Mechanistic Pathway in the Electrochemical Reduction of CO2 on RuO2

Mohammadreza Karamad, Heine Anton Hansen, Jan Rossmeisl, Jens Kehlet Nørskov

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

RuO2 has been reported to reduce CO2 electrochemically to methanol at low overpotential. Herein,we have used density functional theory (DFT) to gain insightinto the mechanism for CO2 reduction on RuO2(110). Wehave investigated the thermodynamic stability of varioussurface terminations in the electrochemical environment andfound CO covered surfaces to be particularly stable, althoughtheir formation might be kinetically limited under mildlyreducing conditions. We have identified the lowest free energypathways for CO2 reduction to formic acid (HCOOH), methanol (CH3OH), and methane (CH4) on partially reduced RuO2(110) covered with 0.25 and 0.5 ML of CO*. We have found that CO2 is reduced to formic acid, which is further reducedto methanol and methane. At 0.25 ML of CO*, the reduction of formate (OCHO*) to formic acid is the thermodynamicallymost difficult step and becomes exergonic at potentials below −0.43 V vs the reversible hydrogen electrode (RHE). On the otherhand, at 0.5 ML of CO*, the reduction of formic acid to H2COOH* is the thermodynamically most difficult step and becomesexergonic at potentials below −0.25 V vs RHE. We have found that CO2 reduction activity on RuO2 changes with CO coverage,which suggests that CO coverage can be used as a tool to tune the CO2 reduction activity. We have shown the mechanism for CO2 reduction on RuO2 to be different from that on Cu. On Cu, hydrocarbons are formed at high Faradaic efficiency throughreduction of CO* at ∼1 V overpotential, while on RuO2, methanol and formate are formed through reduction of formic acid at lower overpotentials. Using our understanding of the CO2 reduction mechanism on RuO2, we suggest reduction of formic acidon RuO2, which should lead to methanol and methane production at relatively low overpotentials.
Original languageEnglish
JournalA C S Catalysis
Volume5
Pages (from-to)4075−4081
Number of pages7
ISSN2155-5435
DOIs
Publication statusPublished - 2015

Keywords

  • Electrocatalysis
  • CO2 reduction
  • Methanol synthesis
  • Density functional theory
  • RuO2

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