Low-coordinated Atoms Research Articles

Tuning structures of Pt shells on Pd nanocubes as neutral glucose oxidation catalysts and sensors

Nanocrystals with high-indexed facets and low-coordinated atoms exhibit promising electrocatalytic activities. Herein, different Pt shell structures on the surface of Pd nanocubes (Pd@Pt NCs) were synthesised by varying the concentration of Pt precursors. The concave Pd@Pt NCs were used as electrocatalysts for neutral glucose oxidation reactions (GORs); the effect of Pt structure on the catalytic performance was studied. In sequential catalysis, stellated Pd@Pt NCs (Pd@Pt SNC) with (211) facets had an electron transfer number (Ne) of 12.69 and a specific activity of 4.69 × 10−9 mol·g·m−2, markedly higher than that of the other concave Pd@Pt NCs. In transient catalysis, Pd NCs with Pt-coated corners (Pd@Pt CNCC) containing (210) and (950) facets demonstrated a sensitivity of 11.06 μA·mM−1·cm−2 and a linear analysis range (2.4–10.6 mM). The high recoveries (98.80%–99.85%) and low relative standards (≤1.06%) in the serum sample corroborate the potential of Pd@Pt CNCC as an enzyme-free glucose sensor.

Preparation of 2D Molybdenum Phosphide via Surface-Confined Atomic Substitution.

The emerging nonlayered 2D materials (NL2DMs) are sparking immense interest due to their fascinating physicochemical properties and enhanced performance in many applications. NL2DMs are particularly favored in catalytic applications owing to the extremely large surface area and low-coordinated surface atoms. However, the synthesis of NL2DMs is complex because their crystals are held together by strong isotropic covalent bonds. Here, nonlayered molybdenum phosphide (MoP) with well-defined 2D morphology is synthesized from layered molybdenum dichalcogenides via surface-confined atomic substitution. During the synthesis, the molybdenum dichalcogenide nanosheetfunctions as the host matrix where each layer of Mo maintains their hexagonal arrangement and forms isotropic covalent bonds with P that substitutes S, resulting in the conversion from layered van der Waals material to a covalently bonded NL2DM. The MoP nanosheets converted from few-layer MoS2 are single crystalline, while those converted from monolayers are amorphous. The converted MoP demonstrates metallic charge transport and desirable performance in the electrocatalytic hydrogen evolution reaction (HER). More importantly, in contrast to MoS2 , which shows edge-dominated HER performance, the edge and basal plane of MoP deliver similar HER performance, which is correlated with theoretical calculations. This work provides a new synthetic strategy for high-quality nonlayered materials with well-defined 2D morphology for future exploration.

Universal strategy engineering grain boundaries for catalytic oxidative desulfurization

The low-coordinated atoms such as edges, single atoms and vacancies have been widely determined as reactive sites for catalytic oxidative desulfurization. However, the grain boundaries (GB) as a favorable atomic configuration has been ignored. In this work, a universal strategy is proposed to engineer grain boundaries into oxides via facile two-step growth. Take the W18O49 nanowires as an example, the engineered GB can work as reactive sites to build stronger interfacial molecular interactions with dibenzothiophene (DBT) due to the low-coordinated W atoms with local electron-rich state, promoting the surface adsorption and activation performance towards DBT. Moreover, the molecular oxygen activation capacity is improved by GB to yield more superoxide radical relative to W18O49. Benefiting from these features, the GB-W18O49 deliver a greatly improved catalytic oxidative desulfurization behavior relative to W18O49 nanowires, in which 97.7% DBT can be removed by GB-W18O49 in 5 h but only 40.4% of W18O49 nanowires.

