pH-Universal Electrocatalytic CO2 Reduction with Ampere-Level Current Density on Doping-Engineered Bismuth Sulfide.

The practical application of the electrocatalytic CO2 reduction reaction (CO2RR) to form formic acid fuel is hindered by the limited activation of CO2 molecules and the lack of universal feasibility across different pH levels. Herein, we report a doping-engineered bismuth sulfide pre-catalyst (BiS-1) that S is partially retained after electrochemical reconstruction into metallic Bi for CO2RR to formate/formic acid with ultrahigh performance across a wide pH range. The best BiS-1 maintains a Faraday efficiency (FE) of ~95 % at 2000 mA cm-2 in a flow cell under neutral and alkaline solutions. Furthermore, the BiS-1 catalyst shows unprecedentedly high FE (~95 %) with current densities from 100 to 1300 mA cm-2 under acidic solutions. Notably, the current density can reach 700 mA cm-2 while maintaining a FE of above 90 % in a membrane electrode assembly electrolyzer and operate stably for 150 h at 200 mA cm-2. In situ spectra and density functional theory calculations reveals that the S doping modulates the electronic structure of Bi and effectively promotes the formation of the HCOO* intermediate for formate/formic acid generation. This work develops the efficient and stable electrocatalysts for sustainable formate/formic acid production.

Lattice Mismatch-Induced Formation of Copper Nanoplates with Embedded Ultrasmall Platinum or Palladium Cores for Tunable Optical Properties.

Although noble metal nanocrystals have been studied extensively in the past decades, the shape-controlled synthesis of non-noble metal nanocrystals has remained challenging with limited success, which is a grand obstacle to their wide applications. Herein, a novel lattice mismatch-involved shape-control mechanism of Cu nanocrystals in a seed-mediated synthesis is reported, which can produce Cu nanoplates in high yield with tailored sizes (28-130 nm), holding great potential in optical and catalytic applications. The lattice mismatch between Cu and the seed is found effective in inducing crystallographic defects for symmetry breaking toward anisotropic nanocrystals. While a too-large lattice mismatch (11.7% for Au seeds) leads to multiple twin defects to form quasi-spherical Cu nanocrystals, an appropriately large lattice mismatch (7.7% for Pt and 6.9% for Pd seeds) successfully induces planar defects for the formation of Cu nanoplates. The size of the Cu nanoplates is customizable by controlling the concentration of the seeds, leading to tunable optical properties. A prototype of a colorimetric indicator with Cu nanoplates, potentially applicable to the safety control of foods and drugs is demonstrated. This mechanism paves a new way for the shape-controlled synthesis of Cu and other metal nanocrystals for a broad range of applications.

Electrical Pulse Induced One-step Formation of Atomically Dispersed Pt on Oxide Clusters for Ultra-Low-Temperature Zinc-Air Battery.

Atomically dispersed sites anchored on small oxide clusters are attractive new catalytic materials. Herein, we demonstrate an electrical pulse approach to synthesize atomically dispersed Pt on various oxide clusters in one step with nitrogen-doped carbon as the support (Pt1 -MOx /CN). As a proof-of-concept application, Pt1 -FeOx /CN is shown to exhibit high activity for oxygen reduction reaction (ORR) with a half-wave potential of 0.94 V vs RHE, in contrast to the poor catalytic performance of atomically dispersed Pt on large Fe2 O3 nanoparticles. Our work has revealed that, by tuning the size of the iron oxide down to the cluster regime, an optimal OH* adsorption strength for ORR is achieved on Pt1 -FeOx /CN due to the regulation of Pt-O bonds. The unique structure and high catalytic performance of Pt1 -FeOx /CN enable the Zinc-Air batteries an excellent performance at ultralow temperature of -40 °C with a high peak power density of 45.1 mW cm-2 and remarkable cycling stability up to 120 h.

Solid-to-Hollow Conversion of Silver Nanocrystals by Surface-Protected Etching.

Although hollow silver nanocrystals possess unique plasmonic properties, there is a lack of robust strategies to synthesize such nanocrystals with high efficiency and controllability. To solve this problem, a new surface-protected etching strategy to convert solid Ag nanocrystals, which are widely available from conventional syntheses, into their hollow counterparts, producing a family of hollow Ag nanocrystals is reported. Hollow Ag nanospheres and nanotubes were prepared conveniently in this way. The key was the surface modification of Ag nanocrystals by a minor amount of Pt prior to a controllable etching process, which accounts for enhanced stability of the Ag surface and subsequent etching of Ag from the inner part of the nanocrystals while retaining the overall crystal morphology. These hollow Ag nanocrystals showed distinctive optical properties, as demonstrated by the enhanced optical transmittance of flexible electrodes fabricated with Ag nanotubes, compared to nanowires. These hollow Ag nanocrystals hold promise in different plasmonic and electronic applications.

