Single Molecular Dispersion of Crown Ether-Decorated Cobalt Phthalocyanine on Carbon Nanotubes for Robust CO2 Reduction through Host-Guest Interactions

Immobilizing molecular catalysts on electro-conductive supports (for example, multi-walled carbon nanotubes, CNTs) represent a promising way to well-defined catalyst/support interfaces, which has shown appreciable performance for catalytic transformation. However, their full potential is far from achieved due to insufficient utilization of the intrinsic activity for each immobilized molecular catalyst, especially at loadings that should allow decent current densities. In the present work, we discover host–guest interaction between tetra-crown ether substituted cobalt phthalocyanine and metal ions, for example K⁺ ions, not only eliminate catalyst aggregation at immobilization procedures but also reinforce catalyst/support interactions by additional electrostatic attractions under operational conditions. Through simple dip-coating procedures, a successful single molecular dispersion is achieved. Such a catalyst/electrode interface is stable and can selectively catalyze CO₂-to-CO conversion with Faradaic efficiency over 96%. Importantly, this interface maintains an almost unchanged turnover frequency (TOF) across all loading conditions, implying a full utilization of the intrinsic activity of supported molecular catalysts. Therefore, a simultaneous achievement of high TOF and high current density (TOF of 111 s⁻¹ at 38 mA cm⁻²) is achieved, in an aqueous H-type electrolyzer at an overpotential of 570 mV.