High-index Facets Research Articles

Highly-Branched PtCu Nanocrystals with Low-Coordination for Enhanced Oxygen Reduction Catalysis.

Low-coordination platinum-based nanocrystals emanate great potential for catalyzing the oxygen reduction reactions (ORR) in fuel cells, but are not widely applied owing to poor structural stability. Here, several PtCu nanocrystals (PtCu NCs) with low coordination numbers were prepared via a facile one-step method, while the desirable catalyst structures were easily obtained by adjusting the reaction parameters. Wherein, the Pt1Cu1 NCs catalyst with abundant twin boundaries and high-index facets displays 15.25 times mass activity (1.647 A mgPt -1 at 0.9 VRHE) of Pt/C owing to the abundant effective active sites, low-coordination numbers and appropriate compressive strain. More importantly, the core-shell and highly developed dendritic structures in Pt1Cu1 NCs catalyst give it an extremely high stability with only 17.2% attenuation of mass activity while 61.1% for Pt/C after the durability tests (30 000 cycles). In H2-O2 fuel cells, Pt1Cu1 NCs cathode also exhibits a higher peak power density and a longer-term lifetime than Pt/C cathode. Moreover, theoretical calculations imply that the weaker adsorption of intermediate products and the lower formation energy barrier of OOH* in Pt1Cu1 NCs collaboratively boost the ORR process. This work offers a morphology tuning approach to prepare and stabilize the low-coordination platinum-based nanocrystals for efficient and stable ORR.

Atomically dispersed NiOx cluster on high-index Pt facets boost ethanol electrooxidation through long-range synergistic sites

Constructing the desired long-range dual sites to enhance the C–C bond-cleavage and CO-tolerate ability during ethanol oxidation reaction is of importance for further applications. Herein, the concept of holding atomically dispersed NiOx cluster supported on Pt-based high-index facets (NiOx/Pt) is proposed to build O-bridged Pt–Ni dual sites. Strikingly, the obtained NiOx/Pt dual sites show 4.97 times specific activity higher than that of commercial Pt/C (0.35 ​mA ​cm−2), as well as outstanding CO-tolerance and durability. The advanced electrochemical in-situ characterizations reveal that the NiOx/Pt can accelerate rapid dehydroxylation and C–C bond-cleavage over the Pt–Ni dual sites. Theoretical calculations disclose that the atomically dispersed NiOx species can lower the adsorption/reaction energy barriers of intermediates. This tactic provides a promising methodology on regulating the surface synergistic sites via engineering atomically dispersed oxide site.

Morphologically and Compositionally Controlled Cs2SbBr6 by Bi and Ag Substitution

AbstractMorphology‐controlled Cs2SbBr6 crystals are synthesized by Bi‐ and Ag‐substitution of the precursor solution. X‐ray diffraction (XRD) together with Raman spectroscopy confirms the lattice tilting and symmetry changes with the dominant appearance of higher index facets by Bi substitution. Ag substitution does not induce crystal symmetry changes in the Cs2BBr6 (B = Sb or Bi) phase, but results in highly defective structures hindering the formation of a smooth surface during the crystal growth. Successful substitution of Bi and limited substitution of Ag into Cs2SbBr6 is also confirmed by energy dispersive X‐ray spectroscopy (EDX). This research provides design principles and practical examples of how to control the morphology of Cs2SbBr6 crystals with structural defects and multiphase formation.

Effect of the cryogenic treatment on the electrocatalytic performance of the active self-supporting nanoporous Pd–Ag catalyst with high-index facets’ preferred orientation

Effect of the cryogenic treatment on the electrocatalytic performance of the active self-supporting nanoporous Pd–Ag catalyst with high-index facets’ preferred orientation

Kinetics-Driven Crystal Facet Evolution Mechanism of Atomically Ordered Intermetallic PtFe Nanocubes toward Electrochemical Catalysis.

