CO2 Reduction to C1 and C2 Compounds on Sulfur-Deficient Mackinawite (FeS): A Density Functional Theory Study

Mackinawite (FeS) has sulfur-deficient surfaces and may have played arole in the prebiotic chemistry of the Earth because of its catalytic CO2-to-organicconversion ability, suggesting its suitability for electrochemical carbon dioxidereduction (CO2RR) for environmentally friendly and sustainable technologies. Toexploit this catalyst, an atomic understanding of the CO2RR mechanism on sulfur-deficient FeS(001) surfaces is required, which we have explored using dispersion-corrected density functional theory calculations. The adsorption energies of CO2onpristine and S-deficient FeS(001) surfaces are-0.17 and-1.62 eV, respectively,indicating that sulfur deficiency favors CO2activation and reduction. In addition,Bader charge population, density of states, and charge density difference analysesconfirmed the activation of CO2molecules via charge transfer (0.89e) from the Featoms to the adsorbates. We also found that the electrochemical CO2RR over thestudied surfaces favors methane in the potential-limiting*CHO ->*CH2O(Delta Gdiff=1.27 eV) and*OHCH2O ->*CH2O(Delta Gdiff= 0.78 eV) steps for reverse water-gas shift and formate pathways, respectively.Concerning C2species, a high surface concentration of the*CO intermediate on the catalyst was found to be crucial, yielding ethanethrough a potential-limiting*CH-CH2 ->*CH2-CH2step (Delta Gdiff= 1.00 eV)

Automated summary

This study provides an atomic-level understanding of the CO2RR mechanism on sulfur-deficient FeS(001) surfaces, revealing that sulfur deficiency promotes CO2 activation and reduction. The results also identify the favorable reaction steps for methane and ethane production in the reverse water-gas shift and formate pathways, respectively.