Mass Transfer at Gas Evolving Surfaces: A Microscopic Study

Abstract

A novel micromosaic electrode was developed to resolve the time‐dependent, mass‐transfer distribution in the close vicinity of bubble phenomena. The electrode, prepared on a silicon wafer using integrated circuit manufacturing technology, consists of a 10 by 10 matrix of coplanar, electrically isolated, square platinum segments on 100 μm centers, surrounded by a relatively large buffer segment. A computer actuated data acquisition and control system was assembled and the software developed to monitor the current to each of the segments and control the potential of selected segments. The effect of a single hydrogen bubble disengagement and of the coalescence of two bubbles, on the free convection limiting current of the reduction of ferric to ferrous ion was measured using the micromosaic electrode in a horizontal face‐up orientation. It was found that the mass‐transfer enhancement due to bubble disengagement is small when compared to that due to coalescence. Increases in the mass‐transfer rate of more than an order of magnitude over the free convection limiting current were observed for the coalescence phenomena.