In Situ TEM Tracking of Disconnection Motion and Atomic Cooperative Reorientation in the Oriented Attachment of Pt Nanoparticles.

The oriented attachment (OA) of nanoparticles (NPs) is an important crystal growth mechanism in many materials. However, a comprehensive understanding of the atomic-scale alignment and attachment processes is still lacking. We conducted in situ atomic resolution studies using high-resolution transmission electron microscopy to reveal how two Pt NPs coalesce into a single particle via OA, which involves the formation of atomic-scale links and a grain boundary (GB) between the NPs, as well as GB migration. Density functional theory calculations showed that the system energy changes as a function of the number of disconnections during the coalescence process. Additionally, the formation and annihilation processes of disconnection are always accompanied by the cooperative reorientation motion of atoms. These results further elucidate the growth mechanism of OA at the atomic scale, providing microscopic insights into OA dynamics and a framework for the development of processing strategies for nanocrystalline materials.

Coordination Confined Thermolysis Synthesis of the Ni Single Atom Catalyst on the N-Doped Commercial Carbon for the Production of Syngas.

The electrochemical conversion of CO2 into controllable syngas (CO/H2) over a wide potential range is challenging. The main electrocatalysts are based on the noble metals Au (Ag) or heavy metal Pb. The development of alternative nonprecious catalysts is of paramount importance for practice. In this work, a simple coordination confined thermal pyrolysis method has been developed for the synthesis of Ni single-atom catalyst loaded onto nitrogen-doped commercial carbon. The catalyst is in the form of NiN3-C, which exhibits a high-performance electrocatalytic reduction of CO2 toward producing syngas with Faraday efficiencies of 62.28% of CO and 36.7% of H2. The Gibbs free energies of COOH* and H* on the NiN3-C structure were estimated by using density functional theory (DFT). The formation of COOH* intermediate is the speed-limiting step in the process, with ΔG COOH* being 0.7 eV, while H* is the speed-limiting step in the hydrogen evolution, respectively. This work provides a feasible method for the achievement of nonprecious catalysts for the resourceful use of CO2.

Self-Supported Nanoporous Au3 Cu Electrode with Enriched Gold on Surface for Efficient Electrochemical Reduction of CO2.

The key to the electrochemical conversion of CO2 lies in the development of efficient electrocatalysts with ease of operation, good conductivity, and rich active sites that fulfil the desired reaction direction and selectivity. Herein, an oxidative etching of Au20 Cu80 alloy is used for the synthesis of a nanoporous Au3 Cu alloy, representing a facile strategy for tuning the surface electronic properties and altering the adsorption behavior of the intermediates. HRTEM, XPS, and EXAFS results reveal that the curved surface of the synthesized nanoporous Au3 Cu is rich in gold with unsaturated coordination conditions. It can be used directly as a self-supported electrode for CO2 reduction, and exhibits high Faradaic efficiency (FE) of 98.12 % toward CO at a potential of -0.7 V versus the reversible hydrogen electrode (RHE). The FE is 1.47 times that over the as-made single nanoporous Au. Density functional theory reveals that *CO has a relatively long distance on the surface of nanoporous Au3 Cu, making desorption of CO easier and avoiding CO poisoning. The Hirshfeld charge distribution shows that the Au atoms have a negative charge and the Cu atoms exhibit a positive charge, which separately bond to the C atom and O atom in the *COOH intermediate through a bidentate mode. This affords the lowest *COOH adsorption free energy and low desorption energy for CO molecules.

Rational Design of Co(II) Dominant and Oxygen Vacancy Defective CuCo2O4@CQDs Hollow Spheres for Enhanced Overall Water Splitting and Supercapacitor Performance.

