Thin solid state reference electrodes for use in solid polymer electrolytes

• Solid state reference electrode design with <10µm profile and >33% porosity.
• Both palladium hydride and iridium oxide reference electrode couples studied.
• Iridium oxide electrode shows the highest stability and accuracy.
• Direct positioning of reference electrode between working and counter electrode.
• Demonstration in a three electrode solid state cell and a fuel cell during start-up.

This paper reports two low-profile (~ 10 μm thick) solid state reference electrodes for use in solid polymer electrolytes. The thin, open geometry of the electrodes enables close positioning between the working and counter electrodes. The first electrode uses the palladium hydride (Pd|PdHx) couple (PHRE), and the second utilises the hydrous iridium oxide (IrOx·yH2O|IrOa·bH2O) couple (IORE). To our knowledge this is the first use of the latter as a reference electrode. The PHRE had a stable potential of + 70 mV vs RHE with a 4 mV h− 1 drift and two hour lifetime, whilst the IORE gave a potential of + 847 mV vs RHE with a drift of 0.3 mV h− 1 and no deterioration after 24 h of use. The use of these reference electrodes in a three-electrode solid state cell and a fuel cell is demonstrated.