Direct ethanol fuel cells using an anion exchange membrane

Direct ethanol fuel cells (DEFCs) with a PtRu anode and a Pt cathode were prepared using an anion exchange membrane (AEM) as an electrolyte instead of a cation exchange membrane (CEM), as in conventional polymer electrolyte fuel cells. The maximum power density of DEFCs significantly increased from 6 mW cm⁻² to 58 mW cm⁻² at room temperature and atmospheric pressure when the electrolyte membrane was changed from CEM to AEM. The anode and cathode polarization curves showed a decrease in the anode potential and an increase in the cathode potential for AEM-type DEFCs compared to CEM-type. This suggests that AEM-type DEFCs have superior catalytic activity toward both ethanol oxidation and oxygen reduction in alkaline medium than in acidic medium. The product species from the exhausted liquid from DEFCs operated at a constant current density were identified by enzymatic analysis. The main product was confirmed to be acetic acid in AEM-type, while both acetaldehyde and acetic acid were detected in 1:1 ratio in CEM-type. The anodic reaction of AEM-type DEFCs can be estimated to be the oxidation of ethanol to acetic acid via a four-electron process under these experimental conditions.