Performance of a PEM water electrolyser based on metallic. iridium electrocatalyst and an Aquivion membrane

Transcription

1 Performance of a PEM water electrolyser based on metallic iridium electrocatalyst and an Aquivion membrane S. Siracusano 1*, V. Baglio 1, S.A. Grigoriev 2, L. Merlo 3, V.N. Fateev 4, A. S. Arico 1 1 CNR-Institute of Advanced Energy Technologies (ITAE) -Via Salita Santa Lucia sopra Contesse, Messina 2 National Research University Moscow Power Engineering Institute, Krasnokazarmennaya, 14, Moscow, Russia 3 Solvay -Viale Lombardia, Bollate (MI) Italy 4 National Research University Kurchatov Institute, Kurchatov sq.,1, Moscow, Russia 11 th May 2016 Tunis, Tunisia

2 PEM Electrolysers Electrolysis of water using renewable energy sources has significant advantages: Production of high purity «green» hydrogen High efficiency (>70 % vs. LHV) Several technologies are currently used for water electrolysis : alkaline systems, solid oxide electrolysers and PEM electrolysers Very promising for grid stabilisation and coupling with renewable power sources Key features of PEM electrolysis High current densities at low cell voltages High efficiency (even at low temperatures); Rapid start-up/response High resistance to duty cycles Eco-friendly system with increased level of safety (no caustic electrolyte circulating) Smaller mass-volume characteristics: compact system High differential pressure, meaning reduced gas compression requirements for the produced hydrogen gas High degree of gases purity Possibility of combining fuel cell and electrolyser (regenerative fuel cell) Drawbacks of PEM electrolysis High cost (PFSA membranes, noble metal electrocatalysts, Ti bipolar plates, expensive coatings) CAPEX Long-term durability up to 100 khrs not yet achieved OPEX

3 HPEM2GAS Project & Partnership description High Performance PEM Electrolyzer for Cost-effective Grid Balancing Applications Horizon 2020 Programme of the FCH Joint Undertaking Beneficiary name CONSIGLIO NAZIONALE DELLE RICERCHE (CNR-ITAE) Country Italy Partner type Research ITM Power (Trading) Ltd (ITM) United Kingdom Industry SOLVAY SPECIALTY POLYMERS ITALY S.P.A. (SLX) IRD FUEL CELLS A/S (INDUSTRIAL RESEARCH & DEVELOPMENT A/S) (IRD) Italy Denmark Industry Industry Stadtwerke Emden GmbH (SWE) Germany Industry HOCHSCHULE EMDEN/LEER (HS EL) Germany Research UNIRESEARCH BV (UNR) Netherlands SME

4 HPEM2GAS objectives Next generation water electrolysers must achieve a good dynamic behaviour (rapid start-up, fast response, wider load and temperature ranges) to provide proper grid-balancing services and thus address the increase of intermittent renewables interfaced to the grid. The overall objective of the HPEM2GAS project is concerning with the development of a low cost PEM electrolyser optimised for grid balancing service The activities are addressed to both stack and balance of plant innovations for an advanced 180 (nominal)-300 kw(transient) PEM electrolyser. TheadvancedsystemwillbedemonstratedinasixmonthfieldtestatEmdeninGermany The aim is to bring the developed technology from TRL4 to TRL6, demonstrating the PEM electrolyser system in a power-to-gas field test Deliver a techno-economic analysis and an exploitation plan to bring the innovations to market

5 PEM Electrolysers Drawbacks to overcome / Aspects to improve Slow oxygen evolution reaction rate Improvement of membrane properties Cost e - Oxygen evolution reaction catalysts: H 2 O H 2 O Ru ; RuO 2 a highest activity; lower stability Ir ; IrO 2 a high activity; a better long-term stability; Membrane Benchmark less efficiency losses due to corrosion. Nafion H 2 O, O 2 H + H + Membrane H 2 O, H 2 Excellent Performance Appropriate electrochemical Stability Suitable Mechanical Properties Rapid Start-up/ Rapid response Dynamic behaviour Anode Cathode Cathode: Anode: 4H + + 4e - 2H 2 2H 2 O 4H + + 4e - + O 2

