Understanding of Strain Effects in the Electrochemical Reduction of CO2 : Using Pd Nanostructures as an Ideal Platform.

Tuning the surface strain of heterogeneous catalysts represents a powerful strategy to engineer their catalytic properties by altering the electronic structures. However, a clear and systematic understanding of strain effect in electrochemical reduction of carbon dioxide is still lacking, which restricts the use of surface strain as a tool to optimize the performance of electrocatalysts. Herein, we demonstrate the strain effect in electrochemical reduction of CO2 by using Pd octahedra and icosahedra with similar sizes as a well-defined platform. The Pd icosahedra/C catalyst shows a maximum Faradaic efficiency for CO production of 91.1 % at -0.8 V versus reversible hydrogen electrode (vs. RHE), 1.7-fold higher than the maximum Faradaic efficiency of Pd octahedra/C catalyst at -0.7 V (vs. RHE). The combination of molecular dynamic simulations and density functional theory calculations reveals that the tensile strain on the surface of icosahedra boosts the catalytic activity by shifting up the d-band center and thus strengthening the adsorption of key intermediate COOH*. This strain effect was further verified directly by the surface valence-band photoemission spectra and electrochemical analysis.