Solid oxide cells with cermet of silver and gadolinium-doped-ceria symmetrical electrodes for high-performance power generation and water electrolysis

A cermet of silver and gadolinium-doped-ceria (Ag-GDC) is investigated as novel symmetrical electrode material for (ZrO₂)_0.92(Y₂O₃)_0.08 (YSZ) electrolyte-supported solid oxide cells (SOCs) operated in fuel cell (SOFC) and electrolysis (SOEC) modes. The electrochemical performances are evaluated by measuring the current density-voltage characteristics and impedance spectra of the SOCs. The activity of hydrogen and air electrodes is investigated by recording overpotential versus current density in symmetrical electrode cells, respectively in hydrogen and air, using a three-electrode method. Conventional hydrogen electrode, Ni-YSZ, and oxygen electrode, LSCF (La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ)-GDC, are tested as comparison. The results show that, as an oxygen electrode, Ag-GDC is more active than LSCF-GDC in catalyzing both oxygen reduction reaction (ORR) in an SOFC and oxygen evolution reaction (OER) in an SOEC. As a hydrogen electrode, Ag-GDC is more active than Ni-YSZ in catalyzing hydrogen oxidation reaction (HOR) in an SOFC and hydrogen evolution reaction (HER) in an SOEC, especially in high steam concentration. An SOC with symmetrical Ag-GDC electrodes operated in a fuel cell mode, with 3% H₂O humidified H₂ as the fuel, displays a peak power density of 395 mWcm^?2 at 800 °C. Its polarization resistance at open circuit voltage is 0.21 Ω cm². Ag-GDC electrode can be operated even at pure steam. An SOEC operated for electrolyzing 100% H₂O, the current density reaches 720 mA cm^?2 under 1.3 V at 800 °C.     

Gadolinium doped ceria-impregnated nickel-yttria stabilised zirconia cathode for solid oxide electrolysis cell

Steam electrolysis (H₂O → H₂ + 0.5O₂) was investigated in solid oxide electrolysis cells (SOECs). The electrochemical performance of GDC-impregnated Ni-YSZ and 0.5% wt Rh-GDC-impregnated Ni-YSZ was compared to a composite Ni-YSZ and Ni-GDC electrode using a three-electrode set-up. The electrocatalytic activity in electrolysis mode of the Ni-YSZ electrode was enhanced by GDC impregnation. The Rh-GDC-impregnated Ni-YSZ exhibited significantly improved performance, and the electrode exhibited comparable performance between the SOEC and SOFC modes, close to the performance of the composite Ni-GDC electrode. The performance and durability of a single cell GDC-impregnated Ni-YSZ/YSZ/LSM-YSZ with an H₂ electrode support were investigated. The cell performance increased with increasing temperature (700 °C-800 °C) and exhibited comparable performance with variation of the steam-to-hydrogen ratio (50/50 to 90/10). The durability in the electrolysis mode of the Ni-YSZ/YSZ/LSM-YSZ cell was also significantly improved by the GDC impregnation (200 h, 0.1 A/cm², 800 °C, H₂O/H₂ = 70/30).     

High efficiency process for the production of pure oxygen based on solid oxide fuel cell–solid oxide electrolyzer technology

This paper presents a novel system for production of pure oxygen based on the integration of a solid oxide fuel cell (SOFC) and a solid oxide electrolyzer (SOEC). In the proposed arrangement, the SOFC provides electricity, heat and H₂O in vapour phase to the SOEC which carries out the inverse reactions of the SOFC, that is the separation of H₂O into H₂ (used as a fuel for the SOFC) and O₂ (representing the yield of the system). Simulations carried out in different operating conditions show that when the integrated SOFC–SOEC device runs at low current densities (less than 1000 A m⁻²), pure oxygen can be generated with an electric consumption comparable to mid-size cryogenic air separation units, and significantly lower than small scale systems based on the PSA technology.     

