High Temperature Steam Electrolysis Research Articles

Evaluation of La2NiO4 as Anode Material for Solid Oxide Electrolyser Cells

Rising capacities in renewable energy production pose major challenges resulting from the decoupling between supply and demand, which requires long-range distribution and storage of electrical power. Electrolysis of water is considered a promising method for converting, storing and distributing surplus electrical energy in chemical form. Stimulated by the large-scale installation of wind parks, interest in high temperature steam electrolysis as a highly efficient means for hydrogen production is reviving. This technology appears to be especially favourable if external heat sources from power plants or industrial facilities can be utilised to assist in sustaining operating temperatures above 600°C.High temperature electrolysis is based on solid oxide electrolyser cells (SOEC) which adopt design concepts and materials developed for solid oxide fuel cells (SOFC). In this work the promising SOFC cathode material La2NiO4+δ is investigated with respect to its suitability as anode for SOEC application. Important material properties characterising electrical conductivity and oxygen transport kinetics are determined on densely sintered samples of La2NiO4+δ. In addition, its performance as air electrode is investigated on asymmetric cells under anodic polarisation at current densities of up to -410 mAcm-2 by means of impedance analysis and I-V measurements. Electrochemical characterisation is conducted at 800°C and 0.2 bar oxygen partial pressure and the long-term stability is studied over several thousand hours. Special emphasis is put on the effect of Cr-poisoning on the oxygen exchange kinetics and SOEC anode performance in dry and humid atmospheres. Results from post-test examination of porous electrode structures as well as dense samples of La2NiO4+δ by microstructural analysis with SEM-EDX and AFM are presented.

A Packaged and Efficient SOEC System Demonstrator

High Temperature Steam Electrolysis, based on solid oxide electrolysis cells (SOEC) is a promising way to produce hydrogen with high efficiencies. The use of steam instead of liquid water requires less energy for the water molecule splitting, and the high temperature operation (between 700 and 900°C) allows the replacement of a part of the electrical energy by heat, which allows in theory a significant increase of the electrical efficiency compared to alkaline and PEM water electrolysis. Most of works in the field of SOEC around the world are carried out at the cell or stack level. Only few results at the system level, that is to say including the stack and all BoP (balance of plant) components, are reported in literature, although it is a key point because the heat management of the system has to be optimized to effectively reach the high electrical efficiency expected.For that purpose, the CEA-LITEN has designed and tested a packaged SOEC system demonstrator. It allows producing between 1 and 2.5 Nm3/h of H2 depending on the selected operating point, based on a single stack and the required auxiliaries, including a steam generator at 150°C and high temperature exchangers to preheat the inlet flows from heat recovered in the exhaust gases. A 25-cell-stack already validated in terms of performance [1] is the "heart" of the system. The stack as well as the other components of the system will be described in details, as well as the test results. The first test is presented in Figure 2. At 700°C, the system produces 1.2 Nm3/h of H2 with a total electrical consumption of 3.9 kWh/Nm3, achieving 92% of efficiency, this efficiency corresponding to the higher heating value (HHV) of the produced hydrogen vs the electrical consumption of the system.Indeed, Fig. 2 shows that during the first 3 hours of operation corresponding to the standby mode and endothermic operation, an external heating (through furnace resistances) is required. But after 3 hours, the operation mode switches from endothermic to slightly exothermic mode, leading to an increase of the hydrogen production up to the targeted flow rate of 1.2 Nm3/h after 5 hours, which is associated to a decrease of the furnace power and an increase of the efficiency. It can be seen that after 5 hours, the furnace power is decreased to zero, without any decrease of the stack temperature. It demonstrates that a 150°C heat source temperature is sufficient for the steam generation, and that a slightly exothermic operating mode of the stack is sufficient to preheat the inlet gas up to 700°C and compensate the heat losses of the system. [1] M. Reytier et al, 20th World Hydrogen Energy Conference, 15-20th June 2014, Gwangiu, Korea; submitted to International Journal of Hydrogen Energy. Figure 1

