The electrochemical reduction of CO₂ into feedstocks, such as carbon monoxide (CO), methane, or higher molecular weight hydrocarbons, is a promising alternative for offsetting greenhouse gas emissions.[1] The transformation, generally mediated by a catalyst of metallic nature under electrochemical conditions, has attracted considerable interest from the scientific community. Since the pioneering work of Hori, the properties of copper, gold or silver have been well studied. While silver and gold have an intrinsic propensity for efficiently reducing CO₂ into CO with high selectivity, copper has shown very variable selectivity, producing a mixture of gaseous hydrocarbons and a variety of different alcohols. Importantly, aside from these selectivity considerations, the viability of a catalytic system on the industrial scale is subjected to the implementation of the latter to bulk electrolysis. In such systems, e.g. flow cells or membrane electrode assembly electrolyzers, the mass transport limitations resulting from the poor solubility of CO₂ in aqueous media, is overcome using a porous gas diffusion layer (GDL). The GDL allows the formation of a gas/electrolyte/catalyst interface where the local concentration of CO₂ rises far above its solubility limit, thus allowing the CO2RR to perform at industry relevant rates. The gases diffuse in and out of the catalytic centre through the diffusion layer’s cross-section, requiring therefore that the catalyst be deposited on the catholyte side of the layer. This is a significant limitation to the types of catalysts that can be adapted to GDLs, since the microporous nature of carbon-based or Teflon based GDLs commonly used in CO₂ electroreduction is not compatible with the deposition of metal catalyst as dense homogeneous layers. Consequently, studies based on flow cells are still scarce in the literature, despite the general consensus that catalysts should be assessed under industrially relevant reaction rates.[2]

In the aim of tackling the above setbacks, herein we describe a novel type of hybrid material, which combines attributes of both metallic and molecular catalysts presenting themselves as nanocrystalline powders that can readily immobilized on GDLs. Their chemical structure consists of silver clusters whose main core is composed of several covalently linked silver atoms in a polymer-like fashion, with organic “ligands” orderly distributed in the outer shell. While The molecule, essentially known as silver acetylide involves stable alkyne-silver covalent bond allowing for the direct modulation of the silver-cluster’s electronic properties by tailoring the chemical structure of the organic moiety. The versatility of these entities as catalysts, is further enhanced by the fact that their synthesis involves only one, extremely reproducible, synthetic step from an alkyne precursor and a silver salt, that can be carried out on a multigram scale without any purification step. The availability of an extremely wide selection of commercially available alkyne precursors at a competitive price allows for the synthesis of large libraries of catalysts.

Herein we demonstrate the ability of two silver-acetylide clusters, to efficiently catalyze the CO₂RR under high reaction rates in a flow cell electrolyzer. Electrolysis current higher than 200 mA/cm2 were achieved with very high selectivity towards CO (95%).