High-index Facets Research Articles

Spatial charge separation and high-index facet dependence in polyhedral Cu2O type-II surface heterojunctions for photocatalytic activity enhancement

Polyhedral 30-faceted Cu2O microcrystal exposed with a {332}–{001} type-II surface heterojunction was synthesized, which displayed an efficient spatial charge separation and high-index facet dependence for photocatalytic activity enhancement.

Аномальные кинетические характеристики транспорта водорода через Pd-Cu-мембраны, модифицированные пентадвойникованными цветкообразными нанокристаллитами с высокоиндексными гранями

A technique that made it possible for the first time to achieve fivefold symmetry in palladium nanocrystallites grown on the surface of a Pd-Cu film has been developed. Pd-40%Cu membrane modification with pentatwinned nanocrystallites with high-index facets made it possible to achieve ultra-high hydrogen permeability up to 10.1 mmol s-1 m-2 at 100 °C. Such permeability, comparable in value to high-temperature analogs, is anomalous, since the predicted values should be more than 2 times lower than those obtained. This result is due to the acceleration of surface dissociative adsorption and recombinative desorption as a result of the pentatwinned particles ultra-high activity in reactions involving hydrogen, which is confirmed by the data on the selectivity of the developed membranes.

Synergistic Effect of Platinum Single Atoms and Nanoclusters Boosting Electrocatalytic Hydrogen Evolution

Maximizing atomic utilization of precious metal-based catalysts is of great significance in heterogeneous catalysis, also becoming a useful strategy to develop efficient electrocatalysts for hydrog...

High-pressure Raman investigation of high index facets bounded α-Fe2O3 pseudocubic crystals

High index facet bounded α-Fe2O3 pseudocubic crystals has gained the attention of the scientific community due to its promising electrochemical sensing response towards aqueous ammonia. The structural stability of α-Fe2O3 pseudocubic crystals is investigated through high-pressure Raman spectroscopy up to 22.2 GPa, and those results are compared with our ab initio theoretical calculations. The symmetry of the experimental Raman-active modes has been assigned by comparison with theoretical data. In addition to the Raman-active modes, two additional Raman features are also detected, whose intensity increases with compression. The origin of these two additional peaks addressed in this study, reveals a strong dependence on the geometry and the low dimensionality as the most plausible explanation.

Water Splitting: High‐Index Faceted RuCo Nanoscrews for Water Electrosplitting (Adv. Energy Mater. 47/2020)

In article number 2002860, Bolong Huang, Xiaoqing Huang and co-workers develop a RuCo nanoscrew with abundant exposed high index facets as an efficient electrocatalyst for water-splitting. This work not only extends the understanding of bimetallic efficient electrocatalysts but also supplies a delicate synthesis strategy to overcome the stability issue of high index facets.

Preparation of Unique Flower-like Pt-Ni Alloy Catalysts As the Cathode of a PEMFC By Electrodeposition Technique

The hydrogen economy can play an important role in the low-carbon economy, and fuel cells technology is an essential part of the hydrogen economy. The proton exchange membrane fuel cell (PEMFC) is one kind of electrochemical reaction device with the advantages of low temperature operation, high conversion efficiency and noiseless, which is expected to widely utilizes in public transportations.The oxygen reduction reaction (ORR) at the cathode is the rate-determining step in PEMFC. To enhance the ORR activity at the cathode, the unique flower-like platinum-nickel binary alloy catalysts were electrodeposited on the commercial carbon cloth by potentiostatic electrodeposition technique, the PtNi alloy effectively improved the oxygen adsorption and desorption paths on the surface. The PtNi alloy catalysts with shorter lattice distance and effects of high-index facets would increase the electrochemical surface area (ECSA) of the catalysts and power density of fuel cell. The samples of the pure platinum and commercial Pt/C catalyst were also prepared as comparison.Morphology, particle size and elemental composition were characterized by SEM, XRD and ICP-MS. In addition, the electrochemical characteristics of the PtNi catalysts were investigated via cyclic voltammetry (CV) and linear sweep voltammetry (LSV) analysis in 0.1 M perchloric acid solution with rotating disk electrode (RDE). In single cell test, the maximum peak power density of PEMFC with homemade PtNi alloy catalyst as the cathode reached 1031 mW/cm2, enhancing about 12% power density, compared to the commercial Pt/C. Figure 1

Platinum nanocrystals enclosed high-index facet as a carrier to support transition metal particles for methanol electrooxidation

Platinum nanocrystals enclosed high-index facet as a carrier to support transition metal particles for methanol electrooxidation

Tunable Concave Surface Features of Mesoporous Palladium Nanocrystals Prepared from Supramolecular Micellar Templates.