The hierarchical CuCo2O4@carbon quantum dots (CQDs) hollow microspheres constructed by 1D porous nanowires have been successfully prepared through a simple CQDs-induced hydrothermal self-assembly technique. XPS analysis shows the CuCo2O4@CQDs possesses the Co(II)-rich surface associated with the oxygen vacancies, which can effectively boost the Faradaic reactions and oxygen evolution reaction (OER) activity. For example, the as-synthesized 3D porous CuCo2O4@CQDs electrode exhibits high activity toward overall electrochemical water splitting, for example, an overpotential of 290 mV for OER and 331 mV for hydrogen evolution reaction (HER) in alkaline media have been achieved at 10 mA cm-2, respectively. Furthermore, an asymmetric supercapacitor (ASC) (CuCo2O4@CQDs//CNTs) delivers a high energy density of 45.9 Wh kg-1 at 763.4 W kg-1, as well as good cycling ability. The synergy of Co(II)-rich surface, oxygen vacancies, and well-defined 3D hollow structures facilitates the subsequent surface electrochemical reactions. This work presents a facile method to fabricate energetic nanocomposites with highly reactive, durable, and universal functionalities.

Solid-State Construction of CuO-Cu2O@C with Synergistic Effects of Pseudocapacity and Carbon Coating for Enhanced Electrochemical Lithium Storage.

The pseudocapacitive effect can improve the electrochemical lithium storage capacity at high-rate current density. However, the cycle stability is still unsatisfactory. To overcome this issue, a multivalent oxide with a carbon coating represents a plausible technique. In this work, a CuO-Cu2O@C composite has been constructed by a one-step bilayer salt-baking process and utilized as anode material for lithium-ion batteries. At a current density of 2.0 A g-1, the as-prepared composite delivered a stable discharge capacity of 431.8 mA h g-1 even after 600 cycles. The synergistic effects of the multivalence, the pseudocapacitive contribution from copper, and the carbon coating contribute to the enhanced electrochemical lithium storage performance. Specifically, the existence of cuprous suboxide improves the electrochemical conductivity, the pseudocapacitive effect enhances the lithium storage capacity, and the presence of carbon ensures cycle stability. The testing results show that CuO-Cu2O@C composite has broad application prospects in portable energy storage devices. The present work provides an instructive precedent for the preparation of transition metal oxides with controllable electronic states and excellent electrochemical performance.

Enhancing photocatalytic CO2 reduction with TiO2-based materials: Strategies, mechanisms, challenges, and perspectives.

The concentration of atmospheric CO2 has exceeded 400 ppm, surpassing its natural variability and raising concerns about uncontrollable shifts in the carbon cycle, leading to significant climate and environmental impacts. A promising method to balance carbon levels and mitigate atmospheric CO2 rise is through photocatalytic CO2 reduction. Titanium dioxide (TiO2), renowned for its affordability, stability, availability, and eco-friendliness, stands out as an exemplary catalyst in photocatalytic CO2 reduction. Various strategies have been proposed to modify TiO2 for photocatalytic CO2 reduction and improve catalytic activity and product selectivity. However, few studies have systematically summarized these strategies and analyzed their advantages, disadvantages, and current progress. Here, we comprehensively review recent advancements in TiO2 engineering, focusing on crystal engineering, interface design, and reactive site construction to enhance photocatalytic efficiency and product selectivity. We discuss how modifications in TiO2's optical characteristics, carrier migration, and active site design have led to varied and selective CO2 reduction products. These enhancements are thoroughly analyzed through experimental data and theoretical calculations. Additionally, we identify current challenges and suggest future research directions, emphasizing the role of TiO2-based materials in understanding photocatalytic CO2 reduction mechanisms and in designing effective catalysts. This review is expected to contribute to the global pursuit of carbon neutrality by providing foundational insights into the mechanisms of photocatalytic CO2 reduction with TiO2-based materials and guiding the development of efficient photocatalysts.

Methane plasma-mediated phase engineering of Ni nanosheets for alkaline hydrogen evolution.

Engineering of the crystal structures of metallic nanomaterials is an alternative avenue to control the size and shape of nanocatalysts. However, the phase-controlled synthesis of Ni nanocatalysts is challenging because of its low reduction potential under mild conditions. We developed a room-temperature CH4 plasma conversion of Ni(OH)2 nanosheets to hexagonal close packed (hcp) Ni while maintaining a pristine shape. Increasing the temperature resulted in the formation of face-centered cubic (fcc) Ni. The hcp Ni nanosheets exhibited an overpotential of 85 mV at 10 mA cm-2 for an electrocatalytic hydrogen evolution reaction (HER) in alkaline solution, which was superior to that of the fcc (122 mV) counterpart. Density-functional-theory calculations demonstrated that during the HER, the d-band center of hcp Ni was closer to the Fermi level, which aided the formation of H2 molecules. This work could facilitate the synthesis of other metastable metals and metallic alloys with high efficiency for various applications.

