Porous NiOx Nanostructures Templated by Polystyrene-block-poly(2-vinylpyridine) Diblock Copolymer Micelles

A facile synthetic route to NiOx nanostructures using various amphiphilic polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) diblock copolymers as templates was investigated. The synthesis targets NiOx nanostructures with a large surface area in order to allow an efficient functionalization, e.g., through loading with dyes to enable photo-induced hole injection for the use in dye-sensitized solar cells or in (photo-)catalytic systems. The complete synthetic process to NiOx contains several steps: (i) the dissolution of the diblock copolymer, (ii) the subsequent addition of Ni2+, followed by the formation of core-corona micelles and eventually, (iii) further addition of Ni2+, resulting in the formation of a macroscopic precipitate. In all cases, (iv) deposition onto different substrates and calcination yielded NiOx films. All intermediates were thoroughly investigated using scanning or transmission electron microscopy, dynamic light scattering, and UV-vis spectroscopy. In contrast to the well-established synthetic route via the commercially available Pluronic F108 triblock copolymer, in our case a variety of different morphologies was found, i.e. spherical particles, toroid structures, or networks. Furthermore, the obtained BET area of about 50 m²/g is comparable to the value for conventionally obtained NiOx surfaces. First dye sensitization experiments with coumarine 343 confirm that the dye binds to the surface, which is a prerequisite for using the material as photo-electrode. The presented route to porous NiOx is easy and provides superior control over the morphology of the intermediates involved in nanostructure formation.