Non-enzymatic electrochemical detection of hydrogen peroxide on highly amidized graphene quantum dot electrodes

An efficient infrared (IR)-assisted technique is developed to synthesize highly amidized graphene quantum dots (GQDs) as a metal-free catalyst for electrochemically detecting hydrogen peroxide. Through the IR-assisted pyrolysis of urea and citric acid at different chemical ratios, the GQDs with very high amidation level (N/C atomic ratio: 23-46 at. %) are synthesized, composed of pyrrolic/pyridinic N, graphitic N, and N-oxide functionalities. Through various electrochemical diagnostics, it is confirmed that highly amidized GQD electrodes enable high catalytic activity toward H2O2 reduction. The catalytic cycle includes the adsorption of H2O2 and two-stage charge transfer steps on highly amidized GQD catalyst, where the substitutional N atoms (i.e., pyridinic N) at the edge of carbon network provide additional electroactive sites for adsorbing H2O2. The amperometric investigation followed by a rigorous linear regression analysis confirms a high selectivity of 1.83 mu A mM(-1) cm(-2) toward H2O2 detection within the concentration range of 0.5-40 mM. The major attributes of the GQD catalytic electrodes include high sensitivity, wide detection range, fast response time, and superior selectivity. Accordingly, the robust design of GQDs developed in this work paves the way for engineering highly selective catalyst as a robust electrochemical sensor for non-enzymatic H2O2 detection at ultra-low concentrations.