Accelerating Anode Reaction with Electro-oxidation of Alcohols over Ru Nanoparticles to Reduce the Potential for Water Splitting.

Generating hydrogen by water electrolysis is a promising and sustainable approach to the production of a green energy carrier, but the sluggish kinetics of the oxygen evolution reaction (OER) at anode leads to a high working potential. Replacing OER with electro-oxidation of organics driven at a low potential offers an effective way to accelerate the sluggish anode reaction, and thus increase hydrogen evolution in water-splitting. Herein, we have prepared a Ru nanoparticles on N-doped carbon nanotubes (Ru-NPs@NCNTs) to implement electro-oxidation of benzyl alcohol toward reducing the anodic potential in watersplitting. The potential of the anode reaction is remarkably decreased from 1.76 to 1.19 V vs RHE at a current density of 10 mA cm-2 with the assistance of a Ru-NPs catalyst. Furthermore, 100% selectivity and 95% yield of valuable benzaldehyde were achieved simultaneously. The Ru-NPs also exhibits good durability and wide applicability to other alcohols. The high performance of Ru-NPs is mainly attributed to the unique horizontal adsorption configuration of benzyl alcohol with surface atoms of the catalyst, shortening the distance between the •OH group and Ru atoms, and increasing the activation rate of the •OH group. This work presents a feasible strategy to boost water-splitting performance and concurrently produce value-added organics under mild conditions.

Three-dimensional MoS2 nanoflowers supported Prussian blue and Au nanoparticles: A peroxidase-mimicking catalyst for the colorimetric detection of hydrogen peroxide and glucose.

Well-dispersed Prussian blue (PB) and Au nanoparticles (Au NPs) loaded three dimensional MoS2 nanoflowers (PB-Au@MoS2 NFs) was synthesized by a simple and economical method. The structure, morphology and composition of the hybrid were characterized by XRD, SEM and EDS. Similar to the reported literature, MoS2 nanoflowers showed peroxidase-like activity in catalyzing the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). This peroxidase-mimicking activity could be enhanced with the introduction of PB and Au NPs. Herein, PB-Au@MoS2 NFs could be used to establish a new platform for the determination of H2O2 and glucose by the chromogenic reaction. Wide linear ranges with 0-15 µM and 0-120 µM for H2O2 and glucose detection were finally obtained. The detection limits were as low as 0.25 µM and 3 µM (with signal to noise ratio of 3), respectively. The established platform was also used successfully for the determination of glucose in human serum and fruit juice samples with excellent sensitivity and stability.

PtPdCu nanodendrites enable complete ethanol oxidation by enhancing CC bond cleavage.

Complete oxidation of ethanol is a pressing need for direct ethanol fuel cells (DEFCs) owning to high energy conversion. However, it holds great challenges on account of sluggish kinetics for CC bond cleavage and high susceptibility to CO poisoning. Herein, ternary PtPdCu nanocrsytals are synthesized and investigated for complete oxidation of ethanol. The obtained ternary PtPdCu nanodendrites (PtPdCu NDs) have a stepped surface, providing abundant active sites. Due to the structural and synergistic effects, ternary PtPdCu NDs exhibit a mass activity of 5.59 A mgPtPd-1 and specific activity of 15.82 mA cm-2 towards ethanol oxidation reaction, which are 6.4 and 3.6 times larger than that of commercial Pt/C. Further studies reveal that ternary PtPdCu NDs show strong abilities of CO anti-poisoning and CC bond cleavage, enhancing the C1 pathway selectivity.

Living Atomically Dispersed Cu Ultrathin TiO2 Nanosheet CO2 Reduction Photocatalyst.

