Reversible/irreversible increase in proton-conductive areas on proton-exchange-membrane surface by applying voltage using current-sensing atomic force microscope

• Proton conductive areas on SPE-bl-1 surface were investigated by current-sensing AFM.
• The number and diameter of proton-conductive spots increased with increasing bias voltage.
• Both irreversible and reversible changes of the proton conductive areas took place.
• Proton conductive paths are dynamically rearranged during power generation in PEFC.

By using a current-sensing atomic force microscope (CS-AFM) under a hydrogen atmosphere, microscopic proton-conductive areas on the membrane surface of sulfonated poly(arylene ether sulfone ketone) block copolymer were investigated. With increasing the bias voltage during the CS-AFM scans, the number and the diameter of proton-conductive spots on the membrane surface continuously increased. Both reversible/irreversible changes in the proton-conductive area on the surface were found. The reversible change indicates that the proton-conductive paths are dynamically rearranged during the power generation in a polymer electrolyte fuel cell. The irreversible change might be related to the enhancement of the performance of the membrane electrode assemblies after being “conditioned” prior to the operation.

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