In ac omparative study of the electrocatalytic CO 2 reduction, cobalt meso-tetraphenylporphyrin(CoTPP) is used as am odel molecular catalyst under both homogeneous and heterogeneous conditions.Inthe former case,employing N,Ndimethylformamide as solvent, CoTPP performs poorly as an electrocatalyst giving low product selectivity in aslow reaction at ah igh overpotential. However,u pon straightforward immobilization of CoTPP onto carbon nanotubes,aremarkable enhancement of the electrocatalytic abilities is seen with CO 2 becoming selectively reduced to CO (> 90 %) at al ow overpotential in aqueous medium. This effect is ascribed to the particular environment created by the aqueous medium at the catalytic site of the immobilized catalyst that facilitates the adsorption and further reaction of CO 2 .T his work highlights the significance of assessing an immobilized molecular catalyst from more than homogeneous measurements alone.

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Earth-abundant transition metal (Fe, Co, or Ni) and nitrogen-doped porous carbon electrocatalysts (M-N-C, where M denotes the metal) were synthesized from cheap precursors via silica-templated pyrolysis. The effect of the material composition and structure (i.e., porosity, nitrogen doping, metal identity, and oxygen functionalization) on the activity for the electrochemical CO2 reduction reaction (CO2RR) was investigated. The metal-free N-C exhibits a high selectivity but low activity for CO2RR. Incorporation of the Fe and Ni, but not Co, sites in the N-C material is able to significantly enhance the activity. The general selectivity order for CO2-to-CO conversion in water is found to be Ni > Fe ≫ Co with respect to the metal in M-N-C, while the activity follows Ni, Fe ≫ Co. Notably, the Ni-doped carbon exhibits a high selectivity with a faradaic efficiency of 93% for CO production. Tafel analysis shows a change of the rate-determining step as the metal overtakes the role of the nitrogen as the most active site. Recording the X-ray photoelectron spectra and extended X-ray absorption fine structure demonstrates that the metals are atomically dispersed in the carbon matrix, most likely coordinated to four nitrogen atoms and with carbon atoms serving as a second coordination shell. Presumably, the carbon atoms in the second coordination shell of the metal sites in M-N-C significantly affect the CO2RR activity because the opposite reactivity order is found for carbon supported metal meso-tetraphenylporphyrin complexes. From a better understanding of the relationship between the CO2RR activity and the material structure, it becomes possible to rationally design high-performance porous carbon electrocatalysts involving earth-abundant metals for CO2 valorization.

Cu is in the spotlight as it represents the only metal capable of catalyzing CO2 reduction to multicarbon products. However, its catalytic performance is determined collectively by a number of parameters including its composition and structure, electrolyte, and cell configuration. It remains a challenge to disentangle and understand the individual effect of these parameters. In this work, we study the effect of the electrode–electrolyte interface on CO2 reduction in water by coating CuO electrodes with polymers of varying hydrophilicities/phobicities. Hydrophilic polymers such as poly­(vinyl alcohol) and poly­(vinylpyrrolidone) exert negligible influence, while hydrophobic polymers such as poly­(vinylidene fluoride) and polyethylene significantly enhance the activity, selectivity, and stability of CuO-derived electrodes toward C2H4 production. From ex situ characterizations, electrolysis in deuterated water, and molecular dynamics simulations, we propose that the improved catalytic performance triggered by hydrophobic polymers originates from restricted water diffusion and a higher local pH near the electrode surface. These observations shed light on interfacial manipulation for promoted CO2-to-C2H4 conversion.