Degradation study of a reversible solid oxide cell (rSOC) short stack using distribution of relaxation times (DRT) analysis

Reversible solid oxide cells (rSOC) can convert excess electricity to valuable fuels in electrolysis cell mode (SOEC) and reverse the reaction in fuel cell mode (SOFC). In this work, a five – cell rSOC short stack, integrating fuel electrode (Ni-YSZ) supported solid oxide cells (Ni-YSZ || YSZ | CGO || LSC-CGO) with an active area of 100 cm², is tested for cyclic durability. The fuel electrode gases of H₂/N₂:50/50 and H₂/H₂O:20/80 in SOFC and SOEC mode, respectively, are used during the 35 reversible operations. The voltage degradation of the rSOC is 1.64% kh^?1 and 0.65% kh^?1 in SOFC and SOEC mode, respectively, with fuel and steam utilisation of 52%. The post-cycle steady-state SOEC degradation of 0.74% kh^?1 suggests improved lifetime during rSOC conditions. The distribution of relaxation times (DRT) analysis suggests charge transfer through the fuel electrode is responsible for the observed degradation.     

Electrochemical performance and durability of flat-tube solid oxide electrolysis cells for H2O/CO2 co-electrolysis

Co-electrolysis of H₂O and CO₂ by high-temperature solid oxide electrolysis cells (SOECs) is a useful approach for energy storage and carbon dioxide reduction. In this study, we conducted H₂O/CO₂ co-electrolysis using a flat-tube SOEC and studied its electrochemical performance and durability. It was found that the increase of temperature and water fraction in fuel gas promote electrochemical performance. In addition, the co-electrolysis was found to be stable with a constant current density of 300 mA cm^?2 for over 1000 h at 750 °C. The contribution of each electrode process to polarization resistance is elucidated by electrochemical impedance spectroscopy and distribution of relaxation time (DRT) analysis. The fuel electrode was found to degrade more significantly against duration time as compared to the oxygen electrode. Post-mortem analysis of the microstructure revealed the loss and sintering of Ni particles in active cathode functional layer at the inlet of the fuel electrode. Based on these results, the degradation mechanism of H₂O/CO₂ co-electrolysis by the flat-tube SOEC was discussed in details.     

High performance and stability of nanocomposite oxygen electrode for solid oxide cells

Solid oxide electrochemical cell (SOC) is a highly promising alternative for fuel conversion and power-to-gas due to its high efficiency and low emission. However, degradation resulting from the electrolyte-electrode interface is a major challenge in both fuel cell mode and electrolysis mode. Here, a co-sintering tri-layer structure cell with nanocomposite oxygen electrode is developed to mitigate the interface issue. A 10 × 10 cm² NiO/YSZ||YSZ||YSZ-La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) cell has been conducted under different fuels in SOFC mode. A power density output of 558 mW/cm² @0.7 V-800 °C in wet H₂ and a durability of 300 h in simulated syngas have been obtained. The performance of LSF, LSCF and SSC oxygen electrodes have been studied in both SOFC and SOEC modes. It suggests that three oxygen electrodes have an order of SSC > LSCF > LSF in electrochemical performance, and an opposite order in stability of SOEC. The degradation of the LSCF and SSC can be derived from the solid-state reactions at the interface between Co-containing perovskites and YSZ during operation. It demonstrates that GDC and Ag modification can enhance the oxygen electrode stability by impeding the solid-state reactions and the nanoparticles sintering. Results suggest that GDC has a negative effect on the cell performance and Ag has a positive effect, implying that enhancing the electric conductivity of YSZ-LSCF is the key to improve the cell performance. Moreover, cell with YSZ-SFM/GDC has been applied in CH₄ assisted SOEC process (CH₄-SOEC), in which a significant reduction of electricity consume can be realized.     

