Search

Angewandte Chemie / International edition 61(15), e202114707 (2022). doi:10.1002/anie.202114707, Electrochemical CO$_2$ reduction is a potential approach to convert CO$_2$ into valuable chemicals using electricity as feedstock. Abundant and affordable catalyst materials are needed to upscale this process in a sustainable manner. Nickel-nitrogen-doped carbon (Ni-N-C) is an efficient catalyst for CO$_2$ reduction to CO, and the single-site Ni−Nx motif is believed to be the active site. However, critical metrics for its catalytic activity, such as active site density and intrinsic turnover frequency, so far lack systematic discussion. In this work, we prepared a set of covalent organic framework (COF)-derived Ni-N-C catalysts, for which the Ni−Nx content could be adjusted by the pyrolysis temperature. The combination of high-angle annular dark-field scanning transmission electron microscopy and extended X-ray absorption fine structure evidenced the presence of Ni single-sites, and quantitative X-ray photoemission addressed the relation between active site density and turnover frequency., Published by Wiley-VCH, Weinheim

Modified as required

Here we report on the most prominent factors influencing the performance of a Cu-based CO2 electrolyzer operating at high currents. Using a flow-electrolyzer design where CO2 gas feed passes directly through the electrode interacting with the Cu catalyst layer, we observed that the selectivity of the electrochemical CO2 reduction in (bulk) pH neutral media can greatly be influenced by adjusting the structure of the electrode. In this, the variations in catalyst loading and ionomer content can profoundly affect the selectivity of CO2RR. We explore the hypothesis that this originates from the overall mass transport variations within the porous catalytic layer of the gas diffusion electrode. As further evidence for this, apart from the CO2 electrolysis results, we propose a special method to benchmark the reactant mass transport in flow-cells using oxygen reduction reaction (ORR) limiting current measurements. Our analysis suggests that a restriction of mass transport is highly desirable due to its connection to a local alkalization and corresponding suppression of pH-dependent reaction products, given the absence of local CO2 concentration limitations. We further show how the electrode structure can be used to push the observed catalytic CO2 reduction selectivity either towards C1 or C2+ products, dependent on the ionomer content and catalyst loading in a cathodic current range of 50 to 700 mA cm−2. Measurements at various KHCO3 electrolyte concentrations agree with the notion of the local pH dictating the overall selectivity and point towards the presence of pronounced concentration gradients within the system. Overall, our work suggests that the differences in electrocatalytic CO2 reduction selectivity at high currents (in a range of pH neutral buffering electrolytes) largely originate from the local concentration gradients defined by the initial catalyst ink formulation and architecture of the catalytic layer, both of which represent a powerful tool for optimization in the production of selected value-added products.

The molecular mechanism of heterosis or hybrid vigor, where F1 hybrids of genetically diverse parents show superior traits compared to their parents, is not well understood. Here, we studied the molecular regulation of heterosis in four F1 cabbage hybrids that showed heterosis for several horticultural traits, including head size and weight. To examine the molecular mechanisms, we performed a global transcriptome profiling in the hybrids and their parents by RNA sequencing. The proportion of genetic variations detected as single nucleotide polymorphisms and small insertion&ndash, deletions as well as the numbers of differentially expressed genes indicated a larger role of the female parent than the male parent in the genetic divergence of the hybrids. More than 86% of hybrid gene expressions were non-additive. More than 81% of the genes showing divergent expressions showed dominant inheritance, and more than 56% of these exhibited maternal expression dominance. Gene expression regulation by cis-regulatory mechanisms appears to mediate most of the gene expression divergence in the hybrids, however, trans-regulatory factors appear to have a higher effect compared to cis-regulatory factors on parental expression divergence. These observations bring new insights into the molecular mechanisms of heterosis during the cabbage head development.