Optimization of the Efficiency of Steam Electrolysis and Co-Electrolysis to Produce Methane According to Heat Power Recovery

Among potential energy storage solutions, many require the development of major infrastructures (hydraulics sites, subterranean cavities, hydrogen storage systems). That is why, more recently, the carbon-free electricity storage into synthetic fuels is of increasing interest, representing an alternative with great potential called "Power to gas ". The manufacture of a synthetic fuel from water, carbon dioxide and carbon-free electricity meets a number of objectives for overall efficiency improvement: - Reducing CO2 emissions from fossil fuel use, - offering CO2 reuse rather than storing it for an indefinite period, - Turning all carbon-free electrical sources (renewable and nuclear), especially during periods of overproduction into a storable product, with the possibly of regenerating electricity during periods of production deficits. In this perspective of reducing CO2 emissions, High Temperature Steam Electrolysis (HTSE) is a promising way to produce massively hydrogen. This process operates at high temperatures (> 700 ° C). The operating conditions with vapor and high temperature reduce the amount of consumed electrical energy by the electrolysis reaction. This has to be realized by increasing the thermal energy part, coming from cheap sources. In addition, this high temperature based technology allows either solid oxide electrolysis of H2O steam to produce H2 and / or co-electrolysis of H2O + CO2 which produces syngas (H2 + CO), paving the way for the production of hydrocarbons including methane. Producing synthetic natural gas then gives the possibility of using immediately all existing infrastructures: transmission and distribution, storage capacity, power generation facilities, etc ... This technology offers very high performance by lowering the amount of electricity required, provided high level of heat recovery, especially to vaporize the water. Here are presented schemes involving several processes with high temperature electrolysis or co-electrolysis technology coupled with a catalytic CO2 or CO hydrogenation reactor. This type of reactors is highly exothermic. Therefore a thermal integration is proposed but an external heat source should also be added, modifying the process schemes. For a power and a level of available heat source temperature, the several schemes to produce methane are therefore optimized and compared according to their efficiencies, produced methane quality, heat recovery and recycled CO2 amount. Moreover for both electrolysis and co-electrolysis, this work provides real operating points for the electrolysis step [1-2], such as voltage, current, possible steam conversion, gas composition, pressure level …etc. The considered catalytic reactor is a Gibbs one. It is shown that in case of low available external heat power, the co-electrolysis mode can offer the best efficiency. Moreover, the co-electrolysis Area Specific Resistance (ASR) is found experimentally close to the steam electrolysis one, leading to a limited impact on the required electrochemical surface. These results confirm the potential of this technology to store the carbon-free electricity: very high efficiencies thanks to the high temperature operation and a very promising help to recycle the CO2 into synthetic fuels. [1] J. Laurencin et al., 2011, Journal of Power Sources, 196, 2080-2093.[2] J. Aicart et al, 2014, Fuel Cells, Vol.14, 3, 430-447 Figure 1

Assessment of Pressure Effects on High Temperature Steam Electrolysis Based on Solid Oxide Technology

