Two-step coupled photoelectrochemical chlorination and oxygenation of C(sp3)–H bonds mediated by chlorine radicals over a modified BiVO4 photoanode

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 CoNi₂O_x chlorine evolution reaction (CER) catalyst. Under 1 sun illumination, the BiVO₄/TiO₂/CoNi₂O_x 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.