Aqueous Synthesis of Ultrathin Platinum/Non-Noble Metal Alloy Nanowires for Enhanced Hydrogen Evolution Activity.

Although aqueous synthesis of nanocrystals is advantageous in terms of the cost, convenience, environmental friendliness, and surface cleanness of the product, nanocrystals of Pt and non-noble metal alloys are difficult to obtain with controlled morphology and composition from this synthesis owing to a huge gap between the reduction potentials of respective metal salts. This huge gap could now be remedied by introducing a sulfite into the aqueous synthesis, which is believed to resemble an electroless plating mechanism, giving rise to a colloid of Pt-M (M=Ni, Co, Fe) alloy nanowires with an ultrasmall thickness (ca. 2.6 nm) in a high yield. The sulfite also leads to the formation of surface M-S bonds and thus atomic-level Pt/M-S(OH) interfaces for greatly boosted hydrogen evolution kinetics under alkaline conditions. An activity of 75.3 mA cm-2 has been achieved with 3 µg of Pt in 1 m KOH at an overpotential of 70 mV, which is superior to previously reported catalysts.

Porous Au-Ag Nanospheres with High-Density and Highly Accessible Hotspots for SERS Analysis.

Colloidal plasmonic metal nanoparticles have enabled surface-enhanced Raman scattering (SERS) for a variety of analytical applications. While great efforts have been made to create hotspots for amplifying Raman signals, it remains a great challenge to ensure their high density and accessibility for improved sensitivity of the analysis. Here we report a dealloying process for the fabrication of porous Au-Ag alloy nanoparticles containing abundant inherent hotspots, which were encased in ultrathin hollow silica shells so that the need of conventional organic capping ligands for stabilization is eliminated, producing colloidal plasmonic nanoparticles with clean surface and thus high accessibility of the hotspots. As a result, these novel nanostructures show excellent SERS activity with an enhancement factor of ∼1.3 × 10(7) on a single particle basis (off-resonant condition), promising high applicability in many SERS-based analytical and biomedical applications.

Compressive strain in Cu catalysts: Enhancing generation of C2+ products in electrochemical CO2 reduction.

Elastic strain in Cu catalysts enhances their selectivity for the electrochemical CO2 reduction reaction (eCO2RR), particularly toward the formation of multicarbon (C2+) products. However, the reasons for this selectivity and the effect of catalyst precursors have not yet been clarified. Hence, we employed a redox strategy to induce strain on the surface of Cu nanocrystals. Oxidative transformation was employed to convert Cu nanocrystals to CuxO nanocrystals; these were subsequently electrochemically reduced to form Cu catalysts, while maintaining their compressive strain. Using a flow cell configuration, a current density of 1 A/cm2 and Faradaic efficiency exceeding 80% were realized for the C2+ products. The selectivity ratio of C2+/C1 was also remarkable at 9.9, surpassing that observed for the Cu catalyst under tensile strain by approximately 7.6 times. In-situ Raman and infrared spectroscopy revealed a decrease in the coverage of K+ ion-hydrated water (K·H2O) on the compressively strained Cu catalysts, consistent with molecular dynamics simulations and density functional theory calculations. Finite element method simulations confirmed that reducing the coverage of coordinated K·H2O water increased the probability of intermediate reactants interacting with the surface, thereby promoting efficient C-C coupling and enhancing the yield of C2+ products. These findings provide valuable insights into targeted design strategies for Cu catalysts used in the eCO2RR.

Single-atom catalysts for electrochemical applications.

The field of small molecule electro-activated conversion is becoming a new star in modern catalytic research toward the carbon-neutral future. The advent of single-atom catalysts (SACs) is expected to greatly accelerate the kinetics of electrocatalytic reactions such as the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), hydrogen oxidation reaction (HOR), etc., owing to their maximum atomic efficiency, unique quantized energy level structure and strong interaction between well-defined active sites and supports. In this feature article, our group's proposed synthesis methodology applied in electrocatalysis is mainly summarized. Furthermore, we elaborate on how to achieve the stabilization of single metal atoms against migration and agglomeration during the preparation of SACs. Moreover, the electrochemical applications of SACs with a focus on the above heterogeneous reactions are presented. Finally, the prospects for the development and deficiencies of these SACs for electrocatalytic reactions are discussed.

Deep mineralization of VOCs in an embedded hybrid structure CoFe2O4/MoS2/PMS wet scrubber system.

