Efficient and selective electroreduction of carbon dioxide to value-added hydrocarbons is vital for building a sustainable carbon-neutral economy. Direct electroreduction of CO2 to hydrocarbons in alkaline electrolytes suffers from the issue of poor selectivity. A solution to the challenge could be a tandem strategy, in which CO2 is selectively reduced to CO first and CO is subsequently reduced in a second reactor to hydrocarbons. We report here a detailed study of the effects of Cu-Pd alloys in activity and selectivity in both steps. For electroreduction of CO2 to CO, we examined intermetallic CuPd alloys and determined that there are several possible thermodynamically stable surface structures with different catalytic properties. In particular, we show that slight off-stoichiometry could abruptly change (100) surfaces from Cu-terminated to Pd-terminated, dramatically affecting the activity of the catalyst. For reduction of CO, we report here highly selective reduction of CO to acetate using Cu-Pd bimetallic random alloys, with &gt;200 mA/cm2 geometric current density and &gt;65% Faradaic efficiency. An asymmetrical C-C coupling mechanism is developed to understand the composition-dependent catalytic performance and high selectivity toward acetate. This mechanism is supported by the computationally predicted shift of CO adsorption from the top-site configuration on Cu (or Cu-rich) surfaces to the Cu-Pd bridge sites of Cu-Pd bimetallic surfaces, which is also associated with the reduction of the CO hydrogenation barrier. We demonstrate that coverage effects could be critical to correctly evaluating the hydrogenation energy of *CO. Further kinetic analysis of the reaction order with respect to CO and the Tafel slope reveals a reaction pathway with *CO-*CHO recombination following a CO hydrogenation step, which could account for the electroreduction of CO to acetate on the Cu-Pd bimetallic catalysts. Our work highlights how heteroatomic alloy surfaces can be tailored to enable distinct reaction pathways and achieve advanced catalytic performance beyond monometallic catalysts.

Mechanistic insights of CuPd alloys in electroreduction of CO2 and CO

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.