Optical and electrochemical study of model zinc electrode pores in alkaline electrolyte

A computer-controlled model single-pore cell has been developed to study zinc electrode discharge behavior in alkaline electrolytes. The cell design allows for simultaneous microscopic and potential performance observations. A quartz-supported, thin-film cadmium reference microelectrode was designed, fabricated and installed in the cell. The cell was designed to create model pores of dimensions comparable to those in commercial zinc electrodes. Zinc electrode discharge behavior was studied in pores of effective radii between 14 and 20 microns at 7 mA/sq cm, 30 mA/sq cm and 1250 mA/sq cm rates of discharge in 7.7M KOH electrolyte. Results are consistent with a dissolution-precipitation discharge reaction mechanism. SEM studies showed significant variations in electrodes surface morphology with location in the pore and rate of discharge. Significant poreOH(-) gradients, with slow relaxation times, were found to exist within the pore at the mA/sq cm rate. Passivation was observed at the 1250 mA/sq cm rate. Zinc electrode discharge behavior in 3.5M KOH-3.4M KF showed a similar discharge reaction mechanism. However, earlier surface film formation in 3.5M KOH-3.4M KF was found to occur. Initial reaction penetration depths in 7.7M KOH and 3.5M KOH-3.4M KF electrolytes were 0.11 cm and 0.10 cm.