FUEL CELL DIAGNOSTICS FOR AUTOMOTIVE APPLICATION

Transcription

1 FUEL CELL DIAGNOSTICS FOR AUTOMOTIVE APPLICATION DR. SEBASTIAN KIRSCH, DR. MAREN RAMONA KIRCHHOFF 13TH INT. AVL SYMPOSIUM ON PROPULSION DIAGNOSTICS BADEN-BADEN

2 ZOOMING INTO A FUEL CELL SYSTEM gas conditioning stack turbocompressor endplate cells clamping system endplate gas diffusion layer (GDL) membrane gas diffusion layer (GDL) bipolar plate (BPP) Fuel Cell Vehicle Fuel Cell System Fuel Cell Stack Membrane-Electrode-Assembly and Bipolar Plates 2

3 MEMBRANE ELECTRODE ASSEMBLY (MEA) U Cell 0.6-1V e - Current for electric motor H 2 from tank O 2 from ambient air Abbreviations: BPP: Bipolar plate GDL: Gas diffusion layer MEA: Membrane Electrode Assembly BPP 600 µm GDL 180 µm Anode Membrane 5 µm 18 µm H 2 2H + + 2e - Cathode 15 µm 2H + + ½O 2 + 2e - H 2 O GDL 180 µm heat & water Overall reaction: H 2 + ½ O 2 H 2 O 3

4 OPERATION FAILURES A HYPOTHETIC COUNTER FLOW SETUP H2 Mechanical Stress due to humidity cycling: Cracking of the membrane coolant air SEM Post-Mortem Analysis dry out as relative humidity (rh) at the inlets is too low Performance reduction 100% 80% 20% 40% 60% Anode Flooding due to bad water management Cathode degradation 14 µm 7µm 70 C Fast Transient Polarizations at varying inlet rh SEM Post-Mortem Analysis 4

5 CONTENT 1. Motivation: Things that go wrong during fuel cell operation 2. Some Diagnostic Tools Required During Development: 1. Polarization Curve Comparisons 2. Infrared Imaging 3. Cell Voltage Monitoring & Temperature mapping 4. Something advanced: X-ray and FIB-SEM sampling 3. Some Fundamental Diagnostic Strategies for Fuel Cell System Operation 1. System Setup Overview 2. System Operating Conditions 3. Diagnostics in Fuel Cell System 4. Examples for Diagnostics in Fuel Cell System 4. Summary 5

6 DU [V] DU [V] voltage [V] DU [V] DU [V] ANALYSIS OF DIFFERENCES IN POLARIZATION CURVES FUNDAMENTALS Two polarization curves 1,25 1,18 Four characteristic scenarios Loss of activity (Pt-loss, de-alloying) Additional (quasi-) Ohmic losses (contam., rh) 0,?? pol. curve 2 pol. curve 1 DU(i) 0 Membrane failures (pinholes & cracks) 0 Additional transport losses (contam., C-corrosion) current density [A/cm²] The shape of DU(i) helps to identify the origin of the failure

7 DU [V] DU [V] DU [V] DU [V] DU [V] ANALYSIS OF DIFFERENCES IN POLARIZATION CURVES FUNDAMENTALS Polarization curves difference Transport Four characteristic scenarios Loss of activity (Pt-loss, de-alloying) Additional (quasi-) Ohmic losses (contam., rh) 0,05 Pin-holes / cracks Activity (Quasi -) Ohmic 0 Membrane failures (pinholes & cracks) 0 Additional transport losses (contam., C-corrosion) 0,00 current density [A/cm²] By fitting DU(i) onto the four characteristic scenarios the individual losses can be quantified

8 INFRARED IMAGING FUNDAMENTALS Fixture for pin-hole & crack detection Example Air IR-camera H2 MEA IR-imaging can be used to detect pin-holes and cracks From the findings failures in the MEA- or BPP design or operation strategy can be anticipated 8

9 MEA Temp [ C] Coolant Temp [ C] Eq. Stack Power [%] Coolant Temp [ C] Min Cell Voltage [V] Eq. Stack Power [%] Min Cell Voltage [V] CELL VOLTAGE MONITORING & TEMPERATURE MAPPING DURING FREEZE START Cathode ice-blockage start load: 10% P el,max start temperature: C Anode ice-blockage start load: 50% P el,max start temperature: -15 C (too) wet ShutDown Overheating inserted temperature sensors to measure the local temperature (between cathode-bpp and GDL) inlet middle outlet Time [s] performance reduction Time [s] -1.5V: emergency stop Risk of overheating progress of cathode electrode ice front Global H2- Starvation Time [s] 9

