Ni-Co-MoS 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-MoSx, Co-MoSx, and Ni-MoSx) with ball-in-ball hollow structures have been synthesized by converting corresponding metal-glycerol spherical precursor with the assistance of (NH4)2MoS4 under a facile solvothermal condition. In this process, (NH4)2MoS4 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 (NH4)2MoS4 played an indispensable role in preparing the uniform hollow sphere with satisfactory morphology and catalytic performance. Noteworthily, compared with ternary Co-MoSx and Ni-MoSx, the quaternary Ni-Co-MoSx 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-MoSx counter electrode (CE), which was much superior to that of Pt CE (8.28%). Besides, Ni-Co-MoSx showed a low η10 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 H2SO4.