Today, with the rapid development of modern and large-scale pig industry, free-range pig farming is still an important part of the breeding industry. Different from large-scale pig farms, there are many shortcomings in feeding management, pig disease prevention and control and so on for small-scale farmers. In the long-term clinical diagnosis and production practice, it is found that sows raised by small-scale farmers often have some problems, such as non-estrus, repeated infertility and "false pregnancy", weak farrowing, stillbirth, and postpartum piglet death. This paper makes a comprehensive analysis on the performance and etiology of the above-mentioned free-range sows, and puts forward the corresponding prevention and control measures, in order to provide a theoretical basis for the feeding and management of rural free-range sows.

Cu oxides catalyze the electrochemical carbon dioxide reduction reaction (CO2RR) to hydrocarbons and oxygenates with favorable selectivity. Among them, the shape-controlled Cu oxide cubes have been most widely studied. In contrast, we report on novel 2-dimensional (2D) Cu(II) oxide nanosheet (CuO NS) catalysts with high C2+ products, selectivities (> 400 mA cm−2) in gas diffusion electrodes (GDE) at industrially relevant currents and neutral pH. Under applied bias, the (001)-orientated CuO NS slowly evolve into highly branched, metallic Cu0 dendrites that appear as a general dominant morphology under electrolyte flow conditions, as attested by operando X-ray absorption spectroscopy and in situ electrochemical transmission electron microscopy (TEM). Millisecond-resolved differential electrochemical mass spectrometry (DEMS) track a previously unavailable set of product onset potentials. While the close mechanistic relation between CO and C2H4 was thereby confirmed, the DEMS data help uncover an unexpected mechanistic link between CH4 and ethanol. We demonstrate evidence that adsorbed methyl species, *CH3, serve as common intermediates of both CH3H and CH3CH2OH and possibly of other CH3-R products via a previously overlooked pathway at (110) steps adjacent to (100) terraces at larger overpotentials. Our mechanistic conclusions challenge and refine our current mechanistic understanding of the CO2 electrolysis on Cu catalysts., Copper oxides (CuO) can selectively catalyze the electrochemical reduction of CO2 to hydrocarbons and oxygenates. Here, the authors study the activity and morphological evolution of 2D CuO nanosheets under applied electrode potentials to conclude the primacy of dendritic shapes and involvement of a new coupling pathway.

