrrolic N. Moreover, the formation energy (Ef) of NiN3-pyrrolic structure is smaller than that of NiN3-pyridinic calculated by density functional theory (DFT), thus confirming the dominated bonding structure of NiN3-pyrrolic further. The optimum material can achieve an ultra-high CO Faradaic efficiency of 99.37% at −0.75 V vs. RHE with a turnover frequency (TOF) of 3498 h−1 and a high CO partial current density of 80 mA cm−2 at −1.15 V vs. RHE, which is among the best Ni catalysts. Based on DFT results, the NiN3-pyrrolic sites can facilitate both the formation of COOH* intermediate and desorption of CO, which can also suppress the competitive hydrogen evolution reaction (HER) simultaneously, thus resulting in high catalytic activity and selectivity from CO2 to CO.