The determination of the flat band potential of metal oxide nanoparticles is essential to understand their electrochemical behavior in aqueous environments. The electrochemical behavior determines the possible applications and governs the environmental impact of a nanomaterial. Hence, a new electrode fabrication method is demonstrated that allows determining the flat band potential of nanoparticles in porous nanoparticle electrodes via electrochemical impedance spectroscopy. In such electrodes, the electrolyte is in contact with the substrate material and contributes significantly to the ac response of the entire electrode. To block the substrate–electrolyte contact, the nanoparticle layers were imbibed in a liquid diacrylate monomer, followed by polymerization. To reestablish the contact between the outermost polymer-covered particles and the electrolyte, an O2 plasma treatment was conducted. Based on this new electrode fabrication procedure, the flat band potential of TiO2, WO3, and Co3O4 nanoparticles in porous electrodes was determined with high precision. We believe that this new and economical method will offer an alternative to expensive ultraviolet photoelectron spectroscopy measurements at synchrotron facilities.

A new method for the preparation of electrically conductive nanoparticle–polymer composite (NPC) films is shown in this work. These films are intended to be applied in displays. Thin layers of percolating nanoparticles in an organic polymer matrix are presented. First, a nanoparticle scaffold with high porosity is prepared. Subsequently, it is infiltrated with a monomer, which is finally polymerized. The formed composite is called an inverse nanocomposite, as the continuous percolating nanoparticle scaffold is formed first and mainly preserved during the whole process. Indium tin oxide (ITO) nanoparticles obtained from flame spray pyrolysis (FSP) are laminated onto a substrate. These porous scaffolds are infiltrated using liquid 1,6-hexanediol diacrylate (HDDA) as monomer. Restructuring of the particle network during the liquid imbibition caused by capillary forces leads to an increased electrical conductivity upon addition of the insulating organic monomer. A further and even stronger increase in the electrical conductivity was achieved after UV-curing of the HDDA-filled nanoparticle films, which is explained by the shrinkage forces of the organic phase during polymerization. With this new method, electrically conductive thin films for optoelectronical applications with almost the conductivity of pure ITO coatings can be produced.

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