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A method is introduced to rapidly (<30 min) synthesize single metal nanoparticles with narrow size distribution in a simple way. It is based on the electrospraying of a metal precursor solution into a surfactant solution, which acts as a reducing and stabilizing agent. This synthesis method is demonstrated for the production of Ag and Au nanoparticles, which are incorporated onto carbonaceous and non-carbonaceous supports. The nanoparticle size depends on the internal diameter of the spraying nozzle. The removal of the stabilizing surfactant (dodecylamine; DDA) is also examined via thermal annealing and oxygen plasma treatments. Thermal annealing at a low temperature rate is found to be the most effective, as it completely removes DDA from the metal nanoparticles without inducing changes in their particle size. To verify that the supported Ag nanoparticles post calcination are surfactant-free and, thus, their surface sites are active, their oxygen reduction reaction (ORR) activity is measured in alkaline media, demonstrating similar values to the ones reported in the literature. [ABSTRACT FROM AUTHOR]

The electrochemical reduction of nitrate (NO 3 - ) and nitrite (NO 2 - ) enables sustainable, carbon-neutral, and decentralized routes to produce ammonia (NH 3 ). Copper-based materials are promising electrocatalysts for NO x - conversion to NH 3 . However, the underlying reaction mechanisms and the role of different Cu species during the catalytic process are still poorly understood. Herein, by combining quasi in situ X-ray photoelectron spectroscopy (XPS) and operando X-ray absorption spectroscopy (XAS), we unveiled that Cu is mostly in metallic form during the highly selective reduction of NO 3 - /NO 2 - to NH 3 . On the contrary, Cu(I) species are predominant in a potential region where the two-electron reduction of NO 3 - to NO 2 - is the major reaction. Electrokinetic analysis and in situ Raman spectroscopy was also used to propose possible steps and intermediates leading to NO 2 - and NH 3 , respectively. This work establishes a correlation between the catalytic performance and the dynamic changes of the chemical state of Cu, and provides crucial mechanistic insights into the pathways for NO 3 - /NO 2 - electrocatalytic reduction.

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.

Electrochemical reduction of CO 2 (CO 2 RR) is an attractive technology to reintegrate the anthropogenic CO 2 back into the carbon cycle driven by a suitable catalyst. This study employs highly efficient multi-carbon (C 2+ ) producing Cu 2 O nanocubes (NCs) decorated with CO-selective Au nanoparticles (NPs) to investigate the correlation between a high CO surface concentration microenvironment and the catalytic performance. Structure, morphology and near-surface composition are studied via operando X-ray absorption spectroscopy and surface-enhanced Raman spectroscopy, operando high-energy X-ray diffraction as well as quasi in situ X-ray photoelectron spectroscopy. These operando studies show the continuous evolution of the local structure and chemical environment of our catalysts during reaction conditions. Along with its alloy formation, a CO-rich microenvironment as well as weakened average CO binding on the catalyst surface during CO 2 RR is detected. Linking these findings to the catalytic function, a complex compositional interplay between Au and Cu is revealed in which higher Au loadings primarily facilitate CO formation. Nonetheless, the strongest improvement in C 2+ formation appears for the lowest Au loadings, suggesting a beneficial role of the Au-Cu atomic interaction for the catalytic function in CO 2 RR. This study highlights the importance of site engineering and operando investigations to unveil the electrocatalyst's adaptations to the reaction conditions, which is a prerequisite to understand its catalytic behavior., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

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.

Copper-based catalysts are established catalytic systems for the electrocatalytic CO 2 reduction reaction (CO 2 RR), where the greenhouse gas CO 2 is converted into valuable industrial chemicals, such as energy-dense C 2+ products, using energy from renewable sources. However, better control over the catalyst selectivity, especially at industrially relevant high current density conditions, is needed to expedite the economic viability of the CO 2 RR. For this purpose, bimetallic materials, where copper is combined with a secondary metal, comprise a promising and a highly tunable catalyst for the CO 2 RR. Nevertheless, the synergy between copper and the selected secondary metal species, the evolution of the bimetallic structural motifs under working conditions and the effect of the secondary metal on the kinetics of the Cu redox behavior require careful investigation. Here, we employ operando quick X-ray absorption fine structure (QXAFS) spectroscopy coupled with machine-learning based data analysis and surface-enhanced Raman spectroscopy (SERS) to investigate the time-dependent chemical and structural changes in catalysts derived from shape-selected ZnO/Cu 2 O nanocubes under CO 2 RR conditions at current densities up to -500 mA cm -2 . We furthermore relate the catalyst transformations observed under working conditions to the catalytic activity and selectivity and correlate potential-dependent surface and subsurface processes. We report that the addition of Zn to a Cu-based catalyst has a crucial impact on the kinetics of subsurface processes, while redox processes of the Cu surface layer remain largely unaffected. Interestingly, the presence of Zn was found to contribute to the stabilization of cationic Cu(i) species, which is of catalytic relevance since Cu(0)/Cu(i) interfaces have been reported to be beneficial for efficient electrocatalytic CO 2 conversion to complex multicarbon products. At the same time, we attribute the increase of the C 2+ product selectivity to the formation of Cu-rich CuZn alloys in samples with low Zn content, while Zn-rich alloy phases result in an increased formation of CO paralleled by an increase of the parasitic hydrogen evolution reaction., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)