A correlation of the hydrogen evolution reaction activity to the defects formed by the decomposition of doped phosphorus species in carbon nanotubes

The phosphorus-doped carbon materials as one of novel carbon catalysts towards the hydrogen evolution reaction (HER) have attracted considerable attention over the past years. However, the role of C-P species palyed in the HER activity is still not clear up to now. Phosphorus-doped carbon nanotubes (P-CNTs) were prepared by chemical vapor deposition and annealed at 900, 1000 and 1200 ℃ to remove all or parts of phosporus species, resulting in four samples with different proportions of graphite-, pyridine- and pyrrole-like P species. The correlations between their HER activity and the contents of three types of P species were investigated. Results showed that the content of graphite-like P decreased with the annealing temperature and no graphite-like P was retained at 1200℃. The HER activity increased with the annealing temperature and the one annealed at 1200 ℃ had the highest HER activity in an acid medium with an overpotential of 0.266 V at a current density of 10 mA/cm−2. Density functional theory calculations revealed that the pentagon- and nine-membered ring defects formed by the destruction of graphite-P species contributed mainly to the HER activity, which gave a deep insight into the active sites for HER.