Development of a Self-Adaptive Direct Methanol Fuel Cell Fed with 20 M Methanol J. Guo 1 , H. Zhang 1 *, J. Jiang 1 , Q. Huang 1 , T. Yuan 1 , H. Yang 1 * 1 Energy Storage Laboratory, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai, 201210, P. R. China Received January 7, 2013; accepted August 26, 2013; published online September 16, 2013 1 Introduction The direct methanol fuel cell (DMFC) has attracted broad interest as a promising power source for portable applications due to its high energy density, system simplicity, quick and easy refueling as well as availability and ease of storage of methanol [1–4]. In order to make the DMFC more competitive with the conventional Li-ion batteries, it is the best choice for the miniature DMFC to be operated in a passive mode and with highly concentrated methanol as fuel. Technically, there are several critical issues that have to be addressed before the widespread applications of the passive DMFCs. These chal- lenges include the crossover of methanol from the anode to the cathode, sluggish kinetics of both anode and cathode reac- tions, the direct use of methanol of high concentration (until pure methanol) within the system to ensure the higher energy density, the management of water and heat and limited life- time [5]. To reach the most remarkable feature of the high energy density of methanol, the DMFC is expected to operate with highly concentrated methanol. However, in a conventional DMFC structure, an increase in concentration of the fed methanol would lead to the increase in methanol crossover. The crossover of methanol not only gives rise to so-called “mixed potential” effect that greatly reduces the output volt- age of the DMFC, but also causes a waste of methanol that lowers the fuel utility [6–8]. To avoid this problem, one essen- tial strategy is the development of a novel less-methanol- permeable proton-exchange membrane [9, 10]. Another route is the use of the oxygen reduction catalysts, which are inac- tive toward methanol oxidation or have a high methanol tol- erance. To date, the Nafion ® membranes are still commonly used in the DMFCs. Under such a condition, the dilute methanol solutions (e.g. 1–4 M) are usually used as fuels in the traditional DMFC to mitigate the side effect of methanol crossover [11]. In this case, the energy density of the DMFC system is quite low. This situation is particularly important for the passive DMFC system. As reported, to operate the passive DMFC system with highly concentrated methanol, the methanol crossover could be suppressed significantly by using porous conductive materials with excessively small pores and by employing a barrier layer at the anode to Abstract A passive and self-adaptive direct methanol fuel cell (DMFC) directly fed with 20 M of methanol is developed for a high energy density of the cell. By using a polypropylene based pervaporation film, methanol is supplied into the DMFC’s anode in vapor form. The mass transport of metha- nol from the cartridge to the anodic catalyst layer can be controlled by varying the open ratio of the anodic bipolar plate and by tuning the hydrophobicity of anodic diffusion layer. An effective back diffusion of water from the cathode to the anode through Nafion film is carried out by using an additive microporous layer in the cathode that consists of 50 wt.% Teflon and KB-600 carbon. Accordingly, the water back diffusion not only ensures the water requirement for the methanol oxidation reaction but also reduces water accu- mulation in the cathode and then avoids serious water flooding, thus improving the adaptability of the passive DMFC. Based on the optimized DMFC structure, a passive DMFC fed with 20 M methanol exhibits a peak power den- sity of 42 mW cm –2 at 25 °C, and no obvious performance degradation after over 90 h continuous operation at a con- stant current density of 40 mA cm –2 . Keywords: Adaptability, Highly Concentrated Methanol, Passive DMFC, Vapor-Feed, Water Management – [ * ] Corresponding authors, zhanghf@sari.ac.cn and yangh@sari.ac.cn 1018 © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim FUEL CELLS 13, 2013, No. 6, 1018–1023 ORIGINAL RESEARCH PAPER DOI: 10.1002/fuce.201200236