Self-supported PdNi dendrite on Ni foam for improving monohydric alcohol and polyhydric alcohols electrooxidation

Despite considerable efforts to study direct alcohol fuel cells (DAFCs), the development of efficient bifunctional catalysts for monohydric alcohol and polyhydric alcohols remains a great challenge. This work reports the preparation of self-supported PdNi dendrites on Ni foam (self-supported PdNi DNTs/NF) with a large specific surface area by a simple self-sacrificing template and hydrothermal method. The presence of NF with enrichment of nucleation sites is crucial for the generation of self-supported PdNi DNTs. The as-obtained self-supported PdNi DNTs/NF exhibits an excellent property for ethanol and glycerol electrooxidation with the mass activity of 2375.7 mA mgcat−1 and 2451.6 mA mgcat−1, the specific activity of 10.07 mA cm−2 and 10.84 mA cm−2, respectively, in alkaline media, which should attribute to abundant high-index facets and low-coordinated atoms on the edge of branches. Furthermore, the PdNi DNTs/NF exhibits outstanding long-term durability in the current–time test for 7200 s with superior anti-CO poisoning performance, possessing a potential application in DAFCs.

The Role of Steps on Silver Nanoparticles in Electrocatalytic Oxygen Reduction

Hydrogen fuel cell technology is an essential component of a green economy. However, it is limited in practicality and affordability by the oxygen reduction reaction (ORR). Nanoscale silver particles have been proposed as a cost-effective solution to this problem. However, previous computational studies focused on clean and flat surfaces. High-index surfaces can be used to model active steps presented in nanoparticles. Here, we used the stable stepped Ag(322) surface as a model to understand the ORR performance of steps on Ag nanoparticles. Our density functional theory (DFT) results demonstrate a small dissociation energy barrier for O2 molecules on the Ag(322) surface, which can be ascribed to the existence of low-coordination number surface atoms. Consequently, the adsorption of OOH* led to the associative pathway becoming ineffective. Alternatively, the unusual dissociative mechanism is energetically favored on Ag(322) for ORR. Our findings reveal the importance of the coordination numbers of active sites for catalytic performance, which can further guide electrocatalysts’ design.

Creating low coordination atoms on MoS2/NiS2 heterostructure toward modulating the adsorption of oxygenated intermediates in lithium-oxygen batteries

To boost the energy efficiency of lithium-oxygen (Li-O2) batteries, it is incredibly vital to explore highly effective electrocatalysts for reversible oxygen redox reactions. Incorporating low coordination atoms (LCAs) on the catalyst surface has shown great potential in improving electrocatalytic performance. Herein, MoS2/NiS2 heterostructure with abundant LCAs is designed toward efficiently promote oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Adopting the MoS2/NiS2 heterostructure as the oxygen electrode, Li-O2 batteries exhibit a high discharge capacity of 12377.4 mAh g−1 at 200 mA g−1 and long cycling life over 1101 h. Density functional theory calculations uncover that the modulated d-band center of interfacial MoS2 and NiS2 originated from the electron interaction between LCAs and adjacent atoms can result in the strong adsorption of oxygen intermediates on the catalyst surface, which contributes to the outstanding catalytic performance. This work emphasizes the key role of LCAs in promoting the development of highly efficient electrocatalysts for Li-O2 batteries.

Crystalline Modulation Engineering of Ru Nanoclusters for Boosting Ammonia Electrosynthesis from Dinitrogen or Nitrate.

Developing highly efficient nitrogen reduction reaction (NRR) and nitrate reduction reaction (NITRR) electrocatalysts is an ongoing challenge. Herein, we report the in situ growth of ultrafine amorphous Ru nanoclusters with a uniform diameter of ∼1.2 nm on carbon nanotubes as a highly efficient electrocatalyst for both the NRR and the NITRR. The amorphous Ru nanoclusters were prepared via a convenient ambient chelated co-reduction method, in which trisodium citrate as a chelating agent played a key role to form amorphous Ru instead of crystalline Ru. The strong d-π interaction between Ru metal and carbon nanotubes led to the homogeneous distribution and good long-term stability of ultrafine Ru nanoclusters. Compared with crystalline Ru, amorphous Ru nanoclusters with abundant low-coordinate atoms can provide more catalytic sites. The amorphous Ru nanoclusters exhibited an NH3 yield of 10.49 μg·h-1·mgcat.-1 and a FENH3 of 17.48% at -0.2 V vs reversible hydrogen electrode (RHE) for NRR. For the NITRR, an NH3 yield of 145.1 μg·h-1·mgcat.-1 and a FENH3 of 80.62% were also achieved at -0.2 V vs RHE. This work provides new insights into crystalline modulation engineering of metal nanoclusters for electrocatalytic ammonia synthesis.

