Assembling Ni-Co phosphides/carbon hollow nanocages and nanosheets with carbon nanotubes into a hierarchical necklace-like nanohybrid for electrocatalytic oxygen evolution reaction.

Currently, designing and developing high-performance, cost-effective yet stable electrocatalysts for oxygen evolution reaction (OER) is a challenging task owing to the existing high overpotential and sluggish OER kinetics. Herein, we successfully fabricated a hierarchical necklace-like nanohybrid via assembling Ni-Co mixed metal phosphides/carbon (NiCoP/C) hollow nanocages and nanosheets with carbon nanotubes (CNTs). It was revealed that Ni-Co-layered double hydroxide/carbon hollow nanocages and nanosheets derived from Co-based MOF polyhedrons (ZIF-67) could pass through CNTs and perpendicularly anchor onto the surface of CNTs, respectively, thus finally constructing a hierarchical CNTs@NiCoP/C nanohybrid via further low-temperature phosphorization. The as-assembled CNTs@NiCoP/C electrocatalyst exhibited promising electrocatalytic performance towards OER with a low overpotential of about 0.297 V for reaching a current density of 10.0 mA cm-2 and a low Tafel slope of 57.35 mV dec-1 in 1.0 M KOH owing to the advantages of its unique superstructure and multiple composition. Furthermore, the present CNTs@NiCoP/C also possessed good long-term operation stability. This synthesis strategy involving the combination of transition metal phosphides and CNTs to form hierarchical nanostructures holds promising potential for designing highly OER-active electrocatalysts.