Prussian blue-derived synthesis of uniform nanoflakes-assembled NiS2 hierarchical microspheres as highly efficient electrocatalysts in dye-sensitized solar cells

It's urgent and challenging to explore cost-effective and robust electrocatalyst in the development of large-scaled dye-sensitized solar cells (DSSCs). In this work, we develop a novel strategy to prepare 3D hierarchical NiS2 microspheres constructed by nanoflakes through a facile chemical etching/anion exchange reaction. Nickel-cobalt Prussian blue analogous (PBA) nanocubes and (NH4)(2)S are employed to initially produce uniform gamma-NiOOH/NiSx hierarchical microspheres, which were then converted to uniform 3D hierarchical NiS2 microspheres by a controlled annealing treatment. Due to their favorable structural features, the as-obtained NiS2 hierarchical microspheres possess large surface areas, high structural void porosity and accessible inner surface. All of these advantages facilitate the mass diffusion and charge transport between electrolyte and counter electrode material. As a result, the titled NiS2 hierarchical microspheres exhibit excellent electrocatalytic activity toward the reduction of I-3(-) ions in DSSCs. A typical DSSC with NiS2 achieves an impressive power conversion efficiency of 8.46% under AM1.5G illumination (100 mW cm(-2)), higher than that of pyrolysis Pt electrodes (8.04%). Moreover, the fast activity onset and relatively long stability further demonstrate that the NiS2 hierarchical microspheres are promising alternatives to Pt in DSSCs.