Key Technical Barriers

The identical individual cells are stacked together through flow field designs. It is a challenge to keep all the cells of the stack at a uniform flow rate and pressure drop [59,60], 

Whilst rehabihty, robustness and durability in the stack cannot reproduce the performance of a singular working cell, it is understood that failure of a stack can occur because of the failure of any one individual cell. 

The failure of an individual cell generally occurs because the ceU did not woik as it was designed due to higher or lower flow rates. 

For example, the loss of power output due to an individual cell failure is only 1 % in a stack of 100 cells. However, the very small deviation caused by the cell failure may be amplified in multiple level manifolds due to water blockage of the cell. This effect of amplification may be serious enough to lead to various other degradations or failure of materials and catalysts or local hotspot or flooding. 

It has been observed that individual cells in a stack often exhibit heterogeneities in cell performance and a fuel cell stack was drastically more susceptible to performance degradation compared to a single cell fuel ceU [61-65]. A fuel ceU stack performs different compared to single cells [66-69]. A larger stack has a shorter lifespan due to early failure of some individual cells. A failure of the operation of a fuel cell stack ultimately occurs due to the loss of structural integrity of one or several of the ceUs, even in short-stack experiments [70-72]. 

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