Electrochemical Reduction of Carbon Dioxide at Gold-Palladium Core-Shell Nanoparticles: Product Distribution versus Shell Thickness

The electrocatalytic reduction of CO2 at carbon-supported Au-Pd core-shell nanoparticles is investigated systematically as a function of the Pd shell thickness. Liquid- and gas-phase products were determined by off-line (HNMR)-H-1 spectroscopy and on-line electrochemical mass spectrometry. Our results uncover the relationship between the nature of the products generated and the Pd shell thickness. CO and H-2 are the only products generated at 1nm thick shells, whereas shells of 5 and 10nm produced HCOO-, CH4 and C2H6. The concentration of HCOO- detected in the electrolyte was dependent on the applied potential and reached a maximum Faradaic efficiency of 27% at -0.5V versus the reversible hydrogen electrode for 10nm thick shells. We conclude that collisions between absorbed hydrogen at relaxed Pd lattices and strongly bound CO-like intermediates promote the complete hydrogenation to C1 and C2 alkanes without the generation of other products, such as alcohols and aldehydes.