Prussian blue-derived synthesis of uniform nanoflakes-assembled NiS 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 NiS microspheres constructed by nanoflakes through a facile chemical etching/anion exchange reaction. Nickel-cobalt Prussian blue analogous (PBA) nanocubes and (NH)S are employed to initially produce uniform γ-NiOOH/NiS hierarchical microspheres, which were then converted to uniform 3D hierarchical NiS microspheres by a controlled annealing treatment. Due to their favorable structural features, the as-obtained NiS 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 NiS hierarchical microspheres exhibit excellent electrocatalytic activity toward the reduction of I ions in DSSCs. A typical DSSC with NiS achieves an impressive power conversion efficiency of 8.46% under AM1.5G illumination (100 mW cm), higher than that of pyrolysis Pt electrodes (8.04%). Moreover, the fast activity onset and relatively long stability further demonstrate that the NiS hierarchical microspheres are promising alternatives to Pt in DSSCs.