Crystal structure engineering in nanoparticles has been regarded as a vital method in catalyst development and design. Herein, PtFe nanocubes, manufactured with ordered PtFe intermetallic structure and a desired facet of {202}, have been successfully prepared via the combination of selective deposition strategy and spatial barrier effect. In-situ X-ray photoelectron spectroscopy found that the growth of the high-index facet and formation of the nanocube for o-PtFe-202 materials arise from the surface Fe2+ modification stabilized effect and the selective deposition of Cl-, respectively. Moreover, density functional theory calculations and X-ray adsorption spectroscopies further proved that the improved oxygen reduction reaction activity and stability of o-PtFe-202 mainly originate from the synergistic effect of the desired high-index facet, ordered crystal structure, and resulting optimal d-band center of Pt. As expected, the o-PtFe-202 exhibits excellent mass activity (2.48 mA·ugPt-1) and specific activity (7.78 mA·cm-2), with only a 7.3% decrease in mass activity after 30 000 cycles.

A Review on the Influence of Crystal Facets on the Product Selectivity of CO2RR over Cu Metal Catalysts.

The electrocatalytic carbon dioxide reduction reaction (ECRR) is promising in converting environmentally harmful CO2 into useful chemicals, but the large-scale application of this technology is seriously limited by its low efficiency and selectivity. Cu-based electrocatalysts displayed attractive ability in converting CO2 to multiple products, and the product selectivity can be manipulated through various approaches. Among them, exposing specific crystal facets through crystal facet engineering has been proven to be highly effective in obtaining specific products and has attracted numerous researchers. However, to our knowledge, few reports have systematically summarized the relationship between the crystal facet control of Cu catalysts and the catalytic products. This review begins by outlining the general mechanism of CO2 electrocatalytic reduction on Cu-based catalysts, and then summarizes the preferences of low-index and high-index Cu facets regarding product selectivity and delves into the synergistic effects between facets (including different Cu facets and interactions between Cu and non-Cu facets) and their impact on CO2 reduction reaction (CO2RR). In addition, the study of the recently developed Cu single-atom catalysts in ECRR was also introduced. Finally, we provide an outlook on the development of high-performance Cu-based catalysts for applications in CO2RR. The purpose of this review is to provide a clear vein and meaningful guidance for the following studies over the crystal facet control of Cu-based electrocatalysts.

Strain engineering of PtMn alloy enclosed by high-indexed facets boost ethanol electrooxidation

Surface strain engineering has proven to be an efficient strategy to enhance catalytic properties of platinum (Pt)-based catalysts for electrooxidation reactions. Herein, the S-doped PtMn concave cubes (CNCs) enclosed with high index facets (HIFs) and regulatable surface strain are successfully fabricated by two steps hydrothermal method. The S element with electrophilic property can modify the near-surface of PtMn nanocrystals, altering the electronic structure of Pt to effectively regulate the adsorption/desorption of intermediates in the ethanol electrooxidation reaction (EOR). The PtMnS1.1 catalyst with optimal surface strain delivered extraordinary catalytic performance on EOR in acidic media, with a specific activity of 2.88 mA/cm2 and mass activity of 1.10 mA/μgPt, which is 4.1 and 2.2 times larger than that of state-of-the-art Pt/C catalyst, respectively. Additionally, the PtMnS1.1 catalyst also achieve excellent catalytic properties in alkaline electrolyte for EOR. The results of kinetic studies indicated that the surface strain and modified electronic structure can degrade the activation energy barrier during the process of EOR, which is beneficial for enhance the reaction rate. This work provides a promising approach to construct highly efficient electrocatalysts with tunable surface strain effects for clean energy electro-chemical reactions.

Nanometric-Mapping and In Situ Quantification of Site-specific Photoredox Activities on 2D Nanoplates.