To manage the grid with renewable electrical sources and ensure their storage, hydrogen chains have to be considered. However, hydrogen must be pressurized before being used or stored. The first levels of compression are less energetic for liquids than for the hydrogen gas, therefore the electrolysis of steam directly under pressure has to be studied. On one hand, with the solid oxide technology, the Open Circuit Voltage (OCV) presents the drawback of increasing with pressure. On the other hand, the pressure might improve the reactive species supply to the electrochemical sites and reduce the related losses. Thus, what are the electrolysis performances under pressure? And is there an energetic gain at the system level to produce pressurized hydrogen? In this context, experimental and modelling approaches have been adopted in order to understand the basic underlying mechanisms of pressurized electrolysis operation. In this frame, SOEC performance tests were realized under pressure in the range of 1 to 10 bars on two types of single commercial cells. They were based on conventional materials and differentiated by their microstructure. Concerning the set-up, the test platform requirements were achieved by developing an innovative mechanical design associated to a specific steam management. Moreover, a previously proposed electrochemical model of solid oxide electrolysis cell was adapted to take into account the pressure effects. The model allows computing all the most important operation parameters such as local current densities, local molar fraction, overpotentials and also the cell microstructural parameters [1]. According to the complete I-V curves from 0 to -1.3 A/cm2 at 800°C with high steam conversion, it has been observed that OCVs respect the Nernst relation under pressure while the limit current appears at higher current values. This work shows that the hydrogen production can be increased thanks to a 10 bars operation at the autothermal voltage. Moreover, these trends have been analyzed with the model. The impact of pressure on the electrochemical performances is much more important in the range of 1 to 5 bars than above. In our experimental conditions, the diffusion improvement in the porous cathode alone can explain this behavior. Finally, the impact of each microstructural parameter on the cell performances with pressure is discussed. The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) Fuel Cells and Hydrogen Joint Undertaking (FCH-JU-2013-1) under grant agreement 621173. [1] J. Laurencin, D. Kane, G. Delette, J. Deseure, F. Lefebvre-Joud, Modelling of solid oxide steam electrolyser : impact of the operating conditions on hydrogen production, 2011, Journal of Power Sources, 196, 2080-2093. Figure 1

Oxygen Nonstoichiometry and Cathodic Property of Ce0.6Mn0.3Fe0.1O2-δ for High Temperature Steam Electrolysis Cell Using LaGaO3-Based Oxide Electrolyte

The reverse operation of SOFCs, so called solid oxide electrolysis cells (SOECs), can efficiently produce hydrogen from high temperature steam. Ni-based metal, which are widely used for anode of the conventional SOFCs, are also widely used for the cathode of SOECs due to its high catalytic activity and high electronic conductivity. However, Ni-based cathodes frequently showed low stability against oxidation resulting in deactivation under SOECs condition. As a result, Ni-based electrodes are easily aggregated and also delaminated from electrolyte. Therefore, it is essentially required to recycle a part of produced hydrogen to the Ni based electrodes for preventing the oxidation of Ni, however, this recycle of the part of hydrogen formed requires the complicated system and also decrease the electrolysis efficiency. In order to solve these problems, recently, oxide cathode have been attracting much attention for the cathod of SOECs instead of Ni-based metal. Since oxide cathode is stable in redox cycles, recycles of hydrogen is not required. However, oxide cathode have some disadvantages, for instance, low catalytic activity and also low electronic conductivity. In this study, Mn- and Fe-doped CeO2 (Ce0.6Mn0.3Fe0.1O2, CMF) was investigated as a new oxide cathode for SOECs. CMF is a mixed ionic and electronic conductor (MIEC), and has been reported as a potential anode catalyst for SOFCs. Although its electrical conductivity is lower than that of the typical perovskites oxide electrode materials (10-1 S/cm at 900 °C), its catalytic activity for electrode reaction was enough high when it is used in SOFCs. Oxygen nonstoichiometry in this CMF was studied by thermogravimetry. It was found that higher oxidation state of Mn and Fe was observed resulting in hole conduction. The origin of this hole conduction was further studied by XPS measurement. On the other hand, in reducing atmosphere, because of the reduction of Ce, n-type semiconduction is observed. Therefore, oxygen nonstoichiometry of CMF is discussed in details from valence number of Ce, Mn, and Fe. On the other hand, CMF cathode showed almost the same performance with that of Ni-SDC cathode in steam electrolysis and hydrogen evolution rate well obeys the Faraday’s law in temperature range of 900-700°C and stable electrolysis performance was observed. The XRD pattern and the SEM images of CMF cathode after the electrolysis measurement revealed that the CMF phase is stably remained and aggregation or delamination were hardly observed. These results suggest that CMF is highly promising as oxide cathode for SOECs