Monte Carlo Simulations of the Metal-Directed Self-Assembly of Y-Shaped Positional Isomers

The rational fabrication of low-dimensional materials with a well-defined topology and functions is an incredibly important aspect of nanotechnology. In particular, the on-surface synthesis (OSS) methods based on the bottom-up approach enable a facile construction of sophisticated molecular architectures unattainable by traditional methods of wet chemistry. Among such supramolecular constructs, especially interesting are the surface-supported metal–organic networks (SMONs), composed of low-coordinated metal atoms and π-aromatic bridging linkers. In this work, the lattice Monte Carlo (MC) simulation technique was used to extract the chemical information encoded in a family of Y-shaped positional isomers co-adsorbed with trivalent metal atoms on a flat metallic surface with (111) geometry. Depending on the intramolecular distribution of active centers (within the simulated molecular bricks, we observed a metal-directed self-assembly of two-dimensional (2D) openwork patterns, aperiodic mosaics, and metal–organic ladders. The obtained theoretical findings could be especially relevant for the scanning tunneling microscopy (STM) experimentalists interested in a surface-assisted construction of complex nanomaterials stabilized by directional coordination bonds.

Pd Clusters on Schiff Base–Imidazole-Functionalized MOFs for Highly Efficient Catalytic Suzuki Coupling Reactions

Subnanometer noble metal clusters have attracted much attention because of abundant low-coordinated metal atoms that perform excellent catalytic activity in various catalytic processes. However, the surface free energy of metals increases significantly with decreasing size of the metal clusters, which accelerates the aggregation of small clusters. In this work, new Schiff base–imidazole-functionalized MOFs were successfully synthesized via the postsynthetic modification method. Highly dispersed Pd clusters with an average size of 1.5 nm were constructed on this functional MOFs and behaved excellent catalytic activity in the Suzuki coupling of phenyboronic acid and bromobenzene (yield of biaryl >99%) under mild reaction conditions. Moreover, the catalyst can be reused six times without loss of activity. Such catalytic behavior is found to closely related to the surface functional groups that promote the formation of small Pd0 clusters in the metallic state.

Pt Concave Nanocubes with High-Index Facets as Electrocatalysts for Glucose Oxidation

The modification of the surface atomic arrangements, especially the exposure of high-index facets, has been considered as a valid strategy to strengthen the catalytic performance of Pt-based nanocrystals. In this article, Pt concave nanocubes (Pt CNCs) with exposed high-index (510) facets are facilely synthesized through a hydrothermal method. Polyvinylpyrrolidone (PVP) and glycine are required for shape control. The mechanism of electrocatalytic oxidation toward glucose by Pt CNCs is fully discussed. The exposed high-index facets consist of abundant low-coordinated atoms (containing edges, steps, and kinks), can supply sufficient active sites for the adsorption of reactants and intermediate species, and thus enhance the catalytic activity in glucose oxidation. By using saturated calomel electrode as the reference electrode, a 1 cm2 platinum sheet as the counter electrode, and glassy carbon electrode (GCE) as the working electrode, the Pt CNC catalyst-decorated GCE exhibits higher peak current densities of 0.25, 0.15, and 0.56 mA cm–2 than those of the commercial Pt/C (10 wt. %)-modified GCE. The Pt CNC catalyst shows a rapid response toward the changes in glucose concentration. The electrocatalytic oxidation of glucose exhibits better performance in neutral and alkaline conditions than in an acidic electrolyte. Above all, the prepared Pt CNC catalysts with high-index (510) facets are expected for their wide use as abiotic catalysts in the electrocatalytic oxidation of glucose.

Effect of ion irradiation on thermal conductivity of phosphorene and underlying mechanism

Defects produced by ion irradiation can effectively modulate many physical properties of phosphorene. In this paper, the molecular dynamics method is used to simulate the ion irradiation process of phosphorene. The relations between the formation probability of defects and the energy of incident ions, ion species and incident angle of ions are revealed. The non-equilibrium molecular dynamics simulation is used to calculate the thermal conductivity of irradiated phosphorene. The effects of the energy of ions, the irradiation dose, the type of ions and the incident angle of ions on the thermal conductivity of phosphorene are systematically investigated. The influence of the vacancies on the phonon participation rate of phosphorene is studied by lattice dynamics method, and the spatial distribution of localized modes is demonstrated. According to the quantum-mechanical perturbation theory and bond relaxation theory, we point out that the dominant physical mechanism of vacancy defects which significantly reduce the thermal conductivity of phosphorene is the strong scattering of phonons by the low-coordinated atoms near the vacancies. This study provides a theoretical basis for tuning the heat transport properties of phosphorene by defect engineering.

