Abstract—An extensive research has been carried out to improve the performance of direct methanol fuel cells (DMFCs) using low methanol concentration below 5 M either in active or passive conditions due to methanol crossover (MCO) problem which the methanol crosses over the membrane and reacts directly with oxygen at cathode. However, a low methanol concentration leads to a low energy density of the fuel cell system and a short runtime which cannot meet the requirement of commercialization. Therefore, it is important to use a high concentration of methanol in DMFC to achieve a high energy density. This study was done to improve the performance of passive vapor feed DMFC by using high methanol concentrations from 12 M (molarity) to neat methanol. From the results obtained, it was showed that the performance of passive vapor feed DMFC that used high methanol concentration improved. It was a linear dependence of current density on methanol concentration which is the current density increased when the methanol concentration increased up to neat. The linear dependence of current density on the concentration suggested that the cell operation was under the rate controlling by the methanol transport. Therefore, it can conclude that high methanol concentration can leads to high energy density achieved by the DMFCs. Index Terms—Direct methanol fuel cell, energy density, methanol concentration I. INTRODUCTION Direct methanol fuel cell is a renewable source of fuel and can offer high power and energy density, low emissions, ambient operating conditions and fast and convenient refueling. It is an appropriate power supply for electronic device [1], [2]. DMFC operates either in active or passive mode. Active DMFC works with additional devices to deliver reactant to the cell such as pump or blower. In contrast with passive DMFC, it eliminates any usage of additional devices in the operation which fuel is stored in fuel reservoir and oxygen supplied to cathode by air- breathing. Completely passive DMFC is preferable due to its simplicity in design and suitable for portable application compared to active DMFC [3]. Based on the previous studies on DMFC, optimum concentration that produces maximum power density for active DMFC is about 1M to 2M while 4M for passive DMFC [4]. Further increasing the methanol concentration will leads in methanol crossover Manuscript received October 9, 2012; revised November 18, 2012. F. A. Halim and U. A. Hasran are with the Fuel Cell Institute, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia (e-mail: fahimah.engukm@gmail.com). M. S. Masdar and S. K. Kamarudin are with Fuel Cell Institute, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia, and Department of Chemical and Process Engineering, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia. problem. This problem occurred when the methanol diffuses through the membrane, reacts at the cathode side and lowers the conversion efficiency [5]. Methanol crossover also results in a waste of fuel [6]. High methanol concentration will cause high methanol crossover rate through the membrane and reduce the cell performance. However, high methanol concentration enables the DMFC to obtain high performance compared to low methanol concentration [4]. An alternative way to lessen this problem is to operate the DMFC in vapor feed because the methanol crossover rate is much lower than in the liquid feed DMFC and the methanol can be fed with high concentration or neat methanol [7]. In vapor feed DMFC, methanol evaporates from nearly pure liquid methanol source and condenses into a highly dilute methanol solution at the anode side. The liquid methanol and air can be delivered in passive manner by natural convection and capillary force [8]. Vapor feed direct methanol fuel cell has potential for a shorter start-up time because of the mass diffusivity is several orders of magnitude greater than in liquid phase. It also has potential to have a higher operating temperature and thus increasing the reaction rates which resulting in higher power outputs [9]. Study on vapor feed DMFC operating with high methanol concentration or neat methanol was reported by some researchers. Hae Kyoung Kim proposed a vapor fed passive DMFC to achieve high energy density by using pure methanol for mobile application. The passive vapor feed DMFC with a humidified MEA showed 20–30mWcm −2 for 15 days with a maximum power of 36mWcm −2 . It also showed 70% higher fuel efficiency and 1.5 times higher energy density for a 4 h operation than the liquid feed passive DMFC. In this work, a porous fired alumina, porous foam, barrier, and vaporizer were used for feeding and controlling methanol in the vapor phase [10]. Guo et al provided a vapor feed DMFCs with passive thermal or fluids management systems. Pure methanol was delivered by the wick structures from a liquid methanol reservoir to an evaporation pad. The liquid was evaporated by different heating manners such as electrical heating, catalyst burning and heat recovery from the cell itself. The results showed that the vapor feed DMFC reached a power density of 16.5 mW/cm 2 at a current density of 60 mA/cm 2 [3]. Besides that, Eccarius et al., introduced a vapor-fed DMFC with completely passive operation on both anode and cathode sides and the effect of methanol concentration on the fuel cell performance were investigated. A polydimethylsiloxane (PDMS) membrane was applied as an evaporator through which the liquid methanol could be evaporated automatically into vapor phase without any energy input [11]. Instead of using a membrane as the vaporizer, Study on a Passive Vapor Feed Direct Methanol Fuel Cell with High Methanol Concentration F. A. Halim, U. A. Hasran, M. S. Masdar, and S. K. Kamarudin 292 DOI: 10.7763/JOCET.2013.V1.66 Journal of Clean Energy Technologies, Vol. 1, No. 4, October 2013