Elucidating Charge Transfer Processes and Enhancing Electrochemical Performance of Laser-Induced Graphene via Surface Engineering with Sustainable Hydrogel Membranes: An Electrochemist's Perspective

Laser-induced graphene (LIG) has emerged as a promising solvent-free strategy for producing highly porous, 3D graphene structures, particularly for electrochemical applications. However, the unique character of LIG and hydrogel membrane (HM) coated LIG requires accounting for the specific conditions of its charge transfer process. This study investigates electron transfer kinetics and the electroactive surface area of LIG electrodes, finding efficient kinetics for the [Fe(CN)6]3-/4- redox process, with a high rate constant of 4.12 x 10-3 cm/s and an electroactive area 28 times higher than the geometric area. The impact of polysaccharide HM coatings (cationic chitosan, neutral agarose and anionic sodium alginate) on LIG's charge transfer behavior is elucidated, considering factors like Ohmic drop across porous LIG and Coulombic interactions/permeability affecting diffusion coefficients, estimated from amperometry. Experimental findings are supported by ab-initio calculations showing a electrostatic potential map’s negative charge distribution upon chitosan chain protonation, having an effect in over a two-fold redox current increase upon switching the pH from 7.48 to 1.73. This feature is absent for other studied HMs. It was also revealed that the chitosan's band gap was reduced to 3.07 eV upon acetylation, due to the introduction of a new LUMO state. This study summarizes the operating conditions enhanced by HM presence, impacting redox process kinetics and presenting unique challenges for prospective LIG/HM systems’ electrochemical applications.