Dual Molecular Catalyst-Based Tandem That Enables Electrocatalytic CO2-Formaldehyde-Methanol Cascade Conversion.

Electrocatalytic CO2 reduction into multielectron products is a promising approach for carbon capture and utilization. Recently, cobalt phthalocyanine (CoPc)-based molecular catalysts have shown potential competence toward electrochemical conversion of CO2 to methanol, a 6e-/6H+ product. Yet, despite the recent advancements, CoPc's tendency to aggregate and the weak CO-intermediate binding generally limit its electrocatalytic activity and selectivity. Herein, we demonstrate that a metal-organic framework (MOF) could be used to construct a tandem electrocatalytic system via immobilization of 2 types of molecular catalysts (CoPc and Fe-porphyrin). Notably, the MOF-based tandem achieves a 3-fold increase in electrocatalytic CO2-to-methanol activity and selectivity compared to a CoPc-only MOF-based catalyst (up to 18% methanol faradaic efficiency at 25 mA/cm2). Additionally, operando spectroscopy and electrochemical analysis show that unlike typical tandem systems, the MOF-based tandem operates uniquely by using a reactive intermediate different from CO (i.e., formaldehyde). Hence, this proof-of-concept approach offers a new means to design molecular electrocatalytic schemes capable of driving complex proton-coupled electron transfer reactions.