Steam Electrolysis Mode Research Articles

23,000 h steam electrolysis with an electrolyte supported solid oxide cell

An electrolyte supported solid oxide cell of 45 cm2 area was operated in the steam-electrolysis mode during more than 23,000 h before scheduled shutdown, of which 20,000 h with a current density of j = −0.9 A cm−2. The cell consisted of a scandia/ceria doped zirconia electrolyte (6Sc1CeSZ), CGO diffusion-barrier/adhesion layers between electrolyte and electrodes, a lanthanum strontium cobaltite ferrite (LSCF) oxygen electrode, and a nickel/gadolinia-doped ceria (Ni/GDC) steam/hydrogen electrode. Voltage degradation in the operation period with j = −0.9 A cm−2 was 7.4 mV/1000 h (0.57%/1000 h) and the increase in the area specific resistance 8 mΩ cm2/1000 h. The final cell voltage was 1.33 V (at 851 °C cell temperature). After dismantling, the cell showed no mechanical damage at electrolyte and H2/H2O electrode; a small fraction of the oxygen electrode was delaminated. Impedance spectroscopy applied at the steady state DC current density confirmed a degradation dominated by an increasing ohmic term, mainly due to ionic conductivity decay in the electrolyte. In addition, a small non-ohmic and at least partly reversible O2 electrode contribution to degradation was identified, affected by a pollution from the (compressor) purge air.

Detailed Study of Degradation Behaviour of Solid Oxide Cells in Electrolysis and Co-Electrolysis Mode

High temperature steam and co-electrolysis has a high potential for the efficient production of hydrogen or syngas. For a further development of this promising technology, development work on materials and cells as well as extensive operational experience is still needed. A main objective is to develop highly efficient and long-term stable cells and stacks using novel electrode materials and to improve the degradation behaviour by elucidating the relevant degradation mechanisms. Fuel electrode supported cells containing perovskite-type air electrodes were fabricated by ceramic processing and sintering techniques to be electrochemically characterized in electrolysis and co-electrolysis operating mode. I-V curves and electrochemical impedance spectra have been recorded for cell characterization. For a systematic investigation of the influence of relevant operating parameters such as temperature, current density and fuel gas humidification on long-term degradation a special test bench has been established which allows electrochemical characterization of 4 cells simultaneously under relevant SOEC conditions. This arrangement allows for variation of one distinct operating parameter while keeping other parameters strictly constant. A series of measurements over 1000 hours each in the temperature range 750-850 °C with different fuel gas humidity (40-80 mol%) and different current densities between 0 and 1.5 A/cm2 has been performed in steam electrolysis mode. Additionally, a second series of measurements has started in co-electrolysis mode at different operating temperatures and different steam-to-CO2 ratios. The progress of degradation was monitored in-operando approximately every 150 h by impedance spectroscopy. It was possible to differentiate different electrode processes, a mass transport limitation on the fuel electrode and the electrolyte resistance. Post-mortem investigations have been conducted to localize and identify the limiting processes and to clarify the correlation between degradation processes and operational parameters. In this paper the selection and preparation of electrode materials and the process of cell manufacturing as well as the experimental setup for cell characterization and long-term measurements are described. Results of electrochemical cell characterization performed at different operational conditions in electrolysis and co-electrolysis mode are shown and degradation phenomena observed and their underlying mechanisms based on different electrochemical processes are explained. ACKNOWLEDGEMENTFinancial support from the Helmholtz Association in the frame of the “Helmholtz Energy Alliance on electrochemical energy storage and conversion” is gratefully acknowledged. References M. P. Hörlein, G. Schiller, F. Tietz, “Development and characterisation of sold oxide elec-trolyser cells, Proc. 11th European SOFC and SOE Forum, Lucerne, Switzerland, 1-4 July 2014, B1316 M. P. Hörlein, G. Schiller, F. Tietz, K.A. Friedrich, „Systematic Parameter Study on the Influence of Humidification and Current Density on SOEC Degradation”, ECS Trans-actions, 68 (1), 3553-3561 (2015) Y. Tanaka, M. Hörlein, G. Schiller, “Numerical Simulation of Steam Electrolysis with a Solid Oxide Cell for Proper Evaluation of Cell Performances”, International Journal of Hydrogen Energy, 41 752-763 (2016)

