(Invited) Bimetallic Electrocatalysts for Electrochemical CO2 Reduction

Abstract

Bimetallic nanoparticles (NPs) offer great flexibility to tailor the activity and selectivity in electrocatalytic conversion of carbon dioxide (CO2) to valuable chemicals. Here, we report on the electrocatalytic behavior of Au-Sn, Au-Ag and Au-Pb NPs, to highlight the effect of the intermetallic phase formation and the bimetallic composition in CO2 electroreduction.Firstly, a series of Au–Sn electrocatalysts with different intermetallic phases were obtained via tin incorporation into the gold lattice through gradual diffusion. Stoichiometric intermetallic phases were formed, and under optimal conditions, two high-value products formed with reasonable current density: formic acid in the liquid phase and syngas in the gas phase. Notably, the phase composition had a massive influence on both the activity and the product distribution. In situ Raman spectroelectrochemistry studies demonstrated that catalytic performance of the AuSn phase was superior to that its parent metals and other bimetallic counterparts.Secondly, the correlation between the electrocatalytic activity and the composition of Au-Ag alloy NPs was studied. The CO Faradaic efficiency (and thus the forming CO:H2 ratio) was changed linearly by controlling the Au:Ag ratio in the alloy. This trend was attributed to the changes in the electronic properties, as there was a monotonous shift in the Fermi level away from the vacuum level with increasing Au content. This shift correspondingly reduces the binding energy of the intermediates (*COOH and *CO), resulting in the gradually enhanced CO2-reduction activity.Finally, I will show results gained with Au-Pb electrodes, where the formation of methane (CH4) was demonstrated. Factors underpinning this unusual behavior were studied by both experimental and theoretical means.