Highly tunable syngas production by electrocatalytic reduction of CO2 using Ag/TiO2 catalysts.

[Display omitted] • CO 2 to syngas with controllable H 2 /CO ratio was investigated using Ag/TiO 2 catalysts. • The H 2 /CO ratio was controlled by oxygen vacancies and phase difference of TiO 2. • The H 2 /CO ratio was increased by the oxygen vacancy defects of TiO 2 anatase. The direct conversion of CO 2 to syngas with controllable H 2 /CO ratio has been investigated using electrochemical reduction of CO 2 in aqueous media. Despite considerable progress on electrocatalytic syngas production, it remains challenging to generate a stable H 2 /CO ratio over a wide range of applied potentials. In this study, we investigated Ag/TiO 2 catalysts, by which we achieved a stable H 2 /CO ratio with high Faradaic efficiency (93–100%) and partial current densities (~164 mA·cm−2) for syngas production in a flow cell. The H 2 /CO ratio was controlled by changing the catalyst properties resulting from oxygen vacancies and phase difference of TiO 2. The H 2 /CO ratio of Ag/TiO 2 catalysts was increased by introducing oxygen vacancy defects in the bulk and on the surface of TiO 2 anatase. Furthermore, the H 2 /CO ratio was also increased by changing the TiO 2 phases from anatase to rutile, even if the rutile phase possessed fewer oxygen vacancies. The 40 wt% Ag/TiO 2 catalysts calcined in different gases (Ag/TiO 2 anatase-air, Ag/TiO 2 anatase-H 2 /Ar, and Ag/TiO 2 rutile-air) exhibited H 2 /CO ratios of 0.1–0.3, 0.5–1.1, and 0.5–1.5, respectively, within the range of potential from −0.35 to −0.65 V (vs. RHE). [ABSTRACT FROM AUTHOR]