(513al) Computational Investigation of Transition Metal Sulfides for Overcoming the Challenges of Electrocatalytic CO2 Reduction

Transition metal chalcogenides such as MoS₂ have been shown to possess more favorable scaling relations for CO₂ reduction than metals but are hindered by high activation barriers for C-H bond formation. One possibility for lowering these barriers is to employ organic co-catalysts that either act as hydride donors or induce polarity reversal (umpolung) on the carbon atom. In the initial phase of this work, we have used DFT to examine the energetics of pathways for CO₂ reduction on the Mo-edge of MoS₂ in the absence of any co-catalyst. Solvation effects were included in all calculations using a hybrid implicit/explicit approach that utilizes explicit water molecules to account for hydrogen bonding and facilitate proton shuttling in transition states. Pathways were examined for reduction of CO₂ to both methanediol and CO. The pathway to methanediol proceeds through formic acid and formaldehyde and involves *COOH and *CHO catalytic intermediates bound to S atoms on the Mo-edge. The rate determining step is found to be transfer of a Mo-bound hydride to *COOH to give formic acid, although the barrier is high. The CO and methanediol formation pathways bifurcate at the common *CHO intermediate, with deprotonation of carbon leading to CO and hydride transfer to carbon (from Mo-H) leading to methanediol via formaldehyde. The transition state leading to CO formation is found to be lower in free energy than the transition state leading to methanediol, indicating that CO is expected to be the dominant CO₂ reduction product. Furthermore, the transition state for H₂ formation via Mo-H is found to be lower than both CO₂ reduction pathways, indicating low Faradaic efficiency. All of this suggests that a C-H formation co-catalyst could potentially lower the barriers of the C-H formation steps to give adequate turnover frequency and improve selectivity to methanediol.