Photocatalytic CO₂ Reduction Using Homogeneous Carbon Dots with a Molecular Cobalt Catalyst

A simple and precious-metal free photosystem for the reduction of aqueous CO₂ to syngas (CO and H₂) is reported consisting of carbon dots (CDs) as the sole light harvester together with a molecular cobalt bis(terpyridine) CO₂ reduction co-catalyst. This homogeneous photocatalytic system operates in the presence of a sacrificial electron donor (triethanolamine) in DMSO/H₂O solution at ambient temperature. The photocatalytic system exhibits an activity of 7.7 ± 0.2 mmol_syngas g_CDs ^-1 (3.6 ± 0.2 mmol_CO g_CDs ^-1 and 4.1 ± 0.1 mmol_H2 g_CDs ^-1) after 24 hours of full solar spectrum irradiation (AM 1.5G). Spectroscopic and electrochemical characterization supports that this photocatalytic performance is attributed to a favorable association between CDs and the molecular cobalt catalyst, which results in improved interfacial photoelectron transfer and catalytic mechanism. This work provides a scalable and inexpensive platform for the development of CO₂ photoreduction systems using CDs.