Durability enhancement of proton exchange membrane fuel cells by ferrocyanide or ferricyanide additives

The chemical stability of proton exchange membranes (PEMs) is a pivotal factor to effectuate reliable and practical durability in proton exchange membrane fuel cells (PEMFCs). Recently, we discovered unexpectedly robust chemical stability of PEMs, which was demonstrated to be attributable to the radical scavenging ability of the ferrocyanide‒ferricyanide (Fc (II)‒Fc (III)) redox cycle. In these previous studies, the Fc (II)‒Fc (III) redox species were introduced into polymer matrices using a strategy of ligand exchange, which somewhat restricts the applicable scope of available polymers. Herein, via an alternative route of physical incorporation, Fc (II)/Fc (III) species are introduced into a variety of perfluorosulfonic acid (PFSA) and sulfonated hydrocarbon PEM matrices. The resulting composite membranes display enhanced durability in PEMFC evaluations, compared with pristine membranes, even considerably beyond the composite membranes using US Department of Energy approved state-of-the-art antioxidant Ce ions. Moreover, the incorporation of Fc (II)/Fc (III) species simultaneously introduces additional proton sites after membrane acidification, thereby increasing both ex situ conductivity and in situ power output. In addition, due to hydrogen bonding between the less ionized protons on Fc (II)/Fc (III) species and the sulfonic groups of the polymer matrices, these additives show adequate retention in the composite membranes. The strategy proposed in the present work appears promising as a universal method to greatly improve the chemical oxidative stability of both PFSA and hydrocarbon-based PEMs. [Display omitted] •Ferrocyanide/ferricyanide as effective antioxidative additives for enhancing PEM stability.•Good additive retention through hydrogen bond interactions with PEM sulfonic acid.•Improved proton conductivity/fuel cell power output from the additional additive protons.•Universal feasibility for incorporation into a broad range of membrane matrices.•Prospective potential to surpass the US DOE utilized Ce ion antioxidative additives.