2 research outputs found
Formation of Active Sites for Oxygen Reduction Reactions by Transformation of Nitrogen Functionalities in Nitrogen-Doped Carbon Nanotubes
Heat treating nitrogen-doped multiwalled carbon nanotubes containing up to six different types of nitrogen functionalities transforms particular nitrogen functionalities into other types which are more catalytically active toward oxygen reduction reactions (ORR). In the first stage, the unstable pyrrolic functionalities transform into pyridinic functionalities followed by an immediate transition into quaternary center and valley nitrogen functionalities. By measuring the electrocatalytic oxidation reduction current for the different samples, we achieve information on the catalytic activity connected to each type of nitrogen functionality. Through this, we conclude that quaternary nitrogen valley sites, N-Q<sub>valley</sub>, are the most active sites for ORR in N-CNTs. The number of electrons transferred in the ORR is determined from ring disk electrode and rotating ring disk electrode measurements. Our measurements indicate that the ORR processes proceed by a direct four-electron pathway for the N-Q<sub>valley</sub> and the pyridinic sites while it proceeds by an indirect two-electron pathway <i>via</i> hydrogen peroxide at the N-Q<sub>center</sub> sites. Our study gives both insights on the mechanism of ORR on different nitrogen functionalities in nitrogen-doped carbon nanostructures and it proposes how to treat samples to maximize the catalytic efficiency of such samples
Synthesis of Palladium/Helical Carbon Nanofiber Hybrid Nanostructures and Their Application for Hydrogen Peroxide and Glucose Detection
We report on a novel sensing platform
for H<sub>2</sub>O<sub>2</sub> and glucose based on immobilization
of palladium-helical carbon nanofiber (Pd-HCNF) hybrid nanostructures
and glucose oxidase (GOx) with Nafion on a glassy carbon electrode
(GCE). HCNFs were synthesized by a chemical vapor deposition process
on a C<sub>60</sub>-supported Pd catalyst. Pd-HCNF nanocomposites
were prepared by a one-step reduction free method in dimethylformamide
(DMF). The prepared materials were characterized by transmission electron
microscopy (TEM), X-ray diffraction (XRD), scanning electron microscopy
(SEM), and Raman spectroscopy. The Nafion/Pd-HCNF/GCE sensor exhibits
excellent electrocatalytic sensitivity toward H<sub>2</sub>O<sub>2</sub> (315 mA M<sup>–1</sup> cm<sup>–2</sup>) as probed
by cyclic voltammetry (CV) and chronoamperometry. We show that Pd-HCNF-modified
electrodes significantly reduce the overpotential and enhance the
electron transfer rate. A linear range from 5.0 μM to 2.1 mM
with a detection limit of 3.0 μM (based on the S/N = 3) and
good reproducibility were obtained. Furthermore, a sensing platform
for glucose was prepared by immobilizing the Pd-HCNFs and glucose
oxidase (GOx) with Nafion on a glassy carbon electrode. The resulting
biosensor exhibits a good response to glucose with a wide linear range
(0.06–6.0 mM) with a detection limit of 0.03 mM and a sensitivity
of 13 mA M<sup>–1</sup> cm<sup>–2</sup>. We show that
small size and homogeneous distribution of the Pd nanoparticles in
combination with good conductivity and large surface area of the
HCNFs lead to a H<sub>2</sub>O<sub>2</sub> and glucose sensing platform
that performs in the top range of the herein reported sensor platforms