The superhydrophilic and superaerophobic properties and electron redistribution synergistically boost cobalt nanoparticle encapsulated N-doped carbon nanotube arrays electrode for the electrocatalytic overall water splitting performance

The development of efficient and stable transition metals (TMs)-based bifunctional electrocatalysts to enhance the hydrogen and oxygen evolution reactions (HER and OER) are critical yet extremely challenging for improving the energy conversion efficiency of overall water splitting (OWS). Thus, by skillfully constructing three-dimensional (3D) array structure and introducing heteroatom N with similar electronegativity to C, a series of self-supported electrodes composed of N-doped carbon nanotube (NCNT) arrays were synthesized via one-step calcination, in which Co was wrapped around the tip of NCNT (Co@NCNT/NF-x, where x = 50, 100, 150). Studies have demonstrated that the resulting Co@NCNT/NF-100 electrode displays the optimal electroactivities in HER (117 mV at 10 mA cm⁻²), OER (207 mV at 10 mA cm⁻²) and OWS (1.57 V at 10 mA cm⁻²) along with long-term stability exceeding 100 h. The oriented arrangement of NCNT arrays facilitates electrolyte permeation and bubbles escape, imparting superhydrophilic and superaerophobic features to the self-supported electrode. Theoretical simulations reveal that the introduction of N into the carbon skeleton can effectively regulate the electronic structure and optimize the adsorption free energy of key intermediates. This work clearly reveals the structure–activity relationship of Co@NCNT/NF-100 electrode and provides valuable insights for designing more advanced TMs-based bifunctional electrocatalysts.