Portable Direct Methanol Fuel Cell Research Articles

Graphene Coating of Nafion Membranes for Enhanced Fuel Cell Performance.

Electrochemically exfoliated graphene (e-G) thin films on Nafion membranes exhibit a selective barrier effect against undesirable fuel crossover. This approach combines the high proton conductivity of state-of-the-art Nafion and the ability of e-G layers to effectively block the transport of methanol and hydrogen. Nafion membranes are coated with aqueous dispersions of e-G on the anode side, making use of a facile and scalable spray process. Scanning transmission electron microscopy and electron energy-loss spectroscopy confirm the formation of a dense percolated graphene flake network, which acts as a diffusion barrier. The maximum power density in direct methanol fuel cell (DMFC) operation with e-G-coated Nafion N115 is 3.9 times higher than that of the Nafion N115 reference (39 vs 10 mW cm-2@0.3 V) at a 5M methanol feed concentration. This suggests the application of e-G-coated Nafion membranes for portable DMFCs, where the use of highly concentrated methanol is desirable.

A Portable Direct Methanol Fuel Cell Power Station for Long-Term Internet of Things Applications

With regard to the best electro-chemical efficiency of an active direct methanol fuel cell (DMFC), the stacks and their balance of plant (BOP) are complex to build and operate. The yield of making the large-scale stacks is difficult to improve. Therefore, a portable power station made of multiple simpler planar type stack modules with only appropriate semi-active BOPs was developed. A planar stack and its miniature BOP components are integrated into a semi-active DMFC stack module for easy production, assembly, and operation. An improved energy management system is designed to control multiple DMFC stack modules in parallel to enhance its power-generation capacity and stability so that the portability, environmental tolerance, and long-term durability become comparable to that of the active systems. A prototype of the power station was tested for 3600 h in an actual outdoor environment through winter and summer. Its performance and maintenance events are analyzed to validate its stability and durability. Throughout the test, it maintained the daily average of 3.3 W power generation with peak output driving capability of 12 W suitable for Internet of Things (IoT) applications.

Hybrid Bi-Cells for Water Independent Direct Methanol Fuel Cells: II. The Miniaturized Fuel Cell System

Methanol, which is used in portable direct methanol fuel cell (DMFC) systems, is an energy-dense liquid fuel. Concentrated methanol is typically carried as a DMFC fuel source and fed to an internal reservoir, which maintains a dilute fuel mixture feeding the fuel cell stack. Active water and fuel management are required to maintain the concentration and volume of this internal reservoir. Water produced and/or carried to the cathode is condensed and recycled to the anode, requiring a radiator and other components. These components are largely responsible for the size and mass of portable DMFCs. A hybrid bi-cell stack approach is put forth here, which reduces the need for active water and fuel management. This configuration combines membrane electrode assemblies (MEAs) made of proton exchange membrane (PEM) and anion exchange membrane (AEM) electrolytes within individual bi-cell units. The water stoichiometry of the electrochemical oxidation and reduction reactions are complementary for the acidic PEM and alkaline AEM MEAs. A transport model is used to show that standard PEM bi-cell stacks have about 4x the demand for active water recycling that hybrid bi-cell stacks do at typical operating conditions. Opportunities to completely eliminate the need for water recycling are shown.

Transport Phenomena in Bi-Cells for Portable Fuel Cell Power Source

The specific energy of neat liquid methanol tends to provide direct methanol fuel cell (DMFC) systems with large energy densities, making them ideal for portable power applications. However, portable DMFC systems are larger than desired. The balance of plant (BOP) is the key contributor to the system volume, and specifically components used for water management. In this study, a theoretical approach is taken to better understand the water management requirements. A passive bi-cell, or pseudo bipolar, configuration is used as a baseline for this study.

Performance of a Direct Methanol Fuel Cell Operating Close to Room Temperature

The direct methanol fuel cell (DMFC) is a promising power source for micro- and various portable electronic devices (mobile phones, PDAs, laptops, and multimedia equipment) with the advantages of easy fuel storage, no need for humidification, and simple design. However, a number of issues need to be resolved before DMFC commercialization, such as the methanol crossover and water crossover, which must be minimized in portable DMFCs. In the present work, a detailed experimental study on the performance of an “in-house” developed DMFC with 25 cm2 of active membrane area, working near the ambient conditions is described. The influence on the DMFC performance of the methanol concentration in the fuel feed solution and of both anode and cathode flowrates was studied. Tailored membrane electrode assemblies (MEAs) were designed in order to select optimal working conditions. Different structures and combinations of gas diffusion layers (GDLs) were tested. Under the operating conditions studied it was shown that, as expected, the cell performance significantly increases with the introduction of gas diffusion layers and that carbon cloth is more efficient than carbon paper both for the anode and cathode GDLs. The results reported allow the setup of tailored MEAs enabling the cell operation at high methanol concentrations (high power densities) without sacrificing performance (i.e., achieving low methanol crossover values). The influence of the different parameters on the cell performance is explained under the light of the predictions from a previously developed one-dimensional model, coupling heat and mass transfer effects. The main gain of this work is to report DMFC detailed experimental data at near ambient temperature which are insufficient in literature. This operating condition is of special interest in portable applications.

