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Biogas refining system including methanation reactor and proton-conducting electrolysis cell has been proposed and investigated based on the simulation including mass and heat balance analysis. Based on the calculation results, carbon deposition was predicted to still occur at the cathode outlet even with the gas humidification when a conventional oxide-ion conducting electrolyte is applied to the electrolysis cell due to the enhanced carbon activity caused by oxide-ion transport from the cathode to the anode. In the case of the proton-conducting electrolyte applied solid oxide electrolysis cell, proton transport from the anode to the cathode was found to mainly promote reverse water-gas shift reaction and methanation reaction without any carbon deposition. Even though the calculation results should be verified by comparing with experimental results, the numerical study suggested that the biogas refining system combined with p-SOEC is a promising technology for generating carbon-neutral methane with a strongly suppressed risk of carbon deposition.

Solid oxide fuel cells (SOFCs) are expected to become widespread as an energy conversion technology that can directly produce electrical energy from fuel. Solid oxide electrolysis cells (SOECs) are essentially SOFCs operating in reverse to produce fuel from electricity. The exchange current density is one of the most important parameters to simulate SOEC/SOFC. In this study, experimental data was evaluated as apparent exchange current density and the effects of SOEC/SOFC operation and different electrode materials were discussed.

Reversible Solid Oxide Cells (r-SOCs) are an attractive electrochemical energy conversion technology that can act as both a Solid Oxide Fuel Cell (SOFC) for power generation, and a Solid Oxide Electrolysis Cell (SOEC) for steam electrolysis. Unfortunately, Ni-zirconia cermet, which is widely used in SOFCs, has the problem that the electronically conductive phases, Ni, agglomerates due to redox reactions and breaks the conductive path, resulting in performance degradation. In this study, we fabricated an alternative fuel electrode with a stable conductive structure using both an ionic conductor Ce0.9Gd0.1O2 (GDC) and an electronic conductor Sr0.9La0.1TiO3 (LST), and we co-impregnate Ni and GDC to the fuel electrode using only Ni as an electrocatalyst. The durability of the conventional fuel electrode and our alternative fuel electrode was compared and evaluated, and the potential of the alternative fuel electrode material was demonstrated.

A high temperature solid oxide electrolysis cell (SOEC) for electrolysis of water is paired with a H-SOEC for hydrogen compression (EHC). SOEC and EHC have been integrated into an electrochemical network (ECN) in a flow-series configuration and then simulated and analyzed. Adding heat and minimizing area specific resistance (ASR) would be highly desirable for further developing highly-efficient SOEC+EHC ECN’s. It is important to note there is a maximum possible heat generation rate with a given ASR when operated below the thermoneutral point. There is a maximal heat addition rate for optimal efficiency of the SOEC, and it is not at thermoneutral. Many developers have expressed interest in the thermal management of electrolyzer cells and in the possible existence of such an optimum. It is important to understand in general that heat removal can allow an increased hydrogen production rate over the thermoneutral path at constant temperature. For this reason, the SOEC+EHC ECN was simulated over a range of currents and ASR’s to determine the heat addition or removal required. If the internal resistance of an SOEC could be lowered sufficiently via the development of new, high-performing materials, the efficiency of hydrogen production could be very high, especially when supplementary heat is provided from solar or other waste heat sources such as nuclear or coal power plants. It is remarkable that a quarter to a third of the energy for the combined high-temperature electrolysis and hydrogen compression system could be provided by solar, nuclear, or coal.

It is shown that lowering area specific resistance (ASR) or Rt (total resistance) should lead to lower capital cost, CAPEX, and also to the lowest possible electrical power consumption per hydrogen produced, OPEX. Many researchers have focused for many years on thinning component layers and developing new higher-performance materials. Thinning of components to lower RT is widely researched. Based on simple correlations, the CAPEX of the solid oxide electrolysis cell (SOEC) stack cost could expect to be lowered by 25 percent by thinning components. In terms of size this low- Rt SOEC stack has the potential to be significantly smaller. Building off the DOE’s progress with SOFC, even lower Rt SOEC and SOFC’s are possible with techniques such as sputtering and Atomic Layer Deposition (ALD) which produce better conducting materials. This is truly remarkable in that the low per kilowatt SOEC stack cost and low power consumption may make the SOEC a truly realizable economically viable SO manifestation.

