Tubular Proton Ceramic Steam Electrolysers

Tubular Proton Ceramic Steam Electrolysers Einar Vøllestad 1, R. Strandbakke 1, Dustin Beeaff 2 and T. Norby 1 1 University of Oslo, Department of Chemistry, 2 CoorsTek Membrane Sciences AS

What are Proton Ceramic Electrochemical Cells? Zr 0.9 Y 0.1 O 1.95

Proton Ceramic Electrochemical Cells Exothermic formation of mobile protons in humid atmospheres H O(g) x 2 vo OO 2OHO Zr 0.9 Y 0.1 O 1.95 + BaO BaZr 0.9 Y 0.1 O 2.95 Kreuer, 2001

Proton Ceramic Electrochemical Cells Exothermic formation of mobile protons in humid atmospheres H O(g) x 2 vo OO 2OHO Zr 0.9 Y 0.1 O 1.95 + BaO BaZr 0.9 Y 0.1 O 2.95 Low E a for mobility facilitates lowered operating temperatures E a,h + 2 3 E a,o 2 Kreuer, 2001

Significant advances for proton ceramic fuel cells and catalytic reactors

but very few reports on Proton Ceramic Electrolysers (PCEs) with moderate success I tn (Acm -2 ) 1 0.1 0.01 Why BZCY the / BGLC slow Ideal development of BZCY / BGLC PCE Un-optimised technology? 8YSZ / LSCF 400 450 500 550 600 650 700 T(C) [1] [4] [2] [3] [5] BCZY (ideal) YSZ (ideal) Cell 2 Cell 3 Matsumoto 201 Babinec 2015 Gan 2012 Li 2013 Bi 2015 * Itn YSZ m LSCF Itn ideal Itn m Composite

PCE presents significant operational advantages but is still limited to small-scale materials development Low activation energy enables intermediate temperature operation Integration with waste heat sources Cheaper manifold materials Produces pressurized dry H 2 and diluted O 2 Alleviates downstream separation and compression 4e - 2H 2 O U 400-700 C Less mature technology Lab-scale button cell tests (1 cm 2 ) Large anode overpotentials Materials with mixed protonic electronic conduction needed to increase reaction zone Partial p-type conduction in BZCY electrolyte material Electronic leakage currents diminish electrical efficiency O 2 +(H 2 O) 4H + 2H 2

Three strategies to improve PCE performance within the ELECTRA project log ((R p (cm 2 ) Mass change (mg) Tubular cells by extrusion and spraycoating Cost-efficient and scalable processing Low sealing area and high mechanical strength for pressurized operation 1.4 1.2 1.0 0.8 0.6 0.4 BaGd 0.8 La 0.2 Co 2 O 6- BaGdCo 1.8 Fe 0.2 O 6- BaPrCo 2 O 6- BaPrCo 1.6 Fe 0.4 O 6- Dry Wet 3 mol% H 0.2 Ba 1-x Gd 0.8 La 0.2+x Co 2 O 6-δ (BGLC) as steam anode Proton incorporation in wet conditions Lowest reported polarization resistance for proton ceramic cells 1.5 1.0 0.0 100 150 200 250 t(min) T (C) 750 700 650 600 550 500 450 400 350 0.5 0.0-0.5-1.0 GBCF / BZCY BSCF / BCY Pr 2 NiO 4 / BCY LSCF / BCY BXCF / BCY BGLC (x=0) / BZCY R. Strandbakke et al., Solid State Ionics (2015) -1.5 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1000/T (K -1 )

Three strategies to improve PCE performance within the ELECTRA project Tubular cells by extrusion and spraycoating Cost-efficient and scalable processing Low sealing area and high mechanical strength for pressurized operation Ba 1-x Gd 0.8 La 0.2+x Co 2 O 6-δ (BGLC) as steam anode Significant hydration in wet conditions Lowest reported polarization resistance for proton ceramic cells Pressurized operation to increase kinetics and limit p-type conduction in BZCY: [h ] = K hydr OH 1 1 2 4 O p H2 O p O2

Scalable production of tubular half-cells by extrusion and spray-coating Paste preparation (BaSO 4, NiO, ZrO 2, Y 2 O 3, CeO 2 ) 2 3 2 Extrusion of 1 m long tube Drying, cutting to 40 cm Spray-coating with suspension of BaSO 4, ZrO 2, Y 2 O 3, CeO 2 Sintering

Processing of steam anodes on sintered tubular half-cells BZCY72- Ba 1-x Gd 0.8 La 0.2+x Co 2 O 6-δ applied as steam anode Fired in air at 1200 C for 5h Infiltrated with nano-crystalline BGLC in isopropanol suspension Thin Pt, Au or silver current collection Capped and sealed at 1000 C using glass ceramic developed by CoorsTek Membrane Sciences 50µm NiO reduction at 800 C for 24 hours in 10% H 2 Cell Area: 6-11 cm 2