Emerging Single-Atom Catalysts/Nanozymes for Catalytic Biomedical Applications.

Single-atom catalysts (SACs) are a type of atomically dispersed nanozymes with the highest atom utilization, which employ low-coordinated single atoms as the catalytically active sites. SACs not only inherit the merits of traditional nanozymes, but also hold high catalytic activity and superb catalytic selectivity, which ensure their tremendous application potential in environmental remediation, energy storage and conversion, chemical industry, nanomedicine, etc. Nevertheless, undesired aggregation effect of single atoms during preactivation and reaction processes is significantly enhanced owing to the high surface free energy of single atoms. In this case, appropriate substrates are requisite to prevent the aggregation event through the powerful interactions between the single atoms and the substrates, thereby stabilizing the high catalytic activity of the catalysts. In this review, the synthetic methods and characterization approaches of SACs are first described. Then the application cases of SACs in nanomedicine are summarized. Finally, the current challenges and future opportunities of the SACs in nanomedicine are outlined. It is hoped that this review may have implications for furthering the development of new SACs with improved biophysicochemical properties and broadened biomedical applications.

Efficient removal of fluoride from neutral wastewater by green synthesized Zr/calcium sulfate whiskers: An experimental and theoretical study

A convenient and effective method was developed to fabricate zirconium-based calcium sulfate whiskers (Zr-CSWs), an environmentally friendly adsorption material designed to clean excessive fluoride from wastewater. Zr-CSWs, which potentially provide high adsorption activity toward fluoride in wastewater, overcome an aggregation problem typical of Zr-based species that may block the pore structure of the supporting material and degenerate its treatment performance. The results indicate that Zr-CSWs show excellent equilibrium adsorption capacity compared to other Zr-based materials in practical water solutions with pH values of 6–7. The adsorption of fluoride on Zr-CSWs was further evaluated in accordance with the Langmuir equation and the pseudosecond-order model. Coexisting anions had a minor effect on the removal of fluoride, and a strong alkali solution regenerated the used adsorbent. Density functional theory (DFT) calculations were performed to determine the mechanism of fluoride removal. The calculations demonstrated that the removal of fluoride by Zr-CSWs was mainly achieved by ion exchange between fluoride ions and OH - on the surface of the adsorbent, where a protonation process created low-coordination Zr atoms. • Zirconium decorated calcium sulfate whisker (Zr-CSW) was prepared in a simple and low-cost way. • Zr-CSW has high capacity and good selectivity for the removal of fluoride in water. • The adsorption follows Langmuir model and pseudosecond-order dynamic equation. • The mechanism for fluoride removal has been revealed by density of functional theory (DFT).

Engineering the low-coordinated single cobalt atom to boost persulfate activation for enhanced organic pollutant oxidation

Two atomically dispersed cobalt catalysts with different nitrogen coordination numbers (denoted as CoSA-Nx-C) were synthesized and firstly compared to activate peroxydisulfate (PDS) for bisphenol A (BPA) degradation. Theoretical calculations unveiled that lowering the CoN coordination number from four to three can apparently increase the electron density of the single Co atom in CoSA-N3-C to enhance PDS conversion. The low-coordinated CoSA-N3-C with CoN3 coordination structure displays a high specific activity of 0.067 L min1 m2, which is 1.31 times greater than that of CoSA-N4-C with normal CoN4 configuration (0.051 L min1 m2) in PDS activation. Electron paramagnetic resonance (EPR) measurements and quenching tests confirmed the primary role of sulfate radical (SO4•−) in BPA oxidation over CoSA-N3-C with PDS. Moreover, CoSA-N3-C delivers favorable durability for PDS activation and potential practicability for realistic wastewater remediation. These findings provide a novel and useful avenue to coordination number modulation of SACs for wider environmental applications.

