A Highly Hydroxide Conductive, Chemically Stable Anion Exchange Membrane, Poly(2,6 dimethyl 1,4 phenylene oxide)-b-Poly(vinyl benzyl trimethyl ammonium), for Electrochemical Applications

Abstract

A chemically stable copolymer [poly(2,6 dimethyl 1,4 phenylene oxide)-b-poly(vinyl benzyl trimethyl ammonium)] with two ion exchange capacities, 3.2 and 2.9 meq g −1 , was prepared as anion exchange membranes (AEM-3.2 and AEM-2.9). These materials showed high OH − conductivities of 138 mS.cm −1 and 106 mS.cm −1 , for AEM-3.2 and AEM-2.9 respectively, at 60 • C, and 95% RH. The OH − conductivity = 45 mS.cm −1 for AEM-3.2 at 60% RH and 60 • C in the absence of CO 2 . Amongst the ions studied, only OH − is fully dissociated at high RH. The lower E a = 10-13 kJ.mol −1 for OH − compared to F − ∼ 20 kJ.mol −1 in conductivity measurements, and of H 2 O from self-diffusion coefficients suggests the presence of a Grotthuss hopping transport mechanism in OH − transport. PGSE-NMR of H 2 O and F − show that the membranes have low tortuosity, 1.8 and 1.2, and high water self-diffusion coefficients, 0.66 and 0.26 × 10 −5 cm 2 .s −1 , for AEM-3.2 and AEM-2.9 respectively. SAXS and TEM show that the membrane has several different sized water environments, ca. 62 nm, 20 nm, and 3.5 nm. The low water uptake, λ = 9-12, reduced swelling, and high OH − conductivity, with no chemical degradation over two weeks, suggests that the membrane is a strong candidate for electrochemical applications. Anion Exchange membranes (AEMs) have been proposed as the separator in electrochemical energy conversion devices such as fuel cells, electrolyzers, or redox flow cells.1 As catalysis is more facile in base, the use of an AEM should allow the use of non-precious metal catalysts and also the oxidation or production of complex fuels beyond hydrogen.2 Significant work has been done in the past decade in this area and many new membranes have been developed with improved mechanical, chemical, and transport properties. An ideal AEM should have high ionic conductivity to achieve practical power densities, 3 good chemical stability to operate under an alkaline environment, 4 and excellent thermal and mechanical properties to survive transient operating conditions. 1,5 Intensive efforts have been made to study AEMs with aromatic backbones such as polysulfone, 6-8 poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), 9-11 and poly(ether ether ketone) 12 due to their high thermal and chemical stability, good mechanical properties, and outstanding film forming ability.13 PPO is a versatile aromatic polymer, which can advantageously be used as a precursor in the preparation of graft, 14 random and copolymers as studied by previous researchers for AEM applications. 9,11,15,16 PPO was found to be favorable in the fabrication of AEMs due to its higher alkaline stability stemming from the absence of strong electron-withdrawing groups. The polymer has been studied using solvent processing techniques earlier 17 but no study reports melt processing for fabricating membranes.Polymer -water/ion interactions are important when it comes to understanding performance of anion exchange membranes.18 Inherently hydroxide (OH − ) transport (5.273 × 10 −5 cm 2 /sec) is ∼50% slower tha...

Partially fluorinated and ammonium-functionalized terpolymers: Effect of aliphatic groups on the properties of anion conductive membranes

“…QPAF‐3 (3) membrane with IEC = 1.46 meq g −1 achieved the highest conductivity of 123 mS cm −1 at 80 °C. The apparent activation energy was estimated from the slopes to be 10.6 to 12.0 kJ mol −1 , which are similar to those of QPAF‐1 (11.7 kJ mol −1 ) and the other aromatic polymer‐based AEMs . The result indicates that they share similar ion‐conducting mechanism involving hydrated OH − ions in water.…”

Beyond catalysis and membranes: visualizing and solving the challenge of electrode water accumulation and flooding in AEMFCs

“…Additionally, moving to AEMFCs allows for the use of lower cost anion-exchange membranes (AEMs) and offers the potential to decrease other balance of plant costs related to humidification and air circulation systems. [2][3][4][5][6][7] The recent, intense effort around AEMFCs has led to the development of several highly conducting, stable AEMs and anion exchange ionomers (AEIs), [8][9][10][11][12][13][14][15][16][17][18][19][20][21] high activity catalysts -still predominantly PGM-containing at the cathode and anode, 5,6,8,[22][23][24][25][26][27] although there has been recent progress on PGM free catalysts [3][4][5][6][28][29][30][31][32][33] -as well as a significant increase in state-ofthe-art performance. [19][20][21][22]34 At least some of this success can be attributed to the willingness of researchers to rapidly and transparently share their accomplishments in this area over…”

Development of Polymeric Membranes Based on Quaternized Polysulfones for AMFC Applications

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