Slot die coating is a pre‐metered process commonly used for producing thin and uniform films. It is an important film fabrication method for applications where precise coating is required. A major concern in slot die coating processes is how to determine the operating limits to set the appropriate range of operating parameters, including coating speed, flow rate, vacuum pressure, coating gap, liquid viscosity and surface tension, etc. Operating limits directly determine the effectiveness and efficiency of the process. In this article, the current state of academic research on operating limits in slot die coating processes is reviewed. Specifically, the theories, mechanisms, and empirical conclusions related to the limits on vacuum pressure, the low‐flow limit, the limit of wet thickness for zero‐vacuum‐pressure cases, the limit of dynamic wetting failure, and the limits of coating speed for a specific flow rate are reviewed. The article concludes with some recommendations for future work. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2508–2524, 2016

(1) Different methods have been applied to fabricate polymeric membranes with non-solvent induced phase separation (NIPS) being one of the mostly widely used. In NIPS, a solvent or solvent blend is required to dissolve a polymer or polymer blend. N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAc), dimethylformamide (DMF) and other petroleum-derived solvents are commonly used to dissolve some petroleum-based polymers. However, these components may have negative impacts on the environment and human health. Therefore, using greener and less toxic components is of great interest for increasing membrane fabrication sustainability. The chemical structure of membranes is not affected by the use of different solvents, polymers, or by the differences in fabrication scale. On the other hand, membrane pore structures and surface roughness can change due to differences in diffusion rates associated with different solvents/co-solvents diffusing into the non-solvent and with differences in evaporation time. (2) Therefore, in this review, solvents and polymers involved in the manufacturing process of membranes are proposed to be replaced by greener/less toxic alternatives. The methods and feasibility of scaling up green polymeric membrane manufacturing are also examined.

A new fabrication process to manufacture a membrane electrode assembly (MEA) by extrusion slot coating of ionomer onto a catalyzed gas diffusion layer (GDL) is presented. Preliminary coating tests were conducted to study the feasibility and effectiveness of directly coating Nafion D2021 onto catalyzed Toray 060 carbon paper. The uniformity of the coated membrane and the penetration of the Nafion dispersion into the catalyst layer were analyzed. Pressing and blowing operations were introduced into the fabrication process to increase the membrane uniformity and to decrease the penetration of Nafion dispersion. The effects of these operations were analyzed. The performance of MEAs fabricated using the new process was measured and compared with MEAs made by traditional methods. It was found that MEAs formed by direct coating have similar electrochemical performance at current densities below 0.8 A/cm 2 as MEAs traditionally fabricated.Polymer electrolyte membrane (PEM) fuel cells are a prominent energy source for portable and transportation applications that require clean, quiet, and efficient power. 1 Significant advances in research and development have been made over the last several decades; 1 however, slow fabrication speeds and high fabrication costs 2 still remain significant barriers to the extensive commercialization of PEM fuel cells.The basic physical design of a single PEM fuel cell consists of two bipolar plates sandwiching one membrane electrode assembly (MEA). A number of cells are connected in series to form a fuel-cell stack. The MEA is constructed from two gas diffusion layers (GDLs), two catalyst layers (typically containing platinum, carbon, and ionomer) and one electrolyte membrane. As the place for oxidation and reduction half reactions, the MEA plays a key role in a fuel cell; its characteristics and quality directly determine the overall performance of an individual cell or a stack. In addition, an extremely large quantity of MEAs will be required to realize widespread use of PEM fuel cells. For example, hundreds of millions MEAs per year would be needed to supply the laptop computer market. 3 Considering other potential big markets, such as the transportation and electronics sectors, the demand for mass production of MEAs will be a critical issue to the commercialization of PEM fuel cells.MEAs are traditionally manufactured by two methods, the membrane-based method or the GDL-based method. 4 In the GDLbased method, a catalyst layer is applied onto one side of the GDL forming a catalyst-coated GDL (CCG). 5 Then, the electrolyte membrane is sandwiched between two CCGs under high temperature and pressure to form the MEA. Because the bond is generated by hot pressing solid catalyst to the membrane, one problem this method can encounter is the relatively low contact area between the membrane and catalyst layer. Tang et al. showed that MEAs made from hot pressing has higher contact resistance and charge-transfer resistance as compared with those made from catalyzed membrane. 6 Good cell performance...

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