Effect of methane concentration on oxygen reduction reaction of carbon films in alkaline solution

Carbon films have been prepared by the hot filament chemical vapor deposition method at different methane concentrations. The morphology, microstructure, and chemical bonding states of the deposited films were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The electrocatalytic oxygen reduction reaction (ORR) activity of these carbon catalysts in alkaline solution was investigated using rotating disk electrode (RDE) voltammetry. The experimental results show that the sp2/sp3 value increases with increasing methane concentration (MC), while the ID/IG value (integral area ratio of D and G band) gradually becomes larger and reaches the maximum at a MC of 3%, then decreases. With an increase in the MC, the ORR peak potential successively shifts to a more positive value and remains a constant at the MC of 3.5%. The peak current density consecutively increases to a summit at the MC of 3% and then begins to decrease. The onset potential shifts positively and the limiting diffusion current density at −1.0 V increases gradually, indicating that the catalytic activity towards ORR of the catalysts is progressively enhanced. When the MC is more than 3%, the catalytic activity begins to decay. Moreover, the catalysts with a better ORR activity have a poorer durability and methanol tolerance.