Evaluation of polarization and hydrogen production efficiency of solid oxide electrolysis stack with La0.6Sr0.4Co0.2Fe0.8O3−δ- Ce0.9Gd0.1O1.95 oxygen electrode

The 30-cell (10 × 10 cm2) LSCF-GDC (La0.6Sr0.4Co0.2Fe0.8O3−δ − Ce0.9Gd0.1O1.95) oxygen electrode supported planar solid oxide electrolyzer cell (SOEC) stack module is manufactured and tested at different operation conditions (operating temperature, steam content, gas flow rate et al.) in steam electrolysis mode for hydrogen production. The i–v curves of each electrolysis are recorded and fitted according to the electrochemical models, the influences of operation conditions on the polarization loss of high temperature water electrolysis are analyzed, and the electrolysis efficiencies are calculated. High operating temperature gives the reduction of Ohmic and activation polarization, and high steam content results in significantly lowered activation polarization. The flow rates of the gas onto the hydrogen electrode and oxygen electrode have great impact on concentration and activation polarization. The electrolysis efficiency can reach the maximal value of 80.8% (electrolysis voltage 1.273 V) when the system operating at 800 °C, with 6 L min−1 90% humidified hydrogen mixed gas, and the rate of resultant hydrogen is 4.57 L min−1.

High Temperature Metal / Metal Oxide Battery

In future there will be a strong demand for large capacity rechargeable batteries to store electrical energy (e.g. from renewable power sources) in long-term stationary applications [1]. A high temperature metal / metal oxide battery can be built up by combining solid oxide fuel cell (SOFC) technology and a metal/metal oxide storage system [2]. Such a type of battery promises charging and discharging capacities of more than 250 W/cm2 [3]. Requirements for a reversible working solid oxide cell (SOC) are a high performance, minimum internal resistance of the cell, and long-term stability at operating conditions. In the present work the performance of solid oxide cells (SOC) operating in fuel cell and steam electrolysis mode over a temperature range of 650-900 °C and as a function of humidity were studied. Results presented were obtained from single SOCs, with an active area of 16 cm2 and button cells with an active area of 0.5 cm2. The SOCs investigated were anode substrate cells (ASC), with nickel-YSZ-cermet steam/hydrogen electrodes, yttria-stabilized zirconia (YSZ) electrolytes, and lanthanum strontium iron cobalt perovskite (LSCF) air electrodes. Current-voltage measurements were coupled with electrochemical impedance spectroscopy (EIS), in order to identify the different loss terms in cell behaviour during the fuel cell and electrolysis mode. EIS measurements are conducted under practical load conditions in SOCs in both modes. The cells show stable current-voltage curves during cycling between fuel cell and electrolysis mode at short cycling times between 2.5 h and 5 h. Measurements at different humidity show that high electrical-to-hydrogen energy conversion efficiencies are achieved and the amount of steam content is the limiting factor for the electrolysis mode. During electrolysis mode remarkable high current densities around -1.3 A/cm2 were achieved at a cell voltage of 1.3 V and a temperature of 800 °C. Below 50 % steam content, however, a strong efficiency loss was observed. It is also well known that the degradation of the SOC during steam electrolysis is still a limiting factor for the long term application [4]. Hence the focus of interest was also the degradation of the air electrode. Increasing the current density and elongating the duration of electrolysis experiments resulted frequently in a very fast delamination of the LSCF electrode.

