Boosting Activity and Selectivity of CO2 Electroreduction by Pre-Hydridizing Pd Nanocubes
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99 GENERAL AND MISCELLANEOUS↗
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Temperature dependent local structure coherence of surface-modified BaTiO 3 nanocubes
BaTiO 3 nanocubes capped by polar tetrafluoroborate (BF 4 − ) ligands are shown to have enhanced ferroelectric order and undergo sharper ferroelectric to paraelectric phase transitions relative to nanocubes capped with nonpolar oleic acid (OA) ligands.
Jiang, Bo↗
Emergent magnetism and exchange bias effect in iron oxide nanocubes with tunable phase and size
Abstract We report a systematic investigation of the magnetic properties including the exchange bias (EB) effect in an iron oxide nanocube system with tunable phase and average size (10, 15, 24, 34, and 43 nm). X-ray diffraction and Raman spectroscopy reveal the presence of Fe 3 O 4 , FeO, and α -Fe 2 O 3 phases in the nanocubes, in which the volume fraction of each phase varies depending upon particle size. While the Fe 3 O 4 phase is dominant in all and tends to grow with increasing particle size, the FeO phase appears to coexist with the Fe 3 O 4 phase in 10, 15, and 24 nm nanocubes but disappears in 34 and 43 nm nanocubes. The nanocubes exposed to air resulted in an α -Fe 2 O 3 oxidized surface layer whose thickness scaled with particle size resulting in a shell made of α -Fe 2 O 3 phase and a core containing Fe 3 O 4 or a mixture of both Fe 3 O 4 and FeO phases. Magnetometry indicates that the nanocubes undergo Morin (of the α -Fe 2 O 3 phase) and Verwey (of the Fe 3 O 4 phase) transitions at ∼250 K and ∼120 K, respectively. For smaller nanocubes (10, 15, and 24 nm), the EB effect is observed below 200 K, of which the 15 nm nanocubes showed the most prominent EB with optimal antiferromagnetic (AFM) FeO phase. No EB is reported for larger nanocubes (34 and 43 nm). The observed EB effect is ascribed to the strong interfacial coupling between the ferrimagnetic (FiM) Fe 3 O 4 phase and AFM FeO phase, while its absence is related to the disappearance of the FeO phase. The Fe 3 O 4 / α -Fe 2 O 3 (FiM/AFM) interfaces are found to have negligible influence on the EB. Our findings shed light on the complexity of the EB effect in mixed-phase iron oxide nanosystems and pave the way to design exchange-coupled nanomaterials with desirable magnetic properties for biomedical and spintronic applications.
Physics↗
In situ TEM measurement of electrical properties of individual BaTiO 3 nanocubes
We report on the measurement of the electrical properties of individual pristine and doped BaTiO 3 nanocubes by using in situ transmission electron microscopy with a two-electrode configuration. The dimensions of the nanocubes tested are between 10 and 20 nm, which rendered their in situ electrical characterization challenging. We characterized 4%Cr and 5%La (atomic percentage) doped BaTiO 3 nanocubes and compared them with the properties of pristine BaTiO3 nanocubes synthesized by the same solvothermal method. We found that the resistance of all three types of nanocubes when displayed in log-scale shows a nearly linear dependence on the applied electric field (R2 ≥ 0.95) over a wide range of electric fields (50–900 kV/cm). Compared with pristine BaTiO 3 nanocubes, the resistance of both 4%Cr and 5%La doped nanocubes showed reduced variation rates with respect to the electric field, with 5%La doping, demonstrating a better reduction in the variation rate. By developing techniques capable of evaluating the properties of individual BaTiO 3 nanocubes, we expect that our work to open the door to the use of BaTiO 3 nanomaterials in the design of future multilayer ceramic capacitors with improved volumetric efficiency and ferroelectrics-enabled nanodevices with advanced functionality.
