Durable Solar-Powered Systems with Ni-Catalysts for Conversion of CO2 or CO to CH4

Abstract

Summary

A photochemical reduction of CO₂ and CO to methane was shown using the nickel carbene complexes [Ni(bpy-bNHCMe)][PF6]2, [Ni(bpy)-(MeNHC)2][PF6]2, and [Ni(bpy-bNHCEt)][PF6]2 as catalysts in combination with the iridium-based photosensitizer Ir(ppy)3. Turnover numbers (TONs) up to 310000 for CO and 19000 for CH₄ and selectivities of 90% for CO₂ reduction products were reached for complex [Ni(bpy-bNHCEt)][PF6]2 in acetonitrile. The experiments were conducted under visible-light irradiation using BIH as sacrificial electron donor (see section SEDs below).v

Advances and special progress

An exceptionally high TON of 570000 for the conversion of CO to CH₄ as well as a TON of 19000 for the conversion of CO₂ to CH₄ could be observed using an earth-abundant metal complex as a catalyst.

Additional remarks

The macrocyclic nickel carbene complex [Ni(bpy)-(MeNHC)2][PF6]2 gave a higher carbon-selective reduction percentage than the related complexes [Ni(bpy-bNHCEt)][PF6]2 and [Ni(bpy-bNHCMe)][PF6]2. The conversion of CO₂ to CO and methane as well as the conversion of a CO/H₂ atmosphere to methane were investigated with complex [Ni(bpy)-(MeNHC)2][PF6]2.

Content of the published article in detail

The article contains results for the reduction of CO₂ to CO and CH₄ and CO to CH₄ under visible-light catalysis using a nickel complex as a catalyst. The catalytic system performs best (referring to the TON of CH₄ production) in acetonitrile with a 1:1 CO/H₂ atmosphere.

Catalysts tested in this study

[Ni(bpy-bNHCMe)][PF6]2 [Ni(bpy)-(MeNHC)2][PF6]2 [Ni(bpy-bNHCEt)][PF6]2

Photosensitizer

Ir(ppy)3

Investigation

	cat	cat conc [µM]	PS	PS conc [mM]	e-D	e-D conc [M]	solvent A	additives	.	λexc [nm]	.	TON CO	TON CH4	TON H2	.	.
1.	[Ni(bpy-bNHCMe)][PF6]2	0.002	Ir(ppy)3	0.1	BIH	0.01	MeCN	TEA, H2O		solar spectrum		8000	5000	34000
2.	[Ni(bpy)-(MeNHC)2][PF6]2	0.002	Ir(ppy)3	0.1	BIH	0.01	MeCN	TEA 5% (v/v), H2O 2% (v/v)		solar spectrum			10000	58000
3.	[Ni(bpy-bNHCMe)][PF6]2	0.002	Ir(ppy)3	0.1	TEA		MeCN			solar spectrum		5000	1000	15000
4.	[Ni(bpy)-(MeNHC)2][PF6]2	0.002	Ir(ppy)3	0.1	BIH	0.01	MeCN	TEA		solar spectrum		108000	4000	278000
5.	[Ni(bpy)-(MeNHC)2][PF6]2	0.002	Ir(ppy)3	0.1	BIH	0.01	MeCN	TEA, H2O		solar spectrum		31000		320000
6.	[Ni(bpy-bNHCEt)][PF6]2	0.002	Ir(ppy)3	0.1	BIH	0.01	MeCN	TEA, H2O		solar spectrum		175000	19000	29000
7.	[Ni(bpy-bNHCEt)][PF6]2	0.002	Ir(ppy)3	0.1	TEA		MeCN			solar spectrum		9000		36000
8.	[Ni(bpy)-(MeNHC)2][PF6]2	0.002	Ir(ppy)3	0.1	TEA		MeCN			solar spectrum		130000	29000	4900000
9.	[Ni(bpy-bNHCMe)][PF6]2	0.002	Ir(ppy)3	0.1	BIH	0.01	MeCN	TEA		solar spectrum		76000		17000
10.	[Ni(bpy)-(MeNHC)2][PF6]2	0.002	Ir(ppy)3	0.1	BIH	0.01	MeCN	TEA 5% (v/v), H2O 2% (v/v)		solar spectrum			570000
11.	[Ni(bpy)-(MeNHC)2][PF6]2	0.002	Ir(ppy)3	0.1	BIH	0.01	MeCN	TEA, H2O		solar spectrum		51000	12000
12.	[Ni(bpy-bNHCEt)][PF6]2	0.002	Ir(ppy)3	0.1	BIH	0.01	MeCN	TEA		solar spectrum		310000		33000
13.	Molecule:100534	0.08		0.4								34000

Investigation-Name: Results for different electron donors and proton donorsExportRefresh

Further Information

The Supporting Information gives quantum yields for described experiments in Table 1.

Sacrificial electron donor

In this study, the experiments were done with the sacrificial electron donor BIH (100508).

Additives

In this study, triethylamine (TEA) and water (H2O) were used as additives.

photochemical CO2 reduction, nickel NHC catalyst, methane generation, CO reduction, iridium photosensitizer, BIH sacrificial donor, visible-light catalysis, solar fuels, artificial photosynthesis, homogeneous photocatalysis, high turnover numbers, acetonitrile solvent, triethylamine additive, photoredox chemistry, earth-abundant metal catalysis