Membranes Development for Alkaline Water Electrolysis

Transcription

1 Membranes Development for Alkaline Water Electrolysis U.F. Vogt, M. Gorbar, M. Schlupp, G. Kaup, A. Bonk, A. Hermosilla, A. Züttel Empa, Laboratory Hydrogen & Energy Überlandstrasse 129 CH-8600 Dübendorf / Switzerland

2 ELYGRID Improvements to Integrate High Pressure Alkaline Electrolyzers for H 2 production from Renewable Energies to Balance the GRID ELYGRID Project aims at contributing to the reduction of the total cost of hydrogen produced via electrolysis coupled to renewable energy sources (mainly wind turbines), and focusing on mega watt size electrolyzers (from 0,5 MW and up). MAIN IDEAS: - Big size alkaline electrolyzers - Reduction of Total Cost of Ownership (TCO) - Prototyping and testing with intermittent feeding - Industrialization and market oriented approach

3 Hydrogen production via alkaline electrolysis Left: Lurgi-Zdansky type alkaline electrolyser in 1949 Right: Electrolyser at Giovanola, Monthey H 2 purity: vol% O 2 purity: vol% Working conditions: 32bar, 85 C, 25wt-% KOH Production rate: 760 m³/h H 2, equ. to 3.3 MW el Energy Consumption: 4,3-4,6 kwh/m³ H 2 Partial load: 25 tp 100 % of nominal capacity 4

4 Cell mountening at IHT, Cell diameter 1.6 m State-of-the-art of Alkaline Elecrolyser Bipolar plate electrolyser design, the same as used by IHT company equipted with Asbestos-chrysotile membrane. Electrode side 1.Cell partition 2.Gasket 3.Electrode mesh 4.Membrane (Asbestos) 5.Hydrogen duct 6.Oxygen duct 7.Electrolyte duct (Ullmann s Encyclopedia, 2006) Cells sandwich 6

5 Cathode Anode Overall H 2 O + e 1 2 H 2 + OH 2OH 1 2 O 2 + H 2 O + 2e H 2 O H O 2 Electrolyzer cell potential: E cell = E 0 + η a + η c + I R E 0 : equilibrium cell potential η a,c : anodic, cathodic over potential I: Applied current Zeng et al., Progress in Energy and Combustion Science 2010, 36,

6 temperatures from 0 to 100 C for KOH conm 0 to 12 M. At concentrations or temperatures nges, greater deviation is expected to occur of data beyond 12 M and above 100 C used ar regression analysis. The standard deviation conductivity at concentrations between 0 and peratures between 0 and 100 C was found to 4th European PEFC & H2 Forum 2 5 July 2013 Luzern, Switzerland parison of the equation to reported data, three exist based on temperature ranges. Below 25 C, viation in specific conductivity was 3.9% with ror of 9%. Between 25 and 75 C the average ecific conductivity was 1.9% with a maximum ove 75 C the average deviation was 3.2% with MEMBRANE ror of 8%. there was a higher average deviation in the ctivity due to a disproportional number of reat low concentrations within this temperature centrationsmembrane below 0.1 M, requirements: the average error in nductivity was 4.7%. At temperatures greater ere was an increase in average error due to which exist ion-permeable in the reported values at these gas-tight ion between chemically the reported data stable and values obproposed equation can be seen in Fig. 3. Dising between the reported values at higher tem- electrically insulating mechanically robust lso be seen in Fig. 3. ensional representation of specific conductivity concentration and temperature, based on the tion, can be seen in Fig. 4. Values of specific alculated using the proposed equation at varions and temperatures, can be found in Tables 6 Principle of water electrolysis Fig. 3. Specific conductivity vs. molarity at 30, 60 and 100 C comparing reported data [3,4,6] to proposed equation. Specific conductivity of KOH Fig. 4. 3D plot of proposed equation showing specific conductivity with respect to temperature and concentration. Specific conductivity of KOH (Giliam, R., et al. 2007) 8

7 Main objectives for Developing a new type of membrane stable at KOH temperatures up to 120 C for KOH concentration of 30wt% Reduction of cell voltage from 1.9 to 1.6 V Increase of current density by a factor 2: ma/cm 2 Improve stack efficiency by 10 % Identification of the limiting factors for membrane functionality (aging, contaminations, )