Solid oxide electrolyzer is expected to be an energy storage device using renewable energy to produce useful fuels. Recently there are strong interests on co-electrolysis of CO2-H2O for producing H2/CO syngas, and even for directly producing liquid fuel or hydrocarbon feedstocks. Further increase in activity and stability of the fuel electrode are required for practical application. In this study, CO2 and CO2-H2O electrolysis were investigated using CuFe2O4 (CFO), La0.6Sr0.4Fe0.8Mn0.2O3 (LSFM) and their composites as cathodes. LaGaO3 based oxide was used for electrolyte and Ba0.6La0.4CoO3 was used for anode. It was found that mixing CFO and LSFM was effective for remarkable improvement of the cell performance in co-electrolysis. Effect of varying CO2/H2O ratio in feed gas was also investigated and the product was always enriched with H2 in comparison with the preset CO2/H2O feed gas due to water-gas-shift reaction (WGS reaction, CO + H2O → CO2 + H2). Since the chemical equilibrium of WGS is thermodynamically preferred to H2 production as decreasing operating temperature, temperature dependence of the co-electrolysis performance using CFO-LSFM composite cathode was also studied. The results indicate that the electrolysis performance was decreased, while the H2 product was increased with decreasing operation temperature. However, considering the cell durability, lowering the operating temperature or the applied electrolysis current density (or working voltage) would be preferable. Degradation of electrolysis performance was also discussed by impedance analysis. Overall, the use of the composite oxides as cathode gives very promising electrochemical performance achieved with excellent Faraday’s efficiency (> 95% of theoretical value), operation stability and reversibility in co-electrolysis.

Solid oxide electrolysis cells (SOECs) convert electrical energy to chemical energy stored in H2 and/or CO and has a great potential to become a key enabling technology in the transition towards renewables. The key challenges for the successful commercialization of SOEC are the limited long-term durability and cost. To ensure high production rate and hence reduce the investment cost, operation at high current densities needs to be considered. Conventional Ni/yttria stabilized zirconia (YSZ) fuel electrode supported SOEC cells demonstrate acceptable long-term durability when operated at below 1 A/cm2, with a number of tests running for years. These cells suffer however severe degradation when operated at above 1 A/cm2, where the major degradation phenomena are reported to be delamination of the oxygen electrode, crack formation in the YSZ electrolyte, depletion of Ni in the active Ni/YSZ electrode, deterioration of the Ni-YSZ interface, and formation of ZrO2 nano-particles on Ni surface. A large part of the cell resistance increase is associated with the Ni/YSZ electrode. By introducing Ce0.8Gd0.2O2- d (CGO) nanoparticles into the Ni/YSZ electrode via solution infiltration, we were able to reduce the cell degradation (evaluated based on cell voltages of 0-1000h) from 699 mV/1000h to 66 mV/1000h when operating the cells at 800 oC and 1.25 A/cm2. The CGO nano-particles facilitate the steam splitting reaction at the Ni/YSZ triple phase boundaries (TPB), reduce the electrode polarization and effectively mitigate the microstructural deterioration typically seen in the non-modified Ni/YSZ electrodes. The remaining 66 mV/1000h degradation is mainly associated with formation of a poorly conducting CeAlO3 phase, which is a reaction product between Al2O3 as the sintering aid and the CGO particles on the Ni grains. An effort to break down the CeAlO3 phase was explored, though not successful. Testing the cell with modified Ni/YSZ electrode was extended to one year. A steam supply failure at 4000 h caused certain damage to the cell and resulted in a higher degradation rate in the second half of the one-year test. A counter-balance strategy was successfully tried out by increasing the cell operating temperature to 830 oC eventually. The test was successfully terminated after reaching one year, with cell voltages of 1124 and 1468 mV at the beginning and end of the test, corresponding to an average degradation rate of 40 mV/kh. The current work shows high potential for modifying conventional SOEC cells for use in high current density electrolysis applications.

The spatial distribution of current and temperature plays important role in the electrochemical performance of Solid Oxide Electrolysis Cells (SOECs). Many numerical predictions of current and temperature distribution have been reported, whereas experimental investigations were rare. In this research, we are applying a electrode-segmentation [1] method to investigate the spatial current and temperature variation in a cathode-supported microtubular SOEC. The electrode-segmentation method shows a remarkable current variation among the segments. The current densities of the midstream and downstream segments are smaller than the upstream segment with an increased cell voltage, implying that the cell suffers from water starvation. Besides, the temperature at each segment increases with the voltage increase. The largest current in the upstream segment is observed, which agrees with the largest temperature rise there. The largest temperature gradient happens between the upstream and midstream segments. References Aydin, T. Koshiyama, H. Nakajima, T. Kitahara, Journal of Power Sources, 279, 218-223 (2015).

