Electrochemical measurements of mass transfer at surfaces with discrete reactive areas

✍ Scribed by Nikola M. Juhasz; William M. Deen

• Book ID: 102694045
• Publisher: American Institute of Chemical Engineers
• Year: 1993
• Tongue: English
• Weight: 792 KB
• Volume: 39
• Category: Article
• ISSN: 0001-1541
• DOI: 10.1002/aic.690391014

✦ Synopsis

The limiting current technique was used to measure area-averaged mass-transfer coefficients f o r surfaces containing many small reactive areas arranged in various patterns. Partially masked platinum electrodes were fabricated using photolithography, and mass-transfer measurements were performed with a rotating disk apparatus. The average mass-transfer coefficient was sensitive to the fraction of the electrode area exposed ( E ) , declining from values near that for a fully exposed surface for E = 0.5 to less than I% of the fully exposed value for E = 0.001. For any given E, the mass-transfer coefficient declined with increased spacing bet ween reactive sites. The results were relatively insensitive to details of the site distribution, such as whether the sites were arranged in regular arrays (square or hexagonal lattices) or distributed randomly over thesurface. For all conditions studied, the mass-transfer coefficient greatly exceeded that predicted by conventional models which apply the stagnant film approximation to the fluid surrounding a representative active site. This finding is qualitatively consistent with recent computational results, which suggest that convective transport enhances mass transfer at partially active surfaces to an extent not accounted for by adjustments in the effective film thickness. 1708 October 1993 . ___ __ , . .