Temperature Distribution Responses of a Micro-Tubular SOEC after an Electric Load Change

1. Introduction In recent years, natural energy sources such as solar and wind power have been introduced into the electric grid. However, the wind and solar power suffer instability with respect to changes in the weather. As the proportion of these energies increases, adequate controls will become necessary to stabilize the grid. Hydrogen generation systems, which employ electrolysis techniques, are expected to be used as large-capacity power storage facilities with the ability to stabilize the electric power supply. In particular, high-temperature steam electrolysis using solid oxide electrolysis cells (SOECs) can generate hydrogen with high efficiency(1—3), because the heat from the overpotential can be recycled as a heat source for the electrolysis reaction. In addition, due to its endothermic reaction, temperature rise of the SOEC will be suppressed. On the other hand, to utilize such the endothermic effect, an understanding of the temperature distribution and its response of an SOEC is not sufficient. Especially, temperature distributions of the micro-tubular SOEC were more comprehensive than that of planar SOEC, because the positions of the anode and cathode current collectors were asymmetrically placed. In this study, the unsteady, two dimensional, tubular numerical model of a cathode supported micro-tubular SOEC was developed to clarify the temperature distributions and its responses. The steady state results were compared with the experimental i-Vcurve, and unsteady temperature responses at each point of micro-tubular SOEC were discussed. 2. Numerical model The model calculates heat-mass-charge transports and electrochemical reactions, simultaneously. The schematic drawing of the numerical model is shown in Fig. 1. The microporous cathode electrode consists of a mixture of Ni and (ZrO2)0.92(Y2O3)0.08 (YSZ); the electrolyte consists of a dense layer of YSZ; and the microporous anode electrode comprises a mixture of La0.8Sr0.2MnO3(LSM) and YSZ. Current collectors were platinum (Pt). The thicknesses of anode electrode, electrolyte and cathode electrode were 200um, 20um and 20um, respectively. The cell length is about 50 mm, with an outer diameter of about 2 mm. Parts of insulator (at z = 0.0~5.0 mm and z = 45~50 mm) were given larger heat capacity, because there are gas sealing material in those places. A mixture of hydrogen and steam (hydrogen/steam ratio = 1) was supplied to anode, and air was supplied to cathode. The operating temperature was 1123K. For the analyses of temperature response, current loads were changed from 0.0 A/cm2 to 0.2 A/cm2, 0.4 A/cm2 and 0.6 A/cm2. Experiments of micro-tubular SOEC were carried out under the similar conditions. 3. Results In Fig. 2, the numerical and experimental i - V curves were compared. The electron voltage difference of the anode electrode and a left end (z = 0 mm) of the cathode electrode was E 1, and that of the anode electrode and a right end (z = 50 mm) of the cathode electrode was E 2. The calculated E 1 and E 2 were a good agreement with the experimental ones. The steady state temperature distributions of current densities of 0.2 A/cm2, 0.4 A/cm2 and 0.6 A/cm2 are shown in Fig. 2 (a), (b) and (c), respectively. The axis of Fig. 3 was corresponding to that of Fig. 1. The local temperature gradients were larger at the end of the cathode (Ni + YSZ) current collecting side of the SOEC, because there was no endothermic reaction in the non-active area (z = 40 ~ 50 mm), and a heat was generated by electronic resistance in that area. In the active area ( z = 10 ~ 40 mm), heat generation and absorption were occurring. In the gases supplied side non-active area (z= 0 ~ 10 mm), there was no endothermic reaction and any heat generations. For the unsteady analysis, the local temperature responses of a current density condition of 0.4 A/cm2 were shown in Fig. 4. The temperature response at z = 40 mm was slower than that of z = 10 mm, because that at z= 40 mm was affected by current collecting side insulator, which have the larger heat capacity.