10 HARD X-RAY CT (SYNCHROTRON) & FIB-SEM (FOCUSED ION BEAM ) A VLIES-BASED GAS DIFFUSION LAYER Motivation: Targets: Flooding and 2-phase flow in the electrodes and the gas diffusion layer causes voltage losses (especially at high current densities) and degradation Sub µm-detailed reconstruction of GDL & MPL Modeling of flooded areas in GDLs & MPLs Fiber H2O liquid Binder/PTFE Reconstruction of fibers and binder in the substrate, as wells as the different components in the MPL. [Göbel et al., J. Power Sources 355, 2017, 8 ] GDL (left): Vlies-Substrate and MPL Resolution: 0,35 µm MPL (right): Microstructure Resolution: 5 nm 10

11 DU [V] CONTENT 1. Motivation: Things that go wrong during fuel cell operation 2. Some Diagnostic Tools Required During Development: 1. Polarization Curve Comparisons 2. Infrared Imaging 3. Cell Voltage Monitoring & Temperature mapping 4. Something advanced: X-ray and FIB-SEM sampling 3. Some Fundamental Diagnostic Strategies for Fuel Cell System Operation 1. System Setup Overview 2. System Operating Conditions 3. Diagnostics in Fuel Cell System 4. Examples for Diagnostics in Fuel Cell System 4. Summary 11

12 Anode Cathode SYSTEM: SETUP OVERVIEW H 2 -Supply Supply the fuel cell with H 2 Remove water from the anode Hydrogen recirculation Hydrogen safety Examples of Components Recirculation blower Jetpump Water separator Pressure regulator Sensors (T, p, dp, concentration) Sensor system/ controller H 2 supply Air Supply Supply the fuel cell with air Humidify the supplied air Remove liquid water Minimize sound emissions PEMFC Cooling Examples of Components Compressor Humidifier Throttle valve Air supply Sensors (T, p, dp, mass flow) Cooling Heat removal Ensure insulation resistance Examples of Components Coolant pump Radiator Heater Thermostat Deionization filter Sensors (T, p, conductivity) 12

13 Anode Cathode SYSTEM: OPERATING CONDITIONS H 2 -Supply Anode inlet temperature Sensor system/ controller Cooling Cooling Coolant inlet temperature Anode inlet pressure Anode differential pressure Relative humidity Gas mixture Stoichiometry H 2 supply Air supply Coolant differential temperature Conductivity PEMFC Air Supply Cathode inlet temperature Cathode inlet pressure Relative humidity Air mass flow 13

14 DIAGNOSTICS IN FUEL CELL SYSTEM Fuel cell stack Deviation from power forecast Cell voltage monitoring State-of-health, cell quality index Degradation models Impedance spectroscopy Fuel cell system: components and media supply Status messages from components Control deviation Model deviation Limit value monitoring Environmental effects Ambient pressure Ambient temperature Standing time Contamination Diagnosis Operating Strategy Sequence control (Freeze) Startup Start/Stop Shutdown Control of operating conditions Adaptation of the operating conditions set Provision of the requested power Fault reaction 14

15 EXAMPLES FOR DIAGNOSTICS IN FUEL CELL SYSTEM Humidity adjustment by means of operating conditions set Provision of the requested power Startup sequence Diagnosis Startup request P Soll I Soll O 2 y Air/Air n 0,9 1,0 1,1 Protected Diagnosis: Single operating parameter outside the permitted range Diagnosis: State-of-health (Cell voltage monitoring) Diagnosis: O 2 -Concentration on the anode side Reaction: 1. Adaptation of operating conditions set 2. Power reduction Reaction: 1. Regeneration measure 2. Power reduction 3. Forced Shutdown Reaction: Startup sequence: Minimization of air/air-start degradation 15

16 DU [V] SUMMARY 1. Motivation: Things that go wrong during fuel cell operation 2. Some Diagnostic Tools Required During Development: 1. Polarization Curve Comparisons 2. Infrared Imaging 3. Cell Voltage Monitoring & Temperature mapping 4. Something advanced: X-ray and FIB-SEM sampling 3. Some Fundamental Diagnostic Strategies for Fuel Cell System Operation 1. System Setup Overview 2. System Operating Conditions 3. Diagnostics in Fuel Cell System 4. Examples for Diagnostics in Fuel Cell System 0,9 1,0 1,1 16

17 Thank you. 17