8 Concept of Asbestos replacement cathode anode cathode anode 2.5 mm 2.5 mm 56% porosity of Asbestos membrane Mg 3 Si 2 O 5 (OH) 4 86% open structure of PPS spacer Dense composite layer 10

9 Supporting Structurte Polyphenylene Sulfide (PPS) felt: T m : 285 C T g : 90 C Chemically stable acids, bases, solvents Porous (~85%) Flexible BUT: Hydrophobic surface Porosity too high gas bubbles break through Repetitive unit of PPS PPS felt 3,3mm BWF Alexander Bonk 11

10 Mineral base fillers Hydrophilic filler material selection Mg 3 Si 2 O 5 (OH) 4 chrysotile Asbestos Chemical corrosion experiment CaSiO 3 wollastonite T = 85 C (120 C running) KOH(25wt%) (35wt% running) (Mg,Fe) 2 SiO 4 olivine filler : KOH = 20 mm : 200 mm BaSO 4 barite 99% purity t(h) = 50, 150, 255, 500; 1000; 2000; 4000; 8000 Synthetic based fillers BaTiO 3 98% purity, perovskite str., electroceramics ZrO 2 3YSZ (TOSOH), technical ceramics, SOFC Method: ICP-MS (Inductively coupled plasma mass spectroscopy) ELYGRID meeting Brussels 4-5 June 2013

11 Corrosion Experiments, 85 C, 24 wt% KOH Dissolution effect of individual materials shows the concentration of elements (mg/l) found by ICP-MS for each particular material versus time in hours Mass loss of the particular filler (%) Time (hours) Asbestos (Mg,Si) Wollastonite (Si,Ca) Olivine (Mg,Si) ZrO 2 (Zr) BaSO 4 (Ba) BaTiO 3 (Ba,Ti)

12 MEMBRANE PRODUCTION Inorganic Filler Hydrophilic surfaces Chemical stability Finally increase of operating Temp. Kickoff-Mee ng Pilot Scale Electrolyser IHT Prepara on of powder-sl Organic Binder PSF ( Fixation of powder to felt Chemical stability Solubility in organic solvents Kickoff-MeeMilling Pilot and S Prepara on Inorganic powder Advanced production from solution BaSO 4, BaTiO 3, ZrO 2 Chemical stability Bariumsulfate (BaSO 4 ) Wollastonite (CaSiO 3 ) Olivine ((Mg,Fe) 2 [SiO 4 ]): Chemical similarity to asbestos Price Polysulphone (PSF) Organic T g : 187 C solvent Organic binder N-methyl-2- pyrolidon (NMP) Inorganic powder Milling media: 5 Velocity: ca 0.67 Time: 1 5 days Organic solvent 14

13 MEMBRANE PRODUCTION NMP PSF patent on membrane manufacturing filed in May

14 Example for layer tape casting on PPS felt/net PPS felt (Polyphenylensulfid) technical textile schematic description of the inversion process Kyoung-Yong Chun et al. Journal of Membrane Science, Volume 169, Issue 2, 2000 coated PPS felt thickness of coating: mm 17

15 SEM pictures of membranes Wollastonite-membrane Baryte-membrane Olivine-membrane 19

16 Pore size distribution determined by Bubble point measurementt (BPM) POROLUX 1000 Measuring principle Pressure Step Max pressure 35 bar Min pore (1) 18 nm Max pore (2) 500 µm Max flow 200 l/min Sample holders mm Pressure sensors 2-50 bar Flow sensors FBP regulator l/min ml/min

17 lab-electrolyzer system for membrane ambient conditions Membrane diameter: 50 mm

18 U/I characteristics of new membranes Resistance measurement Linear increase of current density ma/cm² [250 ma/min] 22

19 Gas purity ambient conditions Dr. PD Ulrich F. Vogt Long term measurement 200 ma/cm² (ca. 3,5 hours) 25 C, ambient pressure Pump speed: 10ml/min Recording of: H 2 gas purity ( 99.9%) O 2 gas purity ( 99.6%) Voltage [V]:

20 Conclusions New composite membranes have been developed Processing by tape casting or screen printing on PPS felts or meshes Electrolysis performance better than that of asbestos High purity of hydrogen/oxygen gases Upscaling of membrane manufacturing to 1.6 m diameter in preparation 27

21 Thank you very much for your attention! Acknowledgement The research leading to these results has received funding from the European Union s Seventh Framework Programme (FP7/ ) for the Fel Cell and Hydrogen Joint Technology Initiative under grant agreement n