6 Aim of this work* Advanced Membrane and Electro-catalysts 1100 g/eq Pt/C cathode catalyst g/eq Nafion Aquivion Long side-chain ionomers Short side-chain ionomer Ir anode catalyst 1 1Developed by Solvay Specialty Polymers The Solvay Aquivion ionomer is characterized by both larger crystallinity and higher glass transition temperature than Nafion *S. Siracusano, V.Baglio, A.Stassi, L.Merlo, E.Moukheiber, A.S.Aricò. Performance analysis of short-side-chain Aquivions perfluorosulfonic acid polymer for proton exchange membrane water electrolysis. Journal of Membrane Science 466(2014) 1 7 *S. Siracusano, V. Baglio, E. Moukheiber, L. Merlo, A.S. Aricò. Performance of a PEM water electrolyser combining an IrRu-oxide anode electrocatalyst and a short-side chain Aquivion membrane. International Journal of Hydrogen Energy 40 (2015)

7 30 %Pt/C Cathode Electro-Catalyst Sulfite-complex route* H 2 PtCl 6 + Na 2 S 2 O 5 /NaHSO 3 Na 6 Pt(SO 3 ) 4 + Vulcan The Pt-sulfite complex/vulcan slurry was decomposed by adding H 2 O 2 PtO x /Vulcan Carbothermal reduction in inert (Ar) atmosphere at 600 C Pt/Vulcan 2.7 nm XRD: Pt cubic and C support hexagonal crystallographic structures TEM: Proper metal particle dispersion and good homogeneity *Aricò AS, Stassi A, Modica E, Ornelas R, Gatto I, Passalacqua E, et al. Performance and degradation of high temperature polymer electrolyte fuel cell catalysts. J Power Sources 2008;178:

8 Metallic Ir Anode Electro-Catalyst Chemical Reducer Synthesis* (H 2 IrCl 6 + H 2 O + KOH(0.5M) Solution (ph ) Stirred at room T NaBH 4 in NaOH 1M The solution was constantly stirred until the end of gas evolution Then the remaining deposits (Ir black powder) were thoroughly washed off (several times) using bi-distilled water in order to bring the ph of the downtake solution within the range. Dry in air at C *S.A. Grigoriev, P. Millet, K.A. Dzhus, H. Middleton, T.O. Saetre, V.N. Fateev Design and characterization of bi-functional electrocatalytic layers for application in PEM unitized regenerative fuel cells // International Journal of Hydrogen Energy, Vol. 35, Issue 10, May 2010, pp

9 Metallic Ir Anode Electro-Catalyst XRD (111) TEM: Agglomerates of fine particles Counts (200) 2.7 nm (220) (311) (222) XRD: Cubic crystallographic structure (JCPDS card no ) Theta SEM-EDX: Iridium (no impurities) Agglomerates of fine particles

10 Single Cell Configuration Low noble metal loadings configuration Formulation: 30 wt. % Pt/C Loading: ~ 0.1 mg/cm 2 Deposition method: doctor blade Composition: 67% (Pt/C) + 33 wt. % ionomer Backinglayer carbon cloth(ht ELAT) Membrane: Aquivion E100-09S Formulation: Ir metallic Loading: ~ 0.4 mg/cm 2 Deposition method: Composition: Backing layer Spray at 80 ºC on membrane Ir + 20 wt.% ionomer Ti-grid

11 Electrochemical Characterization Low noble metal loadings configuration (0.5 mg cm -2 MEA) Cathode: 30% Pt/C Membrane: E100-09S Anode: Ir metallic Potential / V C 40 C 50 C 60 C 70 C 80 C 90 C T / C A cm 1.6 V A cm 1.8 V 30 C Current Density / A cm C C The electro-catalytic activity increased as a function of temperature 60 C C C C

