Although significant research efforts have focused on the exploration of catalysts for the electrochemical reduction of CO2, considerably fewer reports have described how support materials for these catalysts affect their performance, which includes their ability to reduce the overpotential, and/or to increase the catalyst utilization and selectivity. Here Ag nanoparticles supported on carbon black (Ag/C) and on titanium dioxide (Ag/TiO2) were synthesized. In a flow reactor, 40 wt % Ag/TiO2 exhibited a twofold higher current density for CO production than 40 wt % Ag/C. Faradaic efficiencies of the 40 wt % Ag/TiO2 catalyst exceeded 90 % with a partial current density for CO of 101 mA cm−2; similar to the performance of unsupported Ag nanoparticle catalysts (AgNP) but at a 2.5 times lower Ag loading. A mass activity as high as 2700 mA mgAg−1 cm−2 was achieved. In cyclic voltammetry tests in a three-electrode cell, Ag/TiO2 exhibited a lower overpotential for CO2 reduction than AgNP, which, together with other data, suggests that TiO2 stabilizes the intermediate and serves as redox electron carrier to assist CO2 reduction while Ag assists in the formation of the final product, CO.
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