Mechanically flexible pH sensor demonstrating high sensitivity in seawater and long-term operational stability for ocean environmental applications

The development of robust and flexible pH sensors is critical for accurate in-situ monitoring of marine environments, particularly for applications such as ocean acidification research and underwater vehicle-based sensing. In this study, we present a highly stable and flexible pH sensor based on iridium oxide (IrO x ) electrodes with potential for reliable operation in complex marine settings, based on its performance in laboratory-simulated conditions and long-term stability in real seawater. The sensor exhibits a near-Nernstian response with an average sensitivity of −65.07 mV/pH in aqueous solutions (pH 3–10), demonstrating excellent stability after 4000 bending cycles with minimal hysteresis. A rapid response time of 9.29 s and negligible potential drift (±5 mV over 5 min) highlight its precision and repeatability. While cation interference, particularly from Mg²⁺, induces slight potential shifts (4–5 mV), the sensor maintains its Nernstian behavior across all tested interferents including Na⁺, K⁺, Ca²⁺, and Mg²⁺. High-resolution measurements within the marine-relevant pH range (7.9–8.4) confirm excellent sensor performance with sensitivities exceeding −64.5 mV/pH. This targeted validation, combined with the sensor's exceptional mechanical flexibility, underscores its suitability for real-time pH monitoring in dynamic marine systems. These findings demonstrate the sensor’s potential for advancing marine chemistry research and environmental monitoring applications. Download: Download high-res image (123KB) Download: Download full-size image