Electrochemical oxidation of CO on Cu single crystals under alkaline conditions

We perform a joint experimental-theoretical study of the electrochemical oxidation of CO on copper (Cu) under alkaline conditions. Using cyclic voltammetry on Cu single crystal surfaces, we demonstrate that both Cu terraces and steps show CO oxidation activity at potentials just slightly positive (0.03-0.14 V) of the thermodynamic equilibrium potential. The overpotentials are 0.23-0.12 V lower than that of gold (approx. 0.26 V), which up until now has been considered to be the most active catalyst for this process. Our theoretical calculations suggest that Cu's activity arises from the advantageous combination of simultaneous *OH adsorption under CO oxidation potentials and surmountable *CO-*OH coupling barriers. Experimentally observed onset potentials are in agreement with the computed onsets of *OH adsorption. We furthermore show that the onsets of *OH adsorption on steps are more affected by *CO-*OH interactions than on terraces due to a stronger competitive adsorption. Overall, Cu(100) shows the lowest overpotential (0.03 V) of the facets considered.Comment: 16 pages, 3 figures plus supplementary informatio

Preventing Alloy Electrocatalyst Segregation in Air Using Sacrificial Passivating Overlayers

Many alloy electrocatalysts, including intermetallics, are exceptionally sensitive to segregation in air due to the electronic dissimilarity of the constituent metals. We demonstrate that even alloys with strong cohesive energies rapidly segregate upon air exposure, completely burying the less reactive constituent metal beneath the surface. To circumvent this issue, we develop and validate a new experimental approach for bridging the pressure gap between electronic structure characterization performed under ultrahigh vacuum and electrocatalytic activity testing performed under ambient conditions. This method is based on encapsulation of the alloy surface with a sacrificial passivating overlayer of aluminum oxide. These passivating overlayers protect the underlying material from segregation in the air and can be completely and rapidly removed in an alkaline electrochemical environment under potential control. We demonstrate that alloy surfaces prepared, protected, and introduced into the electrolyte in this manner exhibit near-surface compositions consistent with those of the bulk material despite prior air exposure. We also demonstrate that this protection scheme does not alter the electrocatalytic activity of benchmark electrocatalysts. Implementation of this approach will enable reliable correlations between the electrocatalytic activity measured under ambient conditions and the near-surface electronic structure measured under ultrahigh vacuum.</p

Real-Time Detection of Acetaldehyde in Electrochemical CO Reduction on Cu Single Crystals

Copper is known to be versatile in producing various products from electrochemical CO2 reduction reaction (eCO2RR), and the product preference depends on reaction environments. The literature has reported that alkaline electrolytes favor acetate production and proposed hypotheses on reaction pathways accordingly. However, our work shows acetate can also come from the fast non-Faradaic chemical oxidation of acetaldehyde in alkaline environments. This adds uncertainties into measurements of both acetaldehyde and acetate production and leads to untrustful investigations on the reaction mechanism as a consequence. With an electrochemistry-mass spectrometry combined (EC-MS) system, we not only demonstrate why and how the imprecise acetaldehyde and acetate production occurs in previous research but also present immediate detection of acetaldehyde as a function of applied potential on single crystal Cu electrodes during electrochemical CO reduction reaction (eCORR). Moreover, the quantified acetaldehyde-to-ethylene production rate ratio provides insightful information on the acetaldehyde-to-ethylene bifurcation point in eCO2RR and thus helps understand the reaction pathways.</p

Real-Time Detection of Acetaldehyde in Electrochemical CO Reduction on Cu Single Crystals

Copper is known to be versatile in producing various products from electrochemical CO2 reduction reaction (eCO2RR), and the product preference depends on reaction environments. The literature has reported that alkaline electrolytes favor acetate production and proposed hypotheses on reaction pathways accordingly. However, our work shows acetate can also come from the fast non-Faradaic chemical oxidation of acetaldehyde in alkaline environments. This adds uncertainties into measurements of both acetaldehyde and acetate production and leads to untrustful investigations on the reaction mechanism as a consequence. With an electrochemistry-mass spectrometry combined (EC-MS) system, we not only demonstrate why and how the imprecise acetaldehyde and acetate production occurs in previous research but also present immediate detection of acetaldehyde as a function of applied potential on single crystal Cu electrodes during electrochemical CO reduction reaction (eCORR). Moreover, the quantified acetaldehyde-to-ethylene production rate ratio provides insightful information on the acetaldehyde-to-ethylene bifurcation point in eCO2RR and thus helps understand the reaction pathways