Electrochromic nickel oxide ion storage anodes compatible to tungsten oxide as cathode layer are prepared by a combustion reaction with urea as fuel and nickel nitrate as oxidizer at temperatures not higher than 230 °C to stay well within the temperature range in which thermally sensitive intercalated tungsten oxide layers are still stable. The precursors for nickel oxide are well available materials and the preparation of the layers can be performed at low energy input by spin-coating onto the substrate and moderate heating on a hot-plate. Ethanol and acetone where used as solvents and reveal large differences in the resulting film morphologies, electric and electrochromic characteristics. Cyclic voltammetry measurements in contact to lithium perchlorate (LiClO4) in propylene carbonate show remarkable colouration efficiencies at 550 nm of 47 cm2 C−1 for NiO prepared from ethanol solution and 92 cm2 C−1 for NiO prepared from acetone solution, which are, to the best of our knowledge, among the highest reported values for Li+-intercalation into NiO prepared at moderate substrate temperature reported so far. Graphic abstract

Thin, porous films of WO3 were fabricated by solution-based synthesis via spin-coating using polyethylene glycol (PEG), a block copolymer (PIB50-b-PEO45), or a combination of PEG and PIB50-b-PEO45 as structure-directing agents. The influence of the polymers on the composition and porosity of WO3 was investigated by microwave plasma atomic emission spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, X-ray diffraction, and gas sorption analysis. The electrochromic performance of the WO3 thin films was characterized with LiClO4 in propylene carbonate as electrolyte. To analyze the intercalation of the Li+ ions, time-of-flight secondary ion mass spectrometry, and X-ray photoelectron spectroscopy were performed on films in a pristine or reduced state. The use of PEG led to networks of micropores allowing fast reversible electrochromic switching with a high modulation of the optical transmittance and a high coloration efficiency. The use of PIB50-b-PEO45 provided isolated spherical mesopores leading to an electrochromic performance similar to compact WO3, only. Optimum characteristics were obtained in films which had been prepared in the presence of both, PEG and PIB50-b-PEO45, since WO3 films with mesopores were obtained that were interconnected by a microporous network and showed a clear progress in electrochromic switching beyond compact or microporous WO3.

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