Descriptors and Thermodynamic Limitations of Electrocatalytic Carbon Dioxide Reduction on Rutile Oxide Surfaces

A detailed understanding of the electrochemical reduction of CO₂ into liquid fuels on rutile metal oxide surfaces is developed by using DFT calculations. We consider oxide overlayer structures on RuO₂ (1 1 0) surfaces as model catalysts to elucidate the trends and limitations in the CO₂ reduction reaction (CO2RR) based on thermodynamic analysis. We aim to specify the requirements for CO2RR catalysts to establish adsorbate scaling relations and use these to derive activity volcanoes. Computational results show that the OH* binding free energy is a good descriptor of the thermodynamic limitations and it defines the left leg of the activity volcano for CO2RR. HCOOH* is a key intermediate for products formed through further reduction, for example, methanediol, methanol, and methane. The surfaces that do not bind HCOOH* are selective towards formic acid (HCOOH) production, but hydrogen evolution limits their suitability. We determine the ideal binding free energy for H* and OH* to facilitate selective CO2RR over H₂ /CO evolution to be ΔG_B [H]>0.5 eV and -0.5 eV<ΔG_B [OH]<0.1 eV. The Re-containing overlayers considered in this work display excellent promise for selectivity, although they are active at a highly reducing potential.