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

One major challenge to the electrochemical conversion of CO 2 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 CO 2 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 CO 2 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 CO 2 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 CO 2 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 CO 2 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 CO 2 to formic acid in an FE of 48%.