Peroxymonosulfate (PMS)-based advanced oxidation processes in liquid phase systems can actively degrade toluene. In this work, the catechol structural surfactant was introduced to synthesize the dispersed and homogeneous CoFe2O4 nanospheres and embedded into MoS2 nanoflowers to form magnetically separable heterojunction catalysts. The innovative approach effectively mitigated the traditionally low reduction efficiency of transition metal ions during the heterogeneous activation process. In CoFe2O4/MoS2/PMS system, the toluene removal efficiency remained 95% within 2 h. The contribution of SO4⋅-, ·O2-, ·OH, and 1O2 was revealed by radical quenching experiment and electron paramagnetic resonance spectroscopy. The results illustrated that MoS2 offers ample reduction sites for facilitating PMS activation via Fe3+/Fe2+ redox interactions. Furthermore, an investigation into the toluene degradation pathway within the CoFe2O4/MoS2/PMS system revealed its capability to suppress the formation of toxic byproducts. This ambient-temperature liquid-phase method presented promising route for the removal of industrial volatile organic pollutants.

Regulating Sn self-doping and boosting solar water splitting performance of hematite nanorod arrays grown on fluorine-doped tin oxide via low-level Hf doping.

Hematite (α-Fe2O3) nanorod arrays grown on fluorine-doped tin oxide (FTO) substrate exhibit outstanding solar water splitting efficiency, benefiting from Sn self-doping induced by high-temperature annealing. However, this Sn self-doping couldn't be freely controlled without changing the optimized annealing conditions, which limits the further improvement of their photoelectrochemical (PEC) properties. Here, we report a facile hydrothermal synthesis with subsequent annealing approach to regulate the Sn diffusion via hafnium (Hf) doping as well as enhance the PEC performance of hematite photoanode. Upon increasing the Hf doping concentration, the Sn self-doping content was continuously suppressed. The very low doping-level of Hf (i.e., atomic Hf/Fe = 0.13 âˆ¼ 1.54%) was sufficient for enhancing the electrical conductivity. The Hf-doped α-Fe2O3 with the optimized dopant concentration (Hf/Fe = 1.34%, denoted as 0.25-Hf-Fe2O3) showed a photocurrent density of 1.79 mA/cm2 at 1.23 V vs. RHE, 70% higher than that of the Sn self-doped one (Pristine-Fe2O3). The donor density of 0.25-Hf-Fe2O3 increased 2.5 times compared to Pristine-Fe2O3 while its space-charge resistance and charge transfer resistance declined by 40% and 22%, respectively, verifying Hf doping improves the charge carrier density and accelerates the charge transfer for solar water oxidation. We offered here a prospective dopant alternative for preparing superior hematite-based photoanode.

Evolution of the Interfacial Layer and Its Impact on Electric-Field-Cycling Behaviors in Ferroelectric Hf1-xZrxO2.

Doped HfO2 thin films, which exhibit robust ferroelectricity even with aggressive thickness scaling, could potentially enable ultralow-power logic and memory devices. The ferroelectric properties of such materials are strongly intertwined with the voltage-cycling-induced electrical and structural changes, leading to wake-up and fatigue effects. Such field-cycling-dependent behaviors are crucial to evaluate the reliability of HfO2-based functional devices; however, its genuine nature remains elusive. Herein, we demonstrate the coupling mechanism between the dynamic change of the interfacial layer and wake-up/fatigue phenomena in ferroelectric Hf1-xZrxO2 (HZO) thin films. Comprehensive atomic-resolution microscopy studies have revealed that the interfacial layer between the HZO and neighboring nonoxide electrode experienced a thickness/composition evolution during electrical cycling. Two theoretical models associated with the depolarization field are adopted, giving consistent results with the thickening of the interfacial layer during electrical cycling. Furthermore, we found that the electrical properties of the HZO devices can be manipulated by controlling the interface properties, e.g., through the choice of electrode match and hybrid cycling process. Our results unambiguously reveal the relationship between the interfacial layer and field-cycling behaviors in HZO, which would further permit the reliability improvement in HZO-based ferroelectric devices through interface engineering.

Customizable Ligand Exchange for Tailored Surface Property of Noble Metal Nanocrystals.

It is highly desirable, while still challenging, to obtain noble metal nanocrystals with custom capping ligands, because their colloidal synthesis relies on specific capping ligands for the shape control while conventional ligand exchange processes suffer from "the strong replaces the weak" limitation, which greatly hinders their applications. Herein, we report a general and effective ligand exchange approach that can replace the native capping ligands of noble metal nanocrystals with virtually any type of ligands, producing flexibly tailored surface properties. The key is to use diethylamine with conveniently switchable binding affinity to the metal surface as an intermediate ligand. As a strong ligand, it in its original form can effectively remove the native ligands; while protonated, it loses its binding affinity and facilitates the adsorption of new ligands, especially weak ones, onto the metal surface. By this means, the irreversible order in the conventional ligand exchange processes could be overcome. The efficacy of the strategy is demonstrated by mutual exchange of the capping ligands among cetyltrimethylammonium, citrate, polyvinylpyrrolidone, and oleylamine. This novel strategy significantly expands our ability to manipulate the surface property of noble metal nanocrystals and extends their applicability to a wide range of fields, particularly biomedical applications.

