Wall thickness-tunable AgNPs-NCNTs for hydrogen peroxide sensing and oxygen reduction reaction

The nitrogen-rich carbon nanotubes doped with well-dispersed fine silver nanoparticles (AgNPs-NCNTs) were fabricated by carbonization of the silver-polydopamine (AgNPs-PDA) multilayers. The wall thickness of the nanotube is tunable by varying the numbers of the layer-by-layer alternate deposition of Ag and PDA on electrospun polystyrene (PS) fibers. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) demonstrate the tunable tubular structure by various AgNPs-PDA layers and the uniform distribution of fine silver nanoparticles with the size of about 6 nm in the nanotube. The composition of the nanocomposites was characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) demonstrate that the electrochemical properties of AgNPs-NCNTs depend on the numbers of AgNPs-PDA layers. The composite material shows excellent electrocatalytic activity to H2O2 reduction, with a low limit of detection (LOD) of 0.03 μM (S/N ≥ 3) and a sensitivity of 1004.9 μA mM−1 cm−2. Meanwhile, the AgNPs-NCNTs present a high catalytic activity to O2 reduction reaction with near 4-electron transfer process. The related catalysis mechanisms were proposed and validated by rotating disk electrode and dissolved oxygen analysis. This catalyst shows high stability for oxygen reduction over 500 cycles.