The multi-gram synthesis of a phenylacetylide silver cluster catalyst and its application to the electroreduction of CO2 to carbon monoxide is described. The procedure involves one synthetic step from commercially available precursors and yields highly crystalline silver acetylide clusters in quantitative yields with no required purification. The crystal structure of the cluster was resolved from the native powder using cutting-edge electron diffraction techniques (3D-ED), and showed to consist of an infinite silver tubular core with radially disposed phenylacetylene ligands. Its catalytic properties were investigated at industry-relevant rates in a flow cell electrolyser. Faradaic efficiencies for CO above 95% were achieved at current densities reaching 350 mA cm-2. The catalyst’s selectivity and stability were shown to be the result of the unique polymeric structure, a result supported by electrochemical characterisation and DFT modelling.