This Review is focused on the recent progresses in the synthetic approaches to the precise control of structure, size, shape, composition and multi-functionality of metal and metal alloy nanoparticles. Many of these strategies have been developed based on colloidal methods, and to limited extent, the galvanic and other methods. The shape, size and composition often govern the chemical and catalytic properties that are important for electrochemical energy applications. The structure–property relationship and the design in controllable structures and morphologies for specific reactions such as oxygen reduction reaction (ORR) are emphasized.

Synthesis of colloidal metal and metal alloy nanoparticles for electrochemical energy applications

In this paper we will review the state-of-the-art in the application of shape-controlled metal nanoparticles in Electrocatalysis, especially in reactions of interest in PEMFCs such as O2reduction and CO, methanol, ethanol and formic acid electrooxidations. In particular, we will focus our attention on shape-controlled platinum (Pt), gold (Au) and palladium (Pd) nanoparticles. In addition, electrocatalytic applications of shape-controlled Pt-based alloy nanoparticles will be also reviewed. The results reported will highlight how important can be controlling the shape of the nanocatalyst and how effective this parameter may be to improve the activity and thus, develop highly active electrocatalysts.

Shape dependent electrocatalysis

Octahedrally shaped Pt–Ni alloy nanoparticles on carbon supports have demonstrated unprecedented electrocatalytic activity for the oxygen reduction reaction (ORR), sparking interest as catalysts for low-temperature fuel cell cathodes. However, deterioration of the octahedral shape that gives the catalyst its superior activity currently prohibits the use of shaped catalysts in fuel cell devices, while the structural dynamics of the overall catalyst degradation are largely unknown. We investigate the time-resolved degradation pathways of such a Pt–Ni alloy catalyst supported on carbon during cycling and startup/shutdown conditions using an in situ STEM electrochemical liquid cell, which allows us to track changes happening over seconds. Thereby we can precisely correlate the applied electrochemical potential with the microstructural response of the catalyst. We observe changes of the nanocatalysts’ structure, monitor particle motion and coalescence at potentials that corrode carbon, and investigate the dissolution and redeposition processes of the nanocatalyst under working conditions. Carbon support motion, particle motion, and particle coalescence were observed as the main microstructural responses to potential cycling and holds in regimes where carbon corrosion happens. Catalyst motion happened more severely during high potential holds and sudden potential changes than during cyclic potential sweeps, despite carbon corrosion happening during both, as suggested by ex situ DEMS results. During an extremely high potential excursion, the shaped nanoparticles became mobile on the carbon support and agglomerated facet-to-facet within 10 seconds. These experiments suggest that startup/shutdown potential treatments may cause catalyst coarsening on a much shorter time scale than full collapse of the carbon support. Additionally, the varying degrees of attachment of particles on the carbon support indicates that there is a distribution of interaction strengths, which in the future should be optimized for shaped particles. We further track the dissolution of Ni nanoparticles and determine the dissolution rate as a function of time for an individual nanoparticle – which occurs over the course of a few potential cycles for each particle. This study provides new visual understanding of the fundamental structural dynamics of nanocatalysts during fuel cell operation and highlights the need for better catalyst-support anchoring and morphology for allowing these highly active shaped catalysts to become useful in PEM fuel cell applications.

/pdf/real-time-imaging-of-activation-and-degradation-of-carbon-11d4ty8vqh.pdf

Real-time imaging of activation and degradation of carbon supported octahedral Pt–Ni alloy fuel cell catalysts at the nanoscale using in situ electrochemical liquid cell STEM

Nanoarchitectonics, a concept encompassing nanoscale microstructures and atomic arrangements in materials, enables the precise modification of materials for desired applications by controlling their physical and chemical properties, as well as surface charge or energy. Particularly in metal materials, where surface reactions play a critical role, nanoarchitecture becomes the most influential factor affecting activity, selectivity, and stability. Focusing on platinum‐group metals (PGMs) due to their inherently high efficiency in energy and environmental applications, this article provides a comprehensive review of synthetic methods for the morphological control of metal nanomaterials. The morphological control is classified into atomic arrangements in 0D, 1D, and 2D nanocrystals, as well as nanoporous structures, and the mechanisms of major reactions are covered in detail. Each chapter is supplemented with a table featuring several examples, facilitating the reader's understanding of the structural controls of PGMs. Finally, the article outlines future challenges in achieving novel metal nanoarchitecture. The hope is that this review provides valuable insights into the synthesis of PGM‐based nanomaterials and serves as a guide for designing and synthesizing innovative metal nanostructures for diverse applications.

