Electrolyte-gated SrCoO_x FET sensor for highly sensitive detecting pH in extreme alkalinity solution

The pH monitoring is significantly important in chemical industry, biological process, and pollution treatment. However, it remains a great challenge to measure pH in extreme alkalinity conditions. Herein, we employ an electrolyte-gated field-effect-transistor (FET) strategy using non-stoichiometric SrCoO_x with rich oxygen-vacancy defects as channel materials for detecting extreme alkalinity. The corresponding channel can provide effective oxygen-ion-migration sites for reversible transformation of OH⁻ ↔ O²⁻ + H⁺ driven by electric field. The resultant electrolyte-gated FET sensor exhibits a sensitive linear response to high concentrations of alkaline solution, 1–20 M. Significantly, the sensor has the ability to directly indicate the pH values ranging from 14.0 to 17.0 in consideration of ion-activity coefficient data. This work offers a great possibility for directly detecting base concentration as well as pH values in extreme alkaline solutions.