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High current density at specific CO/H 2 molar ratios is the key to the industrial application of heterogeneous electrocatalytic CO 2 reduction reaction (CO 2 RR) to syngas, which is still very challenging. Here, we report a Ni-foam-supported nano-Ag catalyst for CO 2 RR in ionic liquid (IL)-acetonitrile electrolyte originally designed for CO 2 RR-to-CO. It is surprising to find that this is a highly efficient catalytic system for CO 2 RR-to-syngas, the CO/H 2 molar ratio in the syngas can be tuned from 1:5–26:1, and the current density is as high as 363.6, 458.2, and 644.7 mA cm−2 at the CO/H 2 molar ratios of 1:1, 1:2, and 1:3, respectively. The high efficiency of CO 2 RR-to-syngas is attributed to the synergistic stabilization action of nano-Ag and IL cationic C4/5-H for intermediate *COO- to produce CO, as well as cationic C2-H contribution to hydrogen evolution. This work opens a new way to improve catalytic performance of CO 2 RR-to-syngas. [Display omitted] • A nano-Ag catalyst in-situ grown on Ni foam was developed for CO 2 RR-to-syngas in [C 4 mim][PF 6 ]/MeCN electrolyte. • The CO/H 2 molar ratio could be tuned from 1:5–26:1, and the current density was high up to 644.7 mA cm−2. • By replacing the C2-H with methyl, the CO 2 RR product could be readily switched from syngas to pure CO, and the current density is high up to 528.3 mA cm−2. • A new pathway was explored to enhance CO 2 RR-to-syngas performance by adjusting the active protons of imidazolium ionic liquids. [ABSTRACT FROM AUTHOR]