Guanidinium based blend anion exchange membranes for direct methanol alkaline fuel cells (DMAFCs)

• Novel Guanidinium based AEMs have been fabricated for the first time for DMAFCs.
• Chitosan was blended with Guanidinium to provide superior strength and integrity.
• The blends showed impressive selectivity (ionic conductivity/methanol permeability).
• AEMs produced higher fuel cell OCVs (up to 0.67 V) than the commercial A201(0.47 V).

Guanidinium based blend anion exchange membranes (AEMs) for direct methanol alkaline fuel cells have been fabricated and studied. The guanidinium prepolymer is first synthesized through a simple polycondensation process with the ion exchange moieties incorporated directly into the polymer backbone, and then is used to make guanidinium – chitosan (Gu-Chi) blend membranes. Besides, a lipophilic guanidinium prepolymer, synthesized by means of a precipitation reaction between sodium stearate and guanidinium salt, is adopted to tune solubility and mechanical properties of the blend AEMs. Results show that both ionic conductivity and methanol permeability of the AEMs can be tuned by blend composition and chemistry of the guanidinium based prepolymer. The selectivity (ratio of ionic conductivity to methanol permeability) of the fabricated membranes is superior to that of commercial membranes. Under fuel cell tests using 3 M methanol, the open circuit voltage (OCV) value for the blend AEM with 72 wt% of the guanidinium polymer (0.69 V) is much higher than that of the commercial Tokuyama A201 (0.47 V) at room temperature, while the blend AEMs with 50 wt% guanidinium content still show comparable values. Overall, the developed membranes demonstrate superior performance and therefore pose great promise for direct methanol anion exchange fuel cell (DMAFC) applications.

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