Molecular Catalysis of the Electrochemical and Photochemical Reduction of CO2 with Earth-Abundant Metal Complexes. Selective Production of CO vs HCOOH by Switching of the Metal Center

Abstract

Summary

A photochemical reduction of CO₂ to CO or formic acid was shown using the iron complex [Fe(pabop)Cl2][CLO4] or the cobalt complex [Co(pabop)][ClO4]2 as catalysts in combination with the iridium-based photosensitizer Ir(ppy)3. Turnover numbers (TONs) of 270 for CO with the cobalt complex and 5 for formic acid with the iron complex were reached in acetonitrile. The experiments were conducted under visible-light irradiation (λ > 460 nm) using TEA as sacrificial electron donor (see section SEDs below).

Advances and special progress

The authors could demonstrate that switching the metal center has a major influence on the outcome of CO₂ reduction, enabling the generation of either CO or formic acid depending on the employed metal. For the cobalt complex, CO₂ reduction was possible both under electrochemical conditions and photochemically with a photosensitizer under visible light.

Additional remarks

In electrolysis experiments with E = -1.5 V vs SCE, CO formation with high faradaic yields of 82% was possible employing the cobalt catalyst.

Content of the published article in detail

The article contains results for the reduction of CO₂ to CO and formic acid under visible-light catalysis using iron or cobalt complexes as catalysts. The catalytic system performs best (referring to the TON of CO production) in acetonitrile with the cobalt catalyst.

Catalyst

[Fe(pabop)Cl2][CLO4] [Co(pabop)][ClO4]2

Photosensitizer

Ir(ppy)3

Investigation

	cat	cat conc [µM]	PS	PS conc [mM]	e-D	solvent A	.	.	λexc [nm]	.	TON CO	TON HCOOH	.
1.	[Co(pabop)][ClO4]2	0.05	Ir(ppy)3	0.2	TEA	MeCN			>460		270
2.	[Fe(pabop)Cl2][CLO4]	0.05	Ir(ppy)3	0.2	TEA	MeCN			>420			5

Investigation-Name: Table 1Export

Sacrificial electron donor

In this study, the experiments were done with the sacrificial electron donor TEA (100505).

Additives

In this study, no additives were tested.