Combination of electrophoresis and electro-flocculation for the formation of adhering IrO2 pH sensing films

Abstract

We demonstrate a simple scheme to produce dense and adhering IrO2 thin films on ITO substrates via a bipolar pulsing process combining both electrophoresis and electro-flocculation. Our fabrication steps entail the synthesis of negatively-charged IrO2 nanoparticles in size of 3.5 nm using NaClO as an oxidizer in conjunction with Na3IrCl6, citric acid, and NaOH. Subsequently, multiple bipolar potentiostatic pulses are imposed in which alternating positive and negative potentials engender the electrophoresis of IrO2 nanoparticles, followed by their immediate coalescence facilitated by proton-catalyzed electro-floccu-lation. The resulting IrO2 thin films reveal impressive physical properties in surface uniformity, robust structural integrity, and strong adhesion to the substrate. The as-synthesized IrO2 thin film exhibits an amorphous nature with a pH sensing slope between -73.6 and -71.5 mV/pH, characteristic of super-Nernstian behavior. In contrast, the annealed IrO(2 )sample demonstrates a crystalline rutile phase with a pH sensing slope between -49.5 and -54.7 mV/pH, consistent with typical Nernstian response. Our approach provides a new route for the formation of strong and adhering oxide films from their colloidal constituents. (C) 2019 Elsevier Ltd. All rights reserved.