Ionomer-coated & tungsten-based nanoarray materials for proton exchange membrane electrolysis

Abstract

Polymer electrolyte membrane electrolysis is one of the key technologies in harnessing the potential of hydrogen production, although it typically requires expensive platinum group metals (PGM) as catalysts and pure water as feedstock. This thesis aims to address these two drawbacks. First, earth-abundant tungsten was used to synthesize PGM-free and low-PGM-loading catalysts, i.e. tungsten carbide and iridium-doped tungsten trioxide as cathode and anode electrocatalysts separately for PEM electrolysis. Second, 3.5 wt-% saltwater was tried as feed water for electrolysis. In purified water, Nafion ionomer coating was used to provide the necessary acidic environment for the tungsten-based electrodes, which led to improved charge transfer and achieved 100mA/cm2 at a cell voltage of 1.9V. In 3.5 wt-% salt-water, anion exchange ionomer was used to protect the catalyst and Nafion membrane from sodium cation poisoning but was unsuccessful as current densities only reached a stable current density of around 30mA/cm2 at 2V cell potential. Post-mortem analysis revealed cracks on anion exchange ionomer coating and severe corrosion on catalyst layers. Several potential failure mechanisms were presented along with prospective mitigation strategies.