Effect of pressure on high temperature steam electrolysis: Model and experimental tests

In order to improve the industrial attractiveness of high temperature steam electrolysis (HTSE), increasing the operating pressure is one of the most promising solutions. In this context, this study is dedicated to the analysis of the pressure influence on the electrochemical reactions occurring in HTSE. The behavior of half-cells constituted by YSZ electrolytes and Ni/YSZ cathodes or LSCF anodes was simulated by COMSOL multiphysics®. This model highlights that the limiting current density due to the lack of steam is shifted towards higher steam conversion rates by increasing the operating pressure, without negative thermodynamic effect at high current density. Furthermore, the overpressure at the oxygen electrode/electrolyte interface decreases with the operating pressure and, therefore, the risk of delamination is reduced. Experimentally, a positive effect of pressure on the oxygen side performances was observed, contrarily to the model calculation.

A Packaged and Efficient SOEC System Demonstrator

High Temperature Steam Electrolysis, based on solid oxide electrolysis cells (SOEC) is a promising way to produce hydrogen with high efficiencies. The balance of plant (BoP) is a key point for that technology because the heat management of the system has to be optimized to effectively reach the expected high electrical efficiency. For that purpose, the CEA-LITEN has designed and tested a packaged SOEC system demonstrator. It is based on a single 25-cell-stack and the required auxiliaries, including a steam generator at 150°C and high temperature exchangers to superheat the inlet steam flow thanks to the heat recovered in the exhaust gases. At 700°C, the system produces 1.2 Nm3/h of H2 with a total electrical consumption of 3.9 kWh/Nm3, achieving 91% of efficiency, this efficiency corresponding to the higher heating value (HHV) of the produced hydrogen vs the electrical consumption of the system.

Assessment of Pressure Effects on High Temperature Steam Electrolysis Based on Solid Oxide Technology

To manage the grid with renewable electrical sources, hydrogen chains have to be considered. However, hydrogen must be pressurized before being used or stored. Why not performing the High Temperature Steam Electrolysis (HTSE) step directly under pressure? An experimental and modelling approach has been adopted in order to better understand the basic underlying mechanisms of pressurized steam electrolysis operation. Experiments were carried on two different single commercial cathode-supported Solid Oxide Electrolysis Cells (SOEC) at 800°C in the pressure range of 1 to 10 bars. According to the i-V curves, the Open Cell Voltage increases with increasing the pressure. Nevertheless, the limiting current density increases because of a better gas diffusion in through the thick porous cermet support, meaning that the hydrogen production can be improved depending on the voltage. The model, which has been calibrated on the experimental i-V curves recorded at the atmospheric conditions, has been validated for the pressurized operation.

Oxygen Nonstoichiometry and Cathodic Property of Ce0.6Mn0.3Fe0.1O2-δ for High Temperature Steam Electrolysis Cell Using LaGaO3-Based Oxide Electrolyte

Steam electrolysis was studied by using a new oxide cathode of Ce0.6Mn0.3Fe0.1O2- d (CMF). It found that this cathode showed almost same performance compared with a conventional Ni-based cathode without H2 flow and H2 generation rate obeyed the Faraday’s law at 900-700°C. The result of XRD measurement after operation, CMF phase were hardly changed after the steam electrolysis. A long-termed durability test was operated, and it revealed that CMF cathode showed the good stability over 90 h at 800 °C. The impedance spectra were measured under applied DC bias potentials. It revealed that polarization resistance and ohmic resistance were decreased with increasing DC bias potential. This decreasing of ohmic resistance was related to the increasing in electronic conductivity of CMF. CMF was n-type semiconductor and then electronic conductivity of CMF increased with decreasing of oxygen partial pressure.