Steam and Co-Electrolysis Sensitivity Analysis on Ni-YSZ Supported Cells

The present paper investigates the variation in performances in co-electrolysis of steam/CO2 on SOEC single cells caused by the progressive increase of CO2 inlet concentration and current density. Steam electrolysis and co-electrolysis were investigated on circular Ni-YSZ supported cells produced by SOLIDpower (“ASC-700” type cells). The thin film electrolyte is constituted by YSZ and the oxygen electrode by LSCF-GDC. The active area corresponds to 12.56 cm2 (2 cm of radius). The cells were fed with different H2O/CO2 mixtures, while keeping 10% H2 of the inlet molar flow in order to avoid re-oxidation of the Ni-YSZ support. A sensitivity analysis was performed looking in particular at the effects of inlet gas composition, gas flows and temperature on the performances. I-V characterization and EIS measurements at different current densities were carried out for each sequence. In steam electrolysis mode, the reference inlet molar flow was equal to 150 Nml/min (90% H20, 10% H2), at 750°C. The I-V curve showed a voltage of 0.861V at OCV, 1.049V at 0.5 A/cm2 and 1.253V at 1 A/cm2. A sensitivity analysis was performed varying the temperature (700°C, 750°C and 800°C), the inlet air flow (100 Nml/min, 300 Nml/min and 500 Nml/min) and the total inlet fuel flow (from 8 to 16 Nml/min/cm2). In this case, the steam conversion factor was kept constant equal to 50% (adjusting the current imposed). EIS analysis exhibits that ohmic and polarization resistances decrease with current densities lower than 0.4 A/cm2 and then rise with higher values. As expected, the increase of temperature has a positive impact on the performances, while the change of air and fuel flow slightly affects them. In co-electrolysis mode the CO2 and H2O content was varied, keeping constant the total molar flow and the hydrogen fraction as explained before. As shown in the enclosed image, the area specific resistance (ASR) increases with the CO2 concentration in the mixture and gas transport limitation occurs at lower current densities. Also in this case a sensitivity analysis was conducted changing the temperature (from 700°C to 800°C) and the resulting EIS plots demonstrate different ongoing processes favored at high current densities. In particular, the reverse water-gas-shift reaction plays an important role on the overall balance of the gas species, and it directly depends on temperature and inlet fuel composition. Figure 1

9000 Hours Operation of a 25 Solid Oxide Cells Stack in Steam Electrolysis Mode

Hydrogen production through water electrolysis is one of the key processes required in the conversion of electricity to fuels. Carbon free hydrogen produced through water electrolysis can be used as a fuel for hydrogen powered applications (such as fuel cell cars) or grid injection, or as a reactant in downstream processes to produce synthetic fuels such as SNG or methanol. Among available technologies, high temperature electrolysis potentially offers significantly higher electrical to chemical conversion efficiencies compared to alkaline and PEM electrolysers, with values in excess of 100% achievable if additional thermal energy is supplied to the system. High temperature electrolysers are essentially solid oxide fuel cells operated in reverse. Hence, the development of solid oxide electrolysers (SOE) has hugely benefited from the intensive research carried out for the development of Solid Oxide Fuel Cells (SOFCs) in the past decades. A 25 cells stack manufactured by Topsoe Fuel Cells has been tested at EIFER in high temperature electrolysis mode at about 750°C and current densities of 0.57 and 0.72 A/cm2. The applied steam conversion rate was 50%, with a 90 % absolute humidity gas feed. The total duration of the test was almost 9100 hours, split between 8300 current hours and 800 standby hours induced by incidents that occurred during the test. Incidents included losses of the steam and current supplies. After each incident, the stack performance was recovered, indicating a good robustness of the stack towards unexpected and potentially damaging conditions. The main issue during the test has been the considerable increase of the voltage drop between the positive end plate and the bottom stack repeat unit (SRU), before a sharp improvement occurred after about 2000 hours of operation, which has influenced the stack temperature distribution and in turn individual SRU degradation. The maximum observed voltage drop culminated at 2.73 V, before stabilising around 0.6V. The stack has shown an overall voltage degradation of 2% per thousand hours, as can be seen on Figure 1. The corresponding voltage losses were 613 mV and 678 mV per thousand hours, for 0.57 and 0.72 A/cm2 current densities, respectively. This in turn corresponds to an average degradation in the range 0.24 – 0.27 mV per thousand hours per SRU. Moreover, the stack temperature has been adjusted on a few occasion during the test, which highlighted the possibility of using the wide operating temperature range of the solid oxide technology to counter balance the stack degradation and increase the lifetime. Indeed, allowing the stack to increase at a rate of 3°C per thousand hours produced a reduced degradation rate of 1.80 % per thousand hours. Figure 1

