Impact of an electrode-diaphragm gap on diffusive hydrogen crossover in alkaline water electrolysis.

This is the metadata for the research paper "Impact of an electrode-diaphragm gap on diffusive hydrogen crossover in alkaline water electrolysis". In this study we further explore how the hydrogen crossover flux depends on the electrode-diaphragm configuration with a special focus on the influence of the gap distance between the electrode and the diaphragm. Therefore, a comparison of finite- and zero-gap AWE designs is made using Zirfon PERL UTP 220 and Zirfon Perl UTP 500. The effect of a finite gap is investigated both at the anodic and cathodic side. Special attention is given to reproducibility, which appears to be a major challenge between different experiments. We carry out gas crossover experiments using gas chromatography at current densities ranging from 0.1 to 0.3 A.cm-², which are representative values for the minimum load of alkaline electrolyzers. ABSTRACT Hydrogen crossover limits the load range of alkaline water electrolyzers, hindering their integration with renewable energy. This study examines the impact of the electrode-diaphragm gap on crossover, focusing on diffusive transport. Both finite-gap and zero-gap designs employing the state-of-the-art Zirfon UTP Perl 500 and UTP 220 diaphragms were investigated at room temperature and with a 12 wt.% KOH electrolyte. Experimental results reveal a relatively high crossover for a zero-gap configuration, which corresponds to supersaturation levels at the diaphragm-electrolyte interface of 8-80, with significant fluctuations over time and between experiments due to an imperfect zero-gap design. In contrast, a finite-gap (500 μm) has a significantly smaller crossover, corresponding to supersaturation levels of 2-4. Introducing a cathode gap strongly decreases crossover, unlike an anode gap. Our results suggest that adding a small cathode-gap can significantly decrease gas impurity, potentially increase the operating range of alkaline electrolyzers, while maintaining good efficiency.