Retrospect and Prospect: Nanoarchitectonics of Platinum‐Group‐Metal‐Based Materials

National Science Foundation of China [21273180, 60936003, 21021002]; National Fund for Fostering Talents of Basic Science [J1030415]

Synthesis of Ultrafine Size Platinum Nanoparticles on Defective Graphene with Enhanced Performance Towards Methanol Electro-Oxidation

Cube-shaped Pt nanocrystals (with the size of about 160 nm) are prepared by a square-wave potential electrochemical pretreatment at the expense of Pt nanospheres. A cyclic voltammogram of Pt nanospheres in sulphuric acid shows two pairs of hydrogen adsorption/desorption peaks, which corresponds to the characteristics of a Pt polyoriented surface. However, a cyclic voltammogram of cubic Pt nanocrystals in sulphuric acid shows another pair of hydrogen adsorption/desorption peak at 0.22 V (vs. NHE), which corresponds to the characteristics of Pt (100) surface orientation. Cubic Pt nanocrystals show enhanced electrocatalytic activity over Pt nanospheres for methanol oxidation. The peak current density of cubic Pt nanocrystals is 1.39 mA cm–2Pt, which is 1.48 times that of Pt nanospheres. The poison resistant and oxygen reduction reaction (ORR) activity of cubic Pt nanocrystals are also enhanced compared with those of Pt nanospheres.

Improving the Performance of Platinum Nanocrystal Catalysts by Square‐wave Potential Electrochemical Pretreatment

Prognostic value of combined pre- and postoperative albumin-to-alkaline phosphatase ratio for patients with hepatocellular carcinoma undergoing trans-catheter chemoembolisation.

Effects of microwave power, ultrasonic power and extraction time on bioactive flavonoids extraction from Chenopodium ambrosioides

OBJECTIVE
To investigate the effect of Akt2 inhibitor on macrophage polarization in the periapical tissue in a rat model of periapical inflammation.


METHODS
Rat models of periapical inflammation were established in 28 normal SD rats by opening the pulp cavity of the mandibular first molars, followed by injection of normal saline and Akt2 inhibitor into the left and right medullary cavities, respectively. Four rats without any treatment served as the healthy control group. At 7, 14, 21 and 28 days after modeling, 7 rat models and 1 control rat were randomly selected for observation of inflammatory infiltration in the periapical tissues by X-ray and HE staining. Immunohistochemistry was used to detect the expression and localization of Akt2, macrophages and the inflammatory mediators. RT-PCR was performed to detect the mRNA expressions of Akt2, CD86, CD163, inflammatory mediators, miR-155-5p and C/EBPβ to analyze the changes in macrophage polarization.


RESULTS
X-ray and HE staining showed that periapical inflammation was the most obvious at 21 days after modeling in the rats. Immunohistochemistry and RT-PCR showed that compared with those in the control rats, the expressions of Akt2, CD86, CD163, miR-155-5p, C/EBPβ, and IL-10 increased significantly in the rat models at 21 days (P < 0.05). Compared with saline treatment, treatment with the Akt2 inhibitor significantly decreased the expression levels of Akt2, CD86, miR-155-5p and IL-6 and the ratio of CD86+M1/CD163+M2 macrophages (P < 0.05) and increased the expression levels of CD163, C/EBPβ and IL-10 in the rat models (P < 0.05).


CONCLUSION
Inhibition of Akt2 can delay the progression of periapical inflammation in rats and promote M2 macrophage polarization in the periapical inflammatory microenvironment possibly by reducing miR-155-5p expression and activating the expression of C/EBPβ in the Akt signaling pathway.

[Akt2 inhibitor promotes M2 macrophage polarization in rats with periapical inflammation by reducing miR-155-5p expression].

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Improving the Performance of Platinum Nanocrystal Catalysts by Square‐wave Potential Electrochemical Pretreatment

Prognostic value of combined pre- and postoperative albumin-to-alkaline phosphatase ratio for patients with hepatocellular carcinoma undergoing trans-catheter chemoembolisation.

Effects of microwave power, ultrasonic power and extraction time on bioactive flavonoids extraction from Chenopodium ambrosioides

[Akt2 inhibitor promotes M2 macrophage polarization in rats with periapical inflammation by reducing miR-155-5p expression].