Stack performances in high temperature steam electrolysis and co-electrolysis

High Temperature Steam Electrolysis (HTSE), based on solid oxide electrolysis cells (SOE) is a promising way to produce massively hydrogen with high efficiencies. This technology also allows producing syngas (H2 + CO) by co-electrolyzing a mix of steam and CO2. This syngas constitutes the basis to obtain further synthetic fuels. For both HTSE and co-electrolysis, durability and cost are still key points, but additionally for co-electrolysis the outlet H2/CO gas composition has to be tailored to fit with the targeted fuels. Previous works have been carried out to develop a stack design suitable for both applications. Here experiments at stack level in both electrolysis and co-electrolysis modes have been carried out. A 10-cell stack and a 25-cell stack have been tested in electrolysis mode, respectively producing 0.6 Nm3/h and 1.7 Nm3/h of hydrogen at 800 °C below the thermoneutral voltage (1.3 V) for all the cells and a steam conversion around 50%, with a small scattering between the different cells. Gas tightness of the stacks has also been evaluated. Moreover, the operation in co-electrolysis has been validated. Finally a cost analysis of this stack design has been performed and shows all the economical potentialities of this technology.

Composite manganate oxygen electrode enhanced with iron oxide nanocatalyst for high temperature steam electrolysis in a proton-conducting solid oxide electrolyzer

Composite electrode based on La0.8Sr0.2MnO3-δ (LSM) can be utilized in a proton-conducting solid oxide electrolyzer for steam electrolysis; however, the insufficient electro-catalytic activity of LSM still restricts the electrode performance and Faraday current efficiency. In this work, catalytic-active iron oxide nanoparticles are loaded on the surface of LSM composite oxygen electrode to improve electro-catalytic performance as well as extend the three-phase boundaries. SEM and EDS results together confirm the loading of Fe2O3 nanoparticles with the size of approximately 20–40 nm on the surface of LSM composite oxygen electrode. The effects on electrode performance due to different contents of Fe2O3 are loaded into LSM composite electrodes are systemically studied using symmetric cells. The electrical property of LSM is investigated and correlated to the electrochemical performance of the composite oxygen electrode in electrolysis cells. The maximum Faraday current efficiency is approximately 65% with the Fe2O3-loaded LSM composite electrode for steam electrolysis in a proton-conducting solid oxide electrolyzer at 800 °C.

(Invited) Enhanced Steam Electrolysis at Exsolution Titanates

B-site doped, A-site deficient perovskite titanate oxides with formula (M = Ni2+ or Fe3+; x = 0.06; g = (4-n)x/2) were employed as solid oxide electrolysis cell (SOEC) cathodes for hydrogen production via high temperature steam electrolysis (HTSE) at 900 °C. A proportion of B-site dopants were exsolved at the surface in the form of metallic nanoparticles under SOEC operating (reducing) conditions, due in part to the inability of the host lattice to accommodate vacancies (introduced (d) oxygen vacancies () and fixed A-site () and inherent (g) oxygen vacancies) beyond a certain limit. The presence of electrocatalytically active Ni0 or Fe0 nanoparticles and higher concentrations dramatically lowered the activation barrier to steam electrolysis and led to sharp rises in oxide ion mobility compared to the parent material (x = 0). La0.4Sr0.4Ni0.06Ti0.94O2.94 demonstrated discontinuous temperature dependence possibly due to oxygen vacancy trapping at lower temperatures.

Scandium-Doped LSM Anode for Steam Electrolysis in a Proton-Conducting Solid Oxide Electrolyzer

Perovskite La0.8Sr0.2MnO3-δ has been widely used as anode for proton conducting solid oxide steam electrolyzer; however, the insufficient catalytic activity still restricts the activity for electrochemical oxidation of steam. In this work, Sc-doped anode material La0.8Sr0.2Mn1-xScxO3-δ (x=0, 0.02, 0.05, 0.08, 0.1) with the aim of enhancing anode performance is studied. Combined characterization using XRD, TEM, XPS, SEM and EDS confirmed the successful partial replacement of Mn by Sc in B site. The doping of Sc remarkably improves ionic conductivity while accordingly decreases the mixed conductivity due to the increase of oxygen vacancies indicated by TGA and XPS. Electrochemical measurements and ionic conductivity measurements demonstrate LSMS0.05 has the most optimized polarization properties. With LSMS0.05 anode, the Faradic efficiency is maximized to 80% and accordingly enhanced by 25% compared with the electrolyzer with LSM anode for high temperature steam electrolysis by exposing anode to 5%H2O/air.

