Comparative Studies of Atomically Thin Proton Conductive Films to Reduce Crossover in Hydrogen Fuel Cells

Applicability of Single-Layer Graphene as a Hydrogen-Blocking Interlayer in Low-Temperature PEMFCs

“…As clearly visible from the raw polarization data in Figure b, the MEAs made from SLG (CT) membranes show increased ohmic polarization, which is reflected in the 18% higher HFR compared with the SLG (TT) MEA and in the 32% higher HFR compared with the double NXL reference MEA (see Table ). The increase in the HFR for the SLG (CT) MEA is still lower than the increase in the HFR of 61% presented in the study of Kutagulla et al for an SLG-N211 composite membrane, where SLG was also transferred via a direct etching process with APS and tested under the same conditions. The authors reported a decrease in peak power density by 46 and a 63% lower current density at 0.6 V with the implementation of SLG directly transferred from a copper substrate.…”

“…Although the gases were humidified, the absolute water content of the streams at such low temperatures is less than 10% compared to humidified operation at 80 °C. Nevertheless, Kutagulla et al reported a reduction in hydrogen crossover of 46%, which was measured at 80 °C and 100% RH. They applied SLG close to the anode, with a 200 nm thin Nafion coating between the anode catalyst layer and the membrane, instead of incorporating SLG between two Nafion membranes.…”

“…Two different transfer routes, depicted in Figure , were employed to incorporate the SLG into the membrane stack. SLG on a copper substrate (Figure a, which will be referred to as SLG (CT)) was transferred onto NXL as described in the literature. − ,, In brief, CVD SLG (CT) was hot-pressed onto an NXL membrane (150 °C, 2.5 MPa, 7 min), with the SLG facing the membrane, in between two glass fiber-reinforced PTFE sheets with Pacopads, followed by etching of copper with 50 mL of a freshly prepared 0.26 M APS ((NH 4 ) 2 S 2 O 8 )-solution for 1 h, which removed all visible remnants of copper according to the following reaction (eq ) Cu + false( NH 4 false) 2 S 2 O 8 → CuSO 4 + false( NH 4 false) 2 SO 4 Taking the molar amount of the copper substrate and the APS solution into account, there is an excess of APS with a factor of 8 compared to copper (see the Supporting Information). Equation shows the reaction of persulfate ions with water, which is known to occur in neutral and dilute acid solutions …”

“…Furthermore, the authors also found that the proton conductivity of SLG directly correlates with temperature. The combination of the superior sieving properties of SLG and its proton conductivity led to several studies about the potential use of SLG as a crossover-reducing barrier layer in FC applications. ,,,− …”

“…Recently, Kutagulla et al compared different two-dimensional materials on top of Nafion 211 with respect to their ability to reduce the hydrogen crossover in operating fuel cells. The barrier layers were additionally protected by a 200 nm thin Nafion coating facing the anode.…”