12 Electrochemical Characterization -Z" / ohm cm C 40 C 60 C 80 C 90 C 1.5 V -Z" / ohm cm C 40 C 60 C 80 C 90 C Z' / ohm cm 2 Cathode: 30% Pt/C Membrane: E100-09S Anode: Ir Z' / ohm cm 2 Series and polarization resistances decreased as the temperature increased T / C Rs / mω cm 2 Rp / mω cm 2 30 C C C C C

13 Durability Test A cm C Cell Potential / V µv/h Low noble metal loadings configuration (0.5 mg cm -2 MEA) Time / h Interestingly: after the first hours of conditioning the cell potential progressively decreses ( efficiency increases) using the low noble metal loading configuration

14 Comparison: before and after time test 80 C Before time test After time test Similar characteristics in the activation region Decrease of potential at high current after the durability 1.9 V Before 1.55 A cm -2 After 2.25 A cm -2 The enhanced performance for the cell after time test may be related to chemical and diffusionalaspects A modification of the catalyst-electrolyte interface with time may also influence the observed behaviour

15 Comparison: before and after time test Z" / ohm cm h 1000 h After time test Before time test 80 C 1.5 V Activation controlled region Z' / ohm cm 2 Slightly lower series and polarization resistance after the time test in the activation region Rs (Ω cm 2 ) Rp (Ω cm 2 ) Before After

16 Comparison: before and after time test After Room T Anode: H 2 O Cathode: H 2 50 cc Before However, CV analysis shows a significant enhancement of coulombic charge with the time-test; Two phenomena can be responsible of this behaviour: An increase of surface roughness and particle dispersion (lower agglomeration) during the electrochemical operation. This phenomenon may be promoted by the insertion of ionomer micelles among particles An oxidation of the metallic Ir to IrOx causing an increase of the double layer capacitance

17 Investigation of MEA used in long term test Anode side Anode side: No significant change in Counts / a.u nm MEA Used - Anode crystallite size and in the bulk composition before and after test nm MEA Fresh - Anode Theta / degree Cathode side Cathode side: Presence of PTFE due to GDL used as backing layer

18 Investigation of MEA used in long term test MEA Fresh Anode side SEM Ti grid Ti grid MEA Used

19 Investigation of MEA used in long term test SEM-EDX MEA Fresh Anode side MEA Used Elem Wt% At% CK OK FK IrM SK Elem Wt% At% CK OK FK IrM SK An increase of O signal in the used sample No Evidence impurities in the used sample Evidence of surface oxidation?

20 Investigation of MEA used in long term test TEM MEA Fresh Anode side MEA Used Ionomer Ionomer Evidence of an enhanced dispersion after the durability test

21 Investigation of MEA used in long term test XPS Survey High resolution XPS spectra for Ir and O signals in the fresh and used anode F1s Ir4f IrO 2 c/s Used Fresh -O KLL F KLL -O1s -Ir4p1 -Ir4p Binding Energy (ev) -Ir4d5 -Ir4d3 -C1s -S2s -S2p 200 -Ir4f7 -Ir4f5 -F2s 0 Used F/Ir 5.32 O/Ir 3.61 F/Ir 9.80 O/Ir 1.44 Fresh c/s c/s Used Fresh O1s Binding Energy (ev) Ir 55 Shift of the signal of Ir4f from 60.9 ev to 62.5 ev (Ir IrO 2 ) An increase of O signal in the used sample Decrease of F content in the used sample Used Fresh Binding Energy (ev)

22 Conclusions Advanced membrane and electro-catalysts were developed for water electrolysis; The electrochemical activity was investigated in a single cell PEM electrolyserconsisting of a Pt/C cathode, Ir metallic anode and an Aquivion membrane; An excellent performance, of 1.2 A cm -2 at 1.8 V at 90 C, was achieved with low loading configuration (0.5 mg cm -2 MEA); An increase in performance was observed with time; The Physico Chemical investigation of the MEA after the long term test indicated an oxidation of Iridium on the surface. ACKNOWLEDGEMENTS The authors acknowledge the financial support of the EU through the FCH JU HPEM2GAS Project. Work performed was supported by the Fuel Cells and Hydrogen Joint Undertaking in the context of project HPEM2GAS, contract No