Boron subphthalocyanine complexes for CO₂ electroreduction: molecular design and catalytic insights

This study presents molecular boron subphthalocyanine complex precursors ((Cl-B-SubPc) 1 and (Cl-B-SubPc-OC₁₂H₂₃) 2) designed for efficient CO₂ reduction. The resulting heterogeneous catalysts exhibit remarkable total faradaic efficiencies of up to 98%, integrated into practical cell assemblies. Optimizations encompass not only catalyst design but also operational conditions, facilitating prolonged CO₂ electrolysis across various current densities. Varied C₁-, C₂-, and C₃-product yields are observed at different reductive potentials, with electrocatalysis experiments conducted up to 200 mA cm^-2. Comparative electrochemical analyses across H-cell and zero-gap cell electrolyzers show the potential for industrial scale-up. Mechanistic elucidation via in situ UV-vis spectroelectrochemistry, DFT calculations, and ESR spectroscopy demonstrates the involvement of boron N-C sites, initiating radical formation and utilizing boron's Lewis acid behavior in CO₂ capture, followed by proton-coupled electron transfer. Overall, the study underscores the transformative potential of boron subphthalocyanine systems in advancing CO₂ utilization technologies.