Small direct methanol fuel cells with passive supply of reactants

Small, stand-alone, direct methanol fuel cells (DMFCs) that have no auxiliary liquid pumps and gas blowers/compressors are known as passive DMFCs. The devices are ideal for powering portable electronic devices, as this type of fuel cell uniquely has a simple and compact system and no parasitic power losses. This article provides a comprehensive review of experimental and numerical studies of heat and mass transport in passive DMFCs. Emphasis is placed on the mechanisms and key issues of the mass transport of each species through the fuel cell structure under the influence of passive forces. It is shown that the key issue regarding the methanol supply is how to feed high-concentration methanol solution but with minimum methanol crossover through the membrane so that both the system specific energy and cell performance can be maximized. The key issue regarding the oxygen supply is how to enhance the removal of liquid water from the cathode under the air-breathing condition. For water transport, the aim is to transport the water produced on the cathode through the membrane to the anode by optimizing the design of the membrane electrode assembly so that the fuel cell can be operated with pure methanol and with minimum flooding at the cathode. The heat loss from a passive DMFC is usually large and it is therefore critically important to reduce this feature so that the fuel cell can be operated at a sufficiently high temperature, which critically affects the cell performance.