Co9S8-FeCoS2 Two-Phase Nanoparticles Anchored in N, S Co-Doped Honeycomb Carbon Spheres as Highly Efficient Bifunctional Oxygen Catalyst

Abstract Transition metal sulfides (TMS) are considered as candidate oxygen redox catalysts (OER/ORR) due to their high catalytic activity and reversible redox performance. The OER/ORR performance for TMS can be further improved through the multi-doped electrochemical active sites provided by the dual-metallic (Co,Fe) and dual-nonmetallic species (N,S). Herein, a Co9S8-FeCoS2 two-phase nanoparticle anchored in N, S co-doped honeycomb carbon sphere ((Co,Fe)S@N,S-HCS) is synthesized by a multistep process template method. It has been found that the (Co,Fe)S@N,S-HCS possesses a mesoporous structure with a highly graphitized carbon along with the key OER active site of Co9S8 and the major ORR active center of FeCoS2. Also, the synergistic effect of Co9S8-FeCoS2 two-phase nanoparticles can further enhance the activity of OER and ORR. The as-prepared (Co,Fe)S@N,S-HCS exhibits excellent bifunctional activity in alkaline media, with an OER overpotential as low as 310 mV at 10 mA cm-2 and good stability, which exceeds (Fe)S@N,S-HCS, (Co)S@N,S-HCS and the noble metal RuO2. Besides, the ORR activity exhibits a half-wave potential of 0.84 V, which exceed the other two single component sulfides and close to the commercial Pt/C. Therefore, this work provides a significant approach to prepare highly efficient and stable dual-TMS heteroatom modified carbon-based OER/ORR bifunctional oxygen catalyst.