Advanced Water Management in PEFCs: Diffusion Layers with Patterned Wettability

Self Cite

In this paper, we present an experimental study on the development of gas diffusion layer (GDL) materials for fuel cells with dedicated water removal pathways generated using radiation induced grafting of hydrophilic compounds onto the hydrophobic polymer coating. The impact of several material parameters was studied: the carbon substrate type, the coating load, the grafted chemical compound and the pattern design (width and separation of the hydrophilic pathways). The corresponding materials were characterized for their capillary pressure characteristic during water imbibition experiments, in which we also evidenced the differences between injection from a narrow distribution channel in the center of the material (and thus strongly relying on lateral transport) and homogeneous injection from one face of the material. All materials parameters were observed to have a significant influence on the water distribution. In particular, the type of substrate has a dramatic impact, with results ranging from a nearly perfect separation of water between hydrophilic and hydrophobic domains for substrates having a narrow pore size distribution to a fully random imbibition of the material for substrates having a broad pore size distribution.

Section: Resultssupporting

confidence: 90%

Section: Methodsmentioning

confidence: 99%

Advanced Water Management in PEFCs: Diffusion Layers with Patterned Wettability

Forner‐Cuenca

Biesdorf

Lamibrac

et al. 2016

Self Cite

“…The observed expansion of the FC type water clusters in the channel GDL domains sets some boundaries for the dimensioning of recent efforts to separate the transport paths of the liquid water and the gases in the GDL by means of patterned wettability. [48][49][50] It would require hydrophilic domain about every 200 μm such that they could connect to every FC type cluster of 1 nL size, or even every 100 μm for the smallest observed FC clusters in the channel domain of only 0.2 nL, as postulated already in Ref. 48.…”

Section: Discussionmentioning

confidence: 99%

Operando Properties of Gas Diffusion Layers: Saturation and Liquid Permeability

Eller

Roth

Marone

et al. 2016

Polymer electrolyte fuel cells (PEFC) require a sophisticated water management to operate efficiently, especially at high current densities which are needed to reach system cost targets. The description of the complicated two-phase water transport remains a challenge in PEFC models and requires experimental validation on various length scales. In this work, operando X-ray tomographic microscopy (XTM) with scan times of 10 s was used to depict the liquid water at defined conditions at a technically relevant cell temperature of 80 • C. Cells with Toray TGP-H-060 gas diffusion layer (GDL) with microporous layer (MPL) and different rib width were operated with different feed gas humidifications (under-and oversaturated) and current densities between 0.75 to 3.0 A/cm 2 . Based on the quantification of the local and average saturation, the distribution of water cluster size is analyzed. Different categories of the water cluster connectivity are defined and quantified. The analysis is complemented with numerical simulations of the permeability in the liquid phase of the GDL that is correlated to saturation for the different GDL domains. The numerical simulations of the pressure drop of liquid water flow from the catalyst layer toward the gas channels in channel-rib repetition units allows for conclusions on cluster growth mechanisms. In the past two decades, large developments have lead hydrogen fed polymer electrolyte fuel cell (PEFC) technology to the brink of commercialization, e.g. in the stationary sector with more than 100000 deployments in the Enefarm activity 1 as well as in the mobile sector where major car manufacturers have presented first commercial vehicles 2,3 and niche-market commercialization for logistic vehicles. 4While for the automotive market also hydrogen infrastructure is a major barrier for widespread application, in both fields of application, cost of the fuel cell system remains the main hindrance for extensive spread of PEFC technology. Cost is closely tied to materials and manufacturing processes, such as more effective electrocatalyst and more durable membrane materials. These developments are underway and have made significant progress. 5 Cost however is also closely tied to power density of the fuel cell stack. It is obvious that with higher power density less cells or an accordingly smaller cell area with the related reduced material use, is leading to a cost reduction if the high power density materials are of comparable cost.Automotive fuel cells with state of the art materials and cell structures reach today more than 1 W/cm 2 with current densities up to 3 A/cm 2 .5 At such high current densities water management becomes more and more important and has to be properly designed on various scales from the system level to nanoscale structures, including all cell components as flow field plates, gas diffusion layers (GDL), the polymer membrane and the catalyst layer (CL). In order to minimize the ohmic losses, the polymer membrane needs to be well humidified, 6 however at high current den...

“…Details about the coating application can be found in our previous work. 25,26 The coated GDLs were then irradiated using masks (stainless steel, 2 mm thick) with two different designs: 1) 500 μm openings spaced 930 μm and 2) 250 μm openings spaced 1000 μm. The first design provided a hydrophilic areal fraction of 35% and the second a fraction of 25%.…”

Section: Methodsmentioning

confidence: 99%

“…The varied parameters include the dimensions of the pattern, the presence or absence of an MPL, and operating parameters such as humidity and temperature, respectively. This work currently rounds up a series of three papers including a detailed study on the material synthesis parameters (Part I) 26 and the analysis of the impact of various material parameters (substrate, coating load, grafting chemistry, pattern dimensions) on the water distribution in capillary injection experiments (Part II). 27 …”

mentioning

confidence: 99%

Advanced Water Management in PEFCs: Diffusion Layers with Patterned Wettability

Forner‐Cuenca

Biesdorf

Manzi-Orezzoli

et al. 2016

Self Cite

Following our two previous publications on material synthesis and on ex situ characterization, we present an experimental in situ study to evaluate the effects of using gas diffusion layers with patterned wettability at the cathode side of polymer electrolyte fuel cells. The operando performance was assessed using traditional electrochemical diagnostics (such as polarization curves) combined with the pulsed gas analysis (PGA) method, which allows measuring the mass transport losses. Neutron radiography was performed simultaneously in order to image the water distribution during operation. Using this methodology, the effects of changing the pattern, including a microporous layer (MPL), and varying the operation conditions (temperature and relative humidity of the cathode gas) have been systematically evaluated. It has been confirmed that water redistributes according to the engineered pattern and that the power density is significantly increased thanks to reduced mass transport losses under various conditions. © The Author Several attempts have been reported in the literature to develop porous materials for fuel cells with optimized liquid/gas transport characteristic.1,2 The variation of microstructure 3,4 and the optimization of hydrophobic coatings and their content permitted significant improvements in performance, 5-9 while the inclusion of microporous layers led to the state-of-the-art materials that we know today. 10-17However, these materials do not have dedicated pathways for liquid and gas transport, but randomly distributed transport paths defined by the pore size and coating distributions.The perforation of GDLs in specific locations showed improved performances under certain operating conditions. 18,19 The local application of hydrophobic coatings was reported to improve oxygen diffusivity using an ex situ test rig combined with X-ray tomography. [20][21][22] An in situ study by the same research group demonstrated clear improvements when combining these hybrid GDLs with micro-grooved gas channels, but the isolated effect of hybrids GDLs did not lead to significant performance improvements. 23 Recently, we reported a method to produce GDLs with patterned wettability 24,25 based on radiation induced chemical grafting, and were the first to publish operando data with such patterned materials, showing a significant improvement when using them on the cathode of a PEFC. 25 Here, we present a comprehensive study on the impact of GDLs having patterned wettability on the water distribution and performance of the cell. The varied parameters include the dimensions of the pattern, the presence or absence of an MPL, and operating parameters such as humidity and temperature, respectively. This work currently rounds up a series of three papers including a detailed study on the material synthesis parameters (Part I) 26 and the analysis of the impact of various material parameters (substrate, coating load, grafting chemistry, pattern dimensions) on the water distribution in capillary injection experiments (Part II...