A significant contributor to carbon and air-pollutant emissions is the steel industry, which is responsible for 2.8 Gt of CO2 annual emissions and accounts for a quarter of industrial CO2 emissions. A significant and valuable by-product of steelmaking is coke oven gas (COG), which is produced from coke-making via high-temperature dry distillation of coal in the absence of oxygen. COG typically consists of 55-60 vol% hydrogen (H2), 23-27 vol% methane (CH4), 5-8 vol% carbon monoxide (CO) and impurities such as H2S and tars [1]. Every ton of coke produced yields 300-360 m3 of COG and an estimated 650 Mt of COG is produced in the steelmaking industry worldwide each year, with up to 50 % re-utilised within steelmaking [2]. However, the rest is flared, contributing to carbon emissions and wasting valuable and useful gases. In this paper, co-electrolysis of simulated COG (CH4/H2 30/70 vol%) with carbon dioxide using a commercially available solid oxide fuel cell (SOFC) was investigated at 750 °C. The electrochemical performance of an anode supported button cell was characterised using open circuit potential measurements, current-voltage curves and electrochemical impedance spectroscopy. The product gas composition was analysed using quadrupole mass spectrometry (QMS). The QMS measurements show that CH4 was initially converted at the open circuit potential into synthesis gas (H2/CO) via dry reforming of CH4 and the reverse water gas shift reaction, yielding a gas mixture composed of 39.2 vol% H2, 38.3 vol% CO2, 22 vol% CO and low levels of unconverted CH4 (see figure). Increasing the voltage from the OCP to 1.4 V caused the CO2 to decrease and the CO to increase, yielding a gas mixture consisting of 42.6 vol% H2, 26.7 vol% CO2 and 29.5 vol% COincreased the synthesis gas content (H2 + CO) of the output gases by 44% relative to the OCP, with the levels of H2 produced increasing by 9% over this voltage range. In addition, the level of unconverted CH4 increased slightly, indicating that the CO2 conversion processes were competing with catalytic dry reforming of CH4. Possible reaction mechanisms are discussed. The I-V and EIS measurements established that cell electrical performance was increased by addition of CO2 through dry reforming and also improved diffusion of the fuel gases through the anode. The effects of COG fuel variability have also been investigated and show that increasing the CH4/H2 ratio from 10/90 vol% to 40/60 vol% of the COG increased the syngas production by 92%. The I-V curve and EIS measurements show that increasing the CH4/H2 ratio decreased the electrical performance of the cell due to prevalent carbon deposition. This work presents a method of efficiently utilising CO2 and suggests SOFC co-electrolysis of COG is an effective way to increase the usefulness and value of this waste gas stream. References: [1] Czachor M, Laycock C, Carr S, Maddy J, Lloyd G, Guwy A,. Co-electrolysis of simulated coke oven gas using solid oxide electrolysis technology. Energy Conversion and Management, 2020;225:113455. 10.1016/j.enconman.2020.113455 [2] Gao R, Zhang C, Kwak G, Lee Y, Chang S. Techno-economic evaluation of methanol production using by-product gases from iron and steel works. Energy Conversion and Management, 2020;213:112819. 10.1016/j.enconman.2020.112819 Figure. The effect of increasing the voltage on the composition of the anode output gases of an anode-supported cell under a 2:2 fuel/CO2 ratio. The fuel composition was 30/70 vol% CH4/H2. The cell temperature was 750 °C. Figure 1

The successful market introduction and public acceptance of the solid oxide fuel/electrolysis cell technology requires high performance, long-term stability and low costs of the corresponding cells and stacks. However, especially the degradation of SOEC stacks during long-term operation for several thousand hours in electrolysis and reversible SOFC/SOEC mode are not yet well understood. The paper presents the long-term behavior and the degradation results of a 30-cell stack with electrolyte supported cells operated in reversible SOFC/SOEC mode. The stack was supplied by Sunfire GmbH (Dresden/Germany) as part of the German funded project Reversible Solid Oxide Cell. The reversible cycles with duration of 24 h consist of 9 h SOFC operation at 70 % fuel utilization, 9 h SOEC operation at 70 % steam conversion and two switching phases, each with duration of 3 h. The stack is currently being operated for 6300 h under these reversible SOFC/SOEC cycling conditions. After the initial performance test, current-voltage curves and electrochemical impedance spectra were recorded every 2000 h. The electrochemical properties such as open circuit voltages, area specific resistances, power densities, fuel utilization, steam conversion rate and impedance values of the stack and of selected repeat units are presented. The homogeneity among the repeat units is discussed in context with the measured temperature gradients in the stack. The degradation and the change of the resistances, e.g. the ohmic resistances, the polarization resistances of the electrodes and the gas concentration resistances, during the reversible SOFC/SOEC long-term operation are presented and compared to each other. Furthermore, the degradation mechanisms of the different cell and stack components are discussed.

Oxidative coupling of methane (OCM) is one of the most promising technologies for the effective use of methane. In this study, La0.3Sr0.7TiO3 was examined as an anode material for solid oxide electrolysis cell with OCM reaction. X-ray diffraction measurement was conducted for the material characterization, and alternating current impedance and current-voltage measurement were conducted for the cell characterization. The activity test was conducted at different current densities, and the anode gas compositions were analyzed. The electrochemical production rates of CO, CO2, C2H6, and C2H4 were increased linearly as the applied current voltages were increased, while the selectivities of all products were almost constant.

Use of perovskite as a cathode for solid oxide electrolysis cell is limited by its insufficient electrolysis current density or catalytic activity. Most of present perovskites used has a crucial drawback ─ significant segregation of A-site cations (i.e. SrO), likely resulting in the degradation of performance. In this work, spinel oxide of CuFe2O4, which is an alkline earth metal free oxide, is applied as the cathode material to investigate its electrochemical performance, microstructure and chemical composition in the electrolysis of CO2/H2O, steam and CO2. It was found that the exsolution of Cu nanoparticles was observed in CO2/H2O co-electrolysis and the microstructure of CuFe2O4 influenced significantly by operating in different CO2/H2O compositions. Despite the significantly microstructural variation of the CuFe2O4 layer, the cell performs relatively stable electrochemical performance in CO2/H2O and steam electrolysis.

