Enhancing stability of Co9S8 by iron incorporation for oxygen evolution reaction and supercapacitor electrodes

The structural instability of Co9S8 often degrades its electrocatalytic activity during long-term cycling, and rationally enhancing its structural stability remains challenging for energy conversion and storage applications. In this work, the density functional theory was used to predict the stability of Co9S8. The calculated results showed that stability could be improved through Fe-doping at the octahedral site compared to pure Co9S8. To validate the theoretical results, several Fe-incorporated Co9S8 hollow spheres ((Co1-xFex)9S8) with different Co/Fe mole ratios were fabricated by a simple one-step hydrothermal method. The Mössbauer spectra indicated the preference of Fe replacement of Co at the octahedral site. The as-obtained (Co0.92Fe0.08)9S8 hollow spheres exhibited superior electrocatalytic performances with a low overpotential of 268 mV at the current density of 10 mA cm−2, as well as a smaller Tafel slope of 63.9 mV dec−1 and robust stability toward oxygen evolution reaction for 60 h. The resulting (Co0.94Fe0.06)9S8 hollow spheres also exhibited a high capacity of 454 F g−1 at 1 A g−1 and amazing cycling stability with 94.03% capacity retention after 5000 cycles. The superior electrochemical performances look promising and suggest the relevance of the proposed approach for the construction of future improved structures.