Selective visible light reduction of carbon dioxide over iridium(III)-terpyridine photocatalysts

• Main Authors: Wang, Chang-ting, Chen, Jinfan, Xu, Jiayuan, Wei, Fangfang, Yam, Chi Yung, Wong, Keith Man-Chung, Sit, Patrick H-L, Teoh, Wey Yang
• Format: Article
• Published: Elsevier Science Ltd 2021
• Subjects: Q Science (General); QD Chemistry
• Online Access: http://eprints.um.edu.my/33981/

The CO2 reduction reaction is an imperative piece of technology that closes the carbon cycle in many critical energy conversion and chemical manufacturing processes. Here, we report two new iridium (III) terpyridine-based photocatalysts capable of selective reduction of CO2 to CO under visible light (lambda >= 420 nm). The first photocatalyst, Ir-COOH], was functionalized with the carboxyl group on the phenylpyridine, whereas the second, Ir-PhCOOH], was attached to a phenyl spacer on the terpyridine. The Ir-PhCOOH] was characterized by a higher extinction coefficient than Ir-COOH], thus allowing more absorption of photons. Although both photocatalysts require two-electron activation, the Ir-PhCOOH] is more readily activated as a result of the more negatively charged Ir center. These photo catalysts show exclusive selectivities in the production of CO. The turnover frequencies for Ir-COOH] and Ir-PhCOOH] were 19 and 10 h(-1), respectively, under visible light irradiation. The e-e-H-H pathway was identified as the most favorable, consisting of the rate-limiting step in the conversion of *COOH to *CO, and where the barrier is significantly lower for Ir-PhCOOH] than for Ir-COOH]. (C) 2021 Elsevier Ltd. All rights reserved.