In recent years, the establishment of Power to Gas technology is in progress. Promising methods include steam electrolysis and co-electrolysis using the Solid Oxide Electrolysis Cell (SOEC). We have developed a honeycomb electrolytic cell with a larger reactive area per unit volume than the conventional flat and tubular types. Thereby volumetric density of fuel production rate can be greatly improved, leading to a development of compact and high performance steam electrolysis systems. In this study, we address hydrogen production by steam electrolysis with an SOEC having a porous honeycomb support consisting of Ni-YSZ cathode. Current-voltage curves were measured with sampling the cathode outlet gas for gas chromatography. As the results, we confirmed that hydrogen concentration in the outlet increased as the current increased. The experimental results are useful to validate numerical models to design practical honeycomb cells.

A hydrogen-electrode-supported solid oxide cell (SOC) is fabricated by phase-inversion tape casting technique and its electrochemical performance is investigated with particular focus on high fuel utilization operation and reversible operation. Structure of the hydrogen-electrode support layer is also analyzed. Electrochemical performance of the cell is measured and compared with that obtained from a conventional cell having homogenous porous structure in the hydrogen electrode support. Equivalent circuit fitting analysis is performed for quantitative understanding of impedance spectra. The results indicate that the finger-like pores in the hydrogen-support layer introduced by the phase-inversion process can significantly enhance gas diffusion property of the layer and hence improve cell performance particularly at lower reactant concentrations. Also, asymmetry in cell performance between fuel cell and electrolysis cell modes is suppressed, which is desirable for reversible operation of SOCs., 17th International Symposium on Solid Oxide Fuel Cells (SOFC-XVII) July 18, 2021 - July 23, 2021

Solid oxide cells (SOCs), both solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC), have being attracting more and more attention due to its high energy conversion efficiency and fuel flexibility. However, degradation of fuel electrodes after long-term operation remains as one of the main challenges for their commercial application. In particular, migration and coarsening of nickel (Ni) in Ni - yttria-stabilized zirconia (Ni-YSZ) fuel electrodes have strong impacts on the decreases in both active three-phase boundary (TPB) and Ni network connectivity, which result in performance deterioration. One of the mechanisms proposed as an explanation of Ni migration is Ni transport via volatile Ni(OH)x species, so-called evaporation-condensation mechanism [1]. On the other hand, Jiao and Shikazono [2] proposed a model to explain Ni spreading on YSZ surface based on the variation of Ni-YSZ wettability which is modified by the oxygen adsorption. Nevertheless, further investigations are required to understand the mechanisms of Ni migration. In the present study, Ni-film patterned electrodes which can provide well defined TPB configurations are used to investigate the Ni-YSZ degradation under SOFC, SOEC and sequential SOFC and SOEC operations, i.e. reversible operation (RSOC). The edge of sputtered Ni-film contacting with open YSZ surface can be treated as active TPB during operation. Confocal laser scanning microscopy (CLSM, Keyence, VK-X 1000) is used, which enabled in-operando observation of the real-time local morphological change at active TPB [3]. The in-operando potentiostatic experiment was carried out inside a high temperature chamber which was kept at 800oC with 4% H2O-4% H2-92% N2 as fuel gas and 30% O2-70% N2 as oxidant as shown in Fig. 1(a). The correlations between the Ni morphological changes and cells’ electrochemical performances were investigated. The Ni phase dynamically spread and de-percolated only under the SOFC operation, while such a phenomenon was not observed during the SOEC operation, as shown in Figs. 1(c), (d) and (e). Ni coarsening occurred regardless of the operation modes. The competition between Ni-film spreading and breaking-up finally determined the complicated local morphological change and corresponding cell performance variation. The time variations of active TPB and current density showed good correlation as shown in Fig. 1(b). Real-time in-operando observations revealed different Ni migration under SOFC, SOEC and RSOC operations, which may provide new insights for the understanding of Ni-YSZ fuel electrode degradation. Fig. 1. (a) Schematic illustration of in-operando setup. (b) Correlation between current density and Ni morphological evolution. (c)-(e) CLSM images and 3D surface height contour maps of the yellow-frame-enclosed areas after SOFC, SOEC and RSOC modes, respectively. References [1] M. B. Mogensen et al., Fuel Cells, 17, pp. 434-441 (2017). [2] Z. Jiao, N. Shikazono, Acta Materialia, 135, pp.124-131 (2017). [3] Z. Jiao, N. Shikazono, J. Power Sources, 396, pp.119-123 (2018). Figure 1

