Novel In‐Liquid‐Plasma Synthesis and Coating Process for Graphene‐Coated Perfluorosulfonic Acid‐Based Membranes for Application in High‐Performance Direct Methanol Fuel Cells

A novel single synthesis via in‐liquid‐plasma is presented for few‐layer graphene applied as blocking layer in direct methanol fuel cells. Few‐layer graphene suspensions are synthesized from an ethanol precursor. The influence of the applied frequency (within the kHz range), pulse width (up to 1100 ns), gas flow, voltage (within the kV range), and electrode distance was systematically studied and optimized. Raman spectroscopy shows an I (2D/G) ratio of 2.52 and an I (D/G) ratio of 0.80, indicating the presence of few‐layer graphene. This is supported by scanning transmission electron microscopy that demonstrates the formation of low‐crystalline few‐layer graphene. Non‐quantitative hydrocarbon cracking was also observed, causing the formation of aromatic hydrocarbons and multiring systems as byproducts. The analysis of byproducts was carried out by gas chromatography–mass spectrometry, identifying indene, naphthalene, phenylethyne, styrene, and acenaphthylene in concentrations up to 68 mL L −1 . The suspension was stabilized at 50 wt% Fumion as an additive, enabling homogeneous coating and drying properties. The graphene coating was deposited as a blocking layer onto a perfluorosulfonic acid‐based membrane using a specially adapted doctor blading process at a coating speed of 10 cm s −1 . The distribution of few‐layer graphene through the coating was characterized by in situ Raman mapping and scanning electron microscopy, showing a homogeneous distribution of the graphene throughout the layer across the entire thickness of 22.5 μm. The electrochemical performance characterisation in a direct methanol fuel cell setup revealed a significant reduction of methanol crossover. Polarization curves showed an improved power density compared to uncoated membranes.