Phosphorus-doped NiCo2S4 nanocrystals grown on electrospun carbon nanofibers as ultra-efficient electrocatalysts for the hydrogen evolution reaction

The development of highly efficient noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER) is still a challenge nowadays. In this work, we prepared a highly active electrocatalyst containing phosphorus-doped NiCo2S4 nanocrystals grown on carbon nanotube embedded carbon nanofibers (P-NiCo2S4@CNT/CNF). The CNTs are involved in enhancing the electrical conductivity of the three-dimensional CNF network through a facile co-electrospinning method, which can facilitate electron transfer to the attached HER active material. Templated by this nanofiber network, the electroactive NiCo2S4 is confined to grow perpendicularly onto the CNT/CNF template via a hydrothermal reaction, thus exposing more catalytic active sites. Doping of P into the hybrid via a phosphidation reaction improves the electronic structure of the electroactive NiCo2S4, thus decreasing the energy barrier during the HER process. Owing to the synergistic effects from electrical enhancement and the nanostructured morphology, along with P-doping-induced optimization of the electronic structure, the P-NiCo2S4@CNT/CNF hybrid exhibits excellent HER performance, with an ultra-low onset overpotential (η) of 27 mV, a remarkable current density of 10 mA cm-2 at η as low as 74 mV, an impressive exchange current density of 0.79 mA cm-2 and excellent long-term durability. Furthermore, its electroactivity exceeds that of most reported noble-metal-free electrocatalysts and is comparable to that of Pt, suggesting its great potential as a highly efficient HER catalyst.