Cobaloxime-Integrated Covalent Organic Frameworks for Photocatalytic Hydrogen Evolution Coupled with Alcohol Oxidation

We report an azide-functionalized cobaloxime proton-reduction catalyst covalently tethered into the Wurster-type covalent organic frameworks (COFs). The cobaloxime-modified COF photocatalysts exhibit enhanced photocatalytic activity for hydrogen evolution reaction (HER) in alcohol-containing solution with no presence of a typical sacrificial agent. The best performing cobaloxime-modified COF hybrid catalyzes hydrogen production with an average HER rate up to 38 & mu;mol h-1 in ethanol/phosphate buffer solution under 4 h illumination. Ultrafast transient optical spectroscopy characterizations and charge carrier analysis reveal that the alcohol contents functioning as hole scavengers could be oxidized by the photogenerated holes of COFs to form aldehydes and protons. The consumption of the photogenerated holes thus suppresses exciton recombination of COFs and improves the ratio of free electrons that were effectively utilized to drive catalytic reaction for HER. This work demonstrates a great potential of COF-catalyzed HER using alcohol solvents as hole scavengers and provides an example toward realizing the accessibility to the scope of reaction conditions and a greener route for energy conversion. An azide-functionalized cobaloxime proton-reduction catalyst covalently tethered into the Wurster-type covalent organic frameworks is developed for achieving the enhanced photocatalytic activity for hydrogen evolution in alcohol-containing solutions without any sacrificial agent.+image

Automated summary

We report the covalent tethering of an azide-functionalized cobaloxime proton-reduction catalyst into Wurster-type covalent organic frameworks (COFs), which enhances the photocatalytic activity for hydrogen evolution in alcohol-containing solutions without sacrificial agents. The alcohol contents function as hole scavengers, oxidized by the photogenerated holes of COFs to suppress exciton recombination and improve the utilization of free electrons for catalytic reaction.