Hydrogen and synthetic fuel production using pressurized solid oxide electrolysis cells

Wind and solar power is troubled by large fluctuations in delivery due to changing weather. The surplus electricity can be used in a Solid Oxide Electrolyzer Cell (SOEC) to split CO₂ + H₂O into CO + H₂ (+O₂). The synthesis gas (CO + H₂) can subsequently be catalyzed into various types of synthetic fuels using a suitable catalyst. As the catalyst operates at elevated pressure the fuel production system can be simplified by operating the SOEC at elevated pressure. Here we present the results of a cell test with pressures ranging from 0.4 bar to 10 bar. The cell was tested both as an SOEC and as a Solid Oxide Fuel Cell (SOFC). In agreement with previous reports, the SOFC performance increases with pressure. The SOEC performance, at 750 °C, was found to be weakly affected by the pressure range in this study, however the internal resistance decreased significantly with increasing pressure.     

Electrochemical performance of solid oxide electrolysis cell electrodes under high-temperature coelectrolysis of steam and carbon dioxide

The SOEC electrodes during steam (H₂O) electrolysis, carbon dioxide (CO₂) electrolysis, and the coelectrolysis of H₂O/CO₂ are investigated. The electrochemical performance of nickel-yttria stabilised zirconia (Ni-YSZ), Ni-Gd_0.1Ce_0.9O_1.95 (Ni-GDC), and Ni/Ruthenium-GDC (Ni/Ru-GDC) hydrogen electrodes and La_0.8Sr_0.2MnO_3−δ-YSZ (LSM-YSZ), La_0.6Sr_0.4Co_0.8Fe_0.2O_3−δ (LSCF), and La_0.8Sr_0.2FeO_3−δ (LSF) oxygen electrodes are studied to assess the losses of each electrode relative to a reference electrode. The study is performed over a range of operating conditions, including varying the ratio of H₂O/H₂ and CO₂/CO (50/50 to 90/10), the operating temperature (550-800 °C), and the applied voltage. The activity of Ni-YSZ electrodes during H₂O electrolysis is significantly lower than that for H₂ oxidation. Comparable activity for operating between the SOEC and solid oxide fuel cell (SOFC) modes is observed for the Ni-GDC and Ni/Ru-GDC. The overpotential of H₂ electrodes during CO₂ reduction increases as the CO₂/CO ratio is increased from 50/50 to 90/10 and further increases when the electrode is exposed to a 100% CO₂ (800 °C), corresponding to the increase in the area specific resistance. The electrodes exhibit comparable performance during H₂O electrolysis and coelectrolysis, while the electrode performance is lower in the CO₂-electrolysis mode. The activity of all the O₂ electrodes as an SOFC cathode is higher than that as SOEC anodes. Among these O₂ electrodes, LSM-YSZ exhibits the nearest to symmetrical behaviour.     

H2O chemisorption and H2 oxidation on yttria-stabilized zirconia: Density functional theory and temperature-programmed desorption studies

The mechanism of H₂O dissociation as well as the adsorption and oxidation reaction of H₂ on yttria-stabilized zirconia (YSZ), commonly used as part of solid oxide fuel cell (SOFC) anodes, was investigated employing temperature-programmed desorption (TPD) spectroscopy and density functional theory (DFT). In agreement with theory the experimental results show that interaction of gaseous H₂O with YSZ results in dissociative adsorption leading to strongly bound OH surface species. In the interaction of gaseous H₂ with an oxygen-enriched YSZ surface (YSZ + O) similar OH surface species are formed as reaction intermediates in the H₂ oxidation. Our experiments showed that in both the H₂O/YSZ and the H₂/YSZ + O heterogeneous reaction systems noticeable amounts of H₂O are “dissolved” in the bulk as interstitial hydrogen and hydroxyl species. The experimental H₂O desorption data is used to access the accuracy of the H₂/H₂O/YSZ adsorption/desorption and surface reaction kinetics data, employed in previous modeling studies of the electrochemical H₂ oxidation on Ni-pattern/YSZ model anodes by Vogler et al. [J. Electrochem. Soc., 156 (2009) B663] and Goodwin et al. [J. Electrochem. Soc., 156 (2009) B1004]. Finally a refined experimentally validated H₂/H₂O/YSZ adsorption/desorption and surface reaction kinetics data set is presented.     

