Electrocatalytic CO₂ Reduction by Self-Assembled Monolayers of Metal Porphyrins

Abstract

The main issue hindering the successful utilization of CO 2 electroreduction processes in industry is the lack of selective, durable, and efficient catalysts. In this work, a new heterogeneous molecular architecture for CO 2 electrocatalysts is designed by attaching alkyne-terminated metal (Fe and Co) porphyrins via click chemistry to azide-terminated alkyl phosphate self-assembled monolayers (SAMs) on tin-doped indium oxide and fluorinedoped tin oxide electrodes. The electrochemistry of these CO 2 reduction systems is studied using cyclic voltammetry and chronoamperometry, and products are quantified through NMR and gas chromatography. Additionally, atomic force microscopy is used to characterize the morphology of the electrode surfaces. Experiments show that CO 2 reduction is sensitive to the choice of electrode, SAM length, metal porphyrin, and reduction potential. With higher overpotentials and SAMs facilitating fast electron transfer kinetics, the Fe porphyrin favors HCOOH while the Co porphyrin produces more CO. For both metal porphyrins, these product preferences switch with lower overpotentials and SAMs with slower electron transfer rates. The tunability of SAMs allows for a high degree of control over the surface modification of CO 2 electrocatalysts, potentially enabling the design of superior catalysts.

Electrochemical Characterization of Redox Probes Confined in 3D Conducting Polymer Networks

“…[20][21][22] It has been in particular used to decorate self-assembled monolayers (SAMs) assembled on planar surfaces with various redox probes, such as ferrocene [23,24] and porphyrins. [25,26] In this context, Chidsey et al used cyclic voltammetry to show successful ferrocene attachment to azide-terminated SAMs which can be useful for applications such as sensors and electrocatalysis. [27] Barile et al further demonstrated that the modification of an azideterminated electrode with alkyne-terminated metal porphyrins through click chemistry can be applied to the electrocatalytic reduction of CO 2 .…”

“…[27] Barile et al further demonstrated that the modification of an azideterminated electrode with alkyne-terminated metal porphyrins through click chemistry can be applied to the electrocatalytic reduction of CO 2 . [23,25,[27][28][29] This strategy is also applicable to polymers. For introduction of redox probes within polymer matrices the respective azide functionality can be brought into the monomer units.…”

“…A typical click reaction is the copper catalyzed 1,3‐dipolar cycloaddition of azides and alkynes (CuAAC) to regioselectively give 1,4‐triazole products [20–22] . It has been in particular used to decorate self‐assembled monolayers (SAMs) assembled on planar surfaces with various redox probes, such as ferrocene [23,24] and porphyrins [25,26] . In this context, Chidsey et al .…”

“…[ 20 , 21 , 22 ] It has been in particular used to decorate self‐assembled monolayers (SAMs) assembled on planar surfaces with various redox probes, such as ferrocene[ 23 , 24 ] and porphyrins. [ 25 , 26 ] In this context, Chidsey et al . used cyclic voltammetry to show successful ferrocene attachment to azide‐terminated SAMs which can be useful for applications such as sensors and electrocatalysis.…”

Homogeneous Electrocatalytic CO2Reduction Using a Porphyrin Complex with Flexible Triazole Units in the Second Coordination Sphere

“…Iron porphyrins have been extensively studied because of their high stability, selectivity, and activity ,− and are among the most efficient CO 2 reduction catalysts. ,− These complexes have reported high Faradaic efficiencies and turnover numbers during catalysis. , Fe is one of the most abundant and inexpensive first row transition element. Some representative iron porphyrin catalysts are shown in Figure .…”