9000 Hours Operation of a 25 Solid Oxide Cells Stack in Steam Electrolysis Mode

The operation of 25 solid oxide cells stacks in steam electrolysis mode over 9000 hours is reported. The stack has been operated at current densities of 0.57 and 0.72 A/cm2, using a 50% steam conversion, in the 750-780°C temperature range. Performance degradation rates of 2.30%/ kh are reported, with some non-homogeneity in the stack repeat units behavior observed. Stack repeat units located at the bottom of the stack feature degradation rates below 2%/kh. The possibility to use the operating temperature as a buffer to counter the performance degradation is highlighted. The stack performance was not affected by incidents that occurred during the test.

Electrochemical stability of Sm(0.5)Sr(0.5)CoO(3-δ)-infiltrated YSZ for solid oxide fuel cells/electrolysis cells.

Composite SSC (Sm(0.5)Sr(0.5)CoO(3-δ))-YSZ (yttria stabilized zirconia) oxygen electrodes were prepared by an infiltration process. X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) of the composite electrodes showed the formation of SSC perovskite and a well-connected network of SSC particles in the porous YSZ backbone, respectively. The electrochemical performance of the cell was investigated under both fuel cell and steam electrolysis modes using polarization curves and electrochemical impedance spectroscopy (EIS). The cell experienced a large degradation rate at 700 °C with a constant voltage of 0.7 V for over 100 h under power generation operation. The subsequent post-cell SEM micrograph revealed that agglomeration of the infiltrated SSC particles was possibly the cause for the performance deterioration. Furthermore, the long-term stability of the cell was examined at 700 °C with a constant voltage of 1.3 V under steam electrolysis mode. SEM associated with energy dispersive X-ray spectroscopy (EDS) was employed to characterize the post-test cell after the long-term electrolysis operation and it indicated that besides the agglomeration of SSC particles, the delamination of the SSC-YSZ oxygen electrode from the YSZ electrolyte, as well as segregation of cobalt-enriched particles (particularly cobalt oxides) at the interface, was probably responsible for the cell degradation under the steam electrolysis mode.

Calcium manganite as oxygen electrode materials for reversible solid oxide fuel cell.

For an efficient high-temperature reversible solid oxide fuel cell (RSOFC), the oxygen electrode should be highly active for the conversion between oxygen anions and oxygen gas. CaMnO(3-δ) (CM) is a perovskite that can be readily reduced with the formation of Mn(3+) giving rise to oxygen defective phases. CM is examined here as the oxygen electrode for a RSOFC. CaMn(0.9)Nb(0.1)O(3-δ) (CMN) with Nb doping shows superior electric conductivity (125 S cm(-1) at 700 °C) compared with CM (1-5 S cm(-1) at 700 °C) in air which is also examined for comparison. X-ray diffraction (XRD) data show that CM and CMN are compatible with the widely used yttria-stabilized zirconia (YSZ) electrolyte up to 950 °C. Both materials show a thermal expansion coefficient (TEC) close to 10.8-10.9 ppm K(-1) in the temperature range between 100-750 °C, compatible with that of YSZ. Polarization curves and electrochemical impedance spectra for both fuel cell and steam electrolysis modes were investigated at 700 °C, showing that CM presented a polarization resistance of 0.059 Ω cm(2) under a cathodic bias of -0.4 V while CMN gave a polarization resistance of 0.081 Ω cm(2) under an anodic bias of 0.4 V. The phase stability up to 900 °C of these materials was investigated with thermogravimetric analysis (TGA) and variable temperature XRD.