Concave metallic nanocrystals with a high density of low-coordinated atoms on the surface are essential for the realization of unique catalytic properties. Herein, mesoporous palladium nanocrystals (MPNs) that possess various degrees of curvature are successfully synthesized following an approach that relies on a facile polymeric micelle assembly approach. The as-prepared MPNs exhibit larger surface areas compared to conventional Pd nanocrystals and their nonporous counterparts. The MPNs display enhanced electrocatalytic activity for ethanol oxidation when compared to state-of-the-art commercial palladium black and conventional palladium nanocubes used as catalysts. Interestingly, as the degree of curvature increases, the surface-area-normalized activity also increases, demonstrating that the curvature of MPNs and the presence of high-index facets are crucial considerations for the design of electrocatalysts.

Visualizing Hydrogen Oxidation Reaction Activity of Polycrystalline Platinum by Scanning Electrochemical Microscopy

The study of the structure-activity relationship of electrode surfaces is fundamentally important in electrocatalysis research and in situ spatially resolved measurements of catalytic activity at complex surfaces remain challenging. In this study, the electrocatalytic activity of micrometer-sized platinum crystallites for the hydrogen oxidation reaction (e.g. the anode reaction in proton-exchange-membrane fuel cells) is visualized using scanning electrochemical microscopy (SECM). A polycrystalline Pt electrode was galvanically etched to expose the underlying well-defined crystallites which serve as single crystal electrodes in SECM imaging experiments. SECM coupled with electron backscatter diffraction (EBSD) allows correlation of catalytic activity and crystallographic orientation of high-index Pt crystal domains. The structure-reactivity relationship showed that the catalytic activity for hydrogen oxidation reaction (HOR) at potentials near the standard potential for hydrogen increases in the order Pt(100) < Pt(110) < Pt(111), where the Miller index plane represents the terrace orientations of the high-index facets. A clear correlation is observed between increased HOR activity and step-site density on a given base orientation. SECM imaging and localized kinetic measurements at crystal domains from current-potential plots and SECM approach curves show the passivating effect that anion adsorption and oxide growth have on the HOR at more positive potentials.

Revealing high temperature stability of platinum nanocatalysts deposited on graphene oxide by in-situ TEM

This study reveals atomic-scale observations of the high temperature stability of platinum nanoparticles deposited on pristine graphene oxide (PtNPs/GO) and platinum nanoparticles deposited on water-etched graphene oxide (PtNPs/GO-H2O) as two representative catalyst systems for dehydrogenation. With the aid of in-situ transmission electron microscopy (TEM), these two kinds of catalysts can be examined at actual working temperatures up to 800 °C, and notably, PtNPs/GO-H2O exhibits the higher temperature stability even at 700 °C. The statistical data of in-situ time-lapsed TEM images demonstrate the size variations of the sintering Pt nanoparticles which are in accordance with the Ostwald ripening process. We further discover the tendency towards the preferential exposure of high-index Pt nanocrystal facets (higher surface energy sides) for the PtNPs/GO under thermal treatment from 25 °C to 400 °C, which leads to accelerate the nanoparticle aggregations, providing microscopic evidence of the catalyst instability at high temperatures.

Understanding the link between solid/liquid interfaces and photoelectrochemical activity in novel thin-film photoanodes of preferentially oriented high-index rutile TiO2 facets – A work inspired by Michel Che’s research on surface chemistry

This work presents the first report of the deposition of a preferentially oriented film of rutile TiO2 exposing high-index facets. Control of the Cl–/F– mol ratio during the hydrolysis of TiCl4 enabled the deposition of different facets of rutile TiO2 on fluorine-doped tin oxide (FTO) substrates. When ranking films of varying facet composition and orientation, the high-index faceted film was found to have a higher activity photoelectrochemical activity towards water oxidation in spite of its low surface energy, as determined by Raman spectroscopy. Complementary photoelectrochemical studies and electron microscopy revealed the higher activity to originate from both the interaction at the electrode/electrolyte interface and the presence of active sites such as coincidence lattice sites in twin boundaries. This work, inspired by the research legacy of Michel Che, highlights the importance of surface chemistry and the presence of active sites in catalytic materials and showcases the coupling of different characterisation techniques to elucidate the mechanism governing the photoelectrochemical behaviour of supported metal oxides.

