Effect of H2 on formation behavior of carbon nanotubes

Abstract

The effect of H2 gas on the carbon nanotubes (CNTs) synthesis with CO-H2 gas mixture was investigated using mass measurements and scanning electron microscopy (SEM). The maximum weight and yield of the synthesized carbon were obtained when the mixture ratio of H2: CO was 3 : 7 and 9 : 1, respectively. In case of 100% carbon monoxide (CO) without hydrogen (H2) addition, the weight of carbon increased, but CNTs were not observed. The CNTs began to be made when the contents of H2 reaches at least 10%, their structures became more distinct with an increase of H2 addition, and then the shapes of CNTs were more thin and straight. When the contents of H2 was 80% (H2 : CO = 8 : 2), the shapes and growth of CNTs showed an optimal condition. On the other hand, when the contents of H2 was higher than the critical value, the shapes of CNTs became worse due to transition into inactive surface of catalyst. It was considered that the inactive surface of catalyst resulted from decrease of carbon (C) and H2 concentration by facilitation of methane (CH 4) gasification reaction (C + 2H2 → CH4) between C and H2 gases. It was also found that H2 addition had an influence considerably on the shape and structure of CNTs.