Reduction of Aqueous CO₂ to 1-Propanol at MoS₂ Electrodes

Reduction of carbon dioxide in aqueous electrolytes at single-crystal MoS₂ or thin-film MoS₂ electrodes yields 1-propanol as the major CO₂ reduction product, along with hydrogen from water reduction as the predominant reduction process. Lower levels of formate, ethylene glycol, and t-butanol were also produced. At an applied potential of 0.59 V versus a reversible hydrogen electrode, the Faradaic efficiencies for reduction of CO₂ to 1-propanol were 3.5% for MoS₂ single crystals and 1% for thin films with low edge-site densities. Reduction of CO₂ to 1-propanol is a kinetically challenging reaction that requires the overall transfer of 18 e^- and 18 H⁺ in a process that involves the formation of 2 C-C bonds. NMR analyses using ¹³CO₂ showed the production of ¹³C-labeled 1-propanol. In all cases, the vast majority of the Faradaic current resulted in hydrogen evolution via water reduction. H₂S was detected qualitatively when single-crystal MoS₂ electrodes were used, indicating that some desulfidization of single crystals occurred under these conditions.