Photoelectrochemical water oxidation performance promoted by a cupric oxide-hematite heterojunction photoanode

Hematite is a promising material for photoelectrochemical (PEC) water oxidation due to its narrow bandgap and chemical stability in alkaline electrolytes. However, the PEC performance of hematite is known to be inhibited by a short carrier diffusion length and slow kinetics for the oxygen evolution process. The rational control of morphology, crystallinity, and interfacial charge transfer plays an important role in tuning the PEC performance of α-Fe2O3 photoelectrodes. In this study, different iron oxide nano/microstructures are synthesized by the sintering of iron sheets in air at different temperatures. The synergetic effect of the surface morphology and crystallinity on the photocurrent and onset potential of the photoanode is investigated. The coral-like structure with high index (104) facets prepared at a high temperature shows a decreased onset potential, suggesting a strong correlation between the onset potential and crystalline orientation. To further improve the photocurrent density of this hematite photoanode, cupric oxide-hematite heterostructures are explored. An obvious improvement in the photocurrent density is observed from 1.1 to 1.6 V. The resulting α-Fe2O3/CuO photoanode exhibits a photocurrent density of 1.5 mA cm−2 at 1.6 V, 25% higher than that of the pristine hematite. The Mott-Schottky plot and EIS measurement indicate that the α-Fe2O3/CuO heterojunction facilitates the extraction of the accumulated holes in the hematite through a type-II band alignment and the CuO can serve as a catalyst for promoting the oxygen evolution reaction.

Promoting C2+ Production from Electrochemical CO2 Reduction on Shape-Controlled Cuprous Oxide Nanocrystals with High-Index Facets

Morphology and crystal facet controlled Cu2O nanocrystals (NCs) including cubic Cu2O (c-Cu2O) NCs with {100} facets, rhombic dodecahedral Cu2O (d-Cu2O) NCs with {110} facets, and concave octahedral...

High index facets-Ag nanoflower enabled efficient electrochemical detection of lead in blood serum and cosmetics

Abstract Owing to its importance in environmental pollution and human toxicity, the development of a simple and selective sensor for heavy metal ions is a continued research interest in cross-disciplinary areas of analytical chemistry. The colorimetric analysis based conventional complexation assay of Pb2+ is a cumbersome procedure for practical applications. Herein, we report a novel electrochemical sensor approach based on a high index facets (HIF)‑silver nanoflower modified glassy carbon electrode (AgNF@GCE) for anodic stripping voltammetric detection of lead ion in a pH 4.5 acetate buffer solution. Physicochemical techniques such as XPS, FESEM, and electrochemical studies with Fe(CN)63 were adopted for the surface characterization of the AgNF@GCE. Unlike the conventional Ag-nanoparticles, this new system provides a highly crystalline and large surface area with HIF's {422} and {111} for sensitive and selective electrochemical analysis of Pb2+ ion. Under an optimal experimental condition, AgNF@GCE showed a linear calibration plot in the range of 10–700 ppb of Pb2+ ion with a detection limit 0.74 ppb. Eight repetitive measurements of 50 ppb Pb2+ yielded a relative standard deviation value of 2.8%. The sensor showed tolerable interference with other metal ions such as Cu2+, Fe2+, Mg2+, Ni2+, K+, and Na+. As practical applicability, selective detection of lead concentration in blood-serum and cosmetics were successfully analyzed with appreciable recovery values.

Facile Room-Temperature Synthesis of a Highly Active and Robust Single-Crystal Pt Multipod Catalyst for Oxygen Reduction Reaction.

