Physical & Theoretical Chemistry Laboratory, University of Oxford, Oxford OX1 3QZ, UK.
Sensors (Basel). 2022 Apr 25;22(9):3286. doi: 10.3390/s22093286.
A bespoke calibration-free pH sensor using an in situ modified Ir electrode for applications in seawater is reported. The electrochemical behaviour of an iridium wire in air-saturated synthetic seawater was studied and the formation of pH-sensitive surface layers was observed that featured three pH-sensitive redox couples, Ir(III/IV), IrOxOI-/IrOxOII-H, and H/H, where H is adsorbed hydrogen deposited at underpotential conditions. The amperometric properties of the electrochemically activated Ir wire were investigated using linear sweep voltammetry first, followed, second, by square wave voltammetry with the formation conditions in seawater for the optimal pH sensitivity of the redox couples identified. The sensor was designed to be calibration-free by measuring the "super-Nernstian" response, in excess of ca 60 mV per pH unit, of Ir(III/IV) relative to the less sensitive upd H oxidation signal with the pH reported on the total pH scale. The pH dependency of the optimised sensor was 70.1 ± 1.4 mV per pH unit at 25 °C, showing a super-Nernstian response of high sensitivity.
本文报道了一种定制的无校准 pH 传感器，该传感器使用原位修饰的 Ir 电极，可用于海水应用。研究了空气中饱和合成海水中铱丝的电化学行为，观察到形成了 pH 敏感的表面层，其具有三个 pH 敏感的氧化还原对，Ir(III/IV)、IrOxOI-/IrOxOII-H 和 H/H，其中 H 是在欠电位条件下沉积的吸附氢。首先使用线性扫描伏安法研究了电化学激活的 Ir 丝的电流特性，其次使用方波伏安法，确定了最佳 pH 灵敏度的形成条件。通过测量 Ir(III/IV)相对于 upd H 氧化信号的“超 Nernstian”响应（每个 pH 单位超过 60 mV），该传感器设计为无校准，其中 pH 在总 pH 标度上进行报告。在 25°C 时，优化后的传感器的 pH 依赖性为 70.1 ± 1.4 mV/ pH 单位，表现出高灵敏度的超 Nernstian 响应。
