Migration of Ce and Mn Ions in PEMFC and Its Impact on PFSA Membrane Degradation

Abstract

The incorporation of cerium and manganese ions in perfluorosulfonic acid (PFSA) membranes strongly decreases the fluoride ion emission rate from fuel cell membrane electrode assemblies through their scavenging of reactive oxygen species generated during fuel cell operation. Concentration gradients of these ions and water fluxes lead to their migration and even loss from the fuel cell, but little is known about these phenomena that nevertheless impact proton exchange membrane fuel cell durability. We have determined the diffusion behavior of manganese and cerium ions in perfluorosulfonic acid membranes and find the diffusion coefficient of divalent manganese ions to be higher than that of trivalent cerium. We relate this observation to their relative efficacy in mitigating membrane degradation in a proton exchange membrane single cell, where ionic HPLC analysis of effluent water, technique used here for the first time, shows that three times greater loss of manganese ions than cerium ions after 200 hours at open circuit. Fluoride emission from PFSA membranes degraded ex situ and in situ are corroborated by results from detailed infrared, 19 F MAS NMR and X-ray photoelectron spectroscopic analysis.

Holistic approach to chemical degradation of Nafion membranes in fuel cells: modelling and predictions

“…When Ce 3+ ions were introduced by spraying on both anode and cathode side (about 1% of SC-SO 3 H complexed), the same FER value of 1.6 Â 10 À9 mol cm À2 h À1 was measured. 41 Similar results were presented by Zatoń et al, 44 who observed a reduction of 2 orders of magnitude when loading the membrane with 0.04 mmol Ce 3+ g À1 membrane.…”

“…If this basic mitigation strategy is not possible, the number of reactive oxygen species can be reduced using radical scavengers. In the last two decades, various mitigation strategies have been investigated -an excellent overview is given in the review by Zatoń et al 5 Cerium serves either in its ionic form (Ce 3+ , Ce 4+ ) [41][42][43][44] or as solid cerium oxide (ceria, CeO 2 ) 45,46 as a radical scavenger. When ceria is incorporated into the membrane, it dissolves under operating conditions and produces both trivalent and tetravalent cerium ions.…”

“…The authors concluded that the cerium ions leave the membrane and enrich at both anode and cathode catalyst. 104 Zatoń et al 44 also presented evidence that cerium migrates to the electrodes and is additionally eluted from the fuel cell, which limits the applicability of cerium scavengers in PEMFCs. Moreover, at increased Ce loadings (e.g.…”

“…This powerful model allows monitoring and prediction of experimentally accessible data like time traces of chemical species involved 33 and fluoride emission rates (FERs). [35][36][37] Furthermore, we discuss the implications of iron containing ORR catalysts [38][39][40] for membrane degradation and the use of cerium agents [41][42][43][44][45][46][47] as radical scavengers to protect the chemical integrity of the membrane.…”

Effects of Membrane Additives on PEMFC Conditioning

“…[7] When doping with additives such as metal oxides and chemical complexes comprising of certain metal and organic ligand components, membrane durability can dramatically be enhanced. [8][9][10][11][12][13][14][15][16][17] For example, Kjeang et al [15] reported that the lifetime of the MEA with additive CeO 2 was remarkably extended to 1,244 hours, demonstrating six times longer lifetime and 40 times lower fluoride emission rate than its baseline MEA without cerium. However, incorporating additives into proton exchange membranes is a double-edged sword.…”