Ni-Co-MoSx ball-in-ball hollow nanospheres as Pt-free bifunctional catalysts for high-performance solar cells and hydrogen evolution reactions

Multi-shelled micro-/nanomaterials with complex hollow structures have been regarded as a promising kind of advanced catalysts for energy conversion owing to their large specific surface, increased active sites, and shortened paths of charge transfer. Herein, a series of double-shelled transition metal chalcogenides (Ni-Co-MoS x , Co-MoS x , and Ni-MoS x ) with ball-in-ball hollow structures have been synthesized by converting corresponding metal-glycerol spherical precursor with the assistance of (NH 4 ) 2 MoS 4 under a facile solvothermal condition. In this process, (NH 4 ) 2 MoS 4 acted as a multifunctional vulcanizator, which could conveniently afford Mo and S elements at the same time, and the mass ratio of the precursor to (NH 4 ) 2 MoS 4 played an indispensable role in preparing the uniform hollow sphere with satisfactory morphology and catalytic performance. Noteworthily, compared with ternary Co-MoS x and Ni-MoS x , the quaternary Ni-Co-MoS x ball-in-ball nanospheres demonstrated much enhanced catalytic properties in accelerating the reduction of triiodide in dye-sensitized solar cells (DSSCs) and the electrochemical hydrogen evolution reactions (HERs) due to the advantages of multi-elements, moderated surface texture, and larger surface area. Specifically, a prominent power conversion efficiency of 9.63% was achieved by the DSSC assembled with Ni-Co-MoS x counter electrode (CE), which was much superior to that of Pt CE (8.28%). Besides, Ni-Co-MoS x showed a low η 10 of 93.4 mV and a small Tafel slope of 55.0 mV dec −1 when employed as electrocatalysts for HER in 0.5 M H 2 SO 4 .