Comparison of ceria and zirconia based electrolytes for solid oxide electrolysis cells

Steam electrolysis for hydrogen production is investigated in solid oxide electrolysis cell (SOEC). Sc³⁺, Ce⁴⁺, and Gd³⁺ are doped in zirconia (SCGZ) and compared with yttria stabilized zirconia (YSZ) and gadolinium doped ceria (GDC) electrolyte. Electrolyte-supported cells are fabricated. The SCGZ and YSZ electrolytes are dense with >95% relative density while GDC is less densified. The activation energy of conduction of the SCGZ electrolyte is the lowest at 65.58 kJ mol^?1 although phase transformation is detected after electrolyte fabrication process. Cathode-supported cell having SCGZ electrolyte (Ni-SCGZ/SCGZ/BSCF) shows the highest electrochemical performance. Durability test of the cells in electrolysis mode is carried out over 60 h (0.3 A cm^?2, 1073 K, H₂O to H₂ ratio of 70:30). Significant performance degradation of Ni-GDC/YSZ/GDC/BSCF cell is observed (0.0057 V h^?1) whereas the performance of Ni-YSZ/YSZ/BSCF and Ni-SCGZ/SCGZ/BSCF are rather stable under the same operating conditions. The BSCF remains attaching to the SCGZ electrolyte and additional phase transformation is not observed after prolong operation.     

Out-of-cell measurements of H2-H2O effective binary diffusivity in the porous anode of solid oxide fuel cells (SOFCs)

The effective binary diffusivity of H₂ and H₂O in a Ni and yittria-stabilized zirconia (YSZ) anode of the solid oxide fuel cells (SOFCs) was measured between 650 and 800 °C using an electrochemical cell consisting of an oxygen pump, an oxygen sensor, and a porous SOFC anode pellet. The effective binary diffusivity was obtained from the relationship between the current density across the oxygen pump, and the H₂ partial pressure gradient across the anode sample measured using the oxygen sensor. The anode limiting current density and concentration polarization were estimated using the experimental results.     

Preparation of Cu-Ni/YSZ solid oxide fuel cell anodes using microwave irradiation

A microwave irradiation process is used to deposit Cu nanoparticles on the Ni/YSZ anode of an electrolyte-supported solid oxide fuel cell (SOFC). The reaction time in the microwave is only 15 s for the deposition of 6 wt% Cu (with respect to Ni) from a solution of Cu(NO₃)₂·3H₂O and ethylene glycol (HOCH₂CH₂OH). The morphology of the deposited Cu particles is spherical and the average size of the particles is less than 100 nm. The electrochemical performance of the microwave Cu-coated Ni/YSZ anodes is tested in dry H₂ and dry CH₄ at 1073 K, and the anodes are characterized with scanning electron microscopy, electrochemical impedance spectroscopy, and temperature-programmed oxidation. The results indicate that preparation of the anodes by the microwave technique produces similar performance trend as those reported for Cu-Ni/YSZ/CeO₂ anodes prepared by impregnation. Specifically, less carbon is formed on the Cu-Ni/YSZ than on conventional Ni/YSZ anodes when exposed to dry methane and the carbon that does form is more reactive.     