Economical production of highly active and robust Pt catalysts on a large scale is vital to the broad commercialization of polymer electrolyte membrane fuel cells. Here, we report a low-cost, one-pot process for large-scale synthesis of single-crystal Pt multipods with abundant high-index facets, in an aqueous solution without any template or surfactant. A composite consisting of the Pt multipods (40 wt %) and carbon displays a specific activity of 0.242 mA/cm2 and a mass activity of 0.109 A/mg at 0.9 V (versus a reversible hydrogen electrode) for oxygen reduction reaction, corresponding to ∼124% and ∼100% enhancement compared with those of the state-of-the-art commercial Pt/C catalyst (0.108 mA/cm2 and 0.054 A/mg). The single-crystal Pt multipods also show excellent stability when tested for 4500 cycles in a potential range of 0.6-1.1 V and another 2000 cycles in 0-1.2 V. More importantly, the superior performance of the Pt multipods/C catalyst is also demonstrated in a membrane electrode assembly (MEA), achieving a power density of 774 mW/cm2 (1.29 A/cm2) at 0.6 V and a peak power density of ∼1 W/cm2, representing 34% and 20% enhancement compared with those of a MEA based on the state-of-the-art commercial Pt/C catalyst (576 and 834 mW/cm2).

Smart design of exquisite multidimensional multilayered sand-clock-like upconversion nanostructures with ultrabright luminescence as efficient luminescence probes for bioimaging application.

Afacile scalable approach ispresented for the rational design of multidimensional, multilayered sand-clock-like UCNPs (denoted as UCCKs) bounded with high index facets, with a tunable Nd3+ content, and without a template or multiple complicated reaction steps. This was achieved using the seed-mediated growth and subsequent longitudinal direction epitaxial growth with the assistance of oleic acid and NH4F. The as-formed UCCKs composed of aninner layer (NaYF4:Yb,Er,Ca), anintermediate layer (NaYF4:Yb,Ca), and anouter layer (NaNdF4:Yb,Ca). The outer shell, enriched with Nd3+ sensitizer, augmented the near-infrared (NIR) photon absorption, whereasthe intermediate shell, enriched with Yb3+, acted as a bridge for energy transfer from Nd3+ to Er3+ emitter in the inner core alongside with precluding any deleterious energy back-transfer from Er3+ or quenching effect from Nd3+. These unique structural and compositional properties of UCCKs endowed the UCL intensity of UCCKs by 22 and 10 times higher than that of hexagonal UCNP core (NaYF4:Yb,Er,Ca) and hexagonal UCNP core-shell (NaYF4:Yb,Er,Ca@NaYF4:Yb,Ca), respectively. Intriguingly, the UCL intensity increased significantly with increasing the content of Nd3+ in the outer shell. The silica-coated UCCKs were used as excellent long-term luminescence probes for the in vitro bioimaging without any noteworthy cytotoxicity. The presented approach may pave the road for controlling the synthesis of multidimensional UCCKs for various applications. Graphical abstract We developed novel multidimensional multilayered sand-clock-like upconversion nanostructures composed of a spherical inner core (NaYF4:Yb,Er,Ca), hexagonal intermediate shell (NaYF4:Yb,Ca) and two up-down outer shell (NaNdF4:Yb,Ca) with controllable Nd3+ as anefficient and safe probe for bioimaging applications without any quenching effect.

A universal approach for the synthesis of mesoporous gold, palladium and platinum films for applications in electrocatalysis.

High-surface-area mesoporous materials expose abundant functional sites for improved performance in applications such as gas storage/separation, catalysis, and sensing. Recently, soft templates composed of amphiphilic surfactants and block copolymers have been used to introduce mesoporosity in various materials, including metals, metal oxides and carbonaceous compounds. In particular, mesoporous metals are attractive in electrocatalysis because their porous networks expose numerous unsaturated atoms on high-index facets that are highly active in catalysis. In this protocol, we describe how to create mesoporous metal films composed of gold, palladium, or platinum using block copolymer micelle templates. The amphiphilic block copolymer micelles are the sacrificial templates and generate uniform structures with tunable pore sizes in electrodeposited metal films. The procedure describes the electrodeposition in detail, including parameters such as micelle diameters, deposition potentials, and deposition times to ensure reproducibility. The micelle diameters can be controlled by swelling the micelles with different solvent mixtures or by using block copolymer micelles with different molecular weights. The deposition potentials and deposition times allow further control of the mesoporous structure and its thickness, respectively. Procedures for example applications are included: glucose oxidation, ethanol oxidation and methanol oxidation reactions. The synthetic methods for preparation of mesoporous metal films will take ~4 h; the subsequent electrochemical tests will take ~5 h for glucose sensing and ~3 h for alcohol oxidation reaction.

Probing the Irregular Lattice Strain-Induced Electronic Structure Variations on Late Transition Metals for Boosting the Electrocatalyst Activity.

