Titanium coatings deposited by thermal spraying for bipolar plates of PEM electrolyzers

Transcription

1 1 > Titanium coatings - ise13147 > A. S. Gago et al. ISE 213 > September 9, 213 Titanium coatings deposited by thermal spraying for bipolar plates of PEM electrolyzers A. S. Gago, A. S. Ansar, N. Wagner, J. Arnold, K. A. Friedrich Institute of Technical Thermodynamics German Aerospace Center (DLR) Stuttgart, Germany

2 2 > Titanium coatings - ise13147 > A. S. Gago et al. ISE 213 > September 9, 213 Power-to-Gas (P2G) Wind - CO 2 Erdgas, Biogas Solar -H2O Storage carrier - Excess of -H2 generation - Electricity CH4 POWER GAS Wind profile: Intermittent - Alkaline electrolysis Liquid electrolyte (KOH) Additional compressor <.4 A cm -2 Slow response Cheap PEM electrolysis Uses only DI water No additional compressor >1 A cm -2 (expected) Rapid response (dynamic operation) Expensive... for the time being -

3 3 > Titanium coatings - ise13147 > A. S. Gago et al. ISE 213 > September 9, 213 Cost of a PEM electrolyzer stack Balance of cell Balance of stack in a PEM electrolyzer? Catalyst coated membrane (CCM or MEA) Bipolar plates and current collectors made of Titanium

4 4 > Titanium coatings - ise13147 > A. S. Gago et al. ISE 213 > September 9, 213 Strategy for coating stainless steel PVD coating of TiN Coatings for PEM fuel cells: Standard approach: 1 µm Coating 1 Coating 2 Corrosion resistant and conductive coating on stainless steel Y. Wang, D.O. Northwood, Journal of Power Sources 191 (29) 483. The Fe 2+ released from corrosion poison the CCM Coatings for PEM electrolyzers: Our approach: Coating 1: Titanium coating by thermal spraying Coating 2: Surface modification of Titanium < 5 µm Cost reduction? PEMFC: PVD coatings alone meet the DOE requirements. PEM electrolyzers: current Ti bipolar plates have to be coated to reduce the passivation. Dramatic cost reduction for large area bipolar plates Megawatt scale

5 5 > Titanium coatings - ise13147 > A. S. Gago et al. ISE 213 > September 9, 213 Thermal spraying Vacuum Plasma Spraying (VPS) Applications at the DLR: SOFC components Catalyst for alkaline electrolysis Bipolar plates of PEM electrolyzers substrate Water cooled anode Titanium powder (~45 µm) injector Titanium particles Plasma gas Water cooled cathode Plasma jet Adapted from Ti coating Particle impact Inclusions Porosity Unmelted particle Grit blast interface substrate

6 6 > Titanium coatings - ise13147 > A. S. Gago et al. ISE 213 > September 9, 213 Deposition parameters for Ti coatings on Crofer 22 APU Input Output Sample Powder feeder rate Plasma enthalpy (h) Z V Leak rate g min -1 MJ kg -1 mm mm s -1 mbar l cm -2 s -1 CF CF-3 11, CF-31 11, CF-32 11, CF-4 11,7 14, CF-41 11, CF-42 11, CF-56 11, CF-57 11, CF-15 11, Vessel Pressure: 5 mbar Anode type: M3-6mm Injector: Internal Track separation: 1 mm Number of layers: 8 Substrate temperature: 25 ºC Plasma enthalpy Power dissipated in the gas (kw) Plasma gas flow rate (kg s 1 ) P. Fauchais, J. Phys. D: Appl. Phys. 37 (24) R86.

7 7 > Titanium coatings - ise13147 > A. S. Gago et al. ISE 213 > September 9, 213 Coating development 2 (11) 15 h = 9.9 MJ kg -1 h = MJ kg -1 Intensity / a. u. 1 5 TiO.17 (1) (2) TiO.17 (112) (21) (11) (12) (13) h = MJ kg -1 h = 14.6 MJ kg θ / degree - h = MJ kg -1 5 µm Dense coatings of Ti were produced with high plasma enthalpies. Pure Ti-α was obtained as the deposition was performed in vacuum.