In the past decades, the atmospheric CO2 emissions increased with the unrestrained combustion of fossil fuels to meet the growing energy demand, leading to serious environmental pollution and climate issues. The electrochemical CO2 reduction reaction (CO2RR) is a promising alternative to convert CO2 into value-added products, and has the potential to contribute to a carbon-neutral energy cycle by using surplus electricity generated from renewable sources (e.g., solar and wind). Among various materials, copper-based catalysts are most studied, given their unique capability to make hydrocarbons in considerable amounts and at reasonable overpotentials. In this thesis, in-depth understanding of the CO2 electroreduction process was firstly established by adjusting the local reaction environment of a CuOx nanoparticle (NP) model catalyst. A tunable product distribution during catalytic CO2 electroreduction could be achieved by varying areal particle densities and co-feeding CO2 reactant with CO. With higher areal density and lower mean interparticle distances, a shift in faradic efficiency towards C2H4 over CH4 was observed, which was attributed to enhanced CO(g) re-adsorption on catalyst surface sites in close proximity. Furthermore, the electroreduction of CO2 feed with CO-bleeding showed enhanced ethylene production over a broad potential range with various co-feed ratios. The origin of the carbon-atoms in C2H4 under co-feed conditions was traced and quantified by a custom-designed operando differential electrochemical mass spectrometry (DEMS) flow cell, giving unique mechanistic insight in the CO2-CO co-feed system. The co-feed mechanism was extended to novel tandem catalysts, in which a CO producer (Ag, or NiNC) works as local CO feeding source and combines with Cu-based catalysts, showing obvious enhancement in ethylene production compared to purely copper-based systems. Furthermore, a sheet-shaped CuOx catalyst was designed, developed and systematically investigated. In H-Cell measurements, a high activity for CO2RR could be observed, followed by tests in a micro flow cell, demonstrating a record C2H4 partial current density of 229 mA cm 2 and a C2+ partial current density of ~ 410 mA cm-2. Moreover, a combination of operando/(quasi) in situ XAS, WAXS, DEMS, S/TEM techniques were employed to discover structure-activity-selectivity relations under catalytic CO2RR operating conditions, delivering perspectives to design novel catalysts to produce hydrocarbons as the value-added products., CO2-Emissionen sind in den letzten Dekaden immer rasanter gestiegen, da der erhöhte Energiebedarf der wachsenden Weltwirtschaft vor allem durch fossile Energieträger gedeckt wurde und wird. Dies führt zu immer stärkerer Umweltverschmutzung und hat Auswirkungen auf das weltweite Klima. Die elektrochemische CO2-Reduktionsreaktion (CO2RR) bietet hierin eine vielversprechende Chance um CO2 aus der Atmosphäre oder als direkte Abgasverwertung zu entfernen und in höherwertige Produkte zu wandeln. Wird dazu überschüssige Elektrizität aus erneuerbaren Energien wie z.B. Solarenergie oder Windkraft genutzt, hat die CO2RR das Potenzial zu einer CO2-neutralen Energiewirtschaft beizutragen. Unter den bekannten Katalysatoren wurden kupferbasierte Materialien am häufigsten untersucht, da sie die einzigartige Eigenschaft besitzen zu großem Anteil Kohlenwasserstoffe zu produzieren ohne das Überpotential zu stark zu erhöhen. Diese Arbeit stellt zum ersten Mal ein tieferes Verständnis der CO2RR her, indem die lokale Umgebung eines CuOx-Nanopartikel (NP) Modellkatalysators systematisch variiert wurde. Durch Kontrolle der Partikelbeladungsdichte und der Zusammensetzung des Eduktstroms aus CO2 und CO kann die Produktverteilung gezielt eingestellt werden. Mit steigender Beladungsdichte, d.h. sinkendem Interpartikelabstand, wurde eine Verschiebung der Produkteffizienzen von CH4 zu C2H4 beobachtet, die hier auf verstärkte CO(g)-Readsorption auf nahe zusammenliegenden Katalysatorzentren zurückgeführt werden konnte. Des Weiteren ermöglicht der co-feed aus CO2/CO verstärkte Ethylenproduktion in einem breiten Potentialbereich indem das CO2/CO-Verhältnis angepasst wird. Zur Aufdeckung des Reaktionsmechanismus unter CO2/CO co-feed wurde die Herkunft der C-Atome im produzierten Ethylen über Isotopenmarkierung in einer eigens dafür designten Flusszelle für operando differentielle elektrochemische Massenspektrometrie (DEMS) untersucht und quantifiziert. Der vorgestellte co-feed Mechanismus konnte auf neuartige Tandemkatalysatoren übertragen werden. In diesem wird ein CO-produzierender Katalysator (z.B. Ag oder NiNC) mit einem kupferbasierten Katalysator kombiniert, was ebenfalls zu erhöhtere Ethylenproduktion gegenüber rein kupferbasierten Systemen führt. Außerdem, wurden in dieser Arbeit ein neuartiger, plattenförmiger CuOx Katalysator entworfen, synthetisiert und systematisch untersucht. Aufgrund herausragender CO2RR-Aktivität in H-Zellmessungen wurde der Katalysator in einer anwendungsnahen Mikroflusszelle getestet. Dort konnten für C2H4 und C2+ industrierelevante Rekordproduktstromdichten von 229 mA cm 2 bzw. ~410 mA cm 2 gezeigt werden. Weiterhin wurden durch Kombination von operando/(quasi) in situ XAS, WAXS, DEMS und S/TEM Techniken Struktur-Aktivitäts-Selektivitätsbeziehungen für die katalytische CO2RR entdeckt, die neue Wege zum Design von hochaktiven und –selektiven Katalysatoren aufzeigen, um gezielt höherwertige Kohlenwasserstoffe aus CO2 zu produzieren.