Immobilization of NiCo Nanoparticles into N-Doped Carbon Nanotube/Nanofiber Integrated Hierarchically Branched Architectures toward Efficient Overall Water Splitting.

Exploring cost-effective and high-performance bifunctional electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is of paramount importance for the advancement of H production technology, yet remains a huge challenge. Herein, a simple electrospinning-pyrolysis strategy is developed to directly immobilize uniform NiCo nanoparticles into a hierarchical branched architecture constructed by in situ formed N-doped carbon-nanotube-grafted carbon nanofibers. The elaborate construction of such hybrid hierarchical architecture can effectively modulate the electronic structure of the active sites, enlarge the exposure of active sites, and facilitate the electron transfer and mass diffusion, favoring both the HER and OER. As a result, the optimized catalyst requires relatively low overpotentials of 114 and 243 mV for HER and OER, respectively, to deliver a current density of 10 mA cm in 0.1 m KOH electrolyte. When employed as a bifunctional catalyst for overall water splitting, the resultant catalyst shows a low cell voltage of 1.57 V to achieve a current density of 10 mA cm, along with an impressive stability without noticeable attenuation even after 27 h. This work presents a successful demonstration in optimizing the electrocatalytic performance of Ni-based bifunctional electrocatalysts by simultaneously considering modulation of electronic structure, hybridization with carbon substrate, and nanostructuring through a facile synthetic strategy, which provides a new avenue to the design of a rich variety of robust transition-metal-based electrocatalysts for large-scale water electrolysis.