KCl-leakage-free reference electrode based on Ag2O–TeO2 glass and Ti

The primary objective of this study was to develop KCl-leakage-free reference electrodes for biomedical, clinical, and food applications, as well as for use in the semiconductor industry. Accordingly, we developed new reference electrodes based on Ag₂O–TeO₂ glass and Ti, employing Ag₂O–TeO₂ glass/Ti and Ti/Ag₂O–TeO₂ glass/stainless steel (SUS) configurations in particular. The investigations revealed that the pH sensitivity of 25Ag₂O·75TeO₂/Ti (3 %) was significantly lower than that of 25Ag₂O·75TeO₂/SUS (12 %). Ag₇Te₄ observed in Ti samples had a higher Te fraction than Ag₂Te observed in SUS samples. The stronger reducing ability of Ti compared to Fe in SUS facilitated the reduction of Te⁴⁺ ions to Te⁰, which subsequently reacted with Ag⁰. This observation supports the hypothesis that the pH sensitivity of Ag₇Te₄ is lower than that of Ag₂Te. Heat treatment of Ti on 25Ag₂O·75TeO₂/SUS resulted in a gray TiO₂/Ti layer surrounded by ocher-colored precipitates, including the Ag–Te alloy. Increasing the Ti content in Ti/25Ag₂O·75TeO₂/SUS reduced its pH sensitivity. A 1:2 Ti weight ratio achieved a pH sensitivity of 5 %, similar to 25Ag₂O·75TeO₂/Ti (3 %). Dividing Ti into three sections eliminated the central TiO₂/Ti layer, leaving only Ag–Te alloys and TeO₂ as the predominant materials. However, this structural modification had no discernible impact on the pH sensitivity. These findings suggest that Ag–Te alloys and TeO₂ can act as primary pH-responsive sites, with TiO₂/Ti having no significant contribution. Since TeO₂ likely has a higher electrical resistivity than Ag–Te alloys, the observed low pH sensitivity results from that of the minor but electrically conductive Ag–Te alloys. Therefore, 25Ag₂O·75TeO₂/Ti is a promising candidate for developing KCl-leakage-free reference electrodes for pH sensors, offering low pH sensitivity.