Photocathode functionalized with a molecular cobalt catalyst for selective carbon dioxide reduction in water

Palas Baran Pati,Stéphane Jobic,Nicolas Barreau,Etienne Boutin,Marc Robert,Fabrice Odobel,Stéphane Diring,Ruwen Wang

doi:10.1038/s41467-020-17125-4

Abstract

Artificial photosynthesis is a vibrant field of research aiming at converting abundant, low energy molecules such as water, nitrogen or carbon dioxide into fuels or useful chemicals by means of solar energy input. Photo-electrochemical reduction of carbon dioxide is an appealing strategy, aiming at reducing the greenhouse gas into valuable products such as carbon monoxide at low or without bias voltage. Yet, in such configuration, there is no catalytic system able to produce carbon monoxide selectively in aqueous media with high activity, and using earth-abundant molecular catalyst. Upon associating a p-type Cu(In,Ga)Se2 semi-conductor with cobalt quaterpyridine complex, we herein report a photocathode complying with the aforementioned requirements. Pure carbon dioxide dissolved in aqueous solution (pH 6.8) is converted to carbon monoxide under visible light illumination with partial current density above 3 mA cm−2 and 97% selectivity, showing good stability over time.

Highlights

Artificial photosynthesis is a vibrant field of research aiming at converting abundant, low energy molecules such as water, nitrogen or carbon dioxide into fuels or useful chemicals by means of solar energy input
To the best of our knowledge, this work represents the first demonstration where a CIGS electrode has been successfully used for CO2 catalytic reduction
When combined with Co-qPyH molecular catalyst grafted on a titanium dioxide upper protective layer, good selectivity, activity, and negative overpotential were simultaneously obtained under visible-light illumination in neutral aqueous solution

Summary

Results

Long-term electrolysis at −0.51 V vs RHE (2 h) led to an average catalytic current of 1.2 mA cm−2 (Supplementary Fig. 5), and gas chromatography (GC) analysis of the products indicated formation of CO with 80% selectivity and 63% FE along with H2 as the by-product (entry 1, Table 1). Average current density of 0.90 and 3.25 mA cm−2 reported per geometric surface of m-TiO2 was obtained, under applying a bias potential of 0.14 and −0.06 V vs RHE, respectively (Supplementary Fig. 8b). When long-term photoelectrocatalysis experiment was carried out at a bias potential of −0.06 V vs RHE (entry 6, Table 1), an average current density of 0.8 mA cm−2 was recorded. It showed only a slight decay along the 2 h electrolysis (Supplementary Fig. 9). Electrolysis experiment was repeated with 13CO2, and analysis of products via GC/MS compared with experiments under 12CO2 confirmed that CO originated from CO2 (Fig. 6)

Discussion

Findings

Methods