Defect-dependent electrochemistry of exfoliated graphene layers

Graphene electrochemistry is dependent on the quality of produced graphene. Ultrasonic exfoliation of graphite in a solvent with aid of sodium salts is believed to be a convenient method to prepare high-quality graphene layers, although the effect of sodium salts on the yields of exfoliated graphene and electrochemistry of graphene have not been clearly clarified. Herein, different sodium salts (e.g., sodium citrate, sodium phosphate, and sodium pyrophosphate) with different anions are added during ultrasonic exfoliation of graphite in N-methyl-2-pyrrolidone (NMP). Sodium pyrophosphate improves the most efficiently the graphene yield and decreases the number of graphene layers, leading to the highest defect content. On these defect-rich graphene layers, the redox response of K3[Fe(CN)6] exhibits the fastest electron-transfer rate constant. Their active areas are also the largest, as revealed using rotating ring disk electrode and cyclic voltammetry. Moreover, the oxidation signals of biomolecules (e.g., dopamine, uric acid, xanthine, and hypoxanthine), phenolic pollutants (e.g., 4-chlorophenol and 4-nitrophenol), and toxic colorants (e.g., ponceau 4R and rhodamine B) are the mostly enhanced. This work proposes a novel way to synthesize defect-rich exfoliated 2D materials and further to construct universal interfaces for different electrochemical applications.