Electrocatalytic N2 Reduction on FeS2 Nanoparticles Embedded in Graphene Oxide in Acid and Neutral Conditions

The development of stable, low-cost, and highly efficient electrocatalysts for the N2 reduction reaction (NRR) process is challenging but crucial for ammonia production. Herein, we demonstrate the synthesis of pyrite nanoparticles wrapped by graphene oxide (FeS2@GO) acting as a highly efficient NRR catalyst in a wide pH range. The FeS2 nanoparticles are uniformly dispersed across the GO nanosheet, thus leading to the fine exposure of active sites, the promotion of charge transfer, and the increment of a contact surface area, which are all beneficial for a desired catalyst. In the meantime, the low-coordinated Fe atoms are activated as highly active sites, which is in favor of the enhanced electrochemical performance for the NRR. Furthermore, density functional theory (DFT) calculations illustrated that the high activity of N2 reduction over the FeS2@GO catalyst arises from the well-exposed Fe active sites and the increment of charge density at the valence band edge. Benefiting from the well-optimized interface, the barrier of the addition of the first hydrogen atom to N2 forming *NNH species as the potential-determining step is as low as 0.93 eV in N2 electroreduction. The electrochemical test results reveal that, as expected, FeS2@GO exhibits high Faradaic efficiencies (4.7% in 0.1 M HCl solution and 6.8% in 0.1 M Na2SO4 solution) and advanced NH3 yields (78.6 and 27.9 μg h-1 mgcat.-1 in 0.1 M HCl and 0.1 M Na2SO4 solutions, respectively) in both acid and neutral conditions. This work offers a new avenue for exploring novel electrocatalysts, which has great promise to accelerate the practical application of the NRR.

Realizing the Excellent HER Performance of Pt3Pb2S2 by d-Orbital Electronic Modulation.

Exploring new excellent electrocatalysts for the hydrogen evolution reaction (HER) is of significance for the development of hydrogen energy. Herein, a ternary chalcogenide (Pt3Pb2S2) is successfully designed and synthesized using layered PtS2 as a matrix. The energy level of the Pt 5d orbital is upshifted to the Fermi surface after replacing S atoms by Pb atoms, which results in the high conductivity of Pt3Pb2S2. In addition, the low-coordinated Pt atoms inserted in the voids of [Pt2Pb2S2] layers have a lower free energy of H* adsorption than do metallic Pt atoms, which endows Pt3Pb2S2 with excellent HER performance. The overpotential and Tafel slope of Pt3Pb2S2 toward HER activity are measured to be 43 mV at 10 mA cm-2 and 43 mV dec-1, respectively. More importantly, Pt3Pb2S2 shows high intrinsic HER catalytic activity and long-term stability. This work provides a promising strategy for designing novel excellent transition-metal chalcogenide electrocatalysts.

Pt core confined within an Au skeletal frame: Pt@Void@Au nanoframes in a molecular dynamics Perspective

Recently, nanoframe structures have attracted high amount of research interest due to their special properties such as open surface structure, high surface-to-volume ratio, large surface areas, and high densities of low-coordination surface atoms in various fields, especially in catalysis research. Since, stability of nanoparticles is an important factor for their application as catalysts, the present study aimed to evaluate the morphological effect of core and frame on the stability of Pt@void@Au nanoframes, where the Pt core is located inside an Au skeleton, using molecular dynamics simulation at room temperature. Hence, cuboctahedral, Marks-decahedral, decahedral, octahedral, icosahedral, cubic, and tetrahedral morphologies were considered for assessment. According to the simulation results, Au frame with various morphologies and coordination numbers from 3 to 6 was unstable at 300 K. In addition, the contraction and collapse of Au atoms in the frame along with the expansion of Pt atoms in the core, lead to void occupation, and increases the coordination number and formation of a more stable Pt@Au structure. The results also demonstrated that stability of the formed Pt@Au core-shell structure depends on initial morphology and obeys the following trend: Marks-decahedral > cubic > octahedral > icosahedral > decahedral > cuboctahedral > tetrahedral

One-stone, two birds: Alloying effect and surface defects induced by Pt on Cu2−xSe nanowires to boost C-C bond cleavage for electrocatalytic ethanol oxidation