Economic assessment of a power-to-substitute-natural-gas process including high-temperature steam electrolysis

Power-to-Substitute-Natural-Gas (SNG) processes are studied since they can offer solutions for renewable energy storage and transportation. In the present study, an original Power-to-SNG process combining high-temperature steam electrolysis and CO2 methanation is economically assessed. This evaluation is based on experimental data describing the electrolyser performance and its degradation during long-term operation. These data are obtained on a commercial single cell. Tests are originally conducted by imposing voltage and steam conversion rate. The main conclusions of this experimental work are that two fields of current density evolution are evidenced in the tested conditions: a first transient one where the current density absolute value decreases very quickly, followed by a second field where the evolution of current density achieves a steady state. The influence of the operating point seems not significant once this state is achieved.The process assessed here has been developed in a previous work where a precise framework matching with a wide range of applications was defined. The design of the process main units and the calculation of matter and energy fluxes are based on this work. To go further, the economic assessment of this process is proposed. In this study, various scenarios of initial performance of the electrolyser are considered and integrate the performance degradation associated. The SNG production cost is estimated between 211 and 570 €/MWhHHV according to the scenario and the hypotheses considered. The two major items accounting for this high cost are the purchase cost of the electrolyser and its performance degradation. It also evidenced that none of the other items can be neglected. Through a sensitivity analysis, it is shown that an increase of plant annual availability and capacity makes the SNG production cost decrease.

Solar power tower as heat and electricity source for a solid oxide electrolyzer: a case study

High-temperature steam electrolysis (HTSE) consists of the splitting of steam into hydrogen and oxygen at high temperature in solid oxide electrolyzers. Performing the electrolysis process at high temperatures offers the advantage of achieving higher efficiencies as compared to the conventional water electrolysis. Furthermore, this allows the direct use of process heat to generate steam. This paper is related to the FCH JU (Fuel Cells and Hydrogen Joint Undertaking) project ADEL (ADvanced ELectrolyser For hydrogen Production with Renewable Energy Sources), which investigates different carbon-free energy sources to be coupled to the HTSE process. Renewable energy sources are able to provide the high-temperature steam electrolysis (HTSE) process with heat and power. This paper investigates the capability of Concentrating Solar Power (CSP) technologies to provide the HTSE process with the necessary energy demand. The layout of the plant is shown in the following figure. The design of commercial-scale high-temperature steam electrolysis has been carried out. The HTSE plant is coupled to an air cooled solar tower. The configuration and the operating parameters of the solar tower are based on those of the solar tower of Jülich (Germany), which is operated by DLR. This paper presents the results of process analysis performed to evaluate the hydrogen production from a HTSE plant coupled to an 80MWth air solar tower. Additionally, the dynamic behavior of the system during energy fluctuations has been analyzed. The receiver-to-hydrogen efficiency (based on the Higher Heating Value of hydrogen) is 26% at a hydrogen production rate of 680 kg/h in steady-state operation. The overall solar-to-hydrogen efficiency is calculated to be at 18%. Moreover, the analysis under transient conditions shows that a steady-state operation of the plant is only possible for 8 h. Copyright © 2015 John Wiley & Sons, Ltd.

