Ta-ITO Coated Titanium Bipolar Plates for Proton Exchange Membrane Water Electrolyzers

Abstract A novel bi-layer coating composed of a tantalum base layer with an indium tin oxide (ITO) top layer was applied to titanium substrates. Samples were polarized ex-situ in a parameter study, where the pH, potential and temperature of the electrolyte was altered, as well as the polarization duration. The interfacial contact resistance (ICR) after polarization showed an increase with time for the first 24 hours, then stabilized at approx. 30 mΩ cm2. Minor variations were seen in the ICR after polarization at 1.4 VRHE and 2.0 VRHE, but after polarization at 2.5 VRHE and 2.6 VRHE, the ICR increased to 102 and 503 mΩ cm2, respectively. X-ray photoelectron spectroscopy analysis revealed that the oxygen to metal ratio on the tantalum- indium tin oxide coated sample surfaces increased with increasing polarization potential. The surfaces of the samples polarized at 2.5 and 2.6 VRHE showed lower concentrations of oxygen vacancies, an increase in hydroxides and a decrease in metallic character compared to the non-coated and baseline samples. ITO proved to be a promising candidate for use as coating on bipolar plates in proton exchange membrane water electrolyzers.