PEMFCs and AEMFCs directly fed with ethanol: a current status comparative review

The last decade’s research on the performance of proton-exchange membrane direct ethanol fuel cells (PEM-DEFCs) and anion exchange membrane direct ethanol fuel cells (AEM-DEFCs) is included in the present review. Future research challenges are identified along with potential strategies to overcome them. Pt-containing or Pt-free PEM-DEFCs that use acid proton-exchange membranes (typically Nafion type) exhibit relatively low performance (i.e., the state-of-the-art peak power density is 110 mW cm −2 at 145 °C over 4 mg of total Pt loading), while Pt-containing or Pt-free AEM-DEFCs that use low-cost anion-exchange membrane have recently exhibited better performance values (i.e., the state-of-the-art peak power density is about 185 mW cm −2 at 80 °C over Au-modified Pd catalysts supported on carbon nanotubes. The required faster kinetics of the ethanol oxidation and especially for the oxygen reduction reaction seem to be satisfied from one side by the AEM-DEFCs and from the other by PEM-DEFCs only if working at intermediate temperature values (>150 °C). Moreover, new possibilities of using less expensive metal catalysts (as silver, nickel, and palladium) are opening mainly for AEM-DEFCs and the last years for PEM-DEFCs too. Finally, it is worth to be noticed that the best value ever reported (peak power density is 360 mW cm −2 at 60 °C) has been obtained in a very promising alkaline-acid direct ethanol fuel cell (AA-DEFC).