Fabricating graphene hydrogels with controllable pore structure via one-step chemical reduction process

The porous graphene hydrogels (GHs) are of particular interest in various applications, such as energy-storage devices, catalyst and sensors. In this paper, GHs with controllable pore structure are prepared from graphene oxide (GO) aqueous dispersion by a facile chemical reduction method. The pore size distribution (PSD) and specific surface area (SSA) of GHs can be regulated by adjusting the pH value of GO dispersion. It is found that both the pore size and SSA of GHs gradually increase with the pH value of GO dispersion. For the GH prepared at pH = 1.65, the PSD has one peak at 1.83 nm with a SSA of 723.35 m2/g. As the pH value increases to 11.73, the peak moves to 3.2 nm and the SSA keeps rising to 1107.24 m2/g. Rheological measurements show that both the storage modulus and yield stress of the GHs decrease with the increasing pH value. Electrochemical evaluation of GHs as the electrodes of supercapacitors reveals that the specific capacitance reaches the highest value for GH prepared at pH = 5.25, which has a specific pore structure, showing the coexistence of large (3.2 nm) and small pores (1.89 nm).