Mixed potential type hydrogen sensor

The principle of potentiometric hydrogen sensors based on protonic conductors is reviewed. The origin of the potentiometric response in inert gas (Nernst potential) and in air (mixed potential) is discussed. It is shown that the nature of the sensing electrode as well as the morphology influence the mixed potential response. The properties of the solid-state internal reference electrode are also examined and discussed. A H⁺ reversible electrode based on quinhydrone is described. Then, an example of solid-state potentiometric hydrogen sensor is presented. The device incorporates a protonic polymer electrolyte based on polybenzimidazole, a Pt gas diffusion electrode or a Pt grid as sensing electrode and a reference electrode based on Ag-AgCl. The sensing characteristics in nitrogen and dry air are reported. Paper presented at the 9th EuroConference on Ionics, Ixia, Rhodes, Greece, Sept. 15 – 21, 2002.