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PROTONLY project: Graphene layer improves performance of DMFCs

A graphene layer can significantly reduce the permeability of a fuel cell membrane without affecting the proton conductivity too much. ZBT and AMO have worked out how this can be done in the joint PROTONLY project.

Current-voltage characteristics of DMFC MEAs with graphene-coated Nafion™ 115 membranes compared to an uncoated reference (REF_MEA_I). Dotted lines indicate 5-molar operation, solid lines indicate 1-molar operation. Same colour means same membrane. MEA_I (130µg/cm² graphs, red curves) shows very good performance in 5-molar operation.

Membrane with sprayed graphene layer (Photo: AMO GmbH)

Membranes in polymer electrolyte membrane fuel cells (PEMFC), direct methanol fuel cells (DMFC) or vanadium redox flow batteries (VRFB) should simultaneously be as permeable as possible for protons and as dense as possible for operating media. Together with project partner AMO Gesellschaft für Angewandte Mikro- und Optoelektronik from Aachen, Germany, ZBT has made great progress in this direction in the project "PROTONLY - New membrane generation with proton-permeable barrier layers for electrochemical applications".

During the project, a process was developed with which graphene layers can be applied to perfluorosulfonic acid (PFSA) membranes in such a way that the targeted improvements could be achieved, particularly in the field of DMFC applications. Further modification of the entire barrier-membrane-electrode composite also contributed to this.

When operating a DMFC with 5-molar methanol solution, the permeability of a coated Nafion™ 115 membrane was reduced by a factor of almost 20 compared to an uncoated membrane. At the same time, a reduction in protonic conductivity of about 17% was measured. The losses in protonic conductivity are thus 7 percentage points higher than the target set, but this was also set in combination with an improvement in the barrier effect by a factor of 10. Thus, a proton flux reduced by only 17 % with a simultaneous reduction in methanol permeation by a factor of 20 appears to be an enormous success.

As a result of the greatly increased barrier effect with acceptable restriction of the proton conductivity, a 3.8-fold increase in performance was thus recorded in 5-molar DMFC operation compared with an uncoated membrane.

This is explained not least by an increase in the total conductivity through the plane of the entire membrane electrode assembly (MEA) by about 17 % from 3.08 mS/cm to 3.6 mS/cm. Electronic (contact) resistances and crossover-related reaction resistances also play a role in the overall conductivity, which could be significantly reduced by using graphene.

In addition to the DMFC, a fundamental blocking effect was also observed in the vanadium redox flow battery during the project, but here the graphene layer was only stable for a short time. In the case of the PEMFC, the significantly increased blocking effect unfortunately did not compensate for the significantly reduced proton conduction. The measured performance data were lower than those without the graphene layer.

Reg. No.: 49VF170040 (INNO-KOM)
Short title: PROTONLY
Duration: 1 November 2018 - 31 December 2021
Department of Electrochemical Components

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