Owing to the simplicity in practice and continuous fine-tuning ability toward the binding strengths of adsorbates, the strain effect is intensively explored, especially focused on the modulation of catalytic activity in transition metal (TM) based electrocatalysts. Recently, more and more abnormal cases have been found that cannot be explained by the conventional simplified models. In this work, the strain effects in five late TMs, Fe, Co, Ni, Pd, and Pt are studied in-depth regarding the facet engineering, the surface atom density, and the d-band center. Interestingly, the irregular response of Fe lattice to the applied strain is identified, indicating the untapped potential of achieving the phase change by precise strain modulation. For the complicated high-index facets, the surface atom density has become the pivotal factor in determining the surface stability and electroactivity, which identifies the potential of high entropy alloys (HEA) in electrocatalysis. The work supplies insightful understanding and significant references for future research in subtle modulation of electroactivity based on the precise facet engineering in the more complex facets and morphologies.

Facet-Dependent Catalytic Performance of Au Nanocrystals for Electrochemical Nitrogen Reduction.

Nanostructured metal catalysts have attracted great interest due to their extraordinary performance for electrocatalysis including electrochemical nitrogen reduction (ENRR). However, their working mechanisms for ENRR are still not fully understood. Herein, seven monofaceted polyhedral Au nanocrystals were synthesized and systemically compared to elucidate the relation between Au crystal facets and NRR performance. It is found that polyhedra with high-index facets catalytically outperform those with low-index facets. Specifically, Au nanostars enclosed with (321) facets show a high NH3 production rate of 2.6 μg h-1 cm-2 (20 μg h-1 mg-2) and faradaic efficiency of 10.2% at -0.2 V, which are 3.1- and 5.1-folds larger than those of nanocubes enclosed with (100) facets. As revealed by theoretical investigation, a larger energy barrier for reduction of H+ to H* (ΔGH*) hinders occurrence of HER on the Au(321) surface, thus ensuring better NRR selectivity. Meanwhile, a lower energy barrier for formation of N2H2* on the catalyst surface and a larger energy barrier for decomposing the formed N2H2* back into N2 and 2H* jointly favor a higher NH3 production rate. This study provides mechanistic insights into ENRR and rational design of metal nanocrystals for electrocatalysis.

Electrochemical biosensor for detection of MON89788 gene fragments with spiny trisoctahedron gold nanocrystal and target DNA recycling amplification.

Theshape-controlled synthesis of gold nanocrystals via shape induction of hexadecyltrimethylammonium chloride, potassium bromide, and potassium iodide and enantioselective direction of L-cysteineis reported. The resulting gold nanocrystals (STO-Au) offer spiny trisoctahedron nanostructures with good monodispersity and enhanced exposed high-index facets and high catalytic activity. Construction of the electrochemical sensing platform for MON89788 gene involves the modification of STO-Au, thionine (Thi), and labeled bipedal DNA probe 1 or 2 (P1 or P2) for target DNA-induced recycling amplification. In the detection, two surface DNA probes were immobilized on gold electrode via the Au-S bond. Then, hairpin DNA 1 (H1), Thi-STO-Au-P1, and Thi-STO-Au-P2 self-assemble into two-dimensional DNA nanopores (DNPs) on the electrode surface. Target DNA hybridizes with hairpin DNA 2 (H2) to open hairpin structure of H2. The opened H2 binds with H1 in the DNPs to release Thi-STO-Au-P1, Thi-STO-Au-P2, and target DNA by toehold-mediated strand-displacement. The utilization of target DNA-induced recycling allows one target DNA to release 2N STO-Au-labeled DNA strands, promoting significant signal amplification. The detection signal is further enhanced by the catalyzed redox reaction of Thi with STO-Au. The differential pulse voltammetric signal, best measured at - 0.18V vs. Ag/AgCl, decreases linearly with increasing concentration of MON89788 in the range 0.02-8 × 104 fM, and the detection limit is 0.0048 fM (S/N= 3). The proposed method was successfully applied for electrochemical detection of MON89788 gene fragments in the PCR products from genetically modified soybean. Graphical Abstract We develop l-cysteine controlled synthesis of spiny trisoctahedron gold nanocrystals with good monodispersity and highly exposed high-index facets. The architecture achieves to ultrahigh catalytic activity. The electrochemical biosensor based on gold nanocrystals and target DNA recycling amplification provides advantage of sensitivity, repeatability, and regeneration-free.