36 MATERIALS SCIENCE↗
Revisiting the Polyol Synthesis of Silver Nanostructures: Role of Chloride in Nanocube Formation
Chloride (Cl – ) is normally used together with polyvinylpyrrolidone (PVP) in the polyol synthesis of Ag nanocubes. In the literature, shape control is attributed predominantly to the preferential binding of PVP to Ag(100) facets compared to Ag(111) facets, whereas the role of Cl – has not been well studied. Several hypotheses have been proposed regarding the role of Cl – ; however, there is still no consensus regarding the exact influence of Cl – in the shape-controlled synthesis of Ag nanocubes. To examine the influence of Cl – , we undertook a joint theoretical–experimental study. Experimentally, we examined the influence of Cl – concentration on the shape of Ag nanoparticles (NPs) at constant H + concentration. In the presence of H + , in situ formed HNO3 etches the initially formed Ag seeds and slows down the overall reduction of Ag + , which promotes the formation of monodisperse Ag NPs. Ex situ experiments probed the evolution of Cl – during the growth of Ag nanocubes, which involves the initial formation of AgCl nanocubes, and their subsequent dissolution to release Cl – , which adsorbs onto the surfaces of single crystal seeds to impact shape evolution through apparent thermodynamic control. The formation of cubes is independent of the source of AgCl, indicating temporal control of the Cl – chemical potential in solution leads to high-yield synthesis of Ag nanocubes. Increasing the concentration of Cl – alone leads to a progression in shape from truncated octahedra, to cuboctahedra, truncated cubes, and ultimately cubes, directly demonstrating the importance of Cl – in Ag NP shape control. Here, we used ab initio thermodynamics calculations based on density functional theory to probe the role of Cl – in directing shape control. With increasing Cl chemical potential (surface coverage), calculated surface energies γ of Ag facets transition from γ 111 < γ 100 to γ 100 < γ 111 and predict Wulff shapes terminated with an increasing (100) contribution, consistent with experimental observations. The combination of theory and experiment is beneficial for advancing the understanding of nanocrystal formation.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
In Situ TEM Study of Radiation Resistance of Metallic Glass–Metal Core–Shell Nanocubes
Radiation damage can cause significantly more surface damage in metallic nanostructures than bulk materials. Structural changes from displacement damage compromise the performance of nanostructures in radiation environments such as nuclear reactors and outer space, or used in radiation therapy for biomedical treatments. As such, it is important to develop strategies to prevent this from occurring if nanostructures are to be incorporated into these applications. In this work, in situ transmission electron microscope ion irradiation was used to investigate whether a metallic glass (MG) coating mitigates sputtering and morphological changes in metallic nanostructures. Dislocation-free Au nanocubes and Au nanocubes coated with a Ni–B MG were bombarded with 2.8 MeV Au 4+ ions. The formation of internal defects in bare Au nanocubes was observed at a fluence of 7.5 × 10 11 ions/cm 2 (0.008 dpa), and morphological changes such as surface roughening, rounding of corners, and formation of nanofilaments began at 4 × 10 12 ions/cm 2 (0.04 dpa). In contrast, the Ni–B MG-coated Au nanocubes (Au@NiB) showed minimal morphological changes at a fluence of 1.9 × 10 13 ions/cm 2 (0.2 dpa). Finally, the MG coating maintains its amorphous nature under all irradiation conditions investigated.
36 MATERIALS SCIENCE↗
Single-Particle Emission Spectroscopy Resolves d-Hole Relaxation in Copper Nanocubes
Resolving the dynamics of photoexcited d-holes in metallic nanostructures is one step in the rational design of plasmonic photocatalysis. In this work, we track the creation and relaxation of charge carriers in catalytically important plasmonic copper nanocubes using single-particle spectroscopy. We show that interband transitions dominate the absorption and emission of 60–160 nm copper nanocubes, and in contrast to gold nanorods, the LSPR is less important to the emission. Furthermore, we uncover the plasmonic enhancement of emission hidden in ensemble measurements by resolving the size-dependent line shape and quantum yield. Quantum yield analysis reveals the energy dependence of d-hole lifetimes. We demonstrate that the effect of excitation energy on quantum yield is stronger in copper nanocubes than in gold nanocubes of equivalent size due to differences in the band structure and the probabilities of hole scattering. Finally, we establish that emission spectroscopy is useful to understand the physical chemistry of d-holes in plasmonic photocatalysts.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Solution-Phase Synthesis of PdH 0.706 Nanocubes with Enhanced Stability and Activity toward Formic Acid Oxidation
We report palladium is one of the few metals capable of forming hydrides, with the catalytic properties being dependent on the elemental composition and spatial distribution of H atoms in the lattice. Herein, we report a facile method for the complete transformation of Pd nanocubes into a stable phase made of PdH 0.706 by treating them with aqueous hydrazine at a concentration as low as 9.2 mM. Using formic acid oxidation (FAO) as a model reaction, we systematically investigated the structure–catalytic property relationship of the resultant nanocubes with different degrees of hydride formation. The current density at 0.4 V was enhanced by four times when the nanocubes were completely converted from Pd to PdH 0.706 . On the basis of a set of slab models with PdH(100) overlayers on Pd(100), we conducted density functional theory calculations to demonstrate that the degree of hybrid formation could influence both the activity and selectivity toward FAO by modulating the relative stability of formate (HCOO) and carboxyl (COOH) intermediates. Furthermore, this work provides a viable strategy for augmenting the performance of Pd-based catalysts toward various reactions without altering the loading of this scarce metal.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Effect of Ligand Polarity on the Internal Dipoles and Ferroelectric Distortion in BaTiO 3 Nanocubes