The increasing concentration of carbon dioxide (CO2) in the atmosphere since the industrial revolution is a major contributor to climate change. Among the several options to tackle this issue, the removal of CO2 from the atmosphere and its subsequent use is becoming increasingly attractive. This paper presents a techno-economic feasibility study and quantification of the environmental benefits of combining direct air capture (i.e. capturing CO2 from the atmosphere) with co-electrolysis of water and the captured CO2 in a solid oxide electrolyser cell (SOEC). Using Aspen Plus, a direct air carbon capture process is modelled in tandem with SOEC to generate carbon monoxide and hydrogen, which are subsequently converted to fuels. The carbon capture model uses regenerative loops of sodium hydroxide and sodium carbonate as well as calcium hydroxide and calcium carbonate to selectively remove the dilute carbon dioxide from the air. Other than filtered air, the only other output of this process is a stream of gaseous water and carbon dioxide at an elevated temperature, which is fed to a SOEC stack. The SOEC model assumes that carbon dioxide is converted to carbon monoxide by the reverse water gas shift reaction and water is converted to hydrogen and oxygen through electrolysis. The different components of the SOEC and their inherent flows of materials and heat are simulated using unit operations available in Aspen Plus. The gas mixture from the SOEC (mixture of H2/CO/CO2/H2O) is further transformed into profitable fuels such as methane and methanol, whose respective processes are also simulated in Aspen Plus. Clean electricity sources are considered for the model and energy requirements are minimized through process synthesis; for example, there exists some good synergies between the direct air capture process and the SOEC to minimize the energy necessary to bring the SOEC feed to its operating temperature of ca. 800°C. Sensitivity analysis are performed on the entire process (direct air capture/SOEC/fuel synthesis) to reveal the effect of key operating parameters (e.g. conversion inside the SOEC, composition of SOEC inlet) on the production of fuels or amount of electricity requirement per amount of fuel produced.

Steam electrolysis by solid oxide fuel cell technology, known as SOEC, is considered the most efficient and cost effective option for hydrogen production from renewable sources. By using proton-conducting electrolyte, the SOEC operating temperature can be reduced from over 800oC to below 600oC. Technical barriers associated with the conventional oxygen-ion conducting SOECs, such as hydrogen separation from water, oxidation of steam electrode, and instability of oxygen electrode, can be largely mitigated. In this report, an intermediate temperature (400-600°C) electrolysis technology was developed where a novel proton-conductor and a triple-conducting oxide were used as the electrolyte and anode, respectively. The electrolysis cell demonstrated excellent performance and durability at intermediate temperatures, promising a new prospective for next-generation steam electrolysis.

This paper will cover the technical and commercial features of Haldor Topsoe's CO from CO2 technology. Haldor Topsoe's eCOs is a solid oxide electrolysis cell (SOEC) technology that allows the safe, efficient, and cost-competitive production of carbon monoxide directly at the site of facilities where the gas is needed. The CO-generation device uses feedstock carbon dioxide and electrical power to produce CO in quantities ideal for most operations that today rely on cylinder or tube trailer supply.An eCOs Plant is delivered as a stand-alone unit with power, CO2 and product gas connections. Furthermore, the plant ensures high levels of purity, producing CO at 99.5% assay with minimal contaminants and CO2 as the main impurity. An eCOs solution can also be customized to produce CO at 99.995% purity. One eCOs plant is able to deliver between 10 and 100 Nm3 CO gas per hour. Several plants can be operated in parallel if larger quantities are needed. The patented eCOs technology ensures security of supply, eliminates the need to transport hazardous gas, and drastically reduce costs related to storage, rentals and connections. In the longer run, this technology opens up for a whole new segment of green and sustainable chemicals from renewable carbon sources. Field test results from the 12-kW demonstration-unit located in Houston, Texas will be reported, as well as progress towards the 300-kW commercial unit to be delivered in 2018. Results from a 50-kW H2O electrolysis unit located in Foulum, Denmark used for biogas upgrading will also be presented.

Methane-synthesis solid oxide electrolysis cell (MS-SOEC) technology has potential to provide efficient renewable energy storage systems. However, there are few studies focusing on MS-SOEC electrode materials. In this study, several materials were tested experimentally. As anode materials, La0.6Sr0.4MnO3-δ (LSM), La0.6Sr0.4Co0.2Fe0.8O3-δ-Ce0.8Sm0.2O1.9 composite (LSCF-SDC) and platinum were compared. The cell with LSCF-SDC exhibited lower overpotentials and higher stability than LSM. Platinum showed even better performance than LSCF-SDC. Ni-SDC was used for the cathode, and the cathode outlet gas compositions were analyzed for several operation temperatures and current densities. It was found that catalytic activity for methanation was enhanced under polarized conditions. Effects of ruthenium addition to the cathode were also examined. Impedance analysis combined with gas composition measurements revealed high electrochemical activity of ruthenium, while methane production was suppressed possibly due to methane reforming reactions promoted by ruthenium.

It is important to know the electrode kinetics of hydrogen production as well as to understand the effect of the mass transport in the gas phase for the analysis of the molten carbonate electrolysi ...

