Nanostructured surfaces have been shown to greatly enhance the activity and selectivity of many different catalysts. Here we report a nanostructured copper surface that gives high selectivity for ...ethylene formation from electrocatalytic CO2 reduction. The nanostructured copper is easily formed in situ during the CO2 reduction reaction, and scanning electron microscopy (SEM) shows the surface to be dominated by cubic structures. Using online electrochemical mass spectrometry (OLEMS), the onset potentials and relative selectivity toward the volatile products (ethylene and methane) were measured for several different copper surfaces and single crystals, relating the cubic shape of the copper surface to the greatly enhanced ethylene selectivity. The ability of the cubic nanostructure to so strongly favor multicarbon product formation from CO2 reduction, and in particular ethylene over methane, is unique to this surface and is an important step toward developing a catalyst that has exclusive selectivity for multicarbon products.
Cubic nanostructures formed on a polycrystalline copper surface give high selectivity for ethylene formation from carbon dioxide electroreduction. The nanocubes are easily synthesized in situ, and online electrochemical mass spectrometry is used to compare the reactivity to other copper single‐crystal surfaces.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Nanostructured copper cathodes are among the most efficient and selective catalysts to date for making multicarbon products from the electrochemical carbon dioxide reduction reaction (CO2RR). We ...report an in situ X-ray absorption spectroscopy investigation of the formation of a copper nanocube CO2RR catalyst with high activity that highly favors ethylene over methane production. The results show that the precursor for the copper nanocube formation is copper(I)-oxide, not copper(I)-chloride as previously assumed. A second route to an electrochemically similar material via a copper(II)–carbonate/hydroxide is also reported. This study highlights the importance of using oxidized copper precursors for constructing selective CO2 reduction catalysts and shows the precursor oxidation state does not affect the electrocatalyst selectivity toward ethylene formation.
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Copper electrocatalysts derived from an oxide have shown extraordinary electrochemical properties for the carbon dioxide reduction reaction (CO2RR). Using in situ ambient pressure X-ray photoelectron ...spectroscopy and quasi in situ electron energy-loss spectroscopy in a transmission electron microscope, we show that there is a substantial amount of residual oxygen in nanostructured, oxide-derived copper electrocatalysts but no residual copper oxide. On the basis of these findings in combination with density functional theory simulations, we propose that residual subsurface oxygen changes the electronic structure of the catalyst and creates sites with higher carbon monoxide binding energy. If such sites are stable under the strongly reducing conditions found in CO2RR, these findings would explain the high efficiencies of oxide-derived copper in reducing carbon dioxide to multicarbon compounds such as ethylene.
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The activity and selectivity for CO2/CO reduction over Cu electrodes is strongly dependent on the local surface structure of the catalyst and the pH of the electrolyte. Here we investigate a unique, ...Cu nanocube surface (CuCube) as a CO reduction electrode under neutral and basic pH by using online electrochemical mass spectroscopy (OLEMS) to determine the onset potentials and relative intensities of methane and ethylene production. To relate the unique selectivity to the surface structure, the CuCube surface reactivity is compared to polycrystalline Cu and three single crystals under the same reaction conditions. We find that the high selectivity for ethylene over the CuCube surface is most comparable to the Cu(1 0 0) surface, which has a cubic unit cell. However, the suppression of methane production over CuCube is unique to that particular surface. A basic pH is shown to enhance ethylene selectivity on all surfaces, and again the CuCube surface is unique.
Beneath the surface: The high selectivity for two‐carbon products from CO electroreduction is attributed to the unique nanostructure of the surface of a Cu catalyst. The product ratios in pH 7 and 13 electrolytes are compared and ethylene production is enhanced under basic conditions. A discussion of local pH effects is also included.
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FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
A series of model catalysts were prepared by depositing different size Pd
n
clusters on alumina films grown to variable thickness on a Ta(110) support. Samples were characterized by a combination of ...X-ray photoelectron spectroscopy, low energy He
+
scattering, and temperature-programmed reaction and desorption (TPR/TPD). For the activity studies, the samples were first exposed to
18
O
2
at
T
ox
, and then to
13
CO at 180 K, where CO sticks to Pd, but not to the alumina support. CO oxidation activity increased with increasing thickness of the alumina support up to 4.5 nm, but was constant for greater thicknesses. Activity increased, with
T
ox
up to 400 K, but then declined for
T
ox
= 500 K. Activity was also found to be non-monotonically dependent on deposited cluster size, with Pd
n
(
n
6) being generally more reactive than the larger clusters studied. Activity was only weakly correlated with exposed Pd binding sites, which decreased with increasing cluster size, however, there does appear to be a correlation between activity and electronic structure, as probed
via
the Pd 3d binding energy. Unlike previous systems we have studied, the activity of small Pd
n
on these alumina films was quite stable, with essentially no changes observed in up to eight successive TPR experiments.
