Layer Formation from Polymer Carbon-Black Dispersions

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.

Scalable Implementation of Recombination Catalyst Layers to Mitigate Gas Crossover in PEM Water Electrolyzers

“…20,21 The anode and cathode catalyst dispersion were coated on a 140 μm thick glass-fiber-reinforced (gfr) PTFE (CF206, Saint-Gobain) using a slot die (TSE Troller) of 200 mm coating width mounted above a vacuum table (TableCoater, TSE Troller) and were dried at 80 °C under air, using a coating setup as described previously. 22 The cathode, consisting of 85 wt% platinum supported on high surface area Ketjenblack (60% Pt; EC-300J, PK Catalyst) and 15 wt% Nafion™ ionomer (Chemours), had a Pt-loading of 0.25 mg cm −2 +− 0.02 mg cm −2 . The catalyst ink was prepared inhouse with catalyst powder, ionomer solution (D1021, Chemours), deionized water and alcohols using an ultrasonic dispersing device (UW 3200, Bandelin).…”

About drying phenomena of fuel cell and electrolyzer CCM inks: Selectivity of the evaporation of 1‐propanol/water mixtures

“…In addition, there is the possibility that the ratio of solvents to one another changes during and as a result of (selective) drying. This in turn influences the layer properties, affecting ionomer and particle interactions [8,9]. The crucial factor for the subsequent layer properties and thus the cell performance is no longer the properties of the ink in its initial composition (set during ink formulation), but of the ink with its composition during film solidification.…”

“…As a result, numerous examples of different solvent mixtures are used in catalyst inks [7][8][9][10][11]. In particular, mixtures of 1-propanol and water can be found in the fuel cell and electrolyzer literature [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23].…”

“…In addition, some common ionomer dispersions are prepared in a solvent mixture, for example, Nafion as D520 and D2020 (Chemours [5]) or 3M Ionomer 800EW (3M [6]). As a result, numerous examples of different solvent mixtures are used in catalyst inks [7][8][9][10][11]. In particular, mixtures of 1-propanol and water can be found in the fuel cell and electrolyzer literature [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23].…”

“…McCabe–Thiele diagram of 1‐propanol/water mixtures (index 1:1‐propanol) at 17.5°C. Assumed ideal (orange) and real (green) mixture behavior and common ink compositions from literature [8–21]. …”