8 8 > Titanium coatings - ise13147 > A. S. Gago et al. ISE 213 > September 9, 213 Electrochemical characterization Experimental conditions: O2-saturated.5 M H2SO4, temperature: 24 ºC, scan rate: 5 mv s -1 1x1 -² x1-4 1x1 -³ x1-5 j / A cm -² 1x1-4 1x1-5 1x1-6 1x1-7 Plasma Enthalpy (MJ kg -¹ ) E corr / V vs. SHE MJ kg -¹ MJ kg -¹ 11.1 MJ kg -¹ MJ kg -¹ MJ kg -¹ MJ kg -¹ x1-5 4x1-5 2x1-5 i corr / A E / V vs. SHE Leak-rate / mbar l cm -² s -¹ Ti coatings deposited with high plasma enthalpies showed lower corrosion currents (icorr) and higher corrosion potentials (Ecorr) than stainless steel.

9 9 > Titanium coatings - ise13147 > A. S. Gago et al. ISE 213 > September 9, 213 Further improvement of the coating 8x1-5 j / A cm -² 6x1-5 4x1-5 2x1-5 j / A cm -² LV1 6x1-4 5x1-4 4x1-4 3x1-4 2x1-4 1x1-4 Anodization (TiO2-x) - Coated and Ti foil Time / h Electrolyte: O 2 -saturated 5 mm H 2 SO 4 Temperature: 24 ºC E const = 1.8 V vs. SHE Titanium foil Coated stainless steel LV2 LV2 LV3 LV Modification with gold LV Time / h

10 1 > Titanium coatings - ise13147 > A. S. Gago et al. ISE 213 > September 9, 213 Further improvement of the coating j / A cm -² 8x1-5 6x1-5 4x1-5 2x1-5 j / A cm -² 6x1-4 5x1-4 4x1-4 3x1-4 2x1-4 Coated and Ti foil j / A cm -² 1x Time / h LV1 1x1-8 1x1 -² - LV1: LV2: Before After 6 chronoamperopmetry 1.8 V LV2: After V 1x1 -³ LV4 (2): After V Electrolyte: O 2 -saturated 5 mm LV3: H 2 SO After V Temperature: 24 ºC ORR on E LV4: gold After V 1x1-4 const = 1.8 V vs. SHE 1x1-5 1x1-6 1x1-7 Titanium foilti foil 1.23 V Coated stainless steel Anodization (TiO2-x) LV LV2 LV3 LV4 E / V vs. SHE OER on gold Modification with gold LV Time / h

11 11 > Titanium coatings - ise13147 > A. S. Gago et al. ISE 213 > September 9, 213 Corrosion demonstrator (measurement of Fe 2+ ) 5 4 Coated stainless steel [Fe ²+ ] / ppm min 221 min 37 min 1 Titanium Coated stainless steel Time / min Cost of coating the BP of 1 MW PEM electrolyzer: (2 2 A cm -2 ) - 25 x 1 cm 2 = 2.3 / bipolar plate + diverse costs. The stainless steel with flow channels is not included.

12 12 > Titanium coatings - ise13147 > A. S. Gago et al. ISE 213 > September 9, 213 One-to-one comparison (AST for bipolar plates) Simulated cathode of a PEMFC: Electrolyte: O2-saturated.5 M H2SO4 (ph =) Temperature: 7 ºC Econst =.84 vs. RHE Duration of the experiment: 1 hour Simulated anode of a PEM Electrolyzer: Electrolyte: O2-saturated.5 M H2SO4 (ph =) Temperature: 8 ºC Econst = 2 V vs. RHE Duration of the experiment: 24 hours Coating by PVD 5x1-5 Coating by thermal spraying Corrosion Current density / A cm -² 4x1-5 3x1-5 2x1-5 1x1-5 Ti-coated stainless steel? Time / h Y. Wang, D.O. Northwood, Journal of Power Sources 191 (29) 483. No pinholes (SEM not shown). No corrosion of the substrate.

13 13 > Titanium coatings - ise13147 > A. S. Gago et al. ISE 213 > September 9, 213 Conclusions There is an urgent need to reduce the cost of PEM electrolyzers for Power-to-Gas applications. The bipolar plates are very expensive. Dense Ti coatings were produced by plasma spraying (with high h) on stainless steel substrates. The coatings were evaluated in simulated conditions: O2-saturated.5 M H2SO4, 8 ºC, Econst = 2 V. Further improvement of the coating resulted in full protection of the substrate over extended periods of time (demonstrated!). The cost of coating stainless steel bipolar plates of 1 cm 2, for the MegaWatt range, is estimated in 2.3 per piece.

14 14 > Titanium coatings - ise13147 > A. S. Gago et al. ISE 213 > September 9, 213 Thank you for your attention