Theoretical Study of the Morphological and Structural Characteristics of a Hydrated Anion Exchange Membrane Used in Alkaline Fuel Cells Using DFT

Anion-exchange membrane fuel cells (AEMFC) have great potential of commercialization at low cost for their use in automotive transportation, portable batteries and power generators with respect to similar technologies as the proton-exchange membrane fuel cells (PEMFC) due to: a) better kinetic characteristics both for the oxygen reduction reaction as for the hydrocarbon oxidation reducing costs of catalysts, b) lower fuel crossover from anode to the rest of the device, c) simpler water management and d) reduced degree of corrosion [1–3].

Despite the mentioned advantages, the polymeric materials used as electrolytes show low conductivity and chemical stability values, which limit respectively the efficiency and durability of the fuel cell, and as experimentally these factors have not been optimized yet, it is important to understand the related physicochemical phenomena, being the anion transport primordial [1,2,4,5]. Nevertheless, the characteristics of the mechanisms associated with that process are not well known, particularly the Grotthuss mechanism, that is considered to contribute mostly to the hydroxyl ion mobility [1,4].

In order to understand this mechanism and to improve the description of the ion mobility in AEMFCs is mandatory to carry out a rigorous theoretical study, for which the first step is to describe the appropriate structure of a particular anion exchange membrane. So, the aim of the present research is study the morphological and structural characteristics of the quaternized polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene homogeneous membrane synthetized by Qing Hua Zeng and co-workers [6] for different humidification values by means of density functional theory (DFT) techniques, considered the most suitable in terms of prediction and accuracy since there are not almost theoretical studies about structural and morphological characteristics of anion exchange materials used in AEMFC.

With the results obtained, the idea is evaluate the potentiality of DFT techniques to obtain accurate structures for polymeric membranes and use the one generated for future investigations about the physicochemical characteristics of the Grotthuss mechanism for hydroxyl ions in membranes used in AEMFCs, in order to determine the best morphological and structural characteristics of this type of materials from a theoretical approach.

References:

[1]         G. Merle, M. Wessling, K. Nijmeijer, J. Memb. Sci. 377 (2011) 1.

[2]         E. Antolini, E.R. Gonzalez, J. Power Sources 195 (2010) 3431.

[3]         R. Slade, J. Varcoe, Solid State Ionics 176 (2005) 585.

[4]         K.N. Grew, W.K.S. Chiu, J. Electrochem. Soc. 157 (2010) B327.

[5]         B. Pivovar, 2011 Alkaline Membrane Fuel Cell Workshop Final Report, 2012.

[6]         Q.H. Zeng, Q.L. Liu, I. Broadwell, A.M. Zhu, Y. Xiong, X.P. Tu, J. Memb. Sci. 349 (2010) 237.