Imaging Local Proton Fluxes through a Polycarbonate Membrane by Using Scanning Electrochemical Microscopy and Functionalized Alkanethiols

• Published in: Chemphyschem 2009-01, Vol.10 (1), p.174-179
• Main Authors: Baltes, Norman, Heinze, Jürgen
• Format: Article
• Language: English
• Subjects: Applied sciences; cyclic voltammetry; electrochemistry; Electrodes; Exact sciences and technology; Exchange resins and membranes; Fatty Acids - chemistry; Forms of application and semi-finished materials; Hydrogen-Ion Concentration; membranes; microelectrodes; Microscopy, Scanning Probe - methods; Oxidation-Reduction; Polycarboxylate Cement - chemistry; Polymer industry, paints, wood; Potentiometry; Protons; scanning electrochemical microscopy; Sulfhydryl Compounds - chemistry; Technology of polymers
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.200800598

A new application of scanning electrochemical microscopy (SECM) to probe the transport of protons through membranes is described. Herein, a probe ultramicroelectrode (UME) is modified with a self‐assembled monolayer (SAM) of 11‐mercaptoundecanoic acid to qualitatively image areas within different pH regions above a track‐etched membrane. The current response of the modified electrode in the presence of potassium hexacyanoferrate as electroactive component is different in acidic and alkaline solutions. Depending on the pH value of the solution, the SAM‐covered electrode exposes either a neutral or a negatively charged insulating monolayer at pH 3 or 7, respectively, which leads to an increase/decrease in the faradaic current due to electrostatic interactions between the neutral/charged surface and the charged redox mediator. Therefore, local pH changes in the close vicinity of a membrane‐like substrate lead to different current responses recorded at the tip electrode when scanning above the surface. Imaging transport phenomena: A new technique—based on scanning electrochemical microscopy—is developed for imaging proton fluxes across porous membranes. The high pH sensitivity of a carboxylic acid‐modified ultramicroelectrode (UME) to the current response during the oxidation of a hexacyanoferrate mediator can be used to monitor local proton fluxes (see picture).