Effect of Particle Shape and Electrolyte Cation on CO Adsorption to Copper Oxide Nanoparticle Electrocatalysts

Cu2O-derived nanoparticles are efficient catalysts for the electrochemical conversion of CO and CO2 to multicarbon products. Generation of multicarbon products requires dimerization of adsorbed CO, which is accelerated when the coverage of CO is high. The electrolyte cation and the initially exposed crystal plane of the catalyst both affect the reaction rate, but the relation between these effects and CO coverage is unclear, especially given the surface reconstruction that occurs during reduction reactions on Cu2O. We prepared a series of shape-controlled Cu2O nanoparticles with similar sizes but different initially exposed crystal planes [cubes (100), octahedra (111), and dodecahedra (110)], and we used the infrared absorption bands detected in situ to compare the potential-dependent CO coverage on each of the nanomaterials in CO-saturated 0.1 M NaHCO3 and CsHCO3 during cyclic voltammetry. After correcting for the shape of the particle, there was less than 20% difference in the coverage of adsorbed CO on the different structures. The fact that the surface coverages are so similar may be a result of surface reconstruction occurring during the reaction. If so, the fact that it occurs so rapidly shows that the surface structure will not, in practical situations, impact the surface coverage of CO. In CsHCO3, a lower surface coverage of CO was measured, even for potentials at which CO dimerization is very slow. Although Cs+ accelerates the reduction of CO through interaction with adsorbed intermediates, its ability to adsorb to the electrode surface likely enables it to block potential adsorption sites for CO. Therefore, the effect of interaction with intermediates must have more impact than the reduced surface coverage of CO caused by cation adsorption.