Abstract

Fig. 1 | Structure of compounds used in this study. Cobalt complexes [Co2(biqpy)]4+ (1) and [Co(qpy)]2+ (2), molecular sensitizers ([Ru(phen)3]2+, Pheno) and

sacrificial reductant 1,3-dimethyl-2-phenylbenzimidazoline (BIH). Crystal structure of [Co2(biqpy)Cl(MeOH)(H2O)]3+.

Fig. 2 | Photocatalytic CO2 reduction products with [Co2(biqpy)]Cl4 as catalyst.

Fig. 3 | CV plots and infrared spectroelectrochemistry spectra. a, CVs of [Co2(biqpy)]Cl4 in MeCN; b, Infrared

spectroelectrochemistry experiment on [Co2(biqpy)]4+in the presence of 0.5 M TEA in MeCN under CO2; Inset, calculated

structure of the CO2-reduced complex adduct.

Fig. 4 | Proposed

mechanism

It is highly desirable to discover molecular catalysts with controlled selectivity for visible-light-driven CO2 reduction to fuels. In the design of catalysts employing earth-abundant metals, progress has been made for CO production, but formate generation has been observed more rarely. Here, we report a binuclear Co complex bearing a bi-quaterpyridine ligand that can selectively reduce CO2 to HCOO− or CO under visible light irradiation. Selective formate production (maximum of 97%) was obtained with a turnover number of up to 821 in basic acetonitrile solution. Conversely, in the presence of a weak acid, CO2 reduction affords CO with high selectivity (maximum of 99%) and a maximum turnover number of 829. The catalytic process is controlled by the two Co atoms acting synergistically, and the selectivity can be steered towards the desired product by simply changing the acid co-substrate.

2200 2100 2000 1900 1800 1700 1600

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

Ab

so

rban

ce

Energy (cm-1)

1635 cm-1

E = -0.35 V / -0.85 Vb)

0.0 -0.3 -0.6 -0.9 -1.2 -1.5 -1.8 -2.1-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0.30

+ 20% (v%) TEA under CO2

under CO2

under Ar

Potential / V vs SCE

Cu

rren

t/ m

A

a)