Elucidating the chemical depth profile of laser-induced graphene electrodes

Various strategies are being explored to produce clean and renewable fuels and to efficiently convert their stored energy. Among emerging materials, metal-free three-dimensional (3D) hierarchical porous carbon structures have gained attention as promising candidates for electrocatalytic water splitting. In particular, laser-induced graphene (LIG) electrodes stand out due to their high stability, favorable electronic properties, low resistance, and large surface area. During LIG formation, the heat generated by laser irradiation breaks C–O, C=O, and C–N bonds, releasing gaseous products and promoting the rearrangement of carbon atoms into aromatic structures with sp² hybridization. One of the main challenges in advancing these materials lies in understanding their surface chemistry, especially the role of structural defects that enable their functionalization for various applications. In this work, the LIG electrode was fabricated using different laser powers at 100 mm.s^-1. These electrodes were characterized using synchrotron-based X-ray photoelectron spectroscopy (XPS). The chemical depth profiles were investigated by varying the incident photon energies from 100 to 1200 eV (i.e., kinetic energy). The results revealed a decrease in the intensity of the sp³ (C 1s) component and associated defects with increasing kinetic energy. Additionally, the contribution of the sp² (C 1s) component relative to the total oxygen content increases at higher kinetic energies. XPS quantification reveals not only variations in the surface and sub-surface chemical composition with different laser powers but also corresponding changes in the chemical depth profile. These findings highlight important aspects often overlooked when using such electrodes in practical applications, where surface chemistry plays a critical role.