Electrodeposited CuAgHg Multimetallic Thin Films for Improved CO₂Conversion: The Dramatic Impact of Hg Incorporation on Product Selectivity

The CO2 reduction reaction (CO2RR) remains a prominent hurdle in the overall solar to fuel conversion process. A key research direction for CO2RR is tuning of the product selectivity to desired fuels while suppressing the undesired hydrogen-evolving side reaction. In this work, we employed a CuAgHg multimetallic thin-film catalyst for CO2RR. By incorporation of Hg atoms, we attempted to minimize the surface-adsorbed hydrogen atoms during CO2RR, thereby minimizing hydrogen evolution. In situ electrochemical surface interrogation along with vibrational spectroscopy revealed that Hg incorporation led to significantly suppressed surface adsorption of hydrogen atoms, as well as increased surface concentration of the intermediate CO, which is in competitive binding with protons. The two effects combined led to an ethanol-selective CO2RR catalyst; with the optimum composition, the CuAgHg electrode produced 32% ethanol and 41% C2 (ethanol + ethylene) products, comparable to those of the best catalysts reported. Remarkably, this catalysis was possible holding the hydrogen evolving side reaction to mere 10% and achieving 100% overall faradaic efficiency.