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

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.