Degradation of gas diffusion layer in proton exchange membrane fuel cells:A review

Fuel cells, as an energy conversion device for direct and effective conversion of the chemicalenergy of a fuel and oxidant into electrical energy, are on the verge of competing with fossil fuels andother energy sources to produce clean electricity in a variety of sectors. Due to their high efficiency ofenergy conversion, quick start-up, simple design, low working temperature and compatibility with theenvironment, proton exchange membrane (PEM) fuel cells have attracted enormous attention amongthe different types of fuel cells. However, the widespread commercialization of PEM fuel cells forvehicles is still limited due to their cost, performance, and durability, among which fuel cell durabilityis the most challenging aspect [۱]. The gas diffusion layer (GDL), which usually consists of amacroporous substrate and a microporous layer, is inserted between the catalyst layer and bipolar plateof the PEM fuel cell and has multifaceted roles, such as supplying gaseous reactants homogeneously tothe electrode’s active area, removing the formed water out of the cell, electrically connecting theelectrode to the bipolar plate and providing mechanical support to membrane electrode assembly.Indeed, it has been largely proved that using GDLs significantly improves device performance [۲]. Thedegradation of various components of PEM fuel cells has been extensively studied so far. However, theGDL has rarely been examined. Thus, understanding the process of GDL degradation is essential forsuccessful fuel cell commercialization. As presented in Fig. ۱, GDL degradation can be classified into mechanical and chemical degradation [۳].GDL has a structure with the highest compressibility among fuel cell components and thereforeabsorbs the largest clamping force. In most cases, the above phenomena should not cause degradation.But, breaking carbon fibers of the GDL may lead to structural damage and deteriorate its performance[۳]. Freezing produced water in the fuel cell can cause ice formation in different parts of the cell andjoint surfaces of the parts, causing local expansion and mechanical problems after ice melting [۴]. Theaccumulated water on the GDL (produced during the electrochemical reaction or supplied withhydrogen or oxygen gas) can dissolve the carbonaceous material of the GDL and produce hydroxide,oxides, and other species, affecting the GDL properties and cell performance. In addition, thecontinuous flow of inlet gases causes erosion of the GDL surface and mechanical degradation of GDL[۵]. Chemical degradation occurs mainly due to carbon corrosion. Usually, GDL is made of carbon, andin some special conditions, such as starting/shutting down the fuel cell or massive and localized lack offuel, the carbon reacts with water and is washed away, failing the structure [۶]. In conclusion, thedegradation of GDL in PEM fuel cells is critical, hence understanding the mechanism of itsdegradation and studying the contribution of each degradation factor during fuel cell operation isessential. In this case, it is possible to use strategies to mitigate GDL degradation and investigate theeffect of GDL durability on other PEM fuel cell components. moreover, further studies on the durabilityof GDL will extend the lifetime of fuel cell-based vehicles, and stationary systems and promote thecommercialization of PEM fuel cell applications. As a result, considering the drastic impact of GDLsdegradation on the performance of PEM fuel cells, it seems that this issue should be given moreattention.

کلیدواژه ها:

Proton exchange membrane fuel cell ، Gas diffusion layer ، Degradation ، Durability