Polymer anion selective membranes for electrolytic splitting of water. Part I: stability of ion-exchange groups and impact of the polymer binder

Abstract

In this study, the chemical stability of three types of the anion-exchange functional groups in an alkaline environment was tested. The following groups were selected for the test: trimethylbenzylammonium, methyl pyridinium, and tributhylbenzylphosphonium. A KOH solution with various concentrations and temperatures was used as the environment. The trimethylbenzylammonium group showed the highest stability of the materials tested under conditions relevant to water electrolysis. In the next step, four types of polymeric binders, including ethyleneco-methacrylic acid, linear polyethylene, linear polyethylene blended with poly(ethylene-co-vinylalcohol), and low-density polyethylene, were selected to determine their impact on the resulting electrochemical properties of a heterogeneous membrane. This study reveals the morphology of the membrane, ion-exchange capacity, ionic conductivity, and performance in alkaline water electrolysis conducted on a laboratory scale. The material showing the most promising properties was selected for further optimization and testing.

Polymer anion-selective membranes for electrolytic splitting of water. Part II: Enhancement of ionic conductivity and performance under conditions of alkaline water electrolysis

“…1. In the previous study, this functional group was evaluated to be the most stable one under conditions relevant to alkaline water electrolysis [1]. The prepared membranes always contained 66 wt% of the anion-selective phase.…”

“…In the first part of this study [1], the problem of alkaline electrolysis as the only recently established industrial water electrolysis technology was discussed in detail. This especially concerns its economic competitiveness with currently used technologies for fossil fuel-based hydrogen production and the technological challenges that still remain to be solved.…”

“…This is, however, attained at the expense of their ionic conductivity. In the first part of this study [1], attention is focused on the stability of the selected anion-selective functional groups in an alkaline environment at different temperatures and on the influence of the polymer binder on the electrochemical properties of the resulting heterogeneous anion-selective membranes. Besides the properties of the ion-exchange material, the polymer binder was also found to play an important role in the resulting behavior of the membrane.…”

“…The membrane composition was optimized in the first part of this study [1]. The only way to further improve its performance is by artificially increasing the porosity of the surface skin film, which represents an important barrier to the transport of ions across the membrane.…”

“…The heterogeneous membrane samples tested consisted of 66 wt% of anion-selective phase represented by a styrenedivinyl benzene copolymer matrix with quaternary ammonium functional groups, a variable amount of inert polymer matrix represented by low-density polyethylene (LDPE) and a variable amount of the water-soluble component. For this work, LDPE was selected instead of LIPE although the latter material showed the best properties in [1]. This was because its properties are appropriate for the desired application.…”