Performance comparison of portable direct methanol fuel cell mini-stacks based on a low-cost fluorine-free polymer electrolyte and Nafion membrane

A low-cost fluorine-free proton conducting polymer electrolyte was investigated for application in direct methanol fuel cell (DMFC) mini-stacks. The membrane consisted of a sulfonated polystyrene grafted onto a polyethylene backbone. DMFC operating conditions specifically addressing portable applications, i.e. passive mode, air breathing, high methanol concentration, room temperature, were selected. The device consisted of a passive DMFC monopolar three-cell stack. Two designs for flow-fields/current collectors based on open-flow or grid-like geometry were investigated. An optimization of the mini-stack structure was necessary to improve utilization of the fluorine-free membrane. Titanium-grid current collectors with proper mechanical stiffness allowed a significant increase of the performance by reducing contact resistance even in the case of significant swelling. A single cell maximum power density of about 18 mW cm −2 was achieved with the fluorine-free membrane at room temperature under passive mode. As a comparison, the performance obtained with Nafion 117 membrane and Ti grids was 31 mW cm −2. Despite the lower performance, the fluorine-free membrane showed good characteristics for application in portable DMFCs especially with regard to the perspectives of significant cost reduction.

Normally closed electrostatic microvalve with pressure balance mechanism for portable fuel cell application

This paper describes the fabrication and evaluation of an electrostatic microvalve to control the concentration of methanol in direct methanol fuel cell (DMFC) systems. The microvalve uses a novel pressure balance mechanism to realize normally closed operation against pressurized fuel, and maintained close state up to an input pressure of 40 kPa as designed. The driving voltage ranged from 50 V to 110 V depending on the input pressure. The measured results were compared with simulation results, and showed fair agreement with simulation results. Finally, the developed microvalve was applied to a prototyped portable DMFC system, and stable electric generation was demonstrated.

A Novel Design of a Cylindrical Portable Direct Methanol Fuel Cell

Novel designs of a cylindrical and a flat portable direct methanol fuel cell (DMFC) have been proposed in this research. Experimental cells have also been fabricated. Their maximum power output reached 12mW∕cm2 when operating at room temperature and with naturally breathed air. The weight and the volume of the experimental cylindrical cell are 27g and 30cm3, respectively, with 7.5cm3 of methanol inside. Its specific power and volumetric power density are 6.67mW∕g and 6.25mW∕cm3, respectively. The membrane electrode assembly was fabricated by hot pressing the electrodes purchased from E-Tek Co. The catalyst contents are 4.0mg∕cm2 of Pt∕Ru (80wt.% carbon supported) and 4.0mg∕cm2 of Pt (black) for anode and cathode, respectively. The new and compact design will make the portable DMFC lighter and cheaper, and bring it one step closer to be marketable.

단위 셀간 성능편차 및 접속접안 강하 초소화를 위한 극소형 직접메탄올 연료전지 스택의 설계 및 제작

We present a MEMS-based portable Direct Methanol Fuel Cell (micro-DFMC), featured by a platinum sputtered microcolumn electrode and a built-in fuel chamber containing a limited amount of methanol fuel. Also presented is a micro-DMFC stack structure having a common electrolyte sandwiched by the microcolumn electrodes. The single cells with ME16 and PE16 electrodes show the maximum power densities of 31.04±0.29μW/cm2 and 9.75±0.29μW/㎠ respectively; thus indicating the microcolumn electrode (ME16) generates the power density (3.2 times) higher than the planar electrode (PE16). The single cell tests of ME16 and ME4 electrodes (Fig.8) show the maximum power of 31.04±0.29μW/㎠ and 25.23±2.7μW/㎠ respectively; thus demonstrating the increased window frame reduces the normalized standard power deviation (standard deviation over the average power). The normalized deviation of 0.11 in ME4 cell has been reduced to 0.01 in ME16 cell due to the increased window frames. The maximum power density of 4-cell stack is 15.7 times higher than that of the single cell. 4-cell stack produces the power capacity of 20.3mWh/g during 980min operation at the voltage of 450mV with the load resistance of 800Ω.

Compact Direct Methanol Fuel Cells for Portable Applications: A Modeling Study

Consumers demand for portable audio/video/ICT devices has driven the development of advanced power technologies in recent years. Fuel cells are a clean technology with low emissions levels, able to work with renewable fuels and capable, in a next future, to replace conventional power systems meeting the targets of the Kyoto Protocol for a society based on sustainable energy systems. Within such a perspective, the objective of the European project MOREPOWER (Compact direct methanol fuel cells for portable applications) is to develop a low cost, low temperature, portable Direct Methanol Fuel Cell (DMFC; nominal power 250 W) of compact construction and modular design for the potential market area of weather stations, medical devices, signal units, gas sensors and security cameras. This investigation is focused on a conceptual study of the DMFC system carried out in the Matlab/Simulink platform. Two different DMFC configurations were devised in which alternative components arrangements along the methanol recycle line are considered. Based on a number of simulations, the system configuration characterized by a gas-liquid separator for carbon dioxide removal placed upstream the radiator for heat removal shows the most promising results, thanks to an easier design and operability of the radiator itself.