General Energy PEM Membrane Tests

Transcription

1 General Energy PEM Membrane Tests Date 11/03/2016 Author Annette Mosdale, R&D PaxiTech Client Ms. Sophia Hu General Energy Room 404, 321 Talent Building, No East Tianyuan Road Nanjing PR China Phone: Fax: Membrane Samples received: Three sheets of two different PEM membrane samples were received from General Energy in February 2016, GN-211C and GN-212C. No information was provided concerning the physical and electrochemical properties of the different membrane samples. The table below lists the references of the membranes received and gives whatever information was available at the time of the benchmark-tests at PaxiTech. The thicknesses were measured with a Mitutoyo comparator. All three GN-212C membranes were around 60µm. The thickness of the three GN-211C membranes varied between 30 and 40µm. General Energy PEM membrane samples Membrane Ref GN-211C GN-212C Lot N received 01/02/ /02/2016 Thickness (µm) Colour transparent transparent Table 1: General Energy PEM Membrane Samples Membrane Electrode Assembly: Catalyst inks were prepared with a 70% Pt/C powder, a 5.5% Nafion emulsion, ethanol and water. The catalyst coated membranes (CCMs) were prepared by applying the Pt/C catalyst inks directly onto the PEM membranes with an ultrasonic pulverisation system (SonoTek ExactaCoat). The CCM platinum loading was programmed for 0.5 mg/cm² on the anode side and on the cathode side. 1

2 5L+SG MEAs were prepared by hot-pressing gas diffusion layers and 15µm subgaskets onto both sides of the CCMs at 140 C and 40 kg/cm². The anode and cathode GDL were the same. Hot-pressing was carried out using a Carver 30-12H Press. Cell Test Set-Up: 5L+SG MEA: 25cm² single cell - flat gasket - graphite single channel flow field plates with integrated O-ring - 6 bolts - tightened at torque 6Nm Electrochemical Tests: Fuel cell electrochemical tests were carried out with a BioLogic FCT-150S fuel cell test station. Chronoamperometry: The fuel cell is set at a voltage of 0.6V and the current response is measured until stabilisation of the current is reached. Impedance Spectroscopy: Impedance measurements are carried out in the potentiostatic mode, an ac sinus signal is applied around a fixed potential, E. Cell Voltage, E = 0.6V, E ac amplitude = 10mV, Frequency Range = 10000Hz 0.1Hz I-V Polarisation Curve: Polarisation curves are recorded by scanning the cell voltage of the H 2 /air fuel cell from OCV (open circuit voltage) to 0.3V, at a scan rate of 1 mv /sec, and measuring the current produced by the fuel cell. Test Conditions: cell temp. ( C) anode cathode G1 70 H2, 1.1 stoic., dry, 3.0 bar rel air, 2.0 stoic., 50%RH, 3.0 bar rel G2 70 H2, 1.1 stoic., dry, 1.5 bar rel air, 2.0 stoic., 50%RH, 1.5 bar rel AB 70 H2, 1.1 stoic., dry, ambient air, 2.0 stoic., 50%RH, ambientp G3 80 H2, 1.1 stoic., dry, 3.0 bar rel air, 2.0 stoic., 100%RH, 3.0 bar rel G4 80 H2, 1.1 stoic., dry, 1.5 bar rel air, 2.0 stoic., 100%RH, 1.5 bar rel 100% AB 80 H2, 1.1 stoic., dry, ambient air, 2.0 stoic., 100%RH, ambientp Table 2: Test Conditions Cyclic Voltammetry Test Conditions: Cell temperature 80 C H 2 at 0%RH N 2 at 100%RH gas pressures 1.5 bara The voltage is scanned from 0.1 to 0.4 at a scan rate of 0.3mV/sec for hydrogen crossover tests. 2

3 RESULTS 1. CHRONOAMPEROMETRY The average chronoamperometry results, at a cell voltage of 0.6V, obtained with the General Energy membranes in 5L+SG MEAs, at all test conditions, are shown in table 2 below. Each test was repeated at least 3 times. Higher fuel cell performances were achieved at all test conditions with the thinner GN-211C membrane. membrane A/cm² at 0.6V 50% 2bar 50% 0,5bar 50%RH 0bar 100% 2bar 100% 0,5bar 100%RH 0bar GN-211C 0,66 0,55 0,51 1,07 0,86 0,73 GN-212C 0,61 0,52 0,43 0,88 0,72 0,62 Table 3: Chronoamperometry at 0.6V Data 2. Cyclic Voltammetry Hydrogen crossover currents for the General Energy membrane MEAs are shown in Figure 1. Short resistances are calculated from the slope of the crossover CVs and are very acceptable for both types of MEA. In general the crossover currents were slightly higher and the short resistances slightly lower for the GN-211C MEAs as compared to the GN-212C MEAs. 3,0 2,5 GN-211C GN-212C I (ma/cm²) 2,0 1,5 1,0 0,5 0,0 0,0 0,1 0,2 0,3 0,4 Voltage (V vs RHE) Figure 1: Hydrogen Crossover Cyclic Voltammetry 3. PEIS Figure 2 below shows the Nyquist plots obtained at 0.6V for the 3 different Gore Select membranes at cell conditions 80 C, 100%RH, 1.5 bara H 2 /Air. The ohmic part of the impedance was taken from the intersection of the Nyquist plots at Im Z = 0. The thicker the membrane the higher ohmic Z will 3

4 be. Average ohmic Z values were around 120 mω.cm² for the GN-212C MEAs and 92 mω.cm² for the GN-211C MEAs. A comparative plot with a Nafion NR212 (50µm membrane) MEA is also shown (Z ohmic ~100mΩ.cm²). 25cm² - 0,5mg/cm² - I2C6/PET12/12 OR cell/sp C 1.5bara 100%RH Nafion NR212 GN212 GN211-0,006-0,005-0,004 Im Z (Ω) -0,003-0,002-0,001 0,000 0,000 0,005 0,010 0,015 0,020 0,025 0,030 Re Z (Ω) Figure 2: PEIS at 0.6V data at condition G4 4. POLARISATION CURVES Polarisation curves at cell conditions 80 C, 100%RH, 1.5 bara H 2 /Air are shown in figure 3. A comparative curve with a Nafion NR212 (50µm membrane) MEA is also shown. General Energy membrane MEAs compare with Nafion MEA data. 25cm² - 0,5mg/cm² - I2C6/PET12/12 OR cell/sp C 1.5bara 100%RH 1,0 Nafion NR212 GN212 GN211 0,9 0,8 cell voltage (V) 0,7 0,6 0,5 0,4 0,3 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 current density (A/cm²) Figure 3: IVC curves at PaxiTech test condition G4 4

5 CONCLUSIONS The two different General Energy PEM membranes samples received was set up for tests in a 25cm² single cell with standard PaxiTech catalyst layers, GDLs and gasket materials. The sample membranes had thicknesses of 35 and 60µm. Crossover currents measured in cyclic voltammetry experiments were slightly higher for the thinner GN-211C membrane MEAs but remained very acceptable; around 1.63mA/cm². Chronoamperometry data and polarisation curves show that the highest performances were obtained with the thinner GN-211C membrane sample. Fuel cell performances for the GN-211C membrane were very similar to reference data For MEAs made with Nafion NR212 membrane. Future test propositions with these membranes include: PaxiTech air-breathing PEMFC power sources Lifetime and/or durability tests 5