Indirect Laser-Mediated Halogenation of Graphene: Implications for Hydrogen Evolution Reaction.

Laser-assisted functionalization has emerged as a versatile route for patterning and chemical modification of two-dimensional (2D) materials, particularly graphene. However, conventional direct laser processing often induces severe photothermal damage, generating lattice defects that compromise charge transport and limit performance in applications such as electrocatalysis, sensing, and optoelectronics. We present an indirect laser-assisted functionalization strategy that prevents lattice defect formation while allowing covalent halogenation of graphene. N-chlorosuccinimide (NCS) and N-bromosuccinimide (NBS) precursors are selectively irradiated with a 455 nm pulsed laser, generating reactive halogen radicals that diffuse toward the graphene surface and form covalent functionalization without direct exposure of the graphene lattice to the laser. Raman and X-ray photoelectron spectroscopy confirm efficient covalent halogenation. The preserved graphene framework maintains high carrier mobility while introducing catalytically active sites, yielding a 2-fold reduction in overpotential and Tafel slope for the hydrogen evolution reaction compared to pristine graphene. This indirect, radical-mediated pathway provides a generalizable framework for laser-driven, defect-controlled functionalization of graphene and other 2D materials.