Achieving 360 NL h−1 Hydrogen Production Rate Through 30‐Cell Solid Oxide Electrolysis Stack with LSCF–GDC Composite Oxygen Electrode

AbstractA 30‐cell solid oxide electrolysis (SOE) stack consisting of 30‐cell planar Ni–YSZ hydrogen electrode‐supported single cell with La0.6Sr0.4Co0.2Fe0.8O3–δ–Ce0.9Gd0.1O1.95 (LSCF–GDC) composite oxygen electrodes, interconnects, and sealing materials was tested at 750 °C in steam electrolysis mode for hydrogen production. The direction of gas flow in the stack was a cross‐flow configuration, and the stack configuration was designed to open gas flow channels at the air outlet. The electrolysis efficiency of the stack was higher than 100% at 90/10H2O/H2 ratio under <0.5 A cm−2 current density. During hydrogen production, the stack was operated at 750 °C under 0.5 A cm−2 constant current density for more than 500 h with 4.06% k h−1 degradation rate. Up to 73% steam conversion rate and 91.6% current efficiency were obtained; the net hydrogen production rate reached as high as 361.4 NL h−1. Our results suggested that the SOE stack that was designed with LSCF–GDC composite oxygen electrode could be used to conduct large‐scale hydrogen production.

Electrochemical stability of La0.6Sr0.4Co0.2Fe0.8O3−δ-infiltrated YSZ oxygen electrode for reversible solid oxide fuel cells

La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF)-YSZ (yttria stabilized zirconia) oxygen electrodes were developed by an infiltration process for reversible solid oxide fuel cells (RSOFCs). Electrochemical performance of the LSCF-YSZ composite oxygen electrode was investigated in both fuel cell and steam electrolysis modes. Galvanostatic polarization operated at ±600 mA cm−2 and 750 °C showed that the cell has a voltage degradation rate of 3.4% and 4.9% for fuel cell mode and steam electrolysis mode, respectively. Post-test SEM (scanning electronic microscopy) analysis of the electrodes indicates that the agglomeration of infiltrated LSCF particles is possibly responsible for the performance degradation of the cell.

Electrochemical performance and stability of lanthanum strontium cobalt ferrite oxygen electrode with gadolinia doped ceria barrier layer for reversible solid oxide fuel cell

A La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) oxygen electrode and a Gd0.1Ce0.9O2−δ (GDC) barrier layer are prepared for a reversible solid oxide fuel cell (RSOFC). Scanning electron microscopy (SEM) analysis shows that the GDC barrier layer has a honeycomb-like structure and maintains good adhesion with yttria-stabilized zirconia (YSZ) electrolyte and LSCF oxygen electrode. Polarization curves and electrochemical impedance spectra for both fuel cell and steam electrolysis modes are investigated. Repeated fuel cell/steam electrolysis cycles operated at 300 mA cm−2 and 800 °C shows the cell has higher degradation under steam electrolysis mode than under fuel cell mode. Cell degradation in electrolysis mode is attributed to delamination of the GDC barrier layer from the YSZ electrolyte, which has been observed during post-test SEM analysis.

Investigation of 30-cell solid oxide electrolyzer stack modules for hydrogen production

The 30-cell nickel-yttria stabilized zirconia (Ni-YSZ) hydrogen electrode-supported planar solid oxide electrolyzer (SOE) stack modules were manufactured and tested at 800°C in steam electrolysis mode for hydrogen production. The electrolysis efficiency of the stack modules was higher than 100% at a total steam and hydrogen flow of 2.1sccmcm−2, a H2O/H2 ratio of 80/20, and a current density of <0.2Acm−2. The electrolysis efficiency, current efficiency, and actual hydrogen production rate of the stack modules increased with increasing H2O/H2 ratio at a constant current density. However, the electrolysis and current efficiencies decreased steadily at high current densities. During hydrogen production, the stack modules were operated at 800°C and a constant current density of 0.15Acm−2 for up to 1100h. A steam conversion rate of 62% and current efficiency of 87.4% were obtained; the actual hydrogen production rate reached as high as 103.6NLh−1. Post-mortem analysis showed that delamination of the LSM–YSZ oxygen electrode mainly occurred in the steam and air inlet area of the 10×10cm2 cells.

