Tuning the Electronic Properties of Robust Bio-Bond Graphene Papers by Spontaneous Electrochemical Reduction: From Insulators to Flexible Semi-Metals

The novel approach to chemically tuning the electronic properties of bio-bond graphene paper suggested here allows for the facile fabrication of large area, flexible, robust, and highly conductive films. A layer of anodic metal deposited on the surface of the initial laminated graphene oxide-silk films with micrometer thickness is used to initiate the fast and spontaneous electrochemical reduction of graphene oxide to the electrically conductive states at predetermined depths under ambient conditions. By controlling the reaction conditions, a wide range of conductivities from those common for semiconductors to semimetals can be achieved at different stages of the defect-removal process. Ultimately, the electrical conductivity can be increased over 6 orders of magnitude from similar to 1 x 10(-2) S/m for pristine bio-bond graphene oxide paper up to 1.5 x 10(4) S/m for a fully transformed film. The conductivity achieved using this environmentally friendly technique is by far the highest among the reduced graphene oxide papers, and moreover, the mechanical performance and bending resilience of the films remains extremely high. We propose that the mechanism responsible for this process involves the balance of the internal potential drop due to the electric resistance of graphene oxide layers and the diffusion of oxygen containing species to the reactive interface. This electrochemical reduction technique is facile, conducted at ambient conditions, and adaptable for large-scale fabrication of the robust, and lightweight thin film for flexible electronic devices for sensing, energy storage, and wearable electronics where the charge transportation characteristics and great mechanical robustness are critical.