Electrochemically Driven Tandem In‐Plane Reduction and FeCl₃‐ Intercalation of Highly Crystalline Graphene Oxide Thin Films

The current design and understanding of graphene oxide (GO) and reduced GO (rGO) materials rely largely on insights derived from structurally defective and chemically inhomogeneous GO synthesized by Hummers’ method. As a result, this early‐stage knowledge fails to fully exploit the potential benefits of GO. This study explores electrochemical approaches using highly crystalline Brodie's GO for fabricating reduced GO (rGO)‐based transparent conductive films (TCFs) without using toxic reducing agents or heat treatment. The study first demonstrates an in‐plane electrochemical reduction method for fabricating rGO nanocoatings on plastic substrates. During this process, rGO at the rGO/GO/electrolyte three‐phase interface functions as a growing cathode, inducing tandem reduction parallel to the insulating substrate surface. The crystallinity of the GO precursor determines the activation or deactivation of the three‐phase interface at nanometer‐scale thickness. The electrochemical reduction of epoxide groups leads to a well‐extended π‐electron network with suppressed local strains and carbon vacancies. The sheet resistivity of rGO‐based TCFs is further optimized through hole doping via electrochemical FeCl 3 intercalation, breaking the transparency–resistivity limit of available rGO‐TCFs. These discoveries will facilitate the development of next‐generation green graphene processes based on precise synthetic chemistry.