Microstructural and chemical changes after high temperature electrolysis in solid oxide electrolysis cell

Degradation of solid oxide electrolysis cell is probably the main problem in the field of high temperature steam electrolysis. In this study two anode-supported solid oxide fuel cells were tested as a solid oxide electrolysis cell operating from 875°C to 950°C at the applied voltage of 1.5V and 1.7V respectively. Microstructural and chemical changes of the cell components were studied by field emission scanning electron microscope (FESEM), and X-ray diffraction (XRD) analysis before and after the electrolysis. FESEM analysis shows a delamination of anode layer from the electrolyte. Furthermore, formation of impurities like yttrium silicate at the cathode–electrolyte interface and lanthanum zirconate (LZ) at the anode–electrolyte interface were observed after electrolysis. It also reveals that lanthanum zicronate is formed only at the interfaces between anode functional layer La0.65Sr0.3MnO3−δ (LSM)/8mol% yttria stabilized zirconia (YSZ) and electrolyte layer (YSZ) but not at the whole anode layer. Formation of LZ is attributed to the high partial pressure of oxygen at the anode–electrolyte interface while yttrium silicate is formed due to the diffusion of silica from glass sealant into the cathode layer.

Sr2FeNbO6 Applied in Solid Oxide Electrolysis Cell as the Hydrogen Electrode: Kinetic Studies by Comparison with Ni-YSZ

Double-perovskite Sr2FeNbO6 (SFN) has been introduced to the solid oxide electrolysis cell (SOEC) supported by 8 mol% yttria stabilized zirconia (YSZ) electrolyte (500μm thick) with the cell composition of SFN-YSZ/YSZ/LSM-YSZ (La0.8Sr0.2MnO3, LSM). Five groups of contrast tests are designed to investigate the differences between SFN and Ni in electrochemical behavior. The reaction mechanisms of the H2O reduction in Ni-YSZ and SFN-YSZ electrodes are discussed. The results show that the conductivity of SFN in H2/H2O (80 vol% H2O) atmosphere (2.215S cm−1 at 850°C) is much higher than that in air (0.049S cm−1 at 850°C). The electrochemical impedance spectroscopy (EIS) measurement results indicate that, compared with Ni-YSZ, SFN-YSZ is more suitable for high temperature steam electrolysis as the hydrogen electrode. X-ray photoelectron spectroscopy (XPS) analysis suggests that the surface of SFN can also be one of the electrode reaction places besides the triple phase boundary (TPB), which greatly accelerates the reaction process, lowers the energy barrier of the charge transfer process and results in a better performance of SFN-YSZ than Ni-YSZ in the SOEC mode.

Upgrading waste heat from a cement plant for thermochemical hydrogen production

A calcium oxide/steam chemical heat pump (CHP) is presented in the study as a means to upgrade waste heat from industrial processes for thermochemical hydrogen production. The CHP is used to upgrade waste heat for the decomposition of copper oxychloride (CuO.CuCl2) in a copper–chlorine (Cu–Cl) thermochemical cycle. A formulation is presented for high temperature steam electrolysis and thermochemical splitting of water using waste heat of a cement plant. Numerical models are presented for verifying the availability of energy for potential waste heat upgrading in cement plants. The optimal hydration and decomposition temperatures for the calcium oxide/steam reversible reaction of 485 K and 565 K respectively are obtained for the combined heat pump and thermochemical cycle. The coefficient of performance and overall efficiency of 4.6 and 47.8% respectively are presented and discussed for the CHP and hydrogen production from the cement plant.

Hydrogen electrical energy storage by high-temperature steam electrolysis for next-millennium energy security

It would be highly significant if energy, which is intimately related with the continued existence of human beings, were sustainable on the basis of the present resources for the next thousand years. The effectiveness of hydrogen for energy storage by high-temperature steam electrolysis is clarified by showing its features with reference to solar energy and nuclear energy for power storage as examples. It is also shown that use of hydrogen for energy storage would be effective for widespread utilization of current energy resources, such as renewables and nuclear energy, over the next millennium.