Direct alcohol fuel cells operation conditions

The physical modeling for fundamental imderstanding, diagnostics, and design of new materials and operation conditions of direct alcohol fuel cells is addressed in Chap. 8. The modeling of mechanisms and processes at atomistic and single-cell levels is critically reviewed, as well as the theoretical challenges. A multiscale... 

Zhao,T.S. Xu,C.L. Fuel-cells-Direct alcohol fuel-cells Direct methanol fuel-cell overview performance and operational conditions. In Encyclopedia of electrochemical power sources. Elsevier, 2009, pp. 381-389. 

The direct methanol fuel cell is a special form of low-temperature fuel cells based on PEM technology. In the DMFC, methanol is directly fed into the fuel cell without the intermediate step of reforming the alcohol into hydrogen. Methanol is an attractive fuel option because it can be produced from natural gas or renewable biomass resources. It has the advantage of a high specific energy density, since it is liquid at operation conditions. The DMFC can be operated with liquid or gaseous methanoFwater mixtures. 

Importantly, for elevated temperature PEM fuel cell operation, the HPAs may be structurally stable to >600°C, although under anhydrous conditions their stability may be limited to 200°C, and they incorporate some water molecules and protons up to >300°C depending on the system [15]. Because of their structural diversity, these materials are particularly suitable for incorporation into a wide variety of membrane materials for which they can be specifically tailored. They have been studied in four composite systems HPAs infused into perfluorinated sulfonic acid (PFSA) polymers such as Nafion [16,17], HPA cast in inert matrices such as poly (vinyl alcohol) (PVA) [18], HPA immobilized in polymer/silicate nanocomposites via sol-gel methods [19], and HPA directly incorporated into polymer films via functionalization to monomers [20]. Here after a discussion of fundamental studies, we review the various HPA-based materials used for fuel cells. 

There are different kinds of DAFC operation conditions depending of the way the fuel and the oxidant (oxygen/air) are fed into the cell. In complete active fuel cells the liquid fuel (neat alcohol or aqueous solution) is pumped and gas is compressed, using auxiliary pumps and blowers, in order to improve mass transport and reduce concentration polarization losses in the system. On the other hand, in complete passive DAFC the alcohol reaches the anode catalyst layer by natural convection and the cathode breathes oxygen directly from the air. A number of intermediate options have been also studied and tested. 

---