Influence of surface tension on the critical current density at sulfuric acid electrolysis

The hydrogen evolving system such as the water electrolysis generates hydrogen gas at the cathode surface via electrochemical reaction. The current density increases as the cell potential increases with the increased hydrogen generation rate. However, the current density is limited by the formation of hydrogen film on the surface, similar to the critical heat flux (CHF) condition, which is known as critical current density (CCD). Unlike to the boiling system, the influences of hydrodynamic parameters on the CCD is hardly investigated. The present work is motivated by the fact that the CHF is affected by the surface tension. In the present work, the water electrolysis of sulfuric-acid aqueous solution was used to measure the CCD varying the surface tension via surfactant (CTAB). Comparative analyses were performed with the existing results of the boiling system. Both the CCD and hydrogen bubble diameter decreased as the surface tension decreased, similar to those of the boiling system. To investigate relationship between the CCD and the hydrogen bubble diameter, the bubble velocity was estimated by the measured CCD, which is affected by the bubble diameter, the drag coefficient and gas area fraction. Using those parameters, the CCD is predicted within 20% error. The result implies that the influence of surface tension on the CCD is similar to that on the CHF.