A Study Of Ultrathin Alkaline Polymer Electrolyte Membrane For Fuel Cell Application

As one of the most important components of alkaline polymer electrolyte fuel cells（APEFCs）,the physicochemical property of alkaline polymer electrolyte（APE）membranes plays a vital role in cell performance.The APE membranes with excellent performance need to have high ionic conductivity,outstanding stability and mechanical properties.And the recognition has been formed that the ultrathin membranes are one of the keys to the high-performance APEFCs.The advantages of the ultrathin membranes are their low area-specific resistance and fast water transport ability.However,low thickness also brings low mechanical strength of the membranes,resulting in difficulties in the APEFCs assembling and operation.To overcome this issue,some reinforced composite membranes are taken into consideration,the thickness of the membranes can be reduced to 10μm.However,the poor compatibility between components of the composite membranes will result in the loss of ionic components during the operation condition.Furthermore,the introduction of the reinforced components has a negative impact on the ionic conductivity of APE membranes.Therefore,the development of freestanding ultrathin APE membranes is more and more important.Crosslinking is a wise approach to prepare membranes with high mechanical properties,the most common crosslinking method is to lock the polymer chains with crosslinking reagents,ultimately,impurities will be left in the prepared membrane.These impurities can decrease the mechanical strength of the membrane,especially for the ultrathin membranes.Base on the above problem,herein,robust crosslinked ultrathin membranes were prepared via a novel approach named side-chain self-crosslinked reaction.Instead of direct adding crosslinking agents,the crosslinking reaction occurs between the functional groups onto the polymer precursors.After optimizing the reaction conditions,we obtained four quaternary ammonia poly（N-methyl-piperidine-co-p-terphenyl）（cQAPPT）membranes:cQAPPT-C6-18,cQAPPT-C6-10,cQAPPT-C3-10 and cQAPPT-C6-5.All membranes（28μm）exhibited excellent comprehensive performance,and the PPD of four APEFCs reached not less than 1 W/cm².Subsequently,the four ultrathin cQAPPT membranes（10μm）were used to prepare the MEA by the catalyst coated membrane（CCM）approach,only cQAPPT-C6-18 was intact.To clarify the advantage of ultrathin membranes to the high-performance APEFCs,the two MEAs with cQAPPT-C6-18 membranes（10 and 28μm）were used for the single-cell tests.The H₂/O₂ APEFC with the 28μm cQAPPT-c6-18membrane exhibited a satisfactory cell performance with a PPD of 1.42 W/cm² at 3A/cm²,and the high-frequency resistance（HFR）was 20.5 mΩ.Benefited from the lower area-specific resistance（HFR,15.7 mΩ）and the faster water transport ability of the membrane,APEFC using the 10μm ultrathin membrane got a 30%increase in PPD and reached 1.85 W/cm² at 4 A/cm².After the 100 h discharge test,the cell voltage decays by about 25%.Indicating that the ultrathin membrane has good stability under cell operation conditions.This work demonstrates the feasibility of the side-chain self-crosslinking approach for making the freestanding ultrathin APE membrane,the APEFC operation with a freestanding ultrathin membrane,and provides valuable exploration for the application of high-performance APEFCs.