A parallel array structured cobalt sulfide/nitrogen doped carbon nanocage/carbon fiber composite based on microfluidic spinning technology: a novel design to boost overall water splitting

Abstract

Constructing array structures for transition metal-based electrocatalysts is an effective approach to enhance the overall water splitting performance. However, compared with traditional disordered array structures, parallel array structures with an ordered arrangement for transition metal-based materials have been barely reported. Herein, via an innovative microfluidic spinning technology, we synthesized a parallel array structured Co₉S₈/nitrogen doped carbon nanocages/carbon fiber (p-Co₉S₈/NC/CF) composite electrocatalyst, where the composite fibers were precisely controlled to grow uniformly along the same direction. When applied as an electrocatalyst for the oxygen evolution reaction (OER), p-Co₉S₈/NC/CF exhibits superior activity and stability to the traditional disordered array structured counterpart (Co₉S₈/NC/CF) and the commercial RuO₂ catalyst. XAS analysis and DFT calculations confirm that the numerous unoccupied coordination Co–S bonds can optimize the adsorption of OH⁻ and the desorption of O₂ in the OER process, which can accelerate the rate-determining step (*OH → *O), consequently enhancing the OER performance. Furthermore, when applied in overall water splitting, the p-Co₉S₈/NC/CF‖p-Co₉S₈/NC/CF electrolyzer exhibits superior performance to the commercial Pt/C‖RuO₂ electrolyzer. This work provides an effective strategy for structural design through a novel preparation technology and offers a deep insight into structure engineering for transition metal-based electrocatalysts.