Optimization of the electrode-supported tubular solid oxide cells for application on fuel cell and steam electrolysis

Hydrogen electrode-supported tubular solid oxide cells (SOCs) were fabricated by dip-coating and co-sintering method. The electrochemical properties of tubular SOCs were investigated both in fuel cell and electrolysis modes. Ni-YSZ was employed as hydrogen electrode support. The pore ratio of Ni-YSZ support strongly affected the performance of tubular SOCs, especially in steam electrolysis mode. The pore ratio was adjusted by the content of pore-former in support slurry. The results showed that 3 wt.% pore former content is the proper value to produce high performance both in fuel cell and electrolysis modes. In fuel cell mode, the maximum power density reached 743.1 mW cm−2 with H2 (105 sccm) and O2 (70 sccm) as working gases at 850 °C. In electrolysis mode, as the electrolysis voltage was 1.3 V, the electrolysis current density reached 425 mA cm−2 with H2 (35 sccm) and N2 (70 sccm) adsorbed 47% steam as working gases in hydrogen electrode at 850 °C. The stability of tubular SOCs was related to the ratio of NiO/YSZ in the support. The sample with NiO/YSZ = 60/40 shows a better performance than the sample with NiO/YSZ = 50/50.

Determination of Three Dimensional Microstructure Parameters from a Solid Oxide Ni/YSZ Electrode after Electrolysis Operation

The interface structure of a Ni/YSZ electrode tested for 1300 hours in steam electrolysis mode is analyzed. We break down the electrode interface structure measurements into total phase interfaces (e.g. total pore surface area), two-phase interfaces (e.g. Ni/YSZ interface area) and triple-phase boundaries and further analyze these based on their percolation to electron, ion and gas sources. The measurements are compared to previous related work.

Nine Thousand Hours of Operation of a Solid Oxide Cell in Steam Electrolysis Mode

An anode-supported solid oxide fuel cell of 45 cm2 area was operated during 9000 h as electrolyser cell at about 780°C and −1 Acm−2 current density. The cell consisted of yttria-stabilised zircona (YSZ) as electrolyte, the hydrogen electrode of a nickel-YSZ cermet, and the oxygen electrode of strontium-substituted lanthanum ferrite/cobaltite (LSCF). The voltage loss under constant current operation over the entire experiment was 3.8% (40 mV)/1000 h. This value also accounts for experimental incidents, e.g. contact deterioration due to mechanical shocks or a supply failure of feed gas. Degradation during the initial 5600 h was 2.5% /1000 h. It was even lower during the incident-free period of the experiment, i.e. 1.7% /1000 h from 2000 to 5600 h, close to the technical target for an electrolyser system. The low cell voltage (initial Ucell = 1.06 V) together with the known nearly ideal faradaic efficiency mean an (electrical-to-chemical) energy-conversion efficiency ηel above the one achieved with electrolysis at low temperature, with ηel > 100% up to 7600 h (with heat supply). Impedance spectroscopic results indicate that degradation results from an increase in ohmic electrolyte resistance as well as in the reaction overpotential of at least one electrode.

Analysis of the performance of the electrodes in a natural gas assisted steam electrolysis cell

The performance of solid oxide electrolysis (SOE) cells while operating in the natural gas assisted steam electrolysis (NGASE) mode was evaluated. The SOE cells used yttria-stabilized-zirconia (YSZ) as the oxygen ion conducting electrolyte, Co – CeO 2 – YSZ as the H 2 – H 2 O electrode, and Pd-doped CeO 2 . YSZ as the CH 4 -oxidation electrode. The cell electrochemical performance was evaluated as a function of the H 2 O / H 2 ratio and the extent of conversion of CH 4 . The results of this study provide insight into the factors that control electrode performance and further demonstrate the viability of an NGASE cell for the production of H 2 .