Supported atomically dispersed metals are proving to be efficacious photocatalysts for CO2 reduction to solar fuels. While being atom efficient, they suffer from being noble, rare, and costly (Pt, Pd, Au, Ag, Rh) and lacking in long-term stability. Herein, all of these problems are solved with the discovery that atomically dispersed Cu supported on ultrathin TiO2 nanosheets can photocatalytically reduce an aqueous solution of CO2 to CO. The atomically dispersed Cu can be recycled in a straightforward procedure when they become oxidatively deactivated. This advance bodes well for the development of a solar fuels technology founded on abundant, low-cost, nontoxic, atomically dispersed metal photocatalysts.

Ultrathin Metal-Organic Framework Nanosheet-Derived Ultrathin Co3O4 Nanomeshes with Robust Oxygen-Evolving Performance and Asymmetric Supercapacitors.

Ultrathin metal-organic framework (MOF) nanosheets possessing inherent advantages of both two-dimensional (2D) features and MOFs are attracting intensive research interest. The direct manufacture of MOF nanosheets is still a challenge up to now. Here, we have developed a novel bottom-up approach to synthesize zeolitic imidazolate framework-67 (ZIF-67) nanosheets, which can be in situ converted into Co3O4 ultrathin nanomeshes after thermal treatment. Interestingly, the obtained Co3O4 nanomeshes are rich in oxygen defects, providing fruitful active sites for the faradaic reaction. The modified electrode exhibits a large specific capacitance (1216.4 F g-1 at 1 A g-1), as well as a high rate capability (925.5 F g-1 at 20 A g-1). Moreover, an asymmetric supercapacitor made of Co3O4//activated carbon shows an energy density of 46.5 Wh kg-1 at 790.7 W kg-1. Furthermore, the 2D Co3O4 ultrathin nanomeshes show an outstanding performance for the oxygen evolution reaction with an overpotential of 230 mV at the onset potential and a small Tafel slope of 74.0 mV dec-1. The present method presents a facile avenue to the preparation of other 2D ultrathin metal oxide nanostructures with various applications in energy catalysis and conversion.

Synthesis of AgInS2-xAg2S-yZnS-zIn6S7 (x, y, z = 0, or 1) Nanocomposites with Composition-Dependent Activity towards Solar Hydrogen Evolution.

Metal sulfides-based nanomaterials have been used as a class of efficient solar driven photocatalysts. However, the H2-production rate observed over these photocatalysts remains problematic. Here, the AgInS2-xAg2S-yZnS-zIn6S7 (x, y, z = 0 or 1) nanocomposites with controlled compositions have been successfully prepared by a simple hydrothermal method with AgI polyhedrons as silver source. The obtained AgInS2-xAg2S-yZnS-zIn6S7 nanocomposites showed a composition-dependent activity for H2 evolution from aqueous solution under simulated sun-light irradiation. The results showed that the optimized product of AgInS2-Ag2S-ZnS nanoparticles synthesized with the precursor ratio of Ag:Zn = 1:1 exhibited the highest H2 evolution rate of 5.4 mmol·g-1·h-1. Furthermore, the catalyst can be used for 20 h without loss of activity, showing its high stability. It opens a new path to achieve highly efficient solar photocatalyst for H2 evolution from water splitting.

Synthesis of monodisperse chromium nanoparticles from the thermolysis of a Fischer carbene complex.

We successfully synthesized monodisperse chromium nanoparticles from the thermolysis of a Fischer carbene complex.

Facile aqueous synthesis of ß-AgI nanoplates as efficient visible-light-responsive photocatalyst.

Owing to far-ranging industrial applications and theoretical researches, tailored synthesis of well-defined nanocrystals has attracted substantial research interest. Herein, ß-AgI nanoplates have been synthesized through a facile polyvinylpyrrolidone (PVP)-assisted-aqueous-solution (PAAS) method under mild conditions. The parametric studies on the effect of ratio of reactants, solvents and surfactants were performed, revealing that a molar ratio of I(-) to Ag(+) of 1.2 in deionized water and the presence of appropriate PVP as stabilizing agent can stimulate the preferred orientation growth of AgI nanoplates. The as-synthesized AgI nanoplates exhibit excellent photocatalytic activity and enhanced durability towards the degradation of organics, i.e., rhodamine B (RhB), under visible light illumination in comparison with corresponding bulk nanoparticles. A possible photocatalytic reaction mechanism was discussed, revealing O2˙(-) and h(+) are main reactive species and free ˙OH radicals in solution also contribute to the degradation reaction. The superior photocatalytic performance renders the as-achieved AgI nanoplates promising candidates for applications in the fields of environmental purification or water disinfection. The present work opens an avenue to the synthesis of other shaped silver halide nanophotocatalysts.

