Determination of the Flat Band Potential of Nanoparticles in Porous Electrodes by Blocking the Substrate-Electrolyte Contact

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 O-2 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.