Carbon deposition on Ni/YSZ anodes exposed to CO/H2 feeds

Solid oxide fuel cells (SOFC) can be operated with a variety of fuels. In anode-supported SOFC, these fuels may decompose or react catalytically in the anode compartment resulting in mixtures that, in most cases, include high concentrations of H₂ and CO. In this study, the formation of carbon from CO and H₂ mixtures on Ni/YSZ anodes at 1073 K has been investigated using electrochemical and carbon characterization techniques. More carbon is deposited when Ni/YSZ anodes are exposed to CO/H₂ mixtures than to pure CO. Polarization of the anodes reduced the amount of carbon deposited but the extent of the reduction depended on the gas composition.     

Catalytic activity of infiltrated La0.3Sr0.7Ti0.3Fe0.7O3−δ–CeO2 as a composite SOFC anode material for H2 and CO oxidation

Finding cost-effective and efficient anode materials for solid oxide fuel cells (SOFCs) is of prime importance to develop renewable energy technologies. In this paper, La and Fe co-doped SrTiO₃ perovskite oxide, La_0.3Sr_0.7Ti_0.3Fe_0.7O_3?δ (LSTF0.7) composited with CeO₂ is prepared as a composite anode by solution infiltration method. The H₂ and CO oxidation behavior and the electrochemical performance (electrochemical impedance spectra, I–V and I–P curves) of the scandia-stabilized zirconia (ScSZ) electrolyte supported cells fabricated by tape casting with the LSTF0.7–CeO₂ composite anode are subsequently measured at various temperatures (700–850 °C). Electrochemical impedance spectra (EIS) of the prepared cells with the LSTF0.7–CeO₂|ScSZ|La_0.8Sr_0.2MnO₃ (LSM)–ScSZ configuration illustrate that the anode polarization resistance distinguished from the whole cell is 0.072 Ω cm² in H₂, whereas 0.151 Ω cm² in CO at 850 °C. The maximal power densities (MPDs) of the cell at 700, 750, 800 and 850 °C are 217, 462, 612, 815 mW cm^?2 in H₂ and 145, 349, 508, 721 mW cm^?2 in CO, respectively. Moreover, a significant decrease of anode activation energy towards H₂ oxidation is clearly demonstrated, indicating a better electrochemical performance in H₂ than in CO. These results demonstrate an alternative composite anode with high electrocatalytic activity for SOFC practical applications.     

Ba0·5Sr0·5(Co0·8Fe0.2)1-xTaxO3-δ perovskite anode in solid oxide electrolysis cell for hydrogen production from high-temperature steam electrolysis

Among perovskite anodes in solid oxide electrolysis cell (SOEC), Ba_0·5Sr_0·5Co_0·8Fe_0·2O_3-δ (BSCF) has gained much attention due to its dominantly high performance. However, the BSCF still suffers from chemical instability. In this study, the B-site of BSCF is partially substituted by a higher valence Ta⁵⁺ (5, 10, 15 and 20 mol%) to improve its structural stability - Ba_0·5Sr_0·5(Co_0·8Fe_0.2)_1-xTa_xO_3-δ (BSCFTax, 0 ≤ x ≤ 0.20). It is found that doping with higher valence Ta⁵⁺ increases both chemical stability and electrochemical performance of BSCF. Although the BSCFTa0.10 shows the lowest oxygen vacancies indicating by the ratio of adsorbed oxygen vacancies (O_adsorbed) to lattice oxygen (O_lattice), the electrochemical performance increases. The decrease in Co³⁺/Co⁴⁺ ratio results in increasing electronic conductivity in the anode. It is likely that proper amount of Ta⁵⁺ doping provide a balance between ionic and electronic conductivity in the anode and improved electrochemical performance. The symmetrical half-cells with electrolyte support (BSCFTa/YSZ/BSCFTa) are fabricated to determine the area specific resistance (ASR) and activation energy of conduction - BSCFTa0.10 shows the best performance. Cathode-supported Ni-YSZ/YSZ/BSCFTa0.10 also shows higher durability than Ni-YSZ/YSZ/BSCF (operating at current density ?0.45 A cm^?2 in electrolysis mode, 80 h, 800 °C and H₂O to H₂ ratio of 70:30).     

