Determinant Role of Electrogenerated Reactive Nucleophilic Species on Selectivity during Reduction of CO₂ Catalyzed by Metalloporphyrins

Abstract

This work provides insights to understand the selectivity during the reduction of CO2 with metalloporphyrin (MP) catalysts. The attack of a nucleophile on the carbon of the CO2 appears as an important event that triggers the catalytic reaction, and the nature of this nucleophile determines the selectivity between CO (or further reduced species) and HCOOH/HCOO–. For MP, the possible electrogenerated nucleophiles are the reduced metal-center and the hydride donor species, metal-hydride and phlorin-hydride ligand. The reduced metal-center activates the CO2 with the formation of the metal–carbon bond, which then gives rise to the formation of CO. The hydride donor species trigger the CO2 reduction by the attack of the hydride on the carbon of the CO2 (formation of a C–H bond), which results in the formation of HCOOH/HCOO– (formation of the metal-bonded formate intermediate is not involved). The MP with the metals Ni, Cu, Zn, Pd, Ag, Cd, Ga, In, and Sn are predicted to only form the phlorin-hydride intermediate and are thus suitable to produce HCOOH/HCOO–. This agrees well with the available experimental results. The MP with the metals Fe, Co, and Rh can form both the reduced-metal center and the hydride donor species (metal-hydride and phlorin-hydride), and thus are able to form both CO and HCOOH/HCOO–. The production of CO for Fe and Co is indeed observed experimentally, but not for Rh, probably due to the presence of axial ligands that may hinder the formation of the metal-bonded intermediates and thus drive the CO2RR to HCOOH/HCOO– via the phlorin intermediate.

Lateral Adsorbate Interactions Inhibit HCOO− while Promoting CO Selectivity for CO2 Electrocatalysis on Silver

“…According to our analysis, there are therefore two reaction bifurcations before and after formation of *H that generally control the selectivity for CO 2 ER. An analogous finding has been recently reported for CO 2 ER on Cu(100) surfaces and as well as for the selectivity of CO 2 ER on metalloporphyrins …”

Local ionic liquid environment at a modified iron porphyrin catalyst enhances the electrocatalytic performance of CO2 to CO reduction in water

“…However, recent reports suggest that the second and the third redox waves mainly concern the porphyrin core acting as the locus for the addition of the two supplementary electrons and therefore can be formulated as Fe II porph/Fe II porph À and Fe II porph À /Fe II porph 2À couples (porph = porphyrin). 30,31 With the aim to provide a comparative reference, we have investigated, under similar experimental conditions, the non-functionalized iron tetraphenylporphyrin (FeTPP) together with the FeTPPF 8 and the FeTPPF 20 derivatives (see Fig. 1).…”

Lateral Adsorbate Interactions Inhibit HCOO− while Promoting CO Selectivity for CO2 Electrocatalysis on Silver

“…Both Volmer-Tafel and Volmer-Heyrovsky mechanisms for the formation of H 2 also share the first CPET Volmer step of *H d À formation (bottom panel in Figure 1). [13] This approach can be further extended to the formation of higher CPET products from CO 2 ER such as methanol (CH 3 OH) and methane (CH 4 ;s ee extended reaction scheme in Figure S8). An analogous finding has been recently reported for CO 2 ER on Cu(100) surfaces [12] and as well as for the selectivity of CO 2 ER on metalloporphyrins.…”

“…An analogous finding has been recently reported for CO 2 ER on Cu(100) surfaces [12] and as well as for the selectivity of CO 2 ER on metalloporphyrins. [13] This approach can be further extended to the formation of higher CPET products from CO 2 ER such as methanol (CH 3 OH) and methane (CH 4 ;s ee extended reaction scheme in Figure S8). Thet hermodynamically most feasible routes for the formation of CH 3 OH and CH 4 go via *COOH followed by the *CHO species,asbecomes clear from the U L for the various reaction pathways shown in Figures S9 and S10.…”