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

Abstract

Designing\nmultiple composite materials with hierarchical structures\nis an effective approach for enhancing the electrochemical properties\nof electrocatalysts owing to the synergistic effects and structural\nadvantages of the components of materials. Herein, we report highly\nactive electrocatalysts comprising CoS₂ nanoparticles embedded\nin carbon nanotube (CNT)-grafted carbon nanofibers (CNF/CoS₂–CNT) for the oxygen evolution reaction (OER). Catalysts with\ndifferent sulfuration levels were synthesized by pyrolyzing ZIF-67\nin a reducing hydrogen atmosphere, followed by an adjustable sulfuration\nprocess. The main advantages of the obtained hierarchical structure\nare as follows: first, the catalyst is embedded in CNTs <i>in\nsitu</i>, achieving efficient electron transport; then, the CNT\ncoating inhibits catalyst agglomeration during OER; finally, CNFs\nwith a three-dimensional cross-linked nonwoven fabric structure can\neffectively anchor CNTs, avoiding agglomeration. The optimized CNF/CoS₂–CNT catalyst exhibits a high electrolyte-accessible\nsurface area, abundant mass diffusion pathways, and high structural\nintegrity. 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\n(KOH) solution. Remarkably, this catalyst also exhibits excellent\nstability in an electrochemical test containing a KOH solution. The\nfindings indicate that CNF/CoS₂–CNT catalysts with\nhierarchical structures could be potential electrode materials in\nadvanced energy conversion devices.