An All-Solid-State Ti/RuO_x pH Electrode Prepared Based on the Thermal Oxidation Method

The development of all-solid-state precise pH electrodes holds significant importance in various fields, particularly in marine scientific research. To achieve this goal, we proposed a novel fabrication technique for an all-solid-state ruthenium oxide (Ti/RuO_x) pH electrode. We thin-coated the RuCl₃ precursor solution on a titanium wire substrate using a heat gun repeatedly and then calcined it in a mixture of Li₂CO₃ and Na₂O₂ at 400 °C to obtain a ruthenium oxide (RuO_x) film. This RuO_x film was subjected to acid treatment with dilute nitric acid, and a polytetrafluoroethylene heat shrink tube was wrapped around the non-RuO_x film area. Finally, the RuO_x film was fully immersed in a pH 4.00 buffer solution, finalizing the electrode preparation. The RuO_x film exhibits a dense and regular conical morphology. The Ti/RuO_x electrode demonstrates a good near-Nernstian response slope (e.g., -59.04 mV/pH at 25 °C), high linearity (e.g., R² = 0.9999), rapid response (<1 s), low hysteresis (<3 mV), excellent reversibility, and good repeatability in the pH range of 2.00-10.00. After full hydration, the Ti/RuO_x electrode shows a potential drift of 8.5 mV and a drift rate of approximately 0.27 mV/day over a period of 25 days, indicating good long-term stability. Furthermore, the Ti/RuO_x electrode exhibits robust resistance against interference from various ions and low-concentration redox substances, ensuring a long storage life (at least 280 days), and high measurement accuracy (e.g., ± 0.02 pH units) for diverse water samples, including seawater, freshwater, and tap water. This study has evaluated the potential of the Ti/RuO_x electrode as a reliable and accurate tool for pH measurements in marine scientific applications.