Increase in surface coverage by oxygen reduction reaction intermediates with increase in overpotential impeding diffusion of oxygen to the electrode surface.

Polymer electrolyte fuel cells exhibit high potentials at the cathode during start-stop cycles in automotive applications, which leads to carbon support corrosion, and concomitant loss of electrocatalytic activity. In this study, carbon nanomaterials (CNM), predominantly composed of nitrogen doped multi-walled carbon nanotubes (N-MWCNTs) with encapsulated cobalt nanoparticles, were synthesized in-situ by the solid-state pyrolysis (SSP) of melamine and cobalt Oxide (Co3O4). The best formulation of the catalyst exhibited an ORR activity of of 2.3 mA cm−2 at 0.75 V vs. RHE (4.6 mA mg−1). The role played by cobalt to complete the active site was demonstrated as follows: Upon complexing the cobalt site with bipyridine, the ORR onset potential decreased by ∼90 mV. The stability of the above non-precious metal (NPM) catalyst was studied through accelerated stress tests (ASTs) designed to mimic load cycling and start-stop cycling protocols, wherein the catalyst was exposed to high anodic potentials (up to 1.5 V vs. RHE) in an acidic medium. In rotating disk electrode mode, the ORR polarization curve shifted to more negative values by about 20 mV and 14 mV, respectively, after the load cycling and start-stop cycling AST protocols, suggesting high stability. Similar stability was observed in fuel cell mode.

Non-precious metal electrocatalysts obtained by pyrolysis of precursors of metal, nitrogen, and carbon (MNC) are viewed as an inexpensive replacement for platinum-based electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells. The hypothesized ORR active site structure of typical MNC catalysts consists of a transition metal coordinated to the pyridinic/pyrollic type of nitrogen covalently attached to the edges of the graphitic crystallites. One of the drawbacks of all the reported procedures to synthesize these MNC electrocatalysts is the inability to control the formation of a specific active site structure suitable for ORR. Lack of clarity on the active site structure limits the researcher's ability to design a synthesis methodology that maximizes the specific active site density. In this study, we have synthesized a Co(III) dimer ([Co 2 (OH) 2 (OOCCH 3 ) 3 (bpy) 2 ] NO 3 ⋅ 1.5 H 2 O) and demonstrated its ORR activity in alkaline medium. The ORR activity and methanol tolerance property of the Co(III) dimer were compared with those of Ketjenblack carbon (used as support for Co(III) dimer) and commercial 20 wt% Pt/C, respectively. Since Co(III) dimer is a molecular material, its characterization by single-crystal X-ray diffraction, nuclear magnetic resonance, and infrared studies revealed the chemical structure unambiguously. Density functional theory calculation predicted the possibility of both end-on and side-on oxygen adsorption at the metal center of the Co(III) dimer.

This study reports a synthesis of carbon supported graphitic carbon nitride (g-C3N4-KBC) obtained by pyrolysis of melamine with Ketjenblack 600JD carbon (KBC) at 550°C for 4 h in a N2 atmosphere. g-C3N4-KBC oxidizes hydrazine at an onset potential 0.145 V vs. SCE close to the thermodynamic standard potential of hydrazine (0.23 V vs. SHE). In comparison to the controls, KBC and g-C3N4, g-C3N4-KBC oxidizes hydrazine at lower overpotential.Most research has tended to focus on transition metal-based catalysts and few are of carbon material such as graphene nanoflakes, graphene oxide, and carbon nanotubes. A comparison in terms of sensitivity, detection range and stability reveals g-C3N4-KBC electrode’s superiority over other carbon material-based catalysts. To the best of our knowledge, the g-C3N4-KBC catalyst is not reported for sensing hydrazine in the literature.