Transplanting Gold Active Sites into Non-Precious-Metal Nanoclusters for Efficient CO2-to-CO Electroreduction.

Electrocatalytic CO2 reduction reaction (CO2RR) is greatly facilitated by Au surfaces. However, large fractions of underlying Au atoms are generally unused during the catalytic reaction, which limits mass activity. Herein, we report a strategy for preparing efficient electrocatalysts with high mass activities by the atomic-level transplantation of Au active sites into a Ni4 nanocluster (NC). While the Ni4 NC exclusively produces H2, the Au-transplanted NC selectively produces CO over H2. The origin of the contrasting selectivity observed for this NC is investigated by combining operando and theoretical studies, which reveal that while the Ni sites are almost completely blocked by the CO intermediate in both NCs, the Au sites act as active sites for CO2-to-CO electroreduction. The Au-transplanted NC exhibits a remarkable turnover frequency and mass activity for CO production (206 molCO/molNC/s and 25,228 A/gAu, respectively, at an overpotential of 0.32 V) and high durability toward the CO2RR over 25 h.

Atomic-level tuning of Co-N-C catalyst for high-performance electrochemical H2O2 production.

Despite the growing demand for hydrogen peroxide it is almost exclusively manufactured by the energy-intensive anthraquinone process. Alternatively, H2O2 can be produced electrochemically via the two-electron oxygen reduction reaction, although the performance of the state-of-the-art electrocatalysts is insufficient to meet the demands for industrialization. Interestingly, guided by first-principles calculations, we found that the catalytic properties of the Co-N4 moiety can be tailored by fine-tuning its surrounding atomic configuration to resemble the structure-dependent catalytic properties of metalloenzymes. Using this principle, we designed and synthesized a single-atom electrocatalyst that comprises an optimized Co-N4 moiety incorporated in nitrogen-doped graphene for H2O2 production and exhibits a kinetic current density of 2.8 mA cm-2 (at 0.65 V versus the reversible hydrogen electrode) and a mass activity of 155 A g-1 (at 0.65 V versus the reversible hydrogen electrode) with negligible activity loss over 110 hours.

Controlled syngas production by electrocatalytic CO2 reduction on formulated Au25(SR)18 and PtAu24(SR)18 nanoclusters.

Syngas, a gaseous mixture of CO and H2, is a critical industrial feedstock for producing bulk chemicals and synthetic fuels, and its production via direct CO2 electroreduction in aqueous media constitutes an important step toward carbon-negative technologies. Herein, we report controlled syngas production with various H2/CO ratios via the electrochemical CO2 reduction reaction (CO2RR) on specifically formulated Au25 and PtAu24 nanoclusters (NCs) with core-atom-controlled selectivities. While CO was predominantly produced from the CO2RR on the Au NCs, H2 production was favored on the PtAu24 NCs. Density functional theory calculations of the free energy profiles for the CO2RR and hydrogen evolution reaction (HER) indicated that the reaction energy for the conversion of CO2 to CO was much lower than that for the HER on the Au25 NC. In contrast, the energy profiles calculated for the HER indicated that the PtAu24 NCs have nearly thermoneutral binding properties; thus, H2 production is favored over CO formation. Based on the distinctly different catalytic selectivities of Au25 and PtAu24 NCs, controlled syngas production with H2/CO ratios of 1 to 4 was demonstrated at a constant applied potential by simply mixing the Au25 and PtAu24 NCs based on their intrinsic catalytic activities for the production of CO and H2.

Atomically Precise Gold Nanoclusters as Model Catalysts for Identifying Active Sites for Electroreduction of CO2.

Accurate identification of active sites is critical for elucidating catalytic reaction mechanisms and developing highly efficient and selective electrocatalysts. Herein, we report the atomic-level identification of active sites using atomically well-defined gold nanoclusters (Au NCs) Au25 , Au38 , and Au144 as model catalysts in the electrochemical CO2 reduction reaction (CO2 RR). The studied Au NCs exhibited remarkably high CO2 RR activity, which increased with increasing NC size. Electrochemical and X-ray photoelectron spectroscopy analyses revealed that the Au NCs were activated by removing one thiolate group from each staple motif at the beginning of CO2 RR. In addition, density functional theory calculations revealed higher charge densities and upshifts of d-states for dethiolated Au sites. The structure-activity properties of the studied Au NCs confirmed that dethiolated Au sites were the active sites and that CO2 RR activity was determined by the number of active sites on the cluster surface.

