Light-Driven Reduction of CO2 to CO in Water with a Cobalt Molecular Catalyst and an Organic Sensitizer

We report an efficient visible light-driven CO2 reduction system that functions in water and without any noble metal nor rare materials. Using the cobalt complex [Co(qpy)(OH2)2]2+ (1, qpy = 2,2 ':6 ' ,2 '':6 '' ,2'-quaterpyridine) as a catalyst, an organic triazatriangulenium (TATA+) salt as the photosensitizer (PS), BIH + TEOA (BIH = 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]-imidazole and TEOA = triethanolamine) as the sacrificial reductant (SD), CO and formate were first produced with a total TON >3700 upon irradiation in CO2- saturated CH3CN solution with visible light. Upon the addition of a weak Bro''nsted acid (water), catalysis was enhanced and directed toward CO production (19,000 TON, 93% selectivity). The photocatalytic system was further shown to function in pure water as a solvent. High metrics with a TON for CO of 2600 and 94% selectivity were obtained using TEA (triethylamine) as the SD.

Automated summary

We present an efficient visible light-driven CO2 reduction system that operates in water without the use of noble metals or rare materials. By employing a cobalt complex as a catalyst, an organic triazatriangulenium salt as a photosensitizer, and BIH + TEOA as a sacrificial reductant, we achieved CO and formate production with high selectivity and total turnover numbers exceeding 3700. The addition of a weak Brönsted acid further improved the catalysis, resulting in a selectivity of 93% and a total turnover number of 19,000 for CO production. The photocatalytic system demonstrated excellent performance even in pure water, with a turnover number of 2600 and a selectivity of 94% using TEA as the sacrificial reductant.