A Pathway to Significant Reduction of Hydrogen Crossover with Pt Recombination Layer in Proton Exchange Membrane Water Electrolyzers

Abstract

Proton exchange membrane water electrolyzers (PEMWEs) are the major components of the green source of high-purity hydrogen for chemical applications as well as energy storages. However, some technical and economic problems have restricted their widespread development. One of the principal technical issues hampering the extensive use of PEMWEs is hydrogen crossover. The produced hydrogen in the PEMWE cathode compartment is typically stored at high pressure through either an external compressor or electrochemical compression with high pressure PEMWEs which leads to a high overall efficiency [1-3]. However, some produced hydrogen passes through the proton exchange membrane restricting the cell performance, especially when operating under pressure [1, 4]. The hydrogen crossover also causes a serious safety hazard in the anodic compartment where the oxygen is produced because the lower explosion limit of hydrogen in oxygen content is about 4 vol.%. It has been shown that a mitigation strategy is needed to reach this value with a safety margin of 2 vol.% [4, 5]. Although several mitigation strategies have been utilized, the integration of a recombination layer incorporated directly into the membrane has shown the best performance. Recently, Klose et al. [4] showed that integrating Pt nanoparticles as a recombination layer with Pt loading of 0.02 mg cm-2 between a NR-212 and a N115 membrane of a PEMWE can significantly overcome the safety issue. The results indicated no hydrogen in oxygen after 245 hours at 1 A cm-2 which demonstrates the Pt recombination layer effect on hydrogen crossover reduction. However, a strong increase for hydrogen in oxygen content was observed at higher current densities (>1 A cm-2). Thus, a further investigation is still needed to achieve a better recombination layer by optimizing Pt nanoparticles distribution or the position of the recombination layer. In this work, a novel electrode fabrication method, reactive spray deposition technique (RSDT), was employed to deposit a Pt recombination layer directly introduced into the membrane. The microstructural characteristics of the Pt recombination layer were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Thereafter, the stability and cell performance of a full RSDT catalyst coated membrane (86 cm2) were investigated using diagnostic tests including polarization analysis, cyclic voltammetry, and electrochemical impedance spectroscopy. The results revealed significant stability for 1000 hours at 1.8 A cm-2, 50 °C, 400 psi hydrogen pressure with lower catalyst loading compared to commercial membrane electrode assemblies (MEAs) and > 65% reduction in hydrogen crossover.