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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. Controlling the selectivity of the electroreduction of CO2 to value-added products is challenging. Here, authors use sub-second operando Raman spectroscopy to analyze Cu catalyst surfaces and discover the pivotal role of co-adsorbed OH and CO in enhancing ethanol selectivity. [ABSTRACT FROM AUTHOR]

Atomically dispersed precious metals on oxide supports have recently become increasingly interesting catalytic materials. Nonetheless, their non‐trivial preparation and limited thermal and environmental stability constitutes an issue for their potential applications. Here we demonstrate that an oxygen plasma pre‐treatment of the ceria (CeO2) surface serves to anchor Pt single atoms, making them active and resistant towards sintering in the CO oxidation reaction. Through a combination of experimental results obtained on well‐defined CeO2 films and theory, we show that the O2 plasma causes surface nanostructuring and the formation of surface peroxo (O22−) species, favoring the uniform and dense distribution of isolated strongly bonded Pt2+ atoms. The promotional effect of the plasma treatment was further demonstrated on powder Pt/CeO2 catalysts. We believe that plasma functionalization can be applied to other metal/oxide systems to achieve tunable and stable catalysts with a high density of active sites. [ABSTRACT FROM AUTHOR]

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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]

[Display omitted] • NiO reduces later but at a faster pace than Ga 2 O 3 during H 2 activation. • Ni 5 Ga 3 nanoparticles form δ-Ni 5 Ga 3 phase during activation. • Micelle-based Ni 5 Ga 3 nanoparticles show high methanol selectivity at ambient pressure. • Ni 5 Ga 3 nanoparticles more active toward methanol synthesis than Ni 3 Ga 1 nanoparticles. • δ-Ni 5 Ga 3 phase more active toward methanol production than Ga 2 O 3. The hydrogenation of CO 2 into high energy density fuels such as methanol, where the required H 2 is obtained from renewable sources, is of utmost importance for a sustainable society. In recent years, NiGa alloys have attracted attention as promising catalyst material systems for the hydrogenation of CO 2 into methanol at ambient pressures. They thus represent an energy-saving alternative to the Cu-based catalysts employed in today's catalytic industry that require high pressures for the CO 2 hydrogenation. However, the underlying reaction mechanisms for the NiGa system are still under debate. One of the challenges here is to unravel the evolution and coexistence of the different species in the heterogeneous NiGa catalyst system under activation and reaction conditions. To shed light on their evolution under activation in H 2 and their catalytic roles under CO 2 hydrogenation working conditions on well-defined Ni 3 Ga 1 and Ni 5 Ga 3 nanoparticle (NP) catalysts, we employed a multi-probe approach. It included advanced machine learning-based analysis of operando X-ray absorption spectroscopy data combined with operando powder X-ray diffraction and near ambient pressure X-ray photoelectron spectroscopy measurements, as well as reactivity studies using bed-packed mass flow reactors. In addition, we employed atomic force microscopy and scanning transmission electron microscopy for structural characterization. Under H 2 activation at 1 bar total pressure, we concluded the formation of metallic Ni, starting for Ni 3 Ga 1 at 300 °C, and for Ni 5 Ga 3 at 400 °C. At higher temperatures, the formation of NiGa alloys follows. The α'-Ni 3 Ga 1 alloy phase is predominantly formed for the Ni 3 Ga 1 NPs, while the coexistence of α'-Ni 3 Ga 1 , δ-Ni 5 Ga 3 and Ga 2 O 3 phases is observed for the Ni 5 Ga 3 NPs after the H 2 activation. The formation of the Ga 2 O 3 phase also results in the presence of excess metallic Ni. Under CO 2 hydrogenation reaction conditions, Ga partially oxidizes again to form a Ga 2 O 3 -rich particle shell for both NP compositions, yet, to a larger extent for the Ni 3 Ga 1 NPs, which, in turn, feature a higher amount of excess Ni. We reveal that metallic Ni is responsible for the high selectivity of the Ni 3 Ga 1 NPs towards the production of methane in our catalytic tests. In contrast, the Ni 5 Ga 3 NPs display a strong selectivity toward methanol production (>92%), more than one order of magnitude higher than that for the Ni 3 Ga 1 NPs, which we ascribe to the presence of the δ-Ni 5 Ga 3 phase. [ABSTRACT FROM AUTHOR]

Atomically dispersed precious metals on oxide supports have recently become increasingly interesting catalytic materials. Nonetheless, their non‐trivial preparation and limited thermal and environmental stability constitutes an issue for their potential applications. Here we demonstrate that an oxygen plasma pre‐treatment of the ceria (CeO2) surface serves to anchor Pt single atoms, making them active and resistant towards sintering in the CO oxidation reaction. Through a combination of experimental results obtained on well‐defined CeO2 films and theory, we show that the O2 plasma causes surface nanostructuring and the formation of surface peroxo (O22−) species, favoring the uniform and dense distribution of isolated strongly bonded Pt2+ atoms. The promotional effect of the plasma treatment was further demonstrated on powder Pt/CeO2 catalysts. We believe that plasma functionalization can be applied to other metal/oxide systems to achieve tunable and stable catalysts with a high density of active sites. [ABSTRACT FROM AUTHOR]

The nature of the Cu-Zn interaction and especially the role of Zn in Cu/ZnO catalysts used for methanol synthesis from CO 2 hydrogenation are still debated. Migration of Zn onto the Cu surface during reaction results in a Cu-ZnO interface, which is crucial for the catalytic activity. However, whether a Cu-Zn alloy or a Cu-ZnO structure is formed and the transformation of this interface under working conditions demand further investigation. Here, ZnO/Cu 2 O core-shell cubic nanoparticles with various ZnO shell thicknesses, supported on SiO 2 or ZrO 2 were prepared to create an intimate contact between Cu and ZnO. The evolution of the catalyst's structure and composition during and after the CO 2 hydrogenation reaction were investigated by means of operando spectroscopy, diffraction, and ex situ microscopy methods. The Zn loading has a direct effect on the oxidation state of Zn, which, in turn, affects the catalytic performance. High Zn loadings, resulting in a stable ZnO catalyst shell, lead to increased methanol production when compared to Zn-free particles. Low Zn loadings, in contrast, leading to the presence of metallic Zn species during reaction, showed no significant improvement over the bare Cu particles. Therefore, our work highlights that there is a minimum content of Zn (or optimum ZnO shell thickness) needed to activate the Cu catalyst. Furthermore, in order to minimize catalyst deactivation, the Zn species must be present as ZnO x and not metallic Zn or Cu-Zn alloy, which is undesirably formed during the reaction when the precatalyst ZnO overlayer is too thin.

Bismuth is a catalyst material that selectively produces formate during the electrochemical reduction of CO 2 . While different synthesis strategies have been employed to create electrocatalysts with better performance, the restructuring of bismuth precatalysts during the reaction has also been previously reported. The mechanism behind the change has, however, remained unclear. Here, we show that Bi 2 O 3 nanoparticles supported on Vulcan carbon intrinsically transform into stellated nanosheet aggregates upon exposure to an electrolyte. Liquid cell transmission electron microscopy observations first revealed the gradual restructuring of the nanoparticles into nanosheets in the presence of 0.1 M KHCO 3 without an applied potential. Our experiments also associated the restructuring with solubility of bismuth in the electrolyte. While the consequent agglomerates were stable under moderate negative potentials (-0.3 V RHE ), they dissolved over time at larger negative potentials (-0.4 and -0.5 V RHE ). Operando Raman spectra collected during the reaction showed that under an applied potential, the oxide particles reduced to metallic bismuth, thereby confirming the metal as the working phase for producing formate. These results inform us about the working morphology of these electrocatalysts and their formation and degradation mechanisms.

The hydrogenation of CO 2 to methanol over Cu/ZnO-based catalysts is highly sensitive to the surface composition and catalyst structure. Thus, its optimization requires a deep understanding of the influence of the pre-catalyst structure on its evolution under realistic reaction conditions, including the formation and stabilization of the most active sites. Here, the role of the pre-catalyst shape (cubic vs spherical) in the activity and selectivity of ZnO-supported Cu nanoparticles was investigated during methanol synthesis. A combination of ex situ , in situ , and operando microscopy, spectroscopy, and diffraction methods revealed drastic changes in the morphology and composition of the shaped pre-catalysts under reaction conditions. In particular, the rounding of the cubes and partial loss of the (100) facets were observed, although such motifs remained in smaller domains. Nonetheless, the initial pre-catalyst structure was found to strongly affect its subsequent transformation in the course of the CO 2 hydrogenation reaction and activity/selectivity trends. In particular, the cubic Cu particles displayed an increased activity for methanol production, although at the cost of a slightly reduced selectivity when compared to similarly sized spherical particles. These findings were rationalized with the help of density functional theory calculations.

Atomically dispersed precious metals on oxide supports have recently become increasingly interesting catalytic materials. Nonetheless, their non-trivial preparation and limited thermal and environmental stability constitutes an issue for their potential applications. Here we demonstrate that an oxygen plasma pre-treatment of the ceria (CeO 2 ) surface serves to anchor Pt single atoms, making them active and resistant towards sintering in the CO oxidation reaction. Through a combination of experimental results obtained on well-defined CeO 2 films and theory, we show that the O 2 plasma causes surface nanostructuring and the formation of surface peroxo (O 2 2- ) species, favoring the uniform and dense distribution of isolated strongly bonded Pt 2+ atoms. The promotional effect of the plasma treatment was further demonstrated on powder Pt/CeO 2 catalysts. We believe that plasma functionalization can be applied to other metal/oxide systems to achieve tunable and stable catalysts with a high density of active sites., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Direct conversion of carbon dioxide into multicarbon liquid fuels by the CO 2 electrochemical reduction reaction (CO 2 RR) can contribute to the decarbonization of the global economy. Here, well-defined Cu 2 O nanocubes (NCs, 35 nm) uniformly covered with Ag nanoparticles (5 nm) were synthesized. When compared to bare Cu 2 O NCs, the catalyst with 5 at % Ag on Cu 2 O NCs displayed a two-fold increase in the Faradaic efficiency for C 2+ liquid products (30 % at -1.0 V RHE ), including ethanol, 1-propanol, and acetaldehyde, while formate and hydrogen were suppressed. Operando X-ray absorption spectroscopy revealed the partial reduction of Cu 2 O during CO 2 RR, accompanied by a reaction-driven redispersion of Ag on the CuO x  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 CO 2 RR that appear crucial for the C-C coupling and the enhanced yield of liquid products., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)