Performance of Planar High-Temperature Electrolysis Stacks for Hydrogen Production from Nuclear Energy

An experimental program is under way to assess the performance of solid-oxide cells operating in the steam electrolysis mode for hydrogen production in a temperature range from 800 to 900°C. This temperature range is consistent with the planned coolant outlet temperature range of advanced nuclear reactors. Results were obtained from two multiple-cell planar electrolysis stacks with an active area of 64 cm2 per cell. The electrolysis cells are electrolyte-supported, with scandia-stabilized zirconia electrolytes (~140 μm thick), nickel-cermet steam/hydrogen electrodes, and manganite oxygen-side electrodes. The metallic interconnect plates are fabricated from ferritic stainless steel. The experiments were performed in a range of steam inlet mole fractions (0.1 to 0.6), gas flow rates (1000 to 4000 standard cubic centimeters per minute), and current densities (0 to 0.38 A/cm2). Steam consumption rates associated with electrolysis were measured directly using inlet and outlet dewpoint instrumentation. Cell operating potentials and cell current were varied using a programmable power supply. Values of area-specific resistance and stack internal temperatures are presented as a function of current density. Initial stack-average area-specific resistance values <1.5 Ω·cm2 were observed. Hydrogen production rates in excess of 200 normal liters per hour (NL/h) were demonstrated. Internal stack temperature measurements revealed a net cooling effect for operating voltages between the open-cell potential and the thermal neutral voltage. These temperature measurements agreed very favorably with computational fluid dynamics predictions. A continuous long-duration test was run for 1000 h with a mean hydrogen production rate of 177 NL/h. Some performance degradation was noted during the long test. Stack performance is shown to be dependent on inlet steam flow rate.

Progress in high-temperature electrolysis for hydrogen production using planar SOFC technology

Experimental and modeling activities were performed, addressing the performance of solid-oxide cells, operating in steam electrolysis mode for hydrogen production . Experimental results were obtained from a 10-cell planar solid-oxide electrolysis stack. The electrolysis cells are electrolyte-supported, with scandia-stabilized zirconia electrolytes ( ∼ 140 μ m thick), nickel–cermet steam/hydrogen electrodes, and manganite air-side electrodes. Interconnect plates were fabricated from ferritic stainless steel. Experiments were performed over a range of 800– 900 ∘ C steam inlet mole fractions (0.1–0.6), gas flow rates (1000–4000 sccm), and current densities (0– 0.38 A / cm 2 ). Hydrogen production rates up to 90 Normal liters per hour were demonstrated. Stack performance is shown to be dependent on inlet steam flow rate. A three-dimensional computational fluid dynamics (CFD) model was created. Measurements and CFD predictions of internal stack temperatures show a net cooling effect for operating voltages lower than thermal neutral, and a net heating effect at higher voltages. Model results compare favorably with experimental results obtained from the 10-cell stack.

Hydrogen Production Performance of a 10-Cell Planar Solid-Oxide Electrolysis Stack

An experimental study is under way to assess the performance of solid-oxide cells operating in the steam electrolysis mode for hydrogen production over a temperature range of 800-900°C. Results presented in this paper were obtained from a ten-cell planar electrolysis stack, with an active area of 64cm2 per cell. The electrolysis cells are electrolyte supported, with scandia-stabilized zirconia electrolytes (∼140μm thick), nickel-cermet steam/hydrogen electrodes, and manganite air-side electrodes. The metallic interconnect plates are fabricated from ferritic stainless steel. The experiments were performed over a range of steam inlet mole fractions (0.1–0.6), gas flow rates (1000-4000sccm), and current densities (0-0.38A∕cm2). Steam consumption rates associated with electrolysis were measured directly using inlet and outlet dewpoint instrumentation. Cell operating potentials and cell current were varied using a programmable power supply. Hydrogen production rates up to 100Nl∕h were demonstrated. Values of area-specific resistance and stack internal temperatures are presented as a function of current density. Stack performance is shown to be dependent on inlet steam flow rate.