Fabrication and characterization of nanostructured Pd hydride pH microelectrodes

Novel pH microsensors were made by electrodepositing mesoporous Pd films onto Pt microdisks, electrochemically loading the films with hydrogen to form the alpha+beta Pd hydride phase, and then switching to the potentiometric mode to monitor pH. To create a nanostructure, the films were deposited within a molecular template formed by the self-assembly of surfactant molecules, a technique known as true liquid crystal templating. The films retain the micrometer size of the Pt microdisk but offer electroactive areas up to 900 times larger. Optimum hydrogen loading conditions were determined, and the mesoporous Pd microdisks were found to have excellent potentiometric properties. From pH 2 to 12, their potential was Nernstian, highly reproducible, very stable (+/- 1.2 mV over 2 h), and without hysteresis. Their response time was better than 1 s. However, the presence of oxygen reduced their lifetime significantly, thereby requiring frequent reloading. These microelectrodes do not require calibration before and after measurements, a procedure normally essential for potentiometric pH microsensors. To our knowledge, these are the first results where nanostructured materials made by the true liquid crystal templating method have been used in the potentiometric mode; moreover, these are the first results demonstrating the application of nanostructured microdisks in the potentiometric mode.