Journal of Power Sources 196 (2011) 7967–7972 Contents lists available at ScienceDirect Journal of Power Sources jo ur nal homep age: www.elsevier.com/locate/jpowsour Study of operating conditions and cell design on the performance of alkaline anion exchange membrane based direct methanol fuel cells G.K. Surya Prakash ∗ , Frederick C. Krause, Federico A. Viva, S.R. Narayanan, George A. Olah Loker Hydrocarbon Research Institute, Department of Chemistry, University of Southern California 837 Bloom Walk, Los Angeles, CA 90089-1661, USA a r t i c l e i n f o Article history: Received 11 March 2011 Received in revised form 20 May 2011 Accepted 21 May 2011 Available online 27 May 2011 Keywords: Direct methanol fuel cell Alkaline anion exchange membrane Membrane–electrode assembly Optimization a b s t r a c t Direct methanol fuel cells using an alkaline anion exchange membrane (AAEM) were prepared, studied, and optimized. The effects of fuel composition and electrode materials were investigated. Membrane electrode assemblies fabricated with Tokuyama ® AAEM and commercial noble metal catalysts achieved peak power densities between 25 and 168 mW cm -2 depending on the operating temperature, fuel com- position, and electrode materials used. Good electrode wettability at the anode was found to be very important for achieving high power densities. The performance of the best AAEM cells was compara- ble to Nafion ® -based cells under similar conditions. Factors limiting the performance of AAEM MEAs were found to be different from those of Nafion ® MEAs. Improved electrode kinetics for methanol oxi- dation in alkaline electrolyte at Pt–Ru are apparent at low current densities. At high current densities, rapid CO 2 production converts the hydroxide anions, necessary for methanol oxidation, to bicarbonate and carbonate: consequently, the membrane and interfacial conductivity are drastically reduced. These phenomena necessitate the use of aqueous potassium hydroxide and wettable electrode materials for efficient hydroxide supply to the anode. However, aqueous hydroxide is not needed at the cathode. Com- pared to AAEM-based fuel cells, methanol fuel cells based on proton-conducting Nafion ® retain better performance at high current densities by providing the benefit of carbon dioxide rejection. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Direct methanol fuel cells (DMFCs) – based on a proton- conducting polymer electrolyte membrane and a circulating feed of an acid-free, aqueous methanol solution – underwent rapid devel- opment between 1990 and 2005 [1–13]. Nafion ® and other proton exchange membrane (PEM) systems have been widely investigated as electrolytes for DMFCs [14–18]. Operating systems have been demonstrated and a few commercial systems are now available [19–21]. However, more recently, there has been renewed inter- est [22–28] in DMFCs based on alkaline membrane electrolytes because of the possibility of improved electrode kinetics and lower catalyst loading. A recent review by Yu et al. presents a comprehen- sive overview of the current state of the art on direct alcohol fuel cells based on alkaline electrolytes [29]. Recent reports of DMFCs using Tokuyama ® [30] and other membranes [31] are promising, but the power and current densities are lower than those of PEMs. Our goal is to optimize the membrane electrode assembly (MEA) construction and operating conditions in order to maximize the performance of DMFCs based on alkaline anion exchange mem- branes (AAEM) to a practical level. ∗ Corresponding author. Tel.: +1 213 740 5984; fax: +1 213 740 6679. E-mail address: gprakash@usc.edu (G.K.S. Prakash). An alkaline membrane electrolyte can be advantageous to a direct alcohol fuel cell for several reasons. It is known that the kinetics of electro-oxidation of methanol and other alcohols are more rapid in alkaline media [32] compared to acid media due to the weaker binding of chemisorbed intermediates, such as CO; the oxygen reduction reaction is also more facile in alkaline media [33]. The less corrosive alkaline environment invites the possibil- ity of using non-noble metal catalysts at both the anode and the cathode [34]. This presents an opportunity for discovering more selective catalysts, that could facilitate the development of mixed reactant fuel cells [35]. Furthermore, one of the most problematic issues facing Nafion ® -based DMFCs is methanol crossover from the anode to the cathode compartment through the membrane, result- ing in a mixed potential at the cathode, flooding of the cathode, and parasitic consumption of fuel. This problem has been partially solved by using polyvinylidene fluoride–polystyrene sulfonic acid (PVDF–PSSA) membranes developed in our laboratory [14,15]. In alkaline fuel cells, this crossover is likely to be hindered by the electro-osmotic flux of water from the cathode to the anode. Finally, the price of Nafion ® and similar polymers adds significantly to the cost of materials; less expensive membrane materials are desirable. The possibility of using non-noble-metal catalysts with alkaline membranes presents an opportunity for further cost reduction. However, alkaline fuel cells (AFC) are not without disadvan- tages. Most alcohol AFCs include an electrolyte such as potassium 0378-7753/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2011.05.056