Solid oxide fuel cell / electrolysis cell (SOFC / EC) can be expected as energy converters with high efficiency. In SOFC / EC material developments, the coverages of the chemical species at the three-phase boundary (TPB) are directly linked to the electrode performance. Accordingly, it is important to estimate the surface coverages at TPB to develop a new electrode. However, it is difficult to directly analyze and evaluate the coverages at the reaction field of the oxide / metal composites at high temperature (> 600 °C). Therefore, it is required to construct electrochemical kinetics with the various parameters, such as reaction constants and adsorption equilibrium constants. In order to determine the coverages at the TPB, it has demands not only to construct an appropriate electrochemical model but also both to develop a method for fitting a large number of parameters included in the model and to acquire a series of various experimental data sufficient for fitting. These requirements are not fully satisfied in previous researches [1-2]. Therefore, the chemical properties of the electrode surface have not been clarified while the reaction mechanism on the H2 electrode has been understood in FC operation. In this study, the determination method of surface coverage using an electrochemical reaction model for H2 / H2O porous electrodes composed of Ni / YSZ was established. We considered that the local equilibrium between oxygen and oxide ions is achieved in the solid electrolyte, and proposed a H2 electrode reaction model consisting of a competitive adsorption reaction as Langmuir-Hinshelwood type at TPB. Using the model, a relational expression between the electric current density and the coverage could be obtained. The equation includes the parameters of current density (i), oxygen activity (a O), the partial pressures of hydrogen (P H2) and water (P H2O), the kinetics constant of the water generation reaction at FC operation (k a), and the adsorption equilibrium constant of H, O, OH and H2O (K H, K O, K OH and K H2O). a O(eq) is the oxygen activity at equilibrium potential. The i, P H2, P H2O, a O and a O(eq) could be obtained by experimental conditions and data while ka , K H, K O, K OH and K H2O are unknown constants without appropriate fitting. The simple optimization method cannot approximate optimal solutions and determine the coverages because this model is multivariate function, which has 5 parameters. As a method for quantifying the coverage of chemical species by fitting the experimental data to the reaction model, the method using a genetic algorithm was applied. The genetic algorithm is one of the multivariable optimization methods, which efficiently approximates the optimized value of the parameters by alternation of generations created by operations composed of selection, crossover, and mutation [3]. By taking advantage of the characteristics of the genetic algorithm that randomly generates and converges initial value candidates during optimization, multiple optimal solutions can be efficiently obtained with preventing the drop to local optimum by increasing the number of trials. The most effective optimal solution could be determined from them. As the various electrochemical data for estimating the surface coverage at a temperature of 900 °C, the electrochemical data of both FC / EC under 12 conditions, in which P H2 and P H2O were changed were got using the same cell. The current interruption method was used to separate the overvoltage and ohmic voltage loss of the H2/H2O electrode during power generation and electrolysis under constant current, and then, the oxygen activity was calculated from the ohmic free-anode potential (vs. 1 atom O2). Using genetic algorithm, optimization schemes were attempted more than 50,000 times and searched for the parameter set with the smallest error between the experimental value and the estimated value from the obtained optimal solutions. The outline of the optimization process was shown in Fig. 1. As a result of fitting various reaction constants to the model with optimal solutions, the relationship between i and a O could be roughly expressed by multiple reaction rate constants and equilibrium constants, and the coverages could be quantified. Furthermore, it was possible to draw the chemical state at TPB of Ni / YSZ electrodes during FC operation. [1] W. G. Bessler et al., Phys. Chem. Chem. Phys., 12, 13888 (2010). [2] M. Ihara et al., J. Electrochem. Soc., 148(3), A209 (2001). [3] M. Srinivas et al., IEEE, 27(6), 17 (1994). Figure 1

The concept of an electrolysis system, where CO2 is converted into hydrocarbons using renewable electricity, has been attracting much attention because it is expected to be one solution to achieve a decarbonized society. In order to realize an economical electrolysis system, it is important to produce high-value products such as ethylene with high reaction rate (i.e. the operating current density of CO2 electrolysis), and high efficiency (low operation voltage). The anion exchange membrane (AEM) CO2 electrolysis cells using gas diffusion electrodes (GDEs) are more advantageous than the traditional flow cell using a solution purged with CO2, both in terms of higher current density and lower voltage operation. This is because of the efficient CO2 reduction occurring at the three-phase interface of a GDE (i.e. CO2 is directly fed to the vicinity of the electrocatalysts though a gas diffusion layer (GDL)), increasing the current density, and of the cell electrodes being closely spaced, lowering the voltage. However, there are only several studies of the AEM CO2 electrolysis cells for high rate of ethylene production [1]. Here, we investigate ethylene production performance of an AEM CO2 electrolysis cell consisting of copper and copper oxide nanoparticles coated on GDL as a cathode, iridium oxide-coated titanium support as an anode, and an AEM. Among these components, the GDL can play a crucial role in the efficient transport of CO2 and water management, therefore we focus on understanding the effects of GDL properties such as thickness, porosity and density on ethylene production. We evaluated the electroreduction characteristics of the cells under ambient condition by a constant current method in which a constant current is supplied for a period of time. The faradaic efficiency (FE) and partial current density (PCD) of gas products such as ethylene, carbon monoxide, methane and hydrogen are examined as a function of the total current densities (TCD). We found that the FEs and PCDs depended on the density and the thickness of the GDLs. The low density and thick GDL showed high FE and PCD of ethylene due to high gas diffusibility. The FE and the PCD of ethylene at the TCD of 600 mA/cm2 reached a maximum of 50 % and 300 mA/cm2, respectively. References [1] Christine M. Gabardo, Colin P. O’Brien, Jonathan P. Edwards, Christopher McCallum, Yi Xu, Cao-Thang Dinh, Jun Li, Edward H. Sargent, and David Sinton, Joule 3, 1–15, November 20, 2019