Here, surface adsorbates and surrounding matrix species have been demonstrated to affect the properties of nanoscale ferroelectrics and nanoscale ferroelectric composites; potentially counteracting performance losses that can occur in small particle sizes. In this work, the effects of nonpolar oleic acid (OA) and polar tetrafluoroborate (BF 4 - ) ligand capping on the surface of various sizes of BaTiO 3 nanocubes have been investigated with combined neutron diffraction and neutron pair distribution function (PDF), density functional theory (DFT), and ab initio molecular dynamics (AIMD) methods. The low real space PDF region provides an unobstructed view of rhombohedral (split short and long) Ti-O distances in BaTiO 3 nanocubes, mimicking the well-established order-disorder local structure found in bulk BaTiO 3 . Interestingly, the intermediate-range order in nanocubes is found to be orthorhombic, rather than tetragonal. It is concluded that polar ligands adsorbed at BaTiO 3 surfaces stabilize the correlation length scale of local rhombohedral distortions in ferroelectric nanoparticles relative to nonpolar ligands.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Reshaping of Truncated Pd Nanocubes: Energetic and Kinetic Analysis Integrating Transmission Electron Microscopy with Atomistic-Level and Coarse-Grained Modeling
Stability against reshaping of metallic fcc nanocrystals synthesized with tailored far-from-equilibrium shapes is key to maintaining optimal properties for applications such as catalysis. Yet Arrhenius analysis of experimental reshaping kinetics, and appropriate theory and simulation, is lacking. As such, we use TEM to monitor the reshaping of Pd nanocubes of ~25 nm side length between 410 °C (over ~4.5 h) and 440 °C (over ~0.25 h), extracting a high effective energy barrier of E eff ≈ 4.6 eV. We also provide an analytic determination of the energy variation along the optimal pathway for reshaping that involves transfer of atoms across the nanocube surface from edges or corners to form new layers on side {100} facets. The effective barrier from this analysis is shown to increase strongly with the degree of truncation of edges and corners in the synthesized nanocube. Theory matches experiment for the appropriate degree of truncation. In addition, we perform simulations of a stochastic atomistic-level model incorporating a realistic description of diffusive hopping for undercoordinated surface atoms, thereby providing a visualization of the initial reshaping process.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Porous NaTi2(PO4)3@C nanocubes as improved anode for sodium-ion batteries
Highlights: • Porous NaTi{sub 2}(PO{sub 4}){sub 3}@C nanocubes are synthesized. • Oleic acid is utilized as the carbon source. • NaTi{sub 2}(PO{sub 4}){sub 3}@C is to be measured at 0.01–3 V for SIBs. • NaTi{sub 2}(PO{sub 4}){sub 3}@C achieves 201 mAh g{sup −1} at 100 mA g{sup −1} after 100 cycles. • NaTi{sub 2}(PO{sub 4}){sub 3}@C delivers 140 mAh g{sup −1} at 1 A g{sup −1} for 1000 times. - Abstract: The NASICON-type NaTi{sub 2}(PO{sub 4}){sub 3} has drawn much attention as anode material for sodium-ion batteries owing to its stable structural characteristics and low cost. Nevertheless, the insulating property of NaTi{sub 2}(PO{sub 4}){sub 3} and the high working potential of about 2.1 V vs. Na{sup +}/Na lead to its poor cycling stability, low rate performance as well as inferior capacity. In this work, we synthesize the porous NaTi{sub 2}(PO{sub 4}){sub 3}@C nanocubes by hydrothermal method and a subsequent coating process with using oleic acid as the carbon source. When utilized as the anode for sodium-ion battery in the voltage range between 0.01 V and 3.0 V, The as-synthesized porous NaTi{sub 2}(PO{sub 4}){sub 3}@C nanocubes deliver a discharge capacity of 201 mAh·g{sup −1} at the current density of 100 mA g{sup −1} after 100 cycles. Additionally, the reserved capacity of 140 mAh·g{sup −1} could be achieved at the current density of 1 A g{sup −1} after 1000 cycles.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Silver Nanocube and Nanobar Growth via Anisotropic Monomer Addition and Particle Attachment Processes
Understanding the growth mechanism of noble metal nanocrystals during solution synthesis is of significant importance for shape and property control. However, much remains unknown about the growth pathways of metal nanoparticles due to lack of direct observation. Using an in-situ transmission electron microscopy technique, we directly observed Ag nanocube and nanobar growth in aqueous solution through both classical monomer-by-monomer addition and non-classical particle attachment processes. During the particle attachment process, Ag nanocubes and nanobars formed via both oriented and non-oriented attachment. Our calculations, along with dynamics of the observed attachment, showed that van der Waals force overcame hydrodynamic and friction forces and drove the particles toward each other. During classical growth, an anisotropic growth was also revealed, and the resulting unsymmetrical shape constituted an intermediate state for Ag nanocube growth. We hypothesized that the temporary symmetry breaking resulted from different growth rates on {001} surfaces due to a local surface concentration variation caused by the imbalance between the consumption of Ag+ near the surface and the diffusion of Ag+ from bulk to surface.
