Enhancing CO2 electroreduction to syngas by active protons of imidazolium ionic liquids: From performance to mechanism

High current density at specific CO/H2 molar ratios is the key to the industrial application of heterogeneous electrocatalytic CO2 reduction reaction (CO2RR) to syngas, which is still very challenging. Here, we report a Ni-foam-supported nano-Ag catalyst for CO2RR in ionic liquid (IL)-acetonitrile electrolyte originally designed for CO2RR-to-CO. It is surprising to find that this is a highly efficient catalytic system for CO2RR-to-syngas, the CO/H2 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/H2 molar ratios of 1:1, 1:2, and 1:3, respectively. The high efficiency of CO2RR-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 CO2RR-to-syngas.