Abstract
It has been well-established that effects such as cracking are observable when wet layers are dried. In particular, the layer thickness, as well as the surface tension of the liquid, is responsible for this behavior. The layer formation of polymer electrolyte fuel cells and electrolyzer electrodes, however, has not yet been analyzed in relation to these issues, even though the effect of cracks on cell performance and durability has been frequently discussed. In this paper, water propanol polymer-containing carbon-black dispersions are analyzed in situ with regard to their composition during drying. We demonstrate that crack behavior can be steered by slight variations in the initial dispersion when the solvent mixture is near the dynamic azeotropic point. This minor adjustment may strongly affect the drying behavior, leading to either propanol or water-enriched liquid phases at the end of the drying process. If the evaporation of the solvent results in propanol enrichment, the critical layer thickness at which cracks occur will be increased by about 30% due to a decrease in the capillary pressure. Microscopic images indicate that the crack area ratio and width depend on the wet layer thickness and initial liquid phase composition. These results are of much value for future electrode fabrication, as cracks affect electrode properties.
Highlights
Layer formation has already been studied for about a hundred years, both theoretically and experimentally [1]
Crack formation occurs during many processes, including the manufacturing of electrodes for polymer electrolyte membrane (PEM) fuel cells (FC) and electrolyzers (EL)
High wet layer thickness and low propanol content promote the cracking of the layer
Summary
Layer formation has already been studied for about a hundred years, both theoretically and experimentally [1]. Crack formation occurs during many processes, including the manufacturing of electrodes for polymer electrolyte membrane (PEM) fuel cells (FC) and electrolyzers (EL) In these applications, electrodes are mostly manufactured from catalyst dispersions containing perfluorosulfonic acid (PFSA) as proton- and carbon-supported catalysts and as electron-conducting materials [4]. A dispersion consisting of 1-propanol, water, carbon, and Nafion was used With this precious metal-free dispersion, chemical reactions between alcohol and the catalyst were avoided, guaranteeing only physical interactions between the dispersion components during manufacturing. This simplifies the system to the driving mechanism, as apart from that; the dispersion composition corresponds to a typical catalyst dispersion used for electrode production [12,13]. The drying is under precise control and observed by gas-phase Fourier transform infrared (FTIR) spectroscopy [14], as well as crack areas being evaluated in a simple manner to disclose the driving forces
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