Host‐guest tuning of the CO ₂ reduction activity of an iron porphyrin cage

Efficient electrocatalytic CO2 reduction requires developing catalysts with high selectivities and activities, which is simultaneously difficult to achieve. Here, we present a new approach tune the activity based on host-guest chemistry enabled by an iron porphyrin cage catalyst. The design allows hosting of alkali metals in side walls causing change electrostatic potential inside cavity. Density functional theory calculations show that guest potassium ions assist inverting two-electron transfer from iron(0) endothermic exothermic. Accordingly, electrochemical experiments catalyst presence ions, overpotential for decreases, catalytic increases while selectivity retained. A novel coupling between cell mass spectrometer allowed trapping key intermediates. Cryogenic ion spectroscopy characterization intermediates showed details reduced stabilization Fe-COOH interaction at single-molecule level. Key points Host-guest porphyrin-cage results increase catalysis. Electrochemistry—mass spectrometry studying reaction helium tagging infrared photodissociation spectroscopy. DFT pathway cavity working principles reactivity enhancement chemistry.