Cobalt Sulfide Nanoparticles Encapsulated in Carbon Nanotube-Grafted Carbon Nanofibers as Catalysts for Oxygen Evolution

Designing multiple composite materials with hierarchical structures is an effective approach for enhancing the electrochemical properties of electrocatalysts owing to the synergistic effects and structural advantages of the components of materials. Herein, we report highly active electrocatalysts comprising CoS2 nanoparticles embedded in carbon nanotube (CNT)-grafted carbon nanofibers (CNF/CoS2–CNT) for the oxygen evolution reaction (OER). Catalysts with different sulfuration levels were synthesized by pyrolyzing ZIF-67 in a reducing hydrogen atmosphere, followed by an adjustable sulfuration process. The main advantages of the obtained hierarchical structure are as follows: first, the catalyst is embedded in CNTs in situ, achieving efficient electron transport; then, the CNT coating inhibits catalyst agglomeration during OER; finally, CNFs with a three-dimensional cross-linked nonwoven fabric structure can effectively anchor CNTs, avoiding agglomeration. The optimized CNF/CoS2–CNT catalyst exhibits a high electrolyte-accessible surface area, abundant mass diffusion pathways, and high structural integrity. It achieves a current density of 50 mA cm–2 at a low overpotential of 0.35 V for OER in a 1 M potassium hydroxide (KOH) solution. Remarkably, this catalyst also exhibits excellent stability in an electrochemical test containing a KOH solution. The findings indicate that CNF/CoS2–CNT catalysts with hierarchical structures could be potential electrode materials in advanced energy conversion devices.