Potentiometric Scanning Electrochemical Microscopy (SECM) allows the pH distribution at electrode/electrolyte interfaces to be mapped at the micrometer and submicrometer scale using ion-selective ultramicroelectrodes (UMEs) as scanning probes. However, this technique lacks precise control of the tip-to-substrate distance. Herein we propose a novel dual Pt-Pt/IrO_x UME for local in situ pH visualization of 316L stainless steel (316L-SS) corrosion processes with precise tip–substrate distance control using both amperometric and potentiometric SECM modes. Simulations based on COMSOL and experimental approach curves obtained with this dual UME configuration are used to precisely establish the tip–substrate distance. Higher pH values were observed for smaller tip–substrate separations when this probe configuration is used with bulk electrolyte of the same pH. Furthermore, during the corrosion process local anodic and cathodic zones were observed to form, disappear and regenerate at a vertical tip–substrate distance of 12 μm as a result of the localized corrosion and repassivation of 316L-SS.

电位扫描电化学显微镜（SECM）允许使用离子选择超微电极（UME）作为扫描探针在微米和亚微米尺度上绘制电极/电解质界面的pH分布。然而，该技术缺乏对尖端到基底的距离的精确控制。在这里，我们提出了一种新颖的双重Pt-Pt / IrO _xUME可以使用电流型和电位型SECM模式精确地控制针尖与基材的距离，从而对316L不锈钢（316L-SS）腐蚀过程进行局部原位p​​H可视化。基于COMSOL的模拟和通过这种双UME配置获得的实验方法曲线可用于精确确定尖端与基底的距离。当此探针配置与相同pH的散装电解质一起使用时，观察到较高的pH值可实现较小的尖端与底物的分离。此外，在腐蚀过程中，由于局部腐蚀和316L-SS的再钝化，在12 µm的垂直尖端-基底距离处观察到了局部阳极和阴极区域的形成，消失和再生。