Tuning the structure, morphology, and electronic state is of great significance to achieve highly efficient hydrogen evolution reaction (HER) electrocatalysts. In this work, we originally develop a silk-cocoon structured S-rich cobalt polysulfide (CoSx, x ≈ 3.9) catalyst with extremely high HER activity through a facile hydrothermal process. The formation mechanism of the silk-cocoon structured CoSx has been systematically studied and the key factors in the formation of this structure are discussed. Such a nanostructured catalyst has hollow spheres that are interwoven by numerous sub-10 nm nanofibers to form into a three-dimensional conductive network by connection of micrometer long nanofibers. The silk-cocoon structured CoSx shows excellent HER activity with an onset potential of 0 V vs. a reversible hydrogen electrode and a Tafel slope of 41 mV dec−1. The activity is much higher than that of the reported metal sulfide materials and is even comparable to commercial Pt/C. Moreover, the overpotential to yield a current density of 10 mA cm−2 is only 42 mV. We ascribe the high HER activity to the S-rich sites and the conductive silk-cocoon structure, which can benefit the charge transfer of the material. Thus, this work provides a guiding strategy for synthesis of nanostructured transition metal polysulfides with enhanced HER catalytic performance.
