Coupled Metal/Oxide Catalysts with Tunable Product Selectivity for Electrocatalytic CO₂ Reduction

One major challenge to the electrochemical conversion of CO₂ to useful fuels and chemical products is the lack of efficient catalysts that can selectively direct the reaction to one desirable product and avoid the other possible side products. Making use of strong metal/oxide interactions has recently been demonstrated to be effective in enhancing electrocatalysis in the liquid phase. Here, we report one of the first systematic studies on composition-dependent influences of metal/oxide interactions on electrocatalytic CO₂ reduction, utilizing Cu/SnO_x heterostructured nanoparticles supported on carbon nanotubes (CNTs) as a model catalyst system. By adjusting the Cu/Sn ratio in the catalyst material structure, we can tune the products of the CO₂ electrocatalytic reduction reaction from hydrocarbon-favorable to CO-selective to formic acid-dominant. In the Cu-rich regime, SnO_x dramatically alters the catalytic behavior of Cu. The Cu/SnO_x-CNT catalyst containing 6.2% of SnO_x converts CO₂ to CO with a high faradaic efficiency (FE) of 89% and a j_CO of 11.3 mA·cm^-2 at -0.99 V versus reversible hydrogen electrode, in stark contrast to the Cu-CNT catalyst on which ethylene and methane are the main products for CO₂ reduction. In the Sn-rich regime, Cu modifies the catalytic properties of SnO_x. The Cu/SnO_x-CNT catalyst containing 30.2% of SnO_x reduces CO₂ to formic acid with an FE of 77% and a j_HCOOH of 4.0 mA·cm^-2 at -0.99 V, outperforming the SnO_x-CNT catalyst which only converts CO₂ to formic acid in an FE of 48%.