Polymer-Ceramic Composite Diaphragm for Reducing Dissolved Hydrogen Permeability in Alkaline Water Electrolysis

Abstract

The porous diaphragm is a typical separator used in an alkaline water electrolyser. Gas crossover through the diaphragm during electrolysis depends upon the different evolution quantity of hydrogen and oxygen gas which consequently develop the differential pressure between cathode and anode side. This phenomenon limits the cell efficiency and develops safety concerns. In this study, diaphragm was prepared by film casting, which consists of mixing, casting and extraction. We measured the hydrogen flux density of commercial diaphragm (Zirfon PERL) and the prepared diaphragm during the operation. For this purpose, the diaphragm was mounted in a zero-gap design unit cell with Ni foam as electrodes and operated in 30wt% KOH solution at 60oC with atmospheric differential pressure between 0.1 ~ 0.3 bar (cathode side – anode side) controlled by a back-pressure regulator. Results showed that the anodic hydrogen content of commercial diaphragm was up to 2% during the operation but prepared diaphragm was negligible. This is due to the smaller pore size in the prepared diaphragm as compared to the commercial diaphragm confirmed by morphological and surface area analysis.Fig 1. (a) The anodic hydrogen contents as a function of current density and differential pressure and (b) polarization curves at 60oC and 30wt% KOH solution of conventional and prepared diaphragm with nickel foam as electrode Figure 1