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Pulsed CO2 electroreduction (CO2RR) has recently emerged as a facile way to in situ tune the product selectivity, in particular toward ethanol, without re-designing the catalytic system. However, in-depth mechanistic understanding requires comprehensive operando time-resolved studies to identify the kinetics and dynamics of the electrocatalytic interface. Here, we track the adsorbates and the catalyst state of pre-reduced Cu2O nanocubes ( ~ 30 nm) during pulsed CO2RR using sub-second time-resolved operando Raman spectroscopy. By screening a variety of product-steering pulse length conditions, we unravel the critical role of co-adsorbed OH and CO on the Cu surface next to the oxidative formation of Cu-Oad or CuOx/(OH)y species, impacting the kinetics of CO adsorption and boosting the ethanol selectivity. However, a too low OHad coverage following the formation of bulk-like Cu2O induces a significant increase in the C1 selectivity, while a too high OHad coverage poisons the surface for C-C coupling. Thus, we unveil the importance of co-adsorbed OH on the alcohol formation under CO2RR conditions and thereby, pave the way for improved catalyst design and operating conditions.

We explore and utilize correlations between wet-chemical synthesis parameters and the resulting atomic geometry and crystal phase structure of carbon-supported bimetallic PtTi/C alloy nanoparticles with excellent electrocatalytic reactivity and chemical stability during the oxygen reduction reaction in acidic electrolyte environments. We systematically vary wet-chemical synthesis parameters such as reductive annealing temperatures and precursor ratios and study their effect on the characteristics of atomic-scale materials, such as phase structure, crystallite particle size distribution, alloying degree, and ordering degree, using X-ray scattering, spectroscopy and high-resolution electron microscopy coupled to structure and crystal phase modeling and deconvolution using Rietveld techniques. While annealing parameters controlled the ratio of ordered and disordered PtTi alloy phases, precursor ratio adjustment revealed a previously elusive critical Ti threshold ratio, where the formation of undesired TiO2 phases remained suppressed, while the PtTi alloying degree and phase structure remained preserved. The resulting ca. 3 nm sized bimetallic PtTi nanoparticle electrocatalyst showed excellent Pt mass-based oxygen reduction reaction activity at 0.9 VRHE in acidic environments as well as favorable performance and compositional stability during accelerated stress tests relative to a Pt reference catalyst. This behavior could be linked to the stable PtTi and intermetallic Pt3Ti phases. The synthetic conditions uncovered herein offer wet-chemical access to TiO2-free high performance PtTi nanoparticle alloy ORR catalysts for fuel cell cathodes. [ABSTRACT FROM AUTHOR]

INTRODUCTION Following is a discussion of the 2003 A&WMA Critical Review (1,2) that examined the role of carbon dioxide (C[O.sub.2]) sequestration in reducing the quantity of greenhouse gases (GHG) emitted [...]

To rationally design effective and stable catalysts for energy conversion applications, we need to understand how they transform under reaction conditions and reveal their underlying structure-property relationships. This is especially important for catalysts used in the electroreduction of carbon dioxide where product selectivity is sensitive to catalyst structure. Here, we present real-time electrochemical liquid cell transmission electron microscopy studies showing the restructuring of copper(I) oxide cubes during reaction. Fragmentation of the solid cubes, re-deposition of new nanoparticles, catalyst detachment and catalyst aggregation are observed as a function of the applied potential and time. Using cubes with different initial sizes and loading, we further correlate this dynamic morphology with the catalytic selectivity through time-resolved scanning electron microscopy measurements and product analysis. These comparative studies reveal the impact of nanoparticle re-deposition and detachment on the catalyst reactivity, and how the increased surface metal loading created by re-deposited nanoparticles can lead to enhanced C2+ selectivity and stability. Understanding the changes that occur in catalysts during reaction are key to the rational design. Here, the authors use electrochemical transmission electron microscopy and time-resolved product analysis to unveil how cubic copper oxide catalysts evolve during electrochemical CO2 reduction, linking their structural transformations with their selectivity. [ABSTRACT FROM AUTHOR]

