Discrete Cu-Metalloporous Polycarbazole as a Nanoelectromediator for Effective Electrocarboxylation of Benzyl Bromide with CO₂

The electrochemical fixation of carbon dioxide (CO 2 ) into organic halides is one of the most prominent strategies for mitigating atmospheric CO 2 emission, along with the difficulties associated with the toxic and carcinogenic halogenated compounds. Cu-based nanomaterials have been explored for numerous applications in nanotechnology, including electrocatalysis, organic catalytic transformations, and photocatalysis. In this work, we have designed and developed a Cu-embedded carbazole-derived porous organic polymer ( Cu@Cz-POP ) nanohybrid by utilizing the Friedel–Crafts alkylation approach and employing 1,4-dimethoxybenzene as the cross-linking agent comprising unique characteristic features of the extended π-conjugated system along with an active metal center with tunable electrochemical properties. The Brunauer–Emmett–Teller surface area of the conjugated Cz-POP is found to be 1060 m 2 g –1 . The X-ray photoelectron spectroscopy (XPS) study demonstrates the formation of CuO nanoparticles in the polymeric framework. X-ray absorption fine structure analysis (EXAFS) also reveals the existence of CuO with a smaller fraction of Cu in the polymeric framework, which is corroborated with the XPS analysis. The Cu@Cz-POP nanohybrid is fabricated by drop-casting over a Ni foam, showing promising electrocatalytic activity toward electrocarboxylation of benzyl bromide in 0.1 M TBA·BF 4 /CH 3 CN with saturated CO 2 medium with a current density of 120 mA cm –2 delivering 65% yield of phenylacetic acid ( PAA ) as the primary product along with traces of benzyl 2-phenylacetate ( BPA ) and 1,2-diphenylethane ( DPE ), and the turnover frequency is found to be 8.556 × 10 –7 s –1 . Density functional theory calculations demonstrate that CuO is adsorbed more favorably at the N1 nitrogen atom of Cz-POP . An electron transfer from the N1 atom and the aromatic rings of Cz-POP to the CuO center is observed and confirmed by the overlap of alpha orbitals.