Ultra-Small Platinum Nanoparticles Encapsulated in Sub-50 nm Hollow Titania Nanospheres for Low-Temperature Water-Gas Shift Reaction.

Ultra-small platinum nanoparticles loaded over titania is a promising catalyst for the low-temperature water-gas shift (WGS) reaction and shows the potential to work in a mobile hydrogen fuel cell system. Their precise size engineering (<3 nm) and reliable stabilization remain challenging. To address these issues, we report a reverse-micelle synthesis approach, which affords uniform ultra-small platinum nanoparticles (tunable in ∼1.0-2.6 nm) encapsulated in hollow titania nanospheres with a shell thickness of only ∼3-5 nm and an overall diameter of only ∼32 nm. The Pt@TiO2 yolk/shell nanostructured catalysts display extraordinary stability and monotonically increasing activity with the decreasing size of the Pt nanoparticles in the WGS. The size-dependent variation in the electronic property of the Pt nanoparticles and the reducible oxide encapsulation that prevents the Pt nanoparticles from sintering are ascribed as the main reasons for the excellent catalytic performance.

Gold nanoshurikens with uniform sharp tips for chemical sensing by the localized surface plasmon resonance.

Creation of uniform sharp tips in noble metal nanostructures is highly desirable for chemical sensing applications that rely on their localized surface plasmon resonance (LSPR), while it remains a great challenge as typically it is not energetically favorable. Herein, we report a robust synthesis route to a novel family of unique shuriken-shaped Au nanostructures with four in-plane sharp tips in high yield and uniformity. The success of the synthesis relies on the anisotropic crystal growth of quasi-planar Au seeds by taking advantage of the capping effect of a ligand on the specific facets, as well as the predominant deposition of Au over its surface diffusion that accounts for the formation of the sharp tips. The resulting Au nanoshurikens show remarkable LSPR in the near-infrared range of the spectrum, which proves to be sensitive to a minor change in the sharp tips, thus enabling superior chemical sensing activity, as demonstrated by detection of mercury of ultralow concentrations. This novel nanostructure promises not only great potential in monitoring mercury in aquatic ecosystems, but also wide applicability to many other sensing scenarios, such as analyzing various chemicals and biologically active species, with excellent sensitivity.

Self-assembly of noble metal nanoparticles into sub-100 nm colloidosomes with collective optical and catalytic properties.

Self-assembly at the nanoscale represents a powerful tool for creating materials with new structures and intriguing collective properties. Here, we report a novel strategy to synthesize nanoscale colloidosomes of noble metals by assembling primary metal nanoparticles at the interface of emulsion droplets formed by their capping agent. This strategy produces noble metal colloidosomes of unprecedentedly small sizes (<100 nm) in high yield and uniformity, which is highly desirable for practical applications. In addition, it enables the high tunability of the composition, producing a diversity of monometallic and bimetallic alloy colloidosomes. The colloidosomes exhibit interesting collective properties that are different from those of individual colloidal nanoparticles. Specifically, we demonstrate Au colloidosomes with well-controlled interparticle plasmon coupling and Au-Pd alloy colloidosomes with superior electrocatalytic performance, both thanks to the special structural features that arise from the assembly. We believe this strategy provides a general platform for producing a rich class of miniature colloidosomes that may have fascinating collective properties for a broad range of applications.

Holey Au-Ag alloy nanoplates with built-in hotspots for surface-enhanced Raman scattering.

Plasmonic noble metal nanocrystals with interior nanogaps have attracted great attention in surface-enhanced Raman scattering (SERS) applications due to the presence of built-in hotspots. Herein, we report a synthesis route to holey Au-Ag alloy nanoplates by controlled galvanic replacement with Ag nanoplates as the sacrificial template, a sulfite-coordinated Au(i) salt as the Au source, and polyvinylpyrrolidone (PVP) as the capping agent. PVP helps regulate the anisotropic growth of nanopores on the Ag nanoplates to afford a highly holey nanostructure, and the monovalent Au(i) salt plays a critical role in stabilizing these holey nanoplates by rapidly enriching Au in the alloy nanostructures. Numerical simulations and experimental results suggest that these holey Au-Ag alloy nanoplates possess enormous internal hotspots for high sensitivity in the SERS analysis, and high stability for excellent reliability of the analysis under many harsh conditions. We believe that this strategy is potentially applicable to the synthesis of many other types of plasmonic nanostructures with inherent nanogaps for many sensing and imaging applications.