The yolk syncytial layer of loach, Misgurnus fossilis (Teleostei) during early development.

The yolk syncytial layer (YSL) of Teleostei is a dynamic multifunctional temporary system. This paper describes the YSL structure of Misgurnus fossilis (Cobitidae) during its early developmental stages, studied using histological methods. YSL formation is prolonged. From the late blastula stage, the basal surface of the YSL is uneven and has protuberances, but becomes smoother during development. There are syncytial 'islands' with 1-2 yolk syncytial nuclei in the yolk mass. During epiboly, gastrulation and early segmentation, loach YSL is of different thickness in different regions along the dorso-ventral and antero-posterior axes of an embryo. The YSL is thickened in the dorsal region of gastrulae compared with the ventral region. Although the development of M. fossilis is similar to the development of zebrafish, there are important differences in YSL formation and organization that await further study and analysis. The study of YSL organization contributes to our knowledge of teleost developmental diversity and to the biology of temporary structures.

Neurulation in the posterior region of zebrafish, Danio rerio embryos.

The neural tube of amniotes is formed through different mechanisms that take place in the anterior and posterior regions and involve neural plate folding or mesenchymal condensation followed by its cavitation. Meanwhile, in teleost trunk region, the neural plate forms the neural keel, while the lumen develops later. However, the data on neurulation and other morphogenetic processes in the posterior body region in Teleostei remain fragmentary. We proposed that there could be variations in the morphogenetic processes, such as cell shape changes and cell rearrangements, in the posterior region compared to the anterior one at the different stages. Here, we performed morphological and histochemical analyses of morphogenetic processes with an emphasis on neurulation in the zebrafish tail bud (TB) and posterior region. To analyze the posterior expression of sox2 and tbxta we performed whole mount in situ hybridization. We showed that the TB cells of variable shapes and orientation are tightly packed, and the neural and notochord primordia develop first. The shape of the neural primordium undergoes numerous changes as a result of cell rearrangements leading to the development of the neural rod. At the prim-6 stage, the cells of the neural primordium directly form the neural rod. The neuroepithelial cells undergo sequential shape changes. At the stage of the neural rod formation, the apical regions of triangular neuroepithelial cells of the floor plate are enriched in F-actin. The neurocoel development onset is above the apical poles of neuroepithelial cells. The expression domains of sox2 and tbxta become more restricted during the development.

Morphofunctional transformations of the yolk syncytial layer during zebrafish development.

The yolk syncytial layer (YSL) is a provisory extraembryonic structure of teleost fishes and representatives of some other taxa with meroblastic cleavage. The YSL of teleosts is a symplast with polymorphous polyploid nuclei. It is known to perform nutritional, morphogenetic, immune, and, probably, other functions. Data about the YSL organization, functioning and regulation is fragmentary. Although gene expression patterns and other aspects of YSL functioning have been studied in Danio rerio, the morphology of its YSL has not been described in detail. The study of zebrafish YSL structure on sequential developmental stages is necessary to recognize specific features of this important polyfunctional system in this model organism and to extend our knowledge about provisory systems. The thickness of the YSL and the distribution of its nuclei are not uniform on each stage and change during development. During oblong and sphere stages the internal YSL (I-YSL) is filled with yolk inclusions; interphase yolk syncytial nuclei (YSN) and mitotic asters can be seen. During doming and epiboly the external YSL (E-YSL) is thicker than I-YSL. On the subsequent stages the YSL is thickened caudally. The dorsal YSL part is thickened during early segmentation stages and becomes the thinnest YSL region later. The anterior part of the YSL is thin, but enlarges during larval period. The YSN of different size and diverse forms, from regular to lobed, are present and form clusters. The number of irregular-shaped nuclei increases during development. The YSL thickens in the end of endotrophic and in the course of endo-exotrophic period, and its cytoplasm contains numerous yolk inclusions. After yolk exhaustion the YSL is flat. As the YSL degrades, the YSN become pycnotic, and the YSL remnant probably is cleared by phagocytes.