Direct conversion of carbon dioxide into multicarbon liquid fuels by the CO2 electrochemical reduction reaction (CO2RR) can contribute to the decarbonization of the global economy. Here, well‐defined Cu2O nanocubes (NCs, 35 nm) uniformly covered with Ag nanoparticles (5 nm) were synthesized. When compared to bare Cu2O NCs, the catalyst with 5 at % Ag on Cu2O NCs displayed a two‐fold increase in the Faradaic efficiency for C2+ liquid products (30 % at −1.0 VRHE), including ethanol, 1‐propanol, and acetaldehyde, while formate and hydrogen were suppressed. Operando X‐ray absorption spectroscopy revealed the partial reduction of Cu2O during CO2RR, accompanied by a reaction‐driven redispersion of Ag on the CuOx NCs. Data from operando surface‐enhanced Raman spectroscopy further uncovered significant variations in the CO binding to Cu, which were assigned to Ag−Cu sites formed during CO2RR that appear crucial for the C−C coupling and the enhanced yield of liquid products. [ABSTRACT FROM AUTHOR]

Die direkte Umwandlung von Kohlendioxid zu flüssigen Brennstoffen durch die elektrochemische Reduktion von CO2 (CO2RR) kann zu der Dekarbonisierung der weltweiten Wirtschaft beitragen. Hier wurden wohldefinierte Cu2O‐Nanowürfel (NW, 35 nm) synthetisiert, die einheitlich mit Ag‐Nanopartikeln (5 nm) bedeckt wurden. Verglichen mit den reinen Cu2O‐NW zeigte der Katalysator mit 5 at % Ag auf den Cu2O‐NW einen zweifachen Anstieg in der Faraday‐Effizienz für C2+‐Flüssigprodukte (30 % bei −1.0 VRHE) einschließlich Ethanol, 1‐Propanol und Acetaldehyd. Dagegen wurden Formiat und Wasserstoff unterdrückt. Operando‐Röntgenabsorptionsspektroskopie enthüllte die teilweise Reduktion von Cu2O während CO2RR, begleitet von einer reaktionsgetriebenen Redispersion von Ag auf den CuOx‐NW. Operando‐oberflächenverstärkte Raman‐Spektroskopie deckte außerdem signifikante Veränderungen in der CO‐Bindung zu Cu auf, die wir auf die während der CO2RR neugebildeten Ag‐Cu‐Zentren zurückführen. Folglich spielt Ag‐Cu eine zentrale Rolle für die C‐C‐Kupplung und der damit verbundenen erhöhten Ausbeute an Flüssigprodukten. [ABSTRACT FROM AUTHOR]

We have investigated the dynamics of the ethyl groups and their constituent methyl groups in polycrystalline ethylbenzene (EB), 1,2-diethylbenzene (1,2-DEB), 1,3-DEB, and 1,4-DEB using the solid state proton spin relaxation (SSPSR) technique. The temperature and Larmor frequency dependence of the Zeeman spin-lattice relaxation rate is reported and interpreted in terms of the molecular dynamics. We determine that only the methyl groups are reorienting on the nuclear magnetic resonance time scale. The observed barrier of about 12 kJ/mol for methyl group reorientation in the solid samples of EB, 1,2-DEB, and 1,3-DEB is consistent with that of the isolated molecule, implying that in the solid state, intermolecular electrostatic interactions play a minor role in determining the barrier. The lower barrier of 9.3±0.2 kJ/mol for the more symmetric 1,4-DEB suggests that the crystal structure is such that the minimum in the anisotropic part of the intramolecular potential is raised by the intermolecular interactions leading to a 3 kJ/mol decrease in the total barrier. We are able to conclude that the methyl group is well away from the plane of the benzene ring (most likely orthogonal to it) in all four molecules, and that in 1,2-DEB, the two ethyl groups are in the anticonfiguration. Our SSPSR results are compared with the results obtained by microwave spectroscopy and supersonic molecular jet laser spectroscopy, both of which determine molecular geometry better than SSPSR, but neither of which can determine ground electronic state barriers for these molecules. [ABSTRACT FROM AUTHOR]