Xiao, Dongdong↗
Tunable Fluorescence from Dye-Modified DNA-Assembled Plasmonic Nanocube Arrays
Colloidal crystal engineering with DNA on template-confined surfaces is used to prepare arrays of nanocube-based plasmonic antennas and deliberately place dyes with sub-nm precision into their hotspots, on the DNA bonds that confine the cubes to the underlying gold substrate. This combined top-down and bottom-up approach provides independent control over both the plasmonic gap and photonic lattice modes of the surface-confined particle assemblies and allows for the tuning of the interactions between the excited dyes and plasmonically active antennas. Furthermore, the gap mode of the antennas can be modified in situ by utilizing the solvent-dependent structure of the DNA bonds. This is studied by placing two dyes, with different emission wavelengths, under the nanocubes and recording their solvent-dependent emission. Furthermore, it is shown that dye emission not only depends upon the in-plane structure of the antennas but also the size of the gap, which is regulated with solvent. Importantly, this approach allows for the systematic understanding of the relationship between nanoscale architecture and plasmonically coupled dye emission, and points toward the use of colloidal crystal engineering with DNA to create stimuli responsive architectures, which can find use in chemical sensing and tunable light sources.
36 MATERIALS SCIENCE↗
Maximizing the Catalytic Performance of Pd@Au x Pd 1- x Nanocubes in H 2 O 2 Production by Reducing Shell Thickness to Increase Compositional Stability
We report a simple route based upon seed-mediated growth to the synthesis of Pd@Au x Pd 1-x (0.8≤x≤1) core–shell nanocubes. Benefiting from the well-defined {100} facets and an optimal Au/Pd ratio for the surface, the nanocubes bearing a shell made of Au 0.95 Pd 0.05 work as an efficient electrocatalyst toward H 2 O 2 production, with high selectivity of 93–100 % in the low-overpotential region of 0.4–0.7 V. When the Au 0.95 Pd 0.05 alloy is confined to a shell of only three atomic layers in thickness, the electrocatalyst is able to maintain its surface structure and elemental composition, endowing continuous and stable production of H2O2 during oxygen reduction at a high rate of 1.62 mol g( Pd+Au ) -1 h -1 . This work demonstrates a versatile route to the rational development of active and durable electrocatalysts based upon alloy nanocrystals.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Influence of Annealing on Microstructure, Electrochemical, and Magnetic Properties of Co-Doped SrTiO{sub 3} Nanocubes
Effect of annealing on microstructure, electrochemical, and magnetic properties of Co-doped SrTiO{sub 3} nanocubes obtained by the hydrothermal method was studied. X-ray diffraction (XRD) results of all as-prepared and annealed Co-doped SrTiO{sub 3} samples revealed a cubic perovskite structure with the second phases of SrCO{sub 3} and Co{sub 3}O{sub 4}in as-prepared and annealed SrTi{sub 0.90}Co{sub 0.10}O{sub 3} samples, respectively. Agglomerated nanocubes could be clearly observed in all as-prepared and annealed Co-doped samples by scanning electron microscope (SEM) and transmission electron microscope (TEM). X-ray absorption near edge spectroscopy (XANES) results suggested the presence of Co{sup 2+} cations in as-prepared Co-doped SrTiO{sub 3} samples, while both of Co{sup 2+} and Co{sup 3+} cations were found in annealed Co-doped SrTiO{sub 3} samples. The cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) results of as-prepared and annealed SrTi{sub 1-x}Co{sub x}O{sub 3} (x = 0.05, 0.075 and 0.10) electrodes revealed pseudocapacitor behavior of the Faradaic redox reaction type. The specific capacitance (Csc) was affected by the increase of Co content in all as-prepared and annealed Co-doped SrTiO{sub 3} samples with an excellent cycling stability after 200 cycle test of 97.24% and the highest value of 75.28 F g{sup −1} at 1 A g{sup −1} in an annealed SrTi{sub 0.925}Co{sub 0.075}O{sub 3} electrode. Magnetization measurements at room temperature using vibrating sample magnetometer (VSM) revealed diamagnetic behavior of as-prepared SrTiO{sub 3} sample, whereas paramagnetic behavior was observed in all as-prepared Co-doped SrTiO{sub 3} samples. After annealing, undoped sample exhibited paramagnetic behavior, whereas ferromagnetic behavior was observed in all Co-doped SrTiO{sub 3} samples with the increase of saturation magnetization (M{sub s}) at 10 kOe from 0.58 to 1.63 emu/g and the coercive field (H{sub c}) from 43.71 to 123.87 Oe, suggested to originate from the face-center exchange (FCE) mechanism.