Synthesis of Co9S8 nanoflakes by a one-step solvent-free solid-state method for multiple electrocatalytic reactions

Facile fabrication of two-dimensional nanostructures to expose more active sites is a critical factor in developing high-efficiency transition metal sulfide material catalysts. Herein, the one-step solvent-free solid-state method was developed to synthesize Co9S8 (denoted as S-Co9S8) with a nanoflake structure and much improved electronic conductivity, and the carbon substrate or template was not required. Benefiting from the unique properties, the overpotentials of S-Co9S8 catalysts have a decrease of 88.6 mV in acidic HER and 129.9 mV in alkaline OER at 10 mA cm(-2) when compared with 184.9 mV and 436.8 mV of Co9S8 prepared by the traditional hydrothermal reaction (denoted as H-Co9S8), respectively. These low overpotentials are close to the 26 mV of the state-of-art Pt/C (20%) and even slightly exceed the 313.5 mV of the commercial RuO2. The smaller Tafel slope and higher turnover frequency indicate the fast reaction kinetics of S-Co9S8 than that of H-Co9S8. In addition, the S-Co9S8 catalyst delivered a high specific capacitance of 823.8 mF cm(-2), 1.6 times higher than that of H-Co9S8, as well as impressive durability. Our findings provide a promising strategy for fabricating transition metal sulfide with the nanoflake structure and provide a multifunctional electrocatalyst.