Abstract Durability and cost are the major hurdles preventing fuel cell technology from large‐scale commercialization. Membrane degradation due to insufficient chemical stability is one of the main factors affecting fuel cell durability. Using additives as scavenger, the membrane durability can be dramatically enhanced. However, membrane additives normally result in lengthened conditioning, subsequently adding to capital and operational expenditure. It is crucial to understand the root causes of prolonged conditioning process from membrane additives. In this study, four membranes with or without additives were conditioned in a fuel cell and analyzed using various techniques. It is found that the cell voltage exhibits a U‐shaped curve and slow ramping up during conditioning at a constant current, instead of monotonically increasing to a steady state. Experiments also revealed that mostly additives might be overdosed and the releasing of extra additives causes catalyst layer contamination and requires longer conditioning time.