Anthropogenic CO₂ production is one of the leading causes of global warming. Consequently, CO₂ reduction to carbon feedstocks has been proposed as a remediation strategy as part of larger efforts to address climate change. The scope of catalytic transformations for CO₂ reduction is large, but in the context of electrocatalytic CO₂ reduction (ECO₂R), only Cu-based catalysts are capable of performing reductions requiring more than two electrons. However, Cu-based ECO2R is limited by two factors: (1) the lack of product selectivity; and (2) limited understanding of Cu-coordination types. The latter issue may limit our ability to address the former. We performed a targeted search of the American Mineralogist Crystal Structure Database (AMCSD) for complexes containing new Cu coordination geometries, motivating our decision to study tetrahedrite (Cu₁₂Sb₄S₁₃) as a ECO2R catalyst. Tetrahedrite is of interest because it contains low valent Cu (I) and Cu (II) in both tetrahedral Cu-S4 and trigonal planar Cu-S₃ coordination environments. This is of consequence to us because trigonal planar Cu-S3 can achieve lower energy surface rearrangements than tetrahedral Cu-S₄ when intercalating CO₂. We have synthesized Td nanoparticles with mesoporous surfaces to increase the available surface area. Linear scan voltammetry, cyclic voltammetry, and chronoamperometry experiments have been performed and demonstrate that electron transfer on a tetrahedrite catalyst under a CO₂ atmosphere produces a greater current density and passes more charge than under an inert environment. After performing chronoamperometry at -1.5 V (vs. Ag/AgCl) and analyzing our gaseous products using gas chromatography (GC) and our liquid products using 1H nuclear magnetic resonance spectroscopy (NMR), we find that tetrahedrite reduces CO₂ in an aqueous electrolyte to C₂ products.

Laura Perlmutter

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