Co9S8@N,S-codoped carbon core-shell structured nanowires: constructing a fluffy surface for high-density active sites

Developing earth-abundant catalysts to reduce reliance on noble-metal based ones in sustainable electrochemical processes is nowadays of great interest. Particularly, the rational structural design of electrocatalysts with high-density and well-exposed active sites is critically important to reach high catalytic activity. In this work, we have grown Co9S8 nanowires on carbon fiber paper via a hydrothermal route, and notably the Co9S8 nanowires are encapsulated in an unusual fluffy shell layer constructed using a continuous N,S-codoped carbon coating decorated with copious, vertically grown, short N,S-codoped carbon nanotube material. Such a nanowire/nanofluff combined structure provides not only many voids for rapid mass transfer, but also numerous specific surfaces for the loading of active sites, and it can be used well as a bifunctional catalyst in both oxygen evolution and hydrogen evolution reactions. Particularly, the obtained catalysts exhibit good oxygen evolution activity, showing a small overpotential of 290 mV to obtain a geometric current density of 10 mA cm(-2) in 1.0 M KOH electrolyte. Besides, the closely coated carbon layers also successfully prevent the Co9S8 nanowires from dissolution and recrystallization, thus leading favorably to good durability. Indeed, the reported fluffy carbon shell offers a novel structure design, with distinct advantages regarding the exposure of and access to high-density active sites, which can be extended to a variety of functional nanomaterials.