Electrochemical Acceleration of Hydrogen Transfer Through a Methanol Impermeable Metallic Barrier

Abstract

Placing a hydrogen conducting, methanol impermeable metallic barrier like palladium (Pd) is a well-known method for preventing methanol crossover through solid polymer electrolyte for direct methanol fuel cells (DMFCs). It was demonstrated in our study that the hydrogen transfer rate through the barrier was greatly enhanced when a negative bias potential in reference to the cell anode was applied on the barrier, a thin Pd foil of 25 μm thick. The power consumed for such bias application was less than 2% of the operational power of the cell. The current density/voltage curves of the DMFC showed that the proper bias application on the hydrogen saturated Pd barrier increased the cell power by more than five times from the value obtained without the bias modification. But the real advantage of the biased barrier was that it actually reduced the resistance of the polymer electrolyte (Nafion) when it was placed in the electrolyte with the cell current density maintained lower than (equivalent to maintain the cell voltage higher than 0.4 V in our experimental conditions). Eventual falloff of the power delivered by the cell with the barrier in higher current region should be attributed to mismatch of the charge transfer rate at the Pd/Nafion interfaces with the increased overall current density. © 2003 The Electrochemical Society. All rights reserved.