Effect of co-adsorbed water on electrochemical CO2 reduction reaction on transition metal oxide catalysts

Abstract

Density functional theory calculations are utilized to understand the effect of solvent on the stability of intermediates in CO2 reduction reaction (CO2RR) toward methanol and formic acid formation and the competing hydrogen evolution reaction (HER) on twelve rutile (110) transition metal dioxide (TMO) surfaces. To study the solvent effect, one monolayer of water is included in the free energy calculations of adsorbates in CO2RR and HER and compared with the results when water is absent. The emphasis is on the catalytic trends where limiting potential volcano plots for the products are obtained through the scaling relations of adsorbates. We find that cooperative adsorbed (co-adsorbed) water changes the overpotentials for the formation of formic acid and methanol, ranging from 0.2 to 0.5 V. Moreover, co-adsorbed water destabilizes HCOOH on TMOs (except for IrO2 and ZrO2) and therefore the selectivity is shifted more toward formic acid compared to methanol when the model system is improved. We confirm recent experimental observations that the RuO2 catalyst is selective toward HER. Furthermore, NbO2 is predicted to be selective toward formic acid and methanol formation while other TMOs such as MoO2, ZrO2 and OsO2 are predicted to reduce CO2 to CO on their surfaces.