Cell Voltage / V Electrode overpotential significantly influences the faradaic efficiency of PCEs / % -Z // (cm 2 ) 2.5 600 C, 1.5 bar steam 100 2.0 80 60 1.5 1.0 Cell 1 Cell 2 40 20 4 Temperature: 600 C Bias: 30 ma cm -2 0 100 200 300 0 2 Current density / ma cm -2 Cell 1 0-2 Cell 2 2 4 6 8 Z / (cm 2 )

Cell Potential / V Fairly reproducible performance with composite anodes / % -Z // (cm 2 ) 2.5 600 C, 1.5 bar steam 100 Cell 1 Current collector Anode comp Sinterin g T (ᵒC) Anode Single phase Au x = 0.3 1000 2.0 80 60 2 Composite Pt x = 0.3 1200 3 Composite Pt x = 0.3 1200 4 Composite Ag x = 0.3 1200 1.5 1.0 Cell 1 Cell 2 Cell 3 Cell 4 0 100 200 300 Current density / ma cm -2 Variable and high ohmic resistance due to interface reaction layer or parasitic contact resistances? 40 20 0 4 2 0-2 Cell 3 Temperature: 600 C Bias: 30 ma cm -2 Cell 4 Cell 1 Cell 2 2 4 6 8 Z / (cm 2 )

Cell Potential / V log (R p (cm 2 )) R p (cm 2 ) H 2 production / NmL min -1 Electronic leakage suppressed at low temperatures 20 15 10 Current Density / ma cm -2 100 200 Faradaic H 2 production 500 C 600 C 700 C Anode polarization resistance T (C) 800 700 600 500 400 1.0 5 0.5 E a = 0.5 ev 10 500 C 1.5 600 C 700 C 0.0 1.0 Cathode: p tot = 3 bar ph 2 = 0.5 bar Anode: p tot = 3 bar ph 2 O = 1.5 bar po 2 = 30 mbar 1 1 2 3 Current / A -0.5 1.0 1.2 1.4 1.6 1000/T (K -1 )

-Z // (cm 2 ) Cell Potential / V Higher pressures increases performance 1.8 c) 600 C 1.6 700 C 1.4 1.2 1.5 bar steam 4 bar steam 0.25 Temperature: 700C Bias: 15 macm 2 d) 1.0 0 1 2 3 4 5 0.00 Current / A -0.25-0.50 1.5 bar H 2 O, Initial 1.5 bar H 2 O, 65 hrs 4 bar H 2 O, 67 hrs 1.75 2.00 2.25 2.50 Z / (cm 2 )

I tn (Acm -2 ) I tn (Acm -2 ) These initial results represent a significant step towards intermediate-temperature steam electrolysis 1 BCZY (ideal) YSZ 1(ideal) BZCY / BGLC Ideal 0.1 0.01 1E-3 1E-4 0.1 0.01 BZCY / BGLC Un-optimised 400 450 500 550 8YSZ 600 / LSCF 650 700 T(C) 400 450 500 550 600 650 700 [1] [4] [2] [3] [5] BCZY (ideal) YSZ (ideal) Cell 2 Cell 3 Matsumoto 2012 Babinec 2015 Gan 2012 Li 2013 Bi 2015 * BCZY (ideal) YSZ (ideal) Cell 2 Cell 3 Matsumoto 201 Babinec 2015 Gan 2012 Li 2013 Bi 2015 * Itn YSZ m LSCF Itn ideal Itn m Composite T(C)

I tn (Acm -2 ) I tn (Acm -2 ) Conclusions PCEs offer advantages such potential intermediate temperature operation and production of pressurized dry hydrogen Large anode overpotentials and partial p-type conduction in BZCY are main challenges to overcome Scalable and cost-efficient tubular half-cell production achieved using extrusion and spray-coating Tubular PCEs with BGLC anode display highest hydrogen production rate reported 0.1 for proton ceramics Parasitic interface and contact resistances may 0.01 contribute to high ohmic resistance 1E-3 1E-4 1 BCZY (ideal) YSZ 1(ideal) BZCY / BGLC Ideal BZCY / BGLC Un-optimised 0.1 0.01 400 450 500 550 8YSZ 600 / LSCF 650 700 T(C) 400 450 500 550 600 650 700 T(C) [1] [4] BCZY (ideal) YSZ (ideal) Cell 2 Cell 3 Matsumoto 2012 Babinec 2015 Gan 2012 [2] Li 2013 [3] Bi 2015 * [5] BCZY (id YSZ (ide Cell 2 Cell 3 Matsum Babinec Gan 201 Li 2013 Bi 2015 Itn YSZ Itn ideal Itn m Co

Acknowledgements The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement n 621244.