Porous NiOx nanostructures templated by polystyrene-block-poly(2-vinylpyridine) diblock copolymer micelles

Abstract

A facile synthetic route to NiO_x nanostructures using various amphiphilic polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) diblock copolymers as templates was investigated. The synthesis targets NiO_x 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 use in dye-sensitized solar cells or in (photo-)catalytic systems. The complete synthetic process to NiO_x 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 NiO_x 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⁻¹ is comparable to the value for conventionally obtained NiO_x 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 a photo-electrode. The presented route to porous NiO_x is easy and provides superior control over the morphology of the intermediates involved in nanostructure formation.