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Enhancement of three-photon near-infrared quantum cutting in β-NaYF4:Er3+ nanoparticles by Ag nanocubes
Highlights: • Three-photon near-infrared quantum cutting is obtained in β-NaYF{sub 4}:Er{sup 3+} NPs. • Quantum cutting efficiency as high as 242.59% is calculated from decay curves. • Plasmon-enhanced three-photon quantum cutting is achieved by Ag nanocubes. • The maximum quantum cutting enhancement factor reaches 2.86. - Abstract: The near-infrared (NIR) quantum cutting (QC) nanoparticles (NPs) β-NaYF{sub 4}:Er{sup 3+} are prepared by coprecipitation method. Three-photon NIR QC luminescence at 1520 nm ({sup 4}I{sub 13/2} → {sup 4}I{sub 15/2}) is obtained under the excitation of 519 nm ({sup 4}I{sub 15/2} → {sup 2}H{sub 11/2}). The corresponding QC efficiency η{sub QC} calculated from the luminescence decay curves reaches as 242.59%. Furthermore, three-photon NIR QC luminescence is enhanced by the localized surface plasmon resonance of Ag nanocubes (NCs). The influence of Ag NCs concentration on three-photon QC luminescence is investigated, and the results show that the optimal concentration of Ag NCs is 0.10% with the enhancement factor reached a maximum as 2.86. Our study may have potential application as a QC layer to improve the photovoltaic conversion efficiency of germanium (Ge) solar cells.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Insights into the Dynamic Interfacial and Bulk Composition of Copper-Modified, Hydrogen-Alloyed, Palladium Nanocubes under Electrocatalytic Conditions
Understanding and controlling the alloying properties of nanomaterials under electrochemical conditions are critically important for fields ranging from energy storage and catalysis to electrochromic window technology. Hydrogen-absorbing nanomaterials, like palladium, are especially interesting due to their ability to reversibly absorb and store hydrogen in their lattice at near-stoichiometric amounts. Palladium’s work function is also significantly deeper than that of most transition metals, which enables electrochemical underpotential deposition of conformal monolayer and submonolayer amounts of transition metals onto the palladium surface. The simultaneous existence of these two properties is unique and opens new and exciting avenues for electrochemical applications. However, the intersection of surface-modified, hydrogen-alloyed palladium nanomaterials is poorly understood, and specifically, how these structures evolve during electrochemical operating conditions remains an open question. Here, we synthesize {100}-terminated palladium nanocubes and deposit between 0.5 and 22 monolayers of copper at the palladium surface. We then electrochemically alloy these surface-modified structures with hydrogen. Using a combination of analytical electrochemistry, spectroscopy, and microscopy, we track the positional evolution of the Cu at the surface of Pd, its impact on palladium’s ability to absorb hydrogen, and copper’s effect on hydrogen evolution electrocatalysis. We show that Cu readily alloys into the palladium nanocube at potentials more negative than the Cu 2+/0 deposition, but a 0.5 monolayer thick copper layer remains at the Pd surface regardless of potential. Finally, we discuss the implications of these findings within the framework of CO 2 reduction catalysis for carbon–carbon bond-forming chemistry.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