Journal of the Electrochemical Society 163(11), F3197-F3208 (2016). doi:10.1149/2.0271611jes, Published by Electrochemical Society, Pennington, NJ

High temperature co-electrolysis of steam and CO2 based on solid oxide electrolysis cell (SOEC) to produce syngas as a feedstock for the well-known Fischer-Tropsch process is the main aim of the present research. Here Ni-8YSZ/8YSZ/LSCF6428-GDC button cells have been fabricated and the effect of the different microstructural parameters like air electrode thicknesses, fuel electrode porosities, adhesion layer and thermodynamic parameters like gas composition, temperature, on the performance of SOEC has been investigated systematically. The SOEC with 10 μm air electrode thickness, functional layer, fuel electrode having 20 vol% PMMA content, addition of YSZ-GDC adhesion layer gives the better performance in overall results and the voltage obtained for this SOEC at current density of 0.8 A.cm−2 is ~1.25 V at 800°C in 49% N2, 5% H2, 23% CO2 and 23% H2O gas mixture at fuel electrode side. To identify the electrochemical processes occurring at the electrodes of SOEC, distribution function of relaxation time (DRT) analysis of the electrochemical impedance (EIS) data is carried out.

In this study, a novel electrolysis cell based on ethylenediamine (EDA) as a cathodic solvent was developed for NH3 electro-synthesis. The NH3-generating cathode chamber was filled with 0.1 M LiCl/EDA and separated by a cation exchange membrane from the anodic compartment, which was filled with 0.05 M H2SO4 aqueous solution. It appeared that EDA was cathodically stable, and thus electron-stealing medium destruction was substantially avoided. The faradaic efficiency for NH3 synthesis was 17.2%, producing 7.73 × 10−7 mol NH3 for 1 h electrolysis at a cell voltage of 1.8 V with the charge consumption of 1.3 C.

Introduction Ethanol, which is easily produced by the fermentation of biomass products (sugar cane, corn, grain, beetroot, ligno-cellulosic wastes, etc.) is an alternative fuel to feed a fuel cell [1]. Its liquid state (which allows an easy storage) with a low toxicity and its large availability in many countries (Brazil, USA, Spain, France, etc.), together with its high energy density for complete oxidation to CO2 (8 kWh kg-1 compared to 11 kWh kg-1 for gasoline) are important positive points for its use as a fuel [2]. Can we use ethanol directly in a Direct Ethanol Fuel Cell (DEFC) or do we have to convert it into pure hydrogen by electrochemical reforming in a Proton Exchange Membrane Electrolysis Cell (PEMEC)??? Direct Ethanol Fuel Cell The oxidation of ethanol is more difficult to perform than that of methanol with the necessity of breaking the C-C bond to obtain its complete oxidation to CO2. The electrocatalytic reaction has been the subject of numerous studies on several Pt-based electrodes, including Pt-X alloys (with X = Ru, Sn, Mo, etc.) and dispersed nanoparticules [3]. From these studies it appears that breaking the C-C bond at relatively low temperatures (80 to 120°C) is still a challenge, since the main reaction products are acetaldehyde and acetic acid together with a small amount of CO2 [4]. It turns out that a Direct Ethanol Fuel Cell (DEFC) gives electrical performance one order of magnitude lower (Pmax < 0.1 W cm-2) than that obtained with a Proton Exchange Membrane Fuel Cell (PEMFC) fed with pure hydrogen (Pmax ≈ 1 W cm-2). Production of hydrogen by electrochemical processes The principle of the electrochemical decomposition of ethanol is similar to that of water electrolysis using a Proton Exchange Membrane Electrolysis Cell (PEMEC) [5, 6]. Ethanol is fed to the anodic compartment where it can be completely oxidized in the presence of water, producing carbon dioxide and protons, i.e.: C2H5OH + 3 H2O → 2 CO2 + 12 H+ + 12 e- (1) After crossing-over the proton exchange membrane the protons reach the cathode compartment where they are reduced to hydrogen according to reaction (2): 2 H+ + 2 e- → H2 (2) This corresponds to the electrochemical reforming of ethanol into hydrogen and carbon dioxide, according to the overall reaction: C2H5OH + 3 H2O → 6 H2 + 2 CO2 (3) with the thermodynamic data under standard conditions: ΔH = + 348 kJ (mole ethanol)-1 and ΔG = + 97 kJ (mole ethanol)-1. corresponding to a reversible cell voltage UEtOH = ΔG/nF = 0.084V, instead of UH2O = 1.229V for water electrolysis. In this communication the principle of the electrocatalytic oxidation of ethanol either in a DEFC or in a PEMEC will be discussed. The same electrocatalysts are used in both cases since the same electrochemical reaction is involved and the right electrocatalysts are similar, i.e. Pt-based nanoparticles dispersed on a carbon powder such as PtxSn1-x/C and PtxSnyRuz/C catalysts. The current density vs. anode potential curves has been recorded and displays the same behaviour. When comparing the energy efficiency coefficient ε of both processes we arrived at the conclusion that the energy efficiency of the DEFC (εDEFC ≈ 15%) is a little bit greater than that of a PEMFC using hydrogen produced in a PEMEC (ε = εPEMFC x εPEMEC ≈ 0.55 x 0.18 ≈ 10%) when the oxidation process of ethanol stops at the acetic acid stage. But the most important point is that the electrical energy used is much lower, i.e. ≤ 2.2 kWh (Nm3)-1, since U cell ≤ 1.0 V, compared to 4-4.5 kWh (Nm3)-1 for water electrolysis at 1.8-2.0 V. References [1] C. Lamy, C. Coutanceau, J.-M. Léger, in Catalysis for Sustainable Energy Production, P. Barbaro and C. Bianchini (Eds.), Wiley-VCH, Weinheim, 2009, Chap.1, pp. 3-46. [2] C. Lamy, E.M. Belgsir, in Handbook of Fuel Cells: Fundamentals and Survey of Systems, W. Vielstich, A. Lamm and H. Gasteiger (Eds.), Wiley, Chichester, 2003, Vol. 1, Chap. 19, pp. 323-334. [3] F. Vigier, S. Rousseau, C. Coutanceau, J.-M. Léger, C. Lamy, Topics in Catalysis 40 (2006) 111. [4] S. Rousseau,C. Coutanceau, C. Lamy, J.M. Léger, J Power Sources (2006) 158: 18–24 [5] C. Lamy, T. Jaubert, S. Baranton, C. Coutanceau, J Power Sources 245 (2014) 927–936. [6] C. Coutanceau, S. Baranton, Electrochemical Conversion of alcohols for hydrogen production: a short review, Wire Energy Environ 5 (2016) 388–400.

