Halogen Cocatalysis in Electrocatalytic Systems

Renewable-energy-driven electrocatalysis represents a promising strategy for addressing environmental and energy issues as well as achieving net-zero carbon emissions. Halogens, including fluorine, chlorine, bromine, and iodine, are extensively employed in electrocatalytic systems as catalyst constituents, electrolyte components, or additive agents to exert cocatalytic effects that enhance electrocatalytic performance. However, the specific roles of halogens in electrocatalytic reactions remain elusive. This review provides an in-depth overview of the multifaceted cocatalytic roles of halogens in electrocatalysis, focusing on three aspects. i) Incorporating halogens into electrocatalysts as inactive components regulates the electronic and physical properties of the catalyst, thereby influencing the electrocatalytic performance. ii) Halogen-containing additives adhered to the catalyst layer enable manipulation of the catalytic surface electronic structure and the microenvironment at the electrode/electrolyte interface. iii) Halide ions in the electrolyte not only adsorb on the electrode surface to enhance electrocatalytic performance but are also oxidized to mediate the oxidation of small organic molecules. This process prevents overoxidation of reactants and enables the synthesis of valuable halogenated organic compounds. Finally, the remaining challenges and future opportunities in halogen-involved electrocatalytic system are discussed.