Chemical Vapor Deposition-Grown Nickel-Encapsulated N-Doped Carbon Nanotubes as a Highly Active Oxygen Reduction Reaction Catalyst without Direct Metal–Nitrogen Coordination

Abstract

Nickel-encapsulated nitrogen-doped carbon nanotubes (Ni–TiO 2 –NCNTs) are synthesized via chemical vapor deposition by thermal decomposition of acetylene with acetonitrile vapor at 700 °C on the Ni–TiO 2 matrix. TiO 2 is used as a dispersant medium for Ni nanoparticles, which assists in higher CNT growth at high temperatures. A reference catalyst is made by following the similar procedure without acetonitrile vapor, which is called a Ni–TiO 2 –CNT. Acid treatment of these two catalysts dissolved Ni on the surface of CNTs–NCNTs, producing catalysts with enhanced surface area and defects. The transmission electron microscopy–energy-dispersive X-ray spectra analysis of acid-treated version of the catalysts confirmed the presence of encapsulated Ni. Oxygen reduction reaction (ORR) activity of these catalysts was analyzed in 0.1 N KOH solution. Among these, the acid-treated Ni–TiO 2 –NCNT exhibited highest ORR onset potential of 0.88 V versus reversible hydrogen electrode and a current density of 3.7 mA cm –2 at 170 μg cm –2 of catalyst loading. The stability of the acid-treated Ni–TiO 2 –NCNT is proved by cyclic voltammetry and chronoamperometry measurements which are done for 800 cycles and 100 h, respectively. Primarily N doping of CNTs is the reason behind the improved ORR activity.

Low-Temperature Synthesized Pt3Fe Alloy Nanoparticles on Etched Carbon Nanotubes Catalyst Support Using Oxygen-Deficient Fe2O3 as a Catalytic Center for PEMFC Applications

“…For Pt 3 Fe-ECNT-1, this ratio is further increased to 1.21 with a clear downshift in the D- and G-band positions shifted to 1337 and 1586 cm –1 , respectively, because of the Pt–Fe formation over the ECNT surface. In addition, the D′-band arising in the samples indicates the introduction of more defect sites in the structure . The absence of any significant peaks in Region 1 of the Raman spectrum indicates the absence of any unreacted oxide traces in the samples, as observed from XRD studies.…”

“…In addition, the D′-band arising in the samples indicates the introduction of more defect sites in the structure. 36 The absence of any significant peaks in Region 1 of the Raman spectrum indicates the absence of any unreacted oxide traces in the samples, as observed from XRD studies.…”

“…Suitable catalyst supports help in the uniform dispersion of these catalyst nanoparticles and mitigates the detachment of these Pt catalysts due to Ostwald ripening, thus improving the stability. One-dimensional (1D) carbon nanotubes (CNT) are used as potential catalyst support for PEMFC due to their excellent chemical, electrochemical and thermal stability, good electrical conductivity, and appreciable surface area (SA) − Furthermore, unzipping of the one-dimensional (1D) nanostructure usually results in abundant edges and defects, which also change charge transfer properties . Defect-induced carbon supports can provide higher anchoring sites for catalyst nanoparticles than pristine ones .…”

Construction of Functionalized Carbon Nanofiber–g-C3N4 and TiO2 Spheres as a Nanostructured Hybrid Electrode for High-Performance Supercapacitors

“…This result indicates a considerable increase in the porosity of the hybrid catalyst as compared to pristine materials. The higher surface area and pore volume of the hybrid catalyst provide more reactive sites and transport paths; thereby the electrochemical performance could be enhanced . The surface areas and pore volumes of the catalysts are summarized in Table S1.…”

“…The higher surface area and pore volume of the hybrid catalyst provide more reactive sites and transport paths; thereby the electrochemical performance could be enhanced. 47 The surface areas and pore volumes of the catalysts are summarized in Table S1.…”