The high-efficient C-C bond cleavage is the key for ethanol electrooxidation. In this work, PtCu/Cu 2−x Se nanowires (NWs) with abundant surface defects were constructed and exhibited remarkable activity of 5.03 A mg −1 Pt as well as 5.29 A mg −1 Pt for ethanol oxidation and methanol oxidation, respectively, which are 5.0 and 5.3 fold of commercial Pt/C. ex situ, in situ experiments and calculation results reveal that the formation of PtCu alloys lowered the d -band level to promote the adsorption of hydroxyl species. The abundant defects created high density of low-coordinated atoms to boost the reaction kinetics. Thus, PtCu/Cu 2−x Se NWs displayed enhanced C-C bond cleavage ability and high selectivity for C1 products (CO 2 ). The assembled direct ethanol fuel cells (DEFCs) with PtCu/Cu 2−x Se NWs as anode provided an open-circuit voltage (OCV) of 0.773 V and a peak power density of 7.8 mW cm −2 . This work not only give us a potential catalyst for C-C bond cleavage, but also provides an effective strategy to enhance the electrocatalytic activity of ethanol/methanol oxidation. • To boost the C-C bond cleavage for ethanol oxidation, a one-stone, two birds strategy was demonstrated. • PtCu/Cu 2-x Se NWs displayed 5.0 and 5.3-fold mass activity than commercial Pt/C for ethanol and methanol oxidation reaction. • PtCu/Cu 2-x Se NWs displayed higher efficiency to break C-C bond to produce more C1 intermediates than commercial Pt/C.

A leaf-like Co-Silicate/CNT hybrid film as free-standing anode for lithium and sodium storage

Electrode materials with high theoretical capacity and high conductivity are critical for high performance rechargeable batteries. Herein, a leaf-like cobalt silicate nanosheet/carbon nanotube (Co-Silicate/CNT) hybrid film is synthesized through a hydrothermal strategy. The Co-Silicate nanosheets provide large accessible surface area and abundant low-coordinated surface atoms with high reactivity. Meanwhile, the Co-Silicate nanosheets are strongly coupled with internally connected CNTs, which afford fast electron transfer and high mechanical stability. Moreover, the open pores can effectively reduce the ion migration distance and alleviate volume changes during charging and discharging cycle. When used as a binder-free anode for LIBs, the Co-Silicate CNT hybrid film exhibits a high initial charge capacity of 846.8 mA h g−1, a good rate performance (1451.3mAhg−1 when reset to 0.1 A g−1 after additional 80 cycles) and excellent cycle performance (331.72mAhg−1 after 1000 cycles at 10 A g−1). As anode materials for sodium storage, it also shows a good rate performance and cycle performance (246.3mAhg−1 after 500 cycles at 1 A g−1). Reaction mechanism analysis reveals that the good performance results from the optimized 3D “branch-leaf” structure and combined effect of capacitance and insertion mechanism. These results indicate that the Co-Silicate/CNT hybrid film has great potential in practical applications as LIB/SIB electrodes.

High-index planes T-Nb2O5 using self-assembly strategy for aerobic oxidative desulfurization in fuels

High-index planes viewed as reactive facets are possessed of the high-density, low-coordination atoms, which are distributed at catalytic sites with high activity, such as steps, edges and kink sites. Herein, the orthorhombic niobium pentoxide (T-Nb2O5) is synthesized, with the elevated ratio of high-index planes, first for aerobic oxidative desulfurization (ODS) of the refractory aromatic sulfides. Through a solvent evaporation-induced self-assembly strategy, mesoporous structure Nb2O5 with three different crystal phases, amorphous, pseudo-hexagonal and orthorhombic, are prepared using the calcination method. The proportion of high-index facets increases, as raising the calcination temperature, which contributes to the faster production of the superoxide free radical (•O2–) intermediate using molecular oxygen as the green oxidant. Under optimal conditions, a 100% sulfur removal rate is obtained using 650 °C-T-Nb2O5 within 7 h, showing its excellent catalytic performance. The cycle experiments confirm the stability of the prepared 650 °C-T-Nb2O5 after 8 times regeneration process, showing a promising prospect of NbOx-based materials for ODS under mild conditions.