ORIGINAL PAPER New solid-state glass electrodes by using zinc oxide thin films as interface layer W. Vonau & F. Gerlach & U. Enseleit & J. Spindler & T. Bachmann Received: 22 January 2008 / Revised: 21 April 2008 / Accepted: 25 April 2008 / Published online: 22 May 2008 # Springer-Verlag 2008 Abstract Novel glass electrodes for the determination of cations with reversible internal solid contact are introduced. They are based on a semiconducting zinc oxide layer with a maximum thickness of 1 μm in contact with ion selective glasses on one side and with a metal layer on the other side. The metal oxide layer is thereby generated either by ultrasonic spray pyrolysis from zinc acetate solution, by electrochemical deposition from zinc nitrate solution or by spin coating from a dispersion of ZnO in an organic binder. A following activation in a palladium chloride solution allows the chemical reductive deposition of NiP as electronic conductor. Dipping-type and flow through electrodes as well as planar glass electrodes in thick film technology fabricated in the above-mentioned method are described. In this case gold electrodes are applied by screen printing on isolated steel substrates. The zinc oxide layers, created in different manners, are covered afterwards with cation selective glasses in thick film technology. They cause a stabilisation of the half-cell potentials of the all solid state indicator electrodes proved by suitable measurements. Keywords Glass electrode . Internal solid contact . Zinc oxide . Thick film technology Introduction For a long time the fabrication of so-called all-solid-state glass electrodes for the determination of cation activities has been a research objective. This is related to several drawbacks of conventional glass electrodes, such as position dependence when these electrodes are stored and used, pressure and temperature dependence, limitations concerning the miniaturisation and mechanical fragility. In the past there were different approaches for the construction of solid contacts for glass electrodes. These electrodes in their traditional setup with liquid internal electrolytes have been primarily used for pH measurements for a long period. For a considerable time such electrodes have also been available for the determination of activities of further monovalent cations [1]. Electrodes with solid state contacts have been made from metallised ion-conducting glasses (e.g. Corning 015, con- sisting of 72 wt% SiO 2 , 24 wt% Na 2 O and 6 wt% CaO) with discharge conductors consisting of silver [2, 3], amalgams [4] or alloys with low melting points [5, 6]. Glazing [7] and enamelling [8] of metallic base structures are also possible. Screen printing of pH glass on planar metal coated substrates is also described [9]. Last but not least, it was recommended to apply carbon black immobi- lised in polymers (e.g. elastomers) as contact material [10]. A main problem with metallised or carbon-coated oxide glass membrane electrodes is the lack of long-term stability of the half-cell potential owing to the irreversibility of charge J Solid State Electrochem (2009) 13:91–98 DOI 10.1007/s10008-008-0573-8 DO00573; No of Pages W. Vonau (*) : F. Gerlach : U. Enseleit Kurt-Schwabe-Institut für Mess und Sensortechnik e.V. Meinsberg, Kurt-Schwabe-Straße 4, 04720 Ziegra-Knobelsdorf, Germany e-mail: vonau@ksi-meinsberg.de U. Enseleit : J. Spindler : T. Bachmann Faculty of Mechanical Engineering, Hochschule Mittweida (FH) University of Applied Sciences, Technikumplatz 17, 09648 Mittweida, Germany