Defective layered bismuth oxychloride (BiOCl) exhibits excellent photocatalytic activities in water purification and environmental remediation. Herein, in situ single-molecule fluorescence microscopy is used to spatially resolve the photocatalytic heterogeneity and quantify the photoredox activities on individual structural features of BiOCl. The BiOCl nanoplates with respective dominant {001} and {010} facets (BOC-001 and BOC-010) are fabricated through tuning the pH of the solution. The corner position of BOC-001 exhibits the highest photo-oxidation turnover rate of 262.7 ± 30.8s-1µm-2, which is 2.1 and 65.7 times of those of edges and basal planes, respectively. A similar trend is also observed on BOC-010, which can be explained by the heterogeneous distribution of defects at each structure. Besides, BOC-001 shows a higher photoredox activity than BOC-010 at corners and edges. This can be attributed to the superior charge separation ability, active high-index facets of BOC-001, and its co-exposure of anisotropic facets steering the charge flow. Therefore, this work provides an effective strategy to understand the facet-dependent properties of single-crystalline materials at nanometer resolution. The quantification of site-specific photoredox activities on BiOCl nanoplates sheds more light on the design and optimization of 2D materials at the single-molecule level.

Atomic sawtooth-like metal films for vdW-layered single-crystal growth

Atomic sawtooth surfaces have emerged as a versatile platform for growth of single-crystal van der Waals layered materials. However, the mechanism governing the formation of single-crystal atomic sawtooth metal (copper or gold) films on hard substrates (tungsten or molybdenum) remains a puzzle. In this study, we aim to elucidate the formation mechanism of atomic sawtooth metal films during melting–solidification process. Utilizing molecular dynamics, we unveil that the solidification of the liquid copper initiates at a high-index tungsten facet with higher interfacial energy. Subsequent tungsten facets follow energetically favourable pathways of forming single-crystal atomic sawtooth copper film during the solidification process near melting temperature. Formation of atomic sawtooth copper film is guaranteed with a film thickness exceeding the grain size of polycrystalline tungsten substrate. We further demonstrate the successful growth of centimeter-scale single-crystal monolayer hexagonal boron nitride films on atomic sawtooth copper films and explore their potential as efficient oxygen barrier.

Monodispersed mesoscopic star-shaped gold particles via silver-ion-assisted multi-directional growth for highly sensitive SERS-active substrates

Surface-enhanced Raman scattering (SERS) exploits localized surface plasmon resonances in metallic nanostructures to significantly amplify Raman signals and perform ultrasensitive analyses. A critical factor for SERS-based analysis systems is the formation of numerous electromagnetic hot spots within the nanostructures, which represent regions with highly concentrated fields emerging from excited localized surface plasmons. These intense hotspot fields can amplify the Raman signal by several orders of magnitude, facilitating analyte detection at extremely low concentrations and highly sensitive molecular identification at the single-nanoparticle level. In this study, mesoscopic star-shaped gold particles (gold mesostars) were synthesized using a three-step seed-mediated growth approach coupled with the addition of silver ions. Our study confirms the successful synthesis of gold mesostars with numerous sharp tips via the multi-directional growth effect induced by the underpotential deposition of silver adatoms (AgUPD) onto the gold surfaces. The AgUPD process affects the nanocrystal growth kinetics of the noble metal and its morphological evolution, thereby leading to intricate nanostructures with high-index facets and protruding tips or branches. Mesoscopic gold particles with a distinctive star-like morphology featuring multiple sharp projections from the central core were synthesized by exploiting this phenomenon. Sharp tips of the gold mesostars facilitate intense localized electromagnetic fields, which result in strong SERS enhancements at the single-particle level. Electromagnetic fields can be further enhanced by interparticle hot spots in addition to the intraparticle local field enhancements when arranged in multilayered arrays on substrates, rendering these arrays as highly efficient SERS-active substrates with improved sensitivity. Evaluation using Raman-tagged analytes revealed a higher SERS signal intensity compared to that of individual mesostars because of interparticle hot spots enhancements. These substrates enabled analyte detection at a concentration of 10− 9 M, demonstrating their remarkable sensitivity for trace analysis applications.

Wet-Chemical Synthesis of Concave Hexoctahedral Pd and Pd@Pt Nanocrystals for Methanol Electrooxidation.