Electrochemical performance and stability of nano-structured Co/PdO-co-impregnated Y2O3 stabilized ZrO2 cathode for intermediate temperature solid oxide fuel cells

Palladium (Pd) is an attractive cathode catalyst component for solid oxide fuel cells (SOFCs) that has high tendency to agglomerate during operation at around 800 °C. This work shows that such agglomeration can be inhibited by alloying Co into Pd. PdO, Pd_0.95Co_0.05O, Pd_0.90Co_0.10O, and Pd_0.80Co_0.20O were synthesized and characterized. Powder X-ray diffraction patterns at 750 and 900 °C confirmed that PdO decomposition to Pd which normally occurred at 840 °C was suppressed for Co containing Pd alloys while thermal gravimetric analyses indicated improved redox reversibility of PdO ? Pd conversion for alloys during the thermal cycling between 600 and 900 °C. Scanning electron microscopy images supported these arguments. Pd_0.90Co_0.10+yttria stabilized zirconia (YSZ) electrode (i.e., 10 mol % Co containing PdO-impregnated YSZ electrode) displayed the highest oxygen reduction reaction (ORR) performance and stability. The polarization resistance for ORR on Pd_0.90Co_0.10+YSZ cathode is only 0.088 Ω cm² at 750 °C. During polarization test at 750 °C, Pd_0.90Co_0.10+YSZ cathode showed stable performance for 30 h while the performance of Pd+YSZ cathode degraded after 10 h.     

Performance and durability of an anode-supported solid oxide fuel cell with a PdO/ZrO2 engineered (La0.8Sr0.2)0.95MnO3-δ-(Y2O3)0.08(ZrO2)0.92 composite cathode

PdO/ZrO₂ co-infiltrated (La_0.8Sr_0.2)_0.95MnO_3-δ-(Y₂O₃)_0.08(ZrO₂)_0.92 (LSM-YSZ) composite cathode (PdO/ZrO₂+LSM-YSZ), which adsorbs more oxygen than equal amount of PdO/ZrO₂ and LSM-YSZ, is developed and used in Ni-YSZ anode-supported cells with YSZ electrolyte. The cells are investigated firstly at temperatures between 650 and 750 °C with H₂ as the fuel and air as the oxidant and then polarized at 750 °C under 400 mA cm^?2 for up to 235 h. The initial peak power density of the cell is in the range of 438–1207 mW cm^?2 at temperatures from 650 to 750 °C, corresponding to polarization resistance from 1.04 to 0.35 Ω cm². This result demonstrates a significant performance improvement over the cells with other kinds of LSM based cathode. The cell voltage at 750 °C under 400 mA cm^?2 decreases from initial 0.951 to 0.89 V after 170 h of current polarization and remains essentially stable to the end of current polarization. It is identified that the self-limited growth of PdO particles is responsible for the cell voltage decrease by reducing the length of triple phase boundary affecting the high frequency steps involved in oxygen reduction reaction in the cathode.     

Physical characterization and electrochemical performance of copper–iron–ceria–YSZ anode‐based SOFCs in H2 and methane fuels

