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Two-dimensional atomic crystals such as single layer graphene (SLG) and hexagonal boron nitride (hBN) have been shown to be "unexpectedly permeable" to hydrogen ions [1] under ambient conditions with the proton conductivity rising exponentially with temperature. Here we show the first succesful addition of SLG made by a chemical vapour deposition (CVD) method to an operational direct methanol fuel cell (DMFC) significantly enhancing the performance of the cell once the temperature is raised above 60 o C, the temperature at which the proton conductivity of SLG is higher than the Nafion membrane on which it is mounted. Above this temperature, the resistance to proton transport of the system is not affected by the graphene but the barrier properties of graphene inhibit methanol crossover. The performance of the fuel cell is shown to increase linearly with coverage of SLG above this temperature. Results show that the maximum power density is increased at 70 o C by 45% in comparison to the standard membrane electrode assembly (MEA) without graphene. In addition, a

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