Hollow AgI:Ag nanoframes as solar photocatalysts for hydrogen generation from water reduction.

A facile strategy based on the principle of the Kirkendall effect has been developed to synthesize hollow nanoframes and nanoshells of AgI:Ag composites through the controlled anion-exchange reaction between I(-) ions and solid AgBr:Ag (or AgCl:Ag) nanoparticles that serve as templates. Regardless of the morphologies of the template nanoparticles, they can be chemically transformed to hollow AgI:Ag structures with morphologies similar to those of the templates. The synthesized hollow AgI:Ag nanostructures can be used as efficient photocatalysts for H2 generation from water reduction and the decomposition of organic pollutants owing to the enhanced absorption of visible light by the Ag components in the hybrid nanostructures. The hollow nanostructures exhibit a higher photocatalytic performance than the corresponding solid nanoparticles possibly because of the large surface area and unique AgI/Ag interfaces associated with the hollow nanostructures.

Synthesis of three-dimensional AgI@TiO2 nanoparticles with improved photocatalytic performance.

Three-dimensional (3D) TiO2 with an acanthosphere-like morphology composed of nanothorns has been used as a suitable support to fabricate a visible-light-induced 3D AgI@TiO2 nanophotocatalyst. The structural characterization revealed that the size of the obtained AgI@TiO2 nanocomposite was close to that of pristine TiO2 particles, where AgI nanoparticles were evenly dispersed on the surfaces of "thorns" of TiO2. The as-achieved 3D AgI@TiO2 nanophotocatalyst exhibited enhanced photocatalytic performance towards photodegradation of organic pollutants, e.g., rhodamine B (RhB), in comparison with TiO2, P25, AgI and AgI@P25 with the same quantity. The enhanced photocatalytic performance is attributed to the strong visible light absorption and the defined interfaces between AgI nanoparticles and TiO2 nanothorns with efficient separation of photogenerated carriers. The excellent performance of the 3D AgI@TiO2 nanophotocatalyst suggests its promising applications in water treatment and environmental remediation.

Strongly visible-light responsive plasmonic shaped AgX:Ag (X = Cl, Br) nanoparticles for reduction of CO2 to methanol.

Plasmonic shaped AgX:Ag (X = Cl, Br) nanoparticles have been synthesized by a facile and versatile glycerol-mediated solution route. The as-prepared AgX:Ag nanoparticles exhibit regular shapes, i.e., cube-tetrapod-like AgCl:Ag nanoparticles and AgBr:Ag nanoplates. Compared with the pristine AgX, AgX:Ag nanocomposites display stronger absorption in the visible region due to the surface plasmon resonance of silver nanoparticles. The calculation of bandgaps and band positions indicates the as-achieved AgX:Ag nanoparticles can be used as a class of potential photocatalyst for the reduction of CO(2). For example, reduction of CO(2) under visible light irradiation with the assistance of the anisotropic AgX:Ag nanoparticles yields as much as 100 µmol methanol in the products. Furthermore, the AgX:Ag nanoparticles can maintain its structure and activity after 3 runs of reactions. Therefore, the present route opens an avenue to acquire plasmonic photocatalysts for conversion of CO(2) into useful organic compounds.

Large-Scale Growth of Tubular Aragonite Whiskers through a MgCl2-Assisted Hydrothermal Process.

In this paper, we have developed a facile MgCl2-assissted hydrothermal synthesis route to grow tubular aragonite whiskers on a large scale. The products have been characterized by powder X-ray diffraction (XRD), optical microscopy, and scanning electronic microscopy (SEM). The results show the as-grown product is pure tubular aragonite crystalline whiskers with a diameter of 5-10 mm and a length of 100-200 mm, respectively. The concentration of Mg2+ plays an important role in determining the quality and purity of the products. Furthermore, the method can be extended to fabricate CaSO4 fibers. The high quality of the product and the mild conditions used mean that the present route has good prospects for the growth of inorganic crystalline whiskers.