BACKGROUND: Non-precious metal based catalysts have become a hot research material due to their easy availability, low cost and outstanding electrochemical performance. Among them, carbon-based materials like carbon nanotubes and porous carbon with their own characteristics are especially favored by researchers in the field of catalyzing oxygen reduction. Therefore, rational construction of combining porous carbon with carbon nanotubes attracts great research attention on the object to utilize the excellent porosity, large specific surface area of porous carbon and the good electronic conductivity, high stability of carbon nanotubes to catalyze oxygen reduction. In this work, we synthesized two catalysts with different structure of coating carbon nanotubes with porous carbon by paralyzing a mixture of pre-prepared porous carbon, Co3O4 nanoparticles and melamine/glucosamine hydrochloride. Then the composites were applied to fuel cells as cathodic oxygen reduction reaction catalysts, which both exhibited good onset potential and excellent stability.
METHODS: Briefly, the porous carbon was prepared by heating the mixture of glucosamine hydrochloride and Co(NO3)2 6H2O under N2 flowing. Co3O4 nanoparticles were prepared by pyrolyzing cobalt nitrate-impregnated cotton wool. The CNTs/PC was synthesized by pyrolyzing the mixture of porous carbon, Co3O4 nanoparticles and melamine. The CNTs@PC was synthesized by pyrolyzing the mixture of porous carbon, Co3O4 nanoparticles and glucosamine hydrochloride. The cyclic voltammetry, liner sweep voltammetry and chronoamperometry measurements were analyzed to obtained the catalysis performance for oxygen reduction.
RESULTS: Through the rational design of catalyst structure, porous carbon and carbon nanotubes with different structures were constructed to expose more active sites on the surface of the sample. As a result, the onset potential of CNTs/PC and CNTs@PC are all at 0.9 V. After 20,000s chronoamperometry measurement, the current holding rate of CNTs/PC reached 95%, CNTs@PC was 94%, while Pt/C was only 77%. This shows that the prepared catalysts possess outstanding stability compared to Pt/C.
CONCLUSION: In this work, we synthesized two catalysts with different structure by paralyzing a mixture of pre-prepared porous carbon, Co3O4 nanoparticles and melamine/glucosamine hydrochloride, growing carbon nanotubes on the surface (CNTs/PC) and inside (CNTs@PC) of the porous carbon framework. The catalytic property of prepared CNTs/PC and CNTs@PC all possess good onset potential and excellent stability toward ORR. Therefore, a reasonable design of the catalyst structure is required to expose more active sites on the sample surface.