Rigorous electrokinetic results are key to understanding the reaction mechanisms in the electrochemical CO reduction reaction (CORR), however, most reported results are compromised by the CO mass transport limitation. In this work, we determined mass transport-free CORR kinetics by employing a gas-diffusion type electrode and identified dependence of catalyst surface speciation on the electrolyte pH using in-situ surface enhanced vibrational spectroscopies. Based on the measured Tafel slopes and reaction orders, we demonstrate that the formation rates of C2+ products are most likely limited by the dimerization of CO adsorbate. CH4 production is limited by the CO hydrogenation step via a proton coupled electron transfer and a chemical hydrogenation step of CO by adsorbed hydrogen atom in weakly (7 < pH < 11) and strongly (pH > 11) alkaline electrolytes, respectively. Further, CH4 and C2+ products are likely formed on distinct types of active sites.

Electroreduction of carbon dioxide to hydrocarbons and oxygenates on copper involves reduction to a carbon monoxide adsorbate followed by further transformation to hydrocarbons and oxygenates. Simultaneous improvement of these processes over a single reactive site is challenging due to the linear scaling relationship of the binding strength of key intermediates. Herein, we report improved electroreduction of carbon dioxide by exploiting a one-pot tandem catalysis mechanism based on computational and electrochemical investigations. By constructing a well-defined copper-modified silver surface, adsorbed carbon monoxide generated on the silver sites is proposed to migrate to surface copper sites for the subsequent reduction to methane, which is consistent with insights gained from operando attenuated total reflectance surface enhanced infrared absorption spectroscopic investigations. Our results provide a promising approach for designing carbon dioxide electroreduction catalysts to enable one-pot reduction of products beyond carbon monoxide and formate.

Many electrocatalysts can efficiently convert CO2 to CO. However, the further conversion of CO to higher-value products was hindered by the low activity of the CO reduction reaction and the consequent lack of mechanistic insights for designing better catalysts. A flow-type reactor could potentially improve the reaction rate of CO reduction. However, the currently available configurations would pose great challenges in reaction mechanism understanding due to their complex nature and/or lack of precise potential control. Here we report, in a standard electrochemical cell with a three-electrode setup, a supported bulk polycrystalline copper powder electrode reduces CO to hydrocarbons and multicarbon oxygenates with dramatically increased activities of more than 100 mA cm–2 and selectivities of more than 80%. The high activity and selectivity that was achieved demonstrates the practical feasibility of electrochemical CO or CO2 (with a tandem strategy) conversion and enables the experimental exploration of the CO reduction mechanism to further reduced products.