From overlooked to outstanding: a molecular silver complex in heterogeneous CO2 electroreduction

Abstract

Heterogenized molecular transition metal complexes, especially silver-based ones, have shown to be highly efficient as catalysts for electrochemical CO₂ reduction (eCO₂R). Herein we present the application of a silver dithiacyclam polymer (dithiacyclam = 1,8-dithia-4,11-diazacyclotetradecane, Ag(dithiacyclam)) in homogeneous as well as heterogeneous eCO₂R. Although the complex does not exhibit a noteworthy activity in solution, changing the catalyst environment through heterogenization onto a gas diffusion electrode (GDE) and subsequent application in a zero-gap electrolyzer (ZGE) drastically boosts its catalytic performance. At a current density of 50 mA cm⁻² a remarkable FE_CO of 97% is reached. Moreover, we highlight how optimization of the GDE fabrication via ink engineering including the choice of dispersion solvent results in a FE_CO up to 90% at an elevated current density of 300 mA cm⁻². Even at more application oriented current densities of 500 mA cm⁻² the eCO₂R outcompetes the competing hydrogen evolution reaction, achieving a FE_CO of 55%. Although signs of catalyst transformation into silver particles are observed in post-mortem analysis, these particles show higher activity than commercially available silver nanoparticles, thus highlighting that molecular systems can be very promising catalyst precursors for efficient eCO₂R.