Catalyst Identity Matters: Molecular Ag(I)–BIAN Complexes Outperform Ag Nanoparticles in High-Current CO2 Electroreduction

Abstract

Redox-active ligands offer powerful opportunities to modulate catalytic reactivity while minimizing precious metal loading. Herein, we report the mechanochemical synthesis and comprehensive characterization of homoleptic silver(I) bis(arylimino)acenaphthene (Ag–BIAN) complexes and their application in homogeneous and heterogeneous zero-gap CO2 electroreduction. The molecular catalysts exhibit pronounced ligand-centered redox activity, with two reversible reductions assigned to sequential BIAN-based electron uptake. Under a CO2 atmosphere, significant catalytic current enhancement is observed between the first and second ligand-centered reductions, consistent with activation of electrogenerated reduced species. In a zero-gap electrolyzer configuration, the Ag–BIAN complexes achieve Faradaic efficiencies for CO formation of 70–90% at current densities up to 300 mA cm–2. Notably, the tailored molecular design enables a tenfold reduction in silver loading compared to Ag nanoparticle benchmarks while maintaining high catalytic performance. The material cost of the catalysts amounts to only €7.5–9.8 g–1, substantially improving economic feasibility. These findings demonstrate that redox-active ligand frameworks can decouple catalytic activity from metal mass loading and provide a viable molecular alternative to heterogeneous silver systems for efficient CO2-to-CO conversion.