Improved chemical durability in polymer electrolyte membranes with nanocellulose-based gas barrier interlayers

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Enhancing the lifetime of polymer electrolyte fuel cells (PEFCs) is a key factor in accelerating their application in heavy-duty vehicles (HDVs). A major contributing factor to their worsening performance over time is chemical degradation of the polymer electrolyte membrane (PEM). This is largely caused by the generation of reactive oxygen species such as hydroxyl radicals (•OH) or hydrogen peroxide (H2O2), which break down the polymer structure. This radical attack results in a loss of ionic conductivity and thus an increase in cell resistance over the operational lifetime. Here we show that adding an interlayer with suitable gas barrier properties can effectively suppress the generation of reactive oxygen species, slow the rate of membrane thinning, and extend the lifetime of the cell. We found that cellulose nanocrystals (CNC) blends with poly(vinyl sulfonic acid) (PVS) are suitable composite materials for the interlayer, combining low oxygen permeability with reasonable proton conductivity. Accelerated degradation of the PEMs was investigated via open circuit voltage (OCV) holding tests, in which the device lifetime was reproducibly extended by the incorporation of the CNC/PVS interlayer. Post-mortem analysis revealed that the rate of membrane thinning at the anode side of the PEM after 100 h test was just 30 nm/h, compared with 80 nm/h without an interlayer. Our results clearly confirm that the incorporation of CNC/PVS interlayers with low oxygen permeability into PEMs can suppress chemical degradation and significantly improve the durability of PEFCs. The obtained results also indicate that the concept of the gas barrier PEM for the improved chemical durability of PEMs can be widely and universally applied. We anticipate that this will contribute to the development of next-generation devices with sufficient lifetime for efficient use in fuel cell electric vehicles (FCEVs), including heavy-duty FCEVs.