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 generation of Cl^• from chloride salt and activation of energy-demanding C(sp³)-H bonds, highlighting its great potential in advancing green chemical synthesis.