Construction of hierarchical yolk-shell nanospheres organized by ultrafine Janus subunits for efficient overall water splitting.

Although the bimetal sulfide is intensively pursued in catalytic systems, synthesis of ultrafine sized bimetal sulfide Janus subunits is still a great challenge. In this work, ultrafine NiS2/MoS2 Janus subunits organized on yolk-shell nanospheres (NSs) are synthesized by a novel and facile approach. The greatly reduced particle size of both two-dimensional MoS2 and one-dimensional NiS2 on the ultrafine NiS2/MoS2 Janus subunits endows the yolk-shell NSs with numerous intimate interfaces of bimetal sulfide hybrids greatly promoting the intimate electronic interaction and dissociation of water molecules. Benefiting from the ultrafine NiS2/MoS2 Janus subunits, abundant edge sites and the high density of interfaces, the as-prepared NiS2/MoS2 yolk-shell NSs exhibit high electrocatalytic activity with a low η10 value of 135 and 293 mV for the HER and OER, respectively. In addition, a low cell voltage (1.58 V) is achieved by using NiS2/MoS2 yolk-shell NSs as both anode and cathode. This study has significant indications in exploring the ultrafine nanoparticles for the water splitting reaction, fuel cells and organic synthesis.