AbstractThe construction and utilization of a column‐shaped in situ thin‐layer ESR spectroelectrochemical cell for both ambient and low temperature operation is reported. The working electrode is a columnshaped expanded platinum sheet of 9.4 × 4.0 mm that is placed in a 0.25 mm thick column‐shaped, thin‐layer chamber. The solution volume in the thin‐layer chamber is 12 μL, and the total solution volume in the cell ranges between 1 and 3 mL. The application of this cell is demonstrated by time‐resolved ESR spectra for electrooxidized porphyrins in methylene chloride solutions containing 0.3 M tetrabutylammonium perchlorate. The electrochemical behavior of this cell is also demonstrated by the oxidation of ferrocene under the same solution conditions at temperatures between 23 and −75°C. Well‐defined ESR spectra are obtained in as short as 5–10 seconds witho