Based on previous studies of perovskites in the quasi-ternary system LaFeO3–LaCoO3–LaNiO3, La0.97Ni0.5Co0.5O3 (LNC) is chosen as the most promising air-electrode material in the series for solid oxide cells (SOCs). The properties of the material itself have been investigated in detail. However, the evaluation of LNC97 air electrodes in practical SOCs is still at a very early stage. In the present study, SOCs were prepared based on LNC97 air electrodes. The I-U performance of the SOCs in both solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) modes, i.e. reversible SOCs (r-SOCs), was investigated systematically for different air-electrode designs, temperatures and fuel gases. In general, the performance of the r-SOCs tested in the present study is higher than the published results of other LaFeO3–LaCoO3–LaNiO3-based SOCs and is comparable to or even better than state-of-the-art La1−xSrxFe1−yCoyO3 (LSCF)-based SOCs. Mid-term operation of about 1000 h for SOCs in both SOFC and SOEC modes primarily proved the stability of LNC97-based air electrodes. Impedance spectra were systematically applied to understand the polarization processes of the SOCs.

A phenomenological model describing the transport processes across a cation exchange membrane was developed. Using data obtained from conductivity, permeability and transport number experiments, the model quantified the direct and indirect influences of CuCl(aq) chemical potential and electric potential gradients on the fluxes of H+(aq), CuCl(aq) and charged species across a pressed Nafion 117 membrane in contact with 7 mol L-1 HCl(aq). This system is of particular interest for the CuCl(aq)/HCl(aq) electrolytic cell, a key component in the Cu-Cl hybrid thermochemical cycle. It was found that in highly reduced CuCl(aq) solutions, the flux of protons and charged species were influenced by the presence of copper species.

Reversible solid oxide fuel cells (RSOFCs) can operate efficiently in both fuel cell and electrolysis modes. The RSOFC has been considered for generation of electrical power from a variety of fuels and production of chemicals such as hydrogen from steam when coupled with an energy source. The RSOFC is technologically derived from the SOFC, therefore, when the cell is operated in electrolysis mode (referred to as solid oxide electrolysis cell or SOEC mode), it is critical that electrode performance is reversible and system design is configured for efficient operation in both SOEC and SOFC modes. This paper discusses certain aspects of electrode reversibility in SOEC mode for planar RSOFCs and presents a conceptual system design for electrolysis operation.

Metal-supported solid oxide electrolysis cell integrated with metal interconnect by joining process (so-called, with fuel electrode(cathode)-supported electrolysis cell) was fabricated and its electrical performance are investigated under both operation mode of fuel cell(hydrogen) and co-electrolysis(steam and CO2) mode at the intermediate temperature of 750 oC~850 oC. The fuel(or steam) electrode layers are prepared using NiO and YSZ(8 mol% Y2O3-doped ZrO2) at the ratio of 1:1. In order to obtain pores in the cathode, graphite powders of 24 volume % with average particle size of 44 mm are added. In the case of a metal-supported solid oxide electrolysis cell(SOEC) with heat-treated cathode support, 10 mol % Sm2O3-doped CeO2 (SDC) paste is screen-printed on the surface of YSZ and subsequently (La0.6Sr0.4) (Co