Two-step coupled photoelectrochemical chlorination and oxygenation of C(sp³)–H bonds mediated by chlorine radicals over a modified BiVO₄photoanode

Abstract

Photoelectrochemical (PEC) cells are emerging tools for fine chemical synthesis, but often suffer from low solar-to-product conversion efficiency, especially in energy-demanding reactant activation. Herein, we report chlorination and oxygenation of energy-demanding C(sp3)–H bonds using a two-step coupled PEC cell, avoiding the direct generation of high-energy chlorine radicals (Cl˙). The photoanode consists of a BiVO4 semiconductor modified with TiO2 and a CoNi2Ox chlorine evolution reaction (CER) catalyst. Under 1 sun illumination, the BiVO4/TiO2/CoNi2Ox photoanode showed a photocurrent density of 2.9 mA cm−2 for CER at 0.8 V vs. the reversible hydrogen electrode (RHE) with the highest applied bias photon-to-current efficiency of 3.20%. Subsequent homolysis of Cl2 under white light generates Cl˙, activating C(sp3)–H bonds following hydrogen atom transfer. The PEC cell selectively chlorinated hydrocarbons under argon, and enabled oxygenation to afford aldehydes, ketones, and alcohols when the atmosphere was switched to dioxygen, offering a green and efficient synthetic approach. Studies on the reaction mechanism revealed that Cl˙ is the key reactive intermediate responsible for C(sp3)–H bonds activation. This work offers a solar-driven energy-efficient strategy for the generation of Cl˙ from chloride salts and activation of energy-demanding C(sp3)–H bonds, highlighting its great potential in advancing green chemical synthesis. Show more