Nanocrystals (NCs) exposed with high-index facets usually show enhanced electrocatalytic performances. However, it is a great challenge to persevere with high-index facets against their high surface energy during the synthesis. Herein, we successfully synthesize concave hexoctahedral (c-HOH) Pd NCs exposed with 48 high-index {741} facets using a facile one-pot wet-chemical protocol. Control experiments illustrate that l-ascorbic acid plays a critical role in the formation of the c-HOH morphology, acting as both reducing and capping agents. Moreover, we can extend the synthesis for fabricating c-HOH Pd@Pt core-shell NCs by simply introducing a Pt precursor into the reaction solution, attaining remarkably boosted electrocatalysis for methanol electrooxidation reaction (MOR). Integrating the merits of {741} facets, concave structure, and ligand and strain effect of the core-shell structure, c-HOH Pd4@Pt1 core-shell NCs showed an excellent MOR mass activity of 1.18 A mgPGM-1 or 3.60 A mgPt-1, which is 3.80 or 11.61 times higher than that of commercial Pt/C, respectively.

Tuning Crystal Phase of Palladium-Selenium Nanowires for Enhanced Ethylene Glycol Electrocatalytic Oxidation.

Alcohol electrooxidation is pivotal for a sustainable energy economy. However, designing efficient electrocatalysts for this process is still a formidable challenge. Herein, palladium-selenium nanowires featuring distinct crystal phases: monoclinic Pd7Se2 and tetragonal Pd4.5Se for ethylene glycol electrooxidation reaction (EGOR) are synthesized. Notably, the supported monoclinic Pd7Se2 nanowires (m-Pd7Se2 NWs/C) exhibit superior EGOR activity, achieving a mass activity (MA) and specific activity (SA) of 10.4 A mgPd -1 (18.7mA cm-2), which are 8.0 (6.7) and 10.4 (8.2) times versus the tetragonal Pd4.5Se and commercial Pd/C and surpass those reported in the literature. Furthermore, m-Pd7Se2 NWs/C displays robust catalytic activity for other alcohol electrooxidation. Comprehensive characterization and density functional theory (DFT) calculations reveal that the enhanced electrocatalytic performance is attributed to the increased formation of Pd0 on the high-index facets of the m-Pd7Se2 NWs, which lowers the energy barriers for the C─C bond dissociation in CHOHCHOH* and the CO* oxidation to CO2*. This study provides palladium-based alloy electrocatalysts exhibiting the highest mass activity reported to date for the electrooxidation of ethylene glycol, achieved through the crystalline phase engineering strategy.

Oriented Metal Stripping for Highly Reversible Zinc Anode.

Aqueous zinc metal batteries are a viable candidate for next-generation energy storage systems, but suffer from poor cycling efficiency of the Zn anode. Emerging approaches aim to regulate zinc plating behavior to suppress uncontrolled dendrites, while the stripping process is seldom considered. Herein, an oriented metal stripping strategy is demonstrated to stabilize the Zn anode by removing high-index facets for exposing the (002) plane through the addition of anionic additive sodium citrate (SC). Consequently, high-index facets that coordinate strongly with SC are preferentially stripped out due to a reduced stripping barrier, rendering stable (002) facet preponderant in epitaxial plating. After repeat stripping/plating, the ultra-high proportion of 93% for (002) and large-size grains of ≈100µm (six times larger than before) can be obtained. Zn anode shows continuous 25 000 cycles with low overpotential at 100mA cm-2 in symmetric cells and more than 70 h of stable operation even at an ultra-high depth of discharge of 92.3%. Moreover, an extremely long lifespan of 12 000 cycles at 10 A g-1 with a high capacity retention of 89% is achieved by the assembled Zn//I2 battery. This work provides a distinctive approach to improving the stripping process to design highly efficient zinc anodes for promising aqueous zinc metal batteries.

Adsorption and disproportionation of carbon monoxide on faceted-gold surfaces and edges

Localized surface plasmons (LSP) on faceted surfaces of gold nanoparticles enable carbon monoxide disproportionation to be driven at room temperature. In order to expand the known surfaces that catalyze this reaction, we explore the adsorption of carbon monoxide at top, long bridge, short bridge, and hole sites on gold (100), (110), (111), (211), and (311) faceted surfaces, as well as the reaction barriers for disproportionation at the lowest energy adsorption site on each surface and edges between two (311) surfaces and (100) and (110) surfaces. Generally, the less atomically dense, higher index facets promote both good adsorption and reactivity, and the edges show lower barriers for disproportionation. For most of the explored surfaces, adsorption directly on top of a gold atom is most favorable. The lowest activation energy for carbon monoxide disproportionation to amorphous carbon and carbon dioxide is predicted for two carbon monoxides adsorbed on top of atoms on the (311)/(311) edge.

