Studies On Co/N Doped Porous Carbon As Catalysts For Oxygen Reduction

As an efficient and environmentally friendly energy conversion devise, fuel cells have been paid much attention. One obstacle to fuel cell’s cosmic commercialization is the high price of platinum catalyst ued in the cathode. As a result, R&D of non-platinum electrocatalysts is of great imprtance. This work developed a kind of cheap, high-performance non-platinum catalyst for oxygen reduction reaction, discussed its catalytic mechanism and tested its performance in fuel cells.In this work, we prepared a carbon material containing nitrogen and cobalt through high-temperature annealing of glucose, urea and cobalt nitrate. This material has some catalytic activity to oxygen reduction. The introduction of nano-CaCO3 into the synthesis process led to porous carbon catalysts. The porous structure of catalysts could accelerate oxygen reduction reaction. But the introduce of nano-CaCO3 also led to the decrease of catalyst’s nitrogen content and catalytic activity. The method of washing away nano-CaCO3 between the two annealing process has been taken to solve this problem. This method futher accelerated oxygen reduction reaction. The influence of nano-CaCO3 to the catalysts has been verified by further contrast experiments. Also verified was that the three elements in the catalyst are all essential to the catalytic activity. Appropriate porous carbon structure, cobalt and high nitrogen content (especially pyridine nitrogen and graphitic nitrogen) are all responsible for the catalysts’high activity.Optimizing the preparation method such as heat treatment temperature, heating rate,the amount of nano-CaCO3 added, etc. could further increase the catalytic activity step by step. From the RDE LSV test, the limiting current density of this catalyst exceeds that of commercial 10 wt% Pt/C in both acid and alkaline electrolyte. The data also confirmed high selectivity of direct 4e-reaction of this catalyst The microstructure, surface composition and crystal texture in it were characterized by electron microscopy, poweder X-ray diffraction and X-ray photoelectron spectroscopy.This catalyst has been applied to the cathode of direct borohydride fuel cell. The fuel cell offers a highest power density of 80 mW cm-2 at 20 ℃, which also exceeds 10 wt% Pt/C. According to the particle size and pore diameter of the catalyst, a crushing process was applied to it. The particle size of the catalyst after curshing decreased. And the fuel cell using the crushed catalyst can export a higher power density of 86.8 mW cm-2.