Thermal instability and poor electrochemical activity of copper‐ceria‐YSZ anodes at the solid oxide fuel cells (SOFCs) operation temperature (>700 °C) necessitates the use of new strategy to improve the performance of respective anodes for direct hydrocarbon SOFCs. In the present study, iron is incorporated into copper–ceria–YSZ anodes in order to investigate the structural, morphological, and electrochemical properties by using various techniques such as X‐ray diffraction, elemental mapping, current–voltage testing, and electrochemical impedance spectroscopy. X‐ray diffraction shows that copper promotes the reduction of iron oxide, and formation of cubic phase of copper–iron metals is observed after reduction in H₂ at 800 °C. Elemental mapping shows better distribution of metal catalyst inside the pores of copper–ceria–YSZ anodes at 800 °C in the presence of iron. The maximum power densities of copper–ceria–YSZ anodes and copper–iron–ceria–YSZ anodes are observed to be 140 and 195 mW cm^?2 in H₂ fuel and 70 and 90 mW cm^?2 in CH₄ fuel at 800 °C. The maximum power density increases with the increase in Cu–Fe metal loading, temperature and with the addition of 1‐wt% Pd in copper–iron–ceria–YSZ anodes. The decrease in performance from 125 to 100 mW cm^?2 is observed during the exposure of CH₄ fuel for 46 h. Electrochemical impedance spectra show an increase in ohmic and total resistance of cell because of sintering and carbon formation, which affects the catalytic activity of anode lowering the performance of SOFC as suggested by post SEM analysis. Copyright © 2015 John Wiley & Sons, Ltd.     

Electrode performance and analysis of reversible solid oxide fuel cells with proton conducting electrolyte of BaCe0.5Zr0.3Y0.2O3−δ

Reversible solid oxide fuel cells (R-SOFCs) are regarded as a promising solution to the discontinuity in electric energy, since they can generate electric powder as solid oxide fuel cells (SOFCs) at the time of electricity shortage, and store the electrical power as solid oxide electrolysis cells (SOECs) at the time of electricity over-plus. In this work, R-SOFCs with thin proton conducting electrolyte films of BaCe_0.5Zr_0.3Y_0.2O_3−δ were fabricated and their electro-performance was characterized with various reacting atmospheres. At 700 °C, the charging current (in SOFC mode) is 251 mA cm⁻² at 0.7 V, and the electrolysis current densities (in SOEC mode) reaches −830 mA cm⁻² at 1.5 V with 50% H₂O-air and H₂ as reacting gases, respectively. Their electrode performance was investigated by impedance spectra in discharging mode (SOFC mode), electrolysis mode (SOEC mode) and open circuit mode (OCV mode). The results show that impedance spectra have different shapes in all the three modes, implying different rate-limiting steps. In SOFC mode, the high frequency resistance (R_H) is 0.07 Ωcm² and low frequency resistances (R_L) are 0.37 Ωcm². While in SOEC mode, R_H is 0.15 Ωcm², twice of that in SOFC mode, and R_L is only 0.07 Ωcm², about 19% of that in SOFC mode. Moreover, the spectra under OCV conditions seems like a combination of those in SOEC mode and SOFC mode, since that R_H in OCV mode is about 0.13 Ωcm², close to R_H in SOEC mode, while R_L in OCV mode is 0.39 Ωcm², close to R_L in SOFC mode. The elementary steps for SOEC with proton conducting electrolyte were proposed to account for this phenomenon.     

High activity oxide Pr0.3Sr0.7Ti0.3Fe0.7O3−δ as cathode of SOEC for direct high-temperature steam electrolysis

A high activity ferrite Pr_0.3Sr_0.7Ti_0.3Fe_0.7O_3?δ (PSTF) has been synthesized and examined as a cathode of solid oxide electrolysis cell (SOEC) for direct high-temperature steam electrolysis. The SOEC with a configuration of PSTF|YSZ|LSM-YSZ was operated under H₂O concentrations ranging from 20%H₂O/Ar to 60%H₂O/Ar and exhibited excellent electrochemical performances. Polarization resistance of the electrolyzer was as small as 0.43 Ω cm² in 60%H₂O/Ar at 1.85 V at 800 °C. According to AC impendence spectra analyzing, gas diffusion process was the rate-determine-step (RDS) under smaller current density, while under larger current density, transport properties in the electrodes and the interfaces of electrode/electrolyte was RDS. The electrochemical properties of PSTF cathodes were systematically investigated and compared when they were exposed to gas atmosphere with and without safe gas (H₂). The obtained results demonstrated that PSTF electrode could conceivably avoid any hydrogen feeding for steam electrolysis.