▎ 摘　　要

In this work, a new method is developed to synthesize an L-cysteine-based graphene oxide (L-Cy-rGO) electrocatalyst by a chemical synthesis approach. The electrocatalytic studies of L-Cy-rGO for the oxygen reduction reaction (ORR) and hydrazine oxidation reaction (HOR) have been demonstrated, as important fuel-cell oxidation and reduction reactions confirm its bifunctional nature. The electrochemical ORR performance of L-Cy-rGO is significantly improved with an onset potential of 0.77 V vs reversible hydrogen electrode (RHE) and a current density of -2.32 mA/cm(2) in O-2-saturated 0.5 M KOH electrolytes. The electrochemical impedance spectroscopy (EIS) and chronoamperometric (i-t) measurements of the electrocatalyst are also carried out toward determining the feasibility of electron transfer and current/potential stability at the interface. The L-Cy-rGO electrocatalyst shows excellent activity toward ORR in alkaline medium. Furthermore, L-Cy-rGO shows better electrocatalytic activity toward HOR at an onset potential of 1.01 V vs RHE and the maximum current density of 65 mA/cm(2) at a potential of 1.59 V vs RHE at 35 mu M hydrazine hydrate in 0.5 M KOH. The electrochemical studies show that the L-Cy-rGO exhibits the highest electrocatalytic activity toward hydrazine oxidation. Moreover, the L-cysteine-functionalized graphene oxide supporting material plays an excellent role that could be from their synergistic catalytic effect. The L-Cy-rGO electrocatalyst shows excellent electrochemical ORR and HOR performances due to the presence of S- and N-heteroatom-containing surface of GO that enhances the electrocatalytic activity and electron transfer capabilities toward the ORR. Morphological studies based on high-resolution transmission electron microscopy (HRTEM) confirm that the size of L-Cy-rGO is similar to 10 nm. X-ray photoelectron spectroscopy (XPS) analysis confirms the surface functionalization of GO by L-cysteine (L-Cy-rGO) from the binding energies of C-S, C-N, C-O, and C-C signals. Based on these findings, we find that the metal-free amino acid-functionalized carbon-based electrocatalyst shows excellent electrochemical ORR and HOR performances and demonstrate its key role toward enhancement in activities.