Model catalysts containing size-selected Pdn (n=1,2,4,7,10,16,20,25) deposited on rutile TiO2(110) deactivate during repeated CO oxidation temperature-programmed reaction (TPR) cycles, and the ...deactivation process has been probed using a combination of X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), low-energy ion scattering (ISS), temperature-dependent ion scattering (TD-ISS), annealing experiments, and temperature-programmed desorption following exposure to CO and O2 reactants. Results from such experiments suggest the cluster deactivation proceeds via an alloy-like, strong metal-support interaction (SMSI) effect that chemically modifies the clusters via electronic interactions between the supported metal atoms and Ti from the support. Threshold measurements show that this effect detrimentally affects CO-oxidation activity prior to the formation of an encapsulating overlayer by severely weakening the COPd bond strengths for binding configurations on top of the clusters. Oxidation appears to provide means of partially restoring the clusters to their initial state, but after sufficient exposure to reducing environments and elevated temperatures, all Pdn become covered by an overlayer and begin to electronically and chemically resemble freshly deposited atoms, which are completely inactive towards the probe reaction. In addition, we find evidence of oxygen spillover induced by co-adsorbed CO during TPRs for all active Pdn clusters.
•Pdn/TiO2 model-catalysts are shown to deactivate via an SMSI-based mechanism.•SMSI alters cluster chemistry prior to TiOx overlayer formation/detection.•After many reaction cycles the clusters eventually become encapsulated.•Upward Pd XPS BE shifts are consistent with Pd–Ti alloying in SMSI state.•O-spillover is noted during reaction with CO over the clusters.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Nanostructured surfaces have been shown to greatly enhance the activity and selectivity of many different catalysts. Here we report a nanostructured copper surface that gives high selectivity for ...ethylene formation from electrocatalytic CO2 reduction. The nanostructured copper is easily formed in situ during the CO2 reduction reaction, and scanning electron microscopy (SEM) shows the surface to be dominated by cubic structures. Using online electrochemical mass spectrometry (OLEMS), the onset potentials and relative selectivity toward the volatile products (ethylene and methane) were measured for several different copper surfaces and single crystals, relating the cubic shape of the copper surface to the greatly enhanced ethylene selectivity. The ability of the cubic nanostructure to so strongly favor multicarbon product formation from CO2 reduction, and in particular ethylene over methane, is unique to this surface and is an important step toward developing a catalyst that has exclusive selectivity for multicarbon products.
Kubische Nanostrukturen auf einer polykristallinen Kupferoberfläche zeigen eine hohe Selektivität für die Bildung von Ethylen bei der Elektroreduktion von Kohlendioxid. Die Nanowürfel können leicht in situ erzeugt werden. Mithilfe der elektrochemischen Massenspektrometrie wurde ihre Reaktivität im Vergleich zu anderen Kupfer‐Einkristalloberflächen untersucht.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Photoelectron spectroscopy is a powerful tool for investigating the electronic structure of supported clusters, especially when initial state and final state contributions to the electron binding ...energy can be separated. We have performed a combined experimental and theoretical study of ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS) using atomically size-selected Pd n clusters on rutile TiO2(110). Theoretical investigations allow for the UPS and XPS shifts to be split into initial state and final state contributions. In XPS, the occupation of the 4d orbital of Pd controls the initial state shift offering information about the hybridization of the cluster, while the size and the charging of the cluster controls the final state shift. In UPS, we evaluate two methods for calculating the final state shift in periodic unit cells and find that both methods give reasonable results for pristine TiO2; however, using a p-type dopant fails when two separate donor–acceptor pairs are present. The observed UPS shifts can be described by combining the surface dipole and the final state shifts. Metallic contacts to the semiconductor surface result in band alignment between the metallic contact and the cluster, shifting the Fermi level to lie just below the conduction band of the TiO2. Information about the charge state and hybridization of the cluster are revealed by separating the initial and final state effects.
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