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High-throughput screening of electrochemically active materials, such as fuel cells, electrocatalysts, and battery materials, is already accelerating the discovery of interesting new materials. [1][2][3][4] However, measuring the current or potential variations across a large array is limited by complex and costly hardware, and this is restricting the size of material libraries that can be screened in one experiment. Consequently, an optical technique that allows a discrete array of samples, or even a continuous but compositionally varying sample, to be monitored in a single snapshot could have significant advantages as a first screen. Others have reported optical screens for combinatorial electrochemical cells. One technique uses a fluorescent dye in the electrolyte, which monitors local variations such as pH changes. [5][6][7][8] A second technique has also been reported, [9] in which the screen is an array of electrochromic gas sensors to measure H 2 gas produced during a reaction. However, to screen large arrays of materials, the experimental setup required for this technique would soon become cumbersome. Here we introduce a novel technique based on an electrochromic counter electrode (CE) [10] and demonstrate its use as a quantitative, noninvasive, and simple optical screen for methanol oxidation on platinum-based catalysts. The principle of the new optical screen is shown schematically in Figure 1a. The prototype cell consists of an array of working electrodes (where the test materials are deposited), a thin layer of electrolyte, and an electrochromic CE positioned directly opposite the array. In this work we have chosen to investigate methanol oxidation on different masses of Pt catalyst. The electrochromic CE is a WO 3 film on fluorine-doped tin oxide-coated glass. The WO 3 -coated conducting glass acts as an ion-insertion electrode, intercalating protons from the background electrolyte to balance the charge passed at the working electrode; this causes a color change from colorless to blue in the CE. A two-electrode setup is employed, in which the CE also functions as a pseudo-reference electrode.This arrangement allows different intensities of blue color to occur simultaneously across the CE, with darker shades recording the passage of more charge due to more active catalysis occurring at positions on the working electrode array directly opposite. During the experiment a digital optical image is taken of the patterned CE. The current collector for the CE is a transparent conducting oxide, and therefore with the help of a white filter paper acting as a diffuse reflector (and also a cell separator) between the counter and working electrodes, small variations in the absorbance properties of the CE can be quantitatively measured in a single image using a digital camera. Therefore, by calibrating the changes in the color intensity at points across the CE with the charge passed at opposite points on the working-electrode array, a quantified charge-distribution map of the array can be produced. Once the cell ha...

Solutions of solvated electrons in the presence of magnesium offer many advantages for the surface treatment of PTFE when compared to the classical solutions of solvated electrons in the presence of alkalis: the polymer remains white instead of black, its surface is not destroyed and presents a controlled hydrophilic character.