Visible‐Light‐Driven CO₂ Reduction by Mesoporous Carbon Nitride Modified with Polymeric Cobalt Phthalocyanine

Abstract

The integration of molecular catalysts with low-cost, solid light absorbers presents apromising strategy to construct catalysts for the generation of solar fuels.H ere,w er eport aphotocatalyst for CO 2 reduction that consists of apolymeric cobalt phthalocyanine catalyst (CoPPc) coupled with mesoporous carbon nitride (mpg-CN x )a st he photosensitizer.T his precious-metal-free hybrid catalyst selectively converts CO 2 to CO in organic solvents under UV/Vis light (AM 1.5G, 100 mW cm À2 , l > 300 nm) with ac obalt-based turnover number of 90 for CO after 60 h. Notably,t he photocatalyst retains 60 %C Oe volution activity under visible light irradiation (l > 400 nm) and displays moderate water tolerance.The in situ polymerization of the phthalocyanine allows control of catalyst loading and is key for achieving photocatalytic CO 2 conversion.Photocatalytic reduction of CO 2 to produce storable fuels offers an attractive path to capture and utilize the greenhouse gas CO 2 and ultimately implement ac arbon-neutral energy cycle.T he development of efficient, sustainable,a nd economically viable catalysts and light-absorbers lies at the nexus of solar-fuel research on CO 2 utilization. Hybrid photosynthetic systems with molecular catalysts immobilized on solid supports (light-absorbing semiconductors or dye-sensitized semiconductors) have recently emerged as ap romising approach for suspension-based photoreactor applications, because they combine the selectivity of molecules with the durability of heterogeneous materials. [1] While many earth abundant metal based molecular complexes have been reported for CO 2 reduction in homogeneous solution, there are relatively few examples of heterogenization of these catalysts on solid light-absorbers. [2] Thed evelopment of new robust catalyst-photosensitizer interfaces remains achallenge that offers the key for improved photocatalytic activity of colloidal material-molecule hybrid systems.Graphitic carbon nitride (g-CN x )has recently emerged as ap romising semiconductor for photocatalytic applications, [3] including water splitting [4] and CO 2 reduction, [5] because of its nontoxicity,facile synthesis,capability to absorb UV as well as visible light, and durability under photochemical conditions. Ar elatively narrow band gap and sufficiently negative conduction band energy minimum (À1.10 Vv s. NHE at pH 6.6) [4b, 6] allow g-CN x to harvest UV/Vis light and subsequently reduce as urface-bound molecular catalyst via photoinduced electron transfer. In CN x -based photocatalytic systems for CO 2 reduction, different types of co-catalysts have been used, including weakly anchoring phosphonic acid functionalized Ru complexes or Ru-Re dyads, [6,7] molecular cobalt and iron complexes in solution, [8] metalloporphyrins covalently grafted on CN x , [9] single-atom cobalt sites incorporated in the material, [10] and sodium niobite nanowires. [11] Despite encouraging reports with CN x -porphyrin hybrid catalysts, [9,12] aC N x /molecular catalyst system that consists of only earth-abun...

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