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ENERGIX-Stort program energi

FCH JU High temperature electrolyser with novel proton ceramic tubular modules of superior efficiency, robustness, and lifetime economy

Tildelt: kr 2,7 mill.

High temperature electrolysers produce H2 efficiently utilising electricity from renewable sources and steam from solar, geothermal, or nuclear plants. CO2 can be co-electrolysed to produce syngas and fuels. The traditional solid oxide electrolyser cell (SOEC) produces wet H2 at the steam side. ELECTRA in contrast develops a proton ceramic electrolyser cell (PCEC) which pumps out and pressurises dry H2 directly. Delamination of electrodes due to O2 bubbles in SOECs is alleviated in PCECs. The proton conductor is based on state-of-the-art Y:BaZrO3 (BZY) using reactive sintering for dense large-grained films, low grain boundary resistance, and high stability and mechanical strength. A PCEC can also favourably reduce CO2 to syngas in so-called co-ionic mode. Existing HTEs utilise the high packing density of planar stacks, but the hot seal and vulnerability to single cell breakdown results in high stack rejection rate and questionable durability and lifetime economy. ELECTRA uses instead tubular segmented cells, mounted in a novel module with cold seals that allows monitoring and replacement of individual tubes from the cold side. ELECTRA will show a kW-size multi-tube module producing 250 L/h H2 and CO2 to syngas co-electrolysis with DME production. EELECTRA is an EU FCH JU project counting 7 partners (4 SMEs/industry). It is coordinated by University of Oslo, and runs for 3 years 2014-17. Innovative tubular segmented-in-series cells are currently developed along three main production lines with increasing risks and rewards. All cells consist of a porous Ni-BZCY cathode for the H2 side (self-standing or supported on a porous BZCY tube), a thin dense BZCY-based electrolyte, a porous anode for the H2O+O2 side, and a current collector system. The 1st line is based on solid state reactive co-sintering of BZY based electrolyte coated on a slip-cast or extruded NiO based composite tube, with subsequent reduction of NiO to Ni in hydrogen. Various cell architectures of 25 cm tube length were successfully produced with varying contents of Ce dopant and thickness of the electrolyte. In the 2nd line, the BZCY tubes are cut and stacked in series to build voltage and reduce overall current to improve current collection along the tube. The 3rd line takes a closed porous BZY extruded tube, on which segments of cathode, electrolyte, and interconnect are sequentially applied and co-sintered. The cells integrate Y:Ba(Zr,Ce)O3 (BZCY) prepared by reactive solid state sintering (SSRS) with NiO sintering aid. The SSRS mixture is utilized to produce porous BZCY based supports by extrusion using pore formers to tailor the microstructure of the parts. The NiO-BZCY fuel electrode and BZCY electrolyte are dip-coated on the green supports using water-based slurries and masking tape to delineate the bands. The assembly is hang-fired upon co-sintering in air. Typical thickness of the functional layers ranges from 15 to 30 microns. Several interconnect systems were investigated to produce complete segmented-in-series cells based on oxides and glass-metal composite systems. Two materials systems show promising results, in terms of thermos-mechanical and chemical compatibility of the interconnects materials with BZCY based materials. In addition, gastight glass composites were successfully obtained on GEN3 cells, presenting good conductivity between the layers. A number of materials were screened for their compatibility with BCZY based electrolyte and stability as PCEC anode. LSM is found potential candidate electrode material with respect to its stability in reducing conditions and Ba1-xGd0.8La0.2+xCo2O6 (BGLC) with x > 0.3 is a candidate material stable under oxidizing conditions and high steam pressures. BGLC (x = 0, 0.1, 0.2, 0.3 and 0.5) has been tested as oxygen / steam electrodes on button cells and on tubular segments by electrochemical impedance spectroscopy. Results showed a total area specific polarization resistance of 1 ohm.cm2 over both electrodes at 600°C in 5 % H2 in Ar / 2.5 % H2O in 1 atm O2. Single tubular cells with BGLC/BZCY composite oxygen electrodes have been tested in electrolysis mode under high steam pressures (pH2O = 1.5 and 4 bar), and present high hydrogen flux with a faradaic efficiency above 90% at 600°C. A multi-tubular high pressure module with capability to monitor and replace individual tubes has been designed, built, and tested. A patent of this module has been submitted. The balance of plant and techno-economics of the integration of PCEs with various sources of electricity and heat or steam have been modelled. Mass-produced PCEs may be inexpensive and will, with available heat or steam, produce hydrogen competitive to e.g. alkaline electrolysis.

High temperature electrolysers (HTEs) produce H2 efficiently utilising electricity from renewable sources and steam from solar, geothermal, or nuclear plants. CO2 can be co-electrolysed to produce syngas and fuels. The traditional solid oxide electrolyser cell (SOEC) leaves wet H2 at the steam side. ELECTRA in contrast develops a proton ceramic electrolyser cell (PCEC) which pumps out and pressurises dry H2 directly. Delamination of electrodes due to O2 bubbles in SOECs is alleviated in PCECs. The proton conductor is based on state-of-the-art Y:BaZrO3 (BZY) using reactive sintering for dense large-grained films, low grain boundary resistance, and high stability and mechanical strength. A PCEC can favourably reduce CO2 to syngas in co-ionic mode. Existing HTEs utilise the high packing density of planar stacks, but the hot seal and vulnerability to single cell breakdown give high stack rejection rate and questionable durability and lifetime economy. ELECTRA uses instead tubular segmented cells, mounted in a novel module with cold seals that allows monitoring and replacement of individual tubes from the cold side. The tubes are developed along 3 design generations with increasing efforts and rewards towards electrochemical performance and sustainable mass sc ale production. Electrodes and electrolyte are applied using spraying/dipping and a novel solid state reactive sintering approach, facilitating sintering of BZY materials. ELECTRA emphasises development of H2O-O2 anode and its current collection. It will show a kW-size multi-tube module producing 250 L/h H2 and CO2 to syngas co-electrolysis with DME production. Partners excel in ceramic proton conductors, industry-scale ceramics, tubular electrochemical cells, and integration of these in renewable energy schemes including geothermal, wind and solar power. The project counts 7 partners (4 SMEs/industry), is coordinated by University of Oslo, and runs for 3 years.

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ENERGIX-Stort program energi