Electrochromic materials reversibly change colour under the influence of an electric voltage/current. Such materials are of interest for use in various optical smart devices. The electrochromic effect is also obtained with pH indicator solutions which change colour due to a change in pH. A cell where the pH of the solution at the electrode changes due to electrolysis of the water, resulting in a change in the colour of the pH indicator, can be classified as an electrochromic cell. In my Master's thesis I have built two such electrochromic cells: one in a parallel electrode configuration, the other in an inverted sandwich configuration. I tested different electrode materials (metals, graphite) and electrolytes (potassium nitrate, sodium acetate). For the colour response I used the pH indicators bromothymol blue, phenol red and turmeric extract. I used a paper towel as a carrier for the electrolyte/dye. The time response of the cells was tested and compared. I quantified cell performance by chronoamperometry. For the cells with optimal performance I prepared material for the demonstration of electrochromism in secondary schools.
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