High-index facets Pt concave nanocubes with small interface angles induced by N-defective sites in the integrated electrode for methanol oxidation

The construction of an integrated electrode with self-organized growth is of great significance in reducing the Pt loading and improving the performance of the membrane electrode assembly (MEA) in proton exchange membrane fuel cells (PEMFCs). Herein, the square-wave pulse electrodeposition method is used to grow Pt{510}CNC and Pt{720}CNC nanocrystals on carbon fiber paper (CFP)-based reduced graphene oxide (rGO/CFP) and nitrogen-doped reduced graphene oxide (N-rGO/CFP) supports, respectively. Experimental and density functional theory (DFT) calculations show that the introduction of N makes it easier for hydrogen to adsorb on Pt, and the arrangement order of more Pt atoms is disrupted by hydrogen, resulting in the formation of Pt concave nanocubes (Pt CNCs) with small interface angles (α), consisting of {720} facets with more atomic steps. Moreover, the catalytic activities of the prepared two catalysts for methanol oxidation are 3.17 and 2.35 times higher than that of commercial Pt/C, and the maximum power densities of direct methanol fuel cell (DMFC) are also better than that of commercial Pt/C. This work can provide important guidance for the future research of high-index facets noble metal nanocrystals for growth on the surface of defective carbon carriers as integrated electrodes in MEA.

Prestrain Guided Yield of Large Single-Crystal Nickel Foils with High-Index Facets.

Single-crystal metal foils with high-index facets are currently being investigated owing to their potential application in the epitaxial growth of high-quality van der Waals film materials, electrochemical catalysis, gas sensing, and other fields. However, the controllable synthesis of large single-crystal metal foils with high-index facets remains a great challenge because high-index facets with high surface energy are not preferentially formed thermodynamically and kinetically. Herein, single-crystal nickel foils with a series of high-index facets are efficiently prepared by applying prestrain energy engineering technique, with the largest single-crystal foil exceeding 5×8 cm2 in size. In terms of thermodynamics, the internal mechanism of prestrain regulation on the formation of high-index facets is proposed. Molecular dynamics simulation is utilized to replicate and explain the phenomenon of multiple crystallographic orientations resulting from prestrain regulation. Additionally, large-sized and high-quality graphite films are successfully fabricated on single-crystal Ni(012) foils. Compared to the polycrystalline nickel, the graphite/single-crystal Ni(012) foil composites show more than five-fold increase in thermal conductivity, thereby showing great potential applications in thermal management. This study hence presents a novel approach for the preparation of single-crystal nickel foils with high-index facets, which is beneficial for the epitaxial growth of certain two-dimensionalmaterials.

Efficient peracetic acid activation by high-index facets of Cu2O under simulated solar light: The crucial role of uncoordinated Cu atoms

Tuning the facets of transition-metal catalysts to achieve effective micropollutant removal via peracetic acid (PAA) activation is a promising approach. However, within this process, the correlation between PAA activation and the atomic arrangement of the exposed facets is ambiguous. Herein, we present a comprehensive study wherein a series of Cu2O materials, with typical high-index facets ({211}, {311}, and {332}) and low-index facets ({100}, {110}, and {111}), were synthesized. These materials were used to investigate facet-dependent PAA activation for tetracycline (TC) degradation under simulated solar light irradiation. The results demonstrate that Cu2O with high-index {332} facets exhibit the optimal TC degradation (96.65 % within 20 min), and its kobs values are 1.52 and 2.01 times those of Cu2O with {311} and {211} facets, respectively. Detailed identification of the active species proved that •OH, 1O2, and the electron transfer process induced by the reactive Cu (I)–PAA* complexes were involved in TC degradation. In contrast to the {211} and {311} facets, PAA demonstrated a heightened tendency for adsorption and activation into active species on the {332} facets because of the denser uncoordinated Cu atoms. In addition, the facet heterojunction composed of {332} and {100} facets was conducive to the separation of photogenerated electron-hole pairs and charge migration, thus promoting the Cu(II)/Cu(I) cycle. In the practical applicability evaluation, Cu2O with {332} facets effectively removed multiple pollutants as well as actual pharmaceutical wastewater. This study provides a novel strategy for PAA activation by regulating the exposed facets of the catalyst.

Electrochemical biosensor based on the integration of maple leaf-like gold nanocrystal and truncated aptamer for detection of α-amanitin with high sensitivity, selectivity and rapidity

This study reports the fabrication of three-dimensional gold nanocrystals as sensing material in the presence of l-glutathion and high-performance aptamer with 20 bases of α-amanitin via truncation and optimization of along aptamer. The resulting maple leaf–like gold nanocrystal (ML-Au) exhibits an improved catalytic activity due to more exposed high-index facets. The use of truncated aptamer increases the sensitivity by 15 times and reduces the reaction time by two times compared with those of original aptamer. An α-amanitin electrochemical biosensor constructed by integrating ML-Au nanocrystals with truncated aptamer exhibits high sensitivity, selectivity and rapidity. An increase of the α-amanitin concentration in the range of 1 × 10−14–1 × 10−9 M causes a linear decrease in the amperometric current with a limit of detection of 2.9 × 10−15 M (S/N = 3). The proposed analytical method is satisfactorily used for electrochemical sensing of α-amanitin in urine and wild mushroom samples.

Improved hydrogen generation via NaBH4 hydrolysis: Synergistic role of sulfur and C4+-Doping unveils (440) high-index facets and modulates Co2+/Co3+ ratios in the Co3O4 lattice

Sodium borohydride (NaBH4) is crucial for eco-friendly “green” hydrogen (H2) storage, employing controlled release through catalyzed NaBH4 hydrolysis, mitigating its inherent sluggish self-hydrolysis. Precious metal catalysts enhance this process, but face scarcity and cost issues hindering widespread use, prompting interest in Co3O4, specifically with (311) orientation for abundant Co2+ sites. However, excess Co2+ on dominant (311) facets limits catalytic efficacy. This study presents a nuanced synthesis of sulfur (S)- and carbon (C4+)-doped Co3O4 that expose high-index (440) facets and optimize Co2+/Co3+ distribution. The catalytic performance of CoSC-0.1-700 on (440) facets demonstrates remarkable hydrogen generation rate of 4.1 L g−1. min−1 within 10.5 min, 1.81×, 2.42×, and 3.83× higher than control samples, and undoped Co3O4 with (311) dominance, and 1.24× higher than (220). An estimated activation energy (Ea) of 33.63 kJ mol−1, comparable to noble metals, indicates high performance and stability over ten (10) cycles. This approach promises sustainable future in "green" H2 production.

Using Surface Composition and Energy to Control the Formation of Either Tetrahexahedral or Hexoctahedral High-Index Facet Nanostructures.

High-index facet nanoparticles with structurally complex shapes, such as tetrahexahedron (THH) and hexoctahedron (HOH), represent a class of materials that are important for catalysis, and the study of them provides a fundamental understanding of the relationship between surface structures and catalytic properties. However, the high surface energies render them thermodynamically unfavorable compared to low-index facets, thereby making their syntheses challenging. Herein, we report a method to control the shape of high-index facet Cu nanoparticles (either THH with {210} facets or HOH with {421} facets) by tuning the facet surface energy with trace amounts of Te atoms. Density functional theory (DFT) calculations reveal that the density of Te atoms on Cu nanoparticles can change the relative stability of the high-index facets associated with either the THH or HOH structures. By controlling the annealing conditions and the rate of Te dealloying from CuTe nanoparticles, the surface density of Te atoms can be deliberately adjusted, which can be used to force the formation of either THH (higher surface Te density) or HOH (lower surface Te density) nanoparticles.