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There is an urgent need to develop technologies that use renewable energy to convert waste products such as carbon dioxide into hydrocarbon fuels. Carbon dioxide can be electrochemically reduced to hydrocarbons over copper catalysts, although higher efficiency is required. We have developed oxidized copper catalysts displaying lower overpotentials for carbon dioxide electroreduction and record selectivity towards ethylene (60%) through facile and tunable plasma treatments. Herein we provide insight into the improved performance of these catalysts by combining electrochemical measurements with microscopic and spectroscopic characterization techniques. Operando X-ray absorption spectroscopy and cross-sectional scanning transmission electron microscopy show that copper oxides are surprisingly resistant to reduction and copper + species remain on the surface during the reaction. Our results demonstrate that the roughness of oxide-derived copper catalysts plays only a partial role in determining the catalytic performance, while the presence of copper + is key for lowering the onset potential and enhancing ethylene selectivity. Carbon dioxide electroreduction is a promising route to hydrocarbon synthesis, but more efficient and selective catalysts are needed. Here the authors show that plasma-activated copper can catalyse the reduction of carbon dioxide to ethylene with high efficiency and reveal cationic copper as the active site.

This paper reports on the substantial improvement of specimen quality by use of a low voltage (0.05 to ~1 keV), small diameter (~1 μm), argon ion beam following initial preparation using conventional broad-beam ion milling or focused ion beam. The specimens show significant reductions in the amorphous layer thickness and implanted artifacts. The targeted ion milling controls the specimen thickness according to the needs of advanced aberration-corrected and/or analytical transmission electron microscopy applications.

Nature Communications 7 Article number: 12123 (2016); Published 30 June 2016; Updated 12 September 2016 An incorrect version of the Supplementary Information was inadvertently published with this Article in which the image for Supplementary Fig. 7 was missing. The Article has now been updated to include the correct version of the Supplementary Information.

The consolidation of crystalline powders to obtain dense microstructures is typically achieved through a combination of volume and grain boundary diffusion. In situ transmission electron microscopy was utilized to study neck formation between adjacent nickel particles during the early stages of sintering. It was found that the presence of carbon during consolidation of Ni lowers the reduction temperature of nickel oxides on the particle surface and therefore has the potential to accelerate consolidation. In the absence of carbon, the surface oxides remain present during the early stage of sintering and neck formation between particles is limited by self-diffusion of nickel through the oxide layer. This study provides direct experimental evidence that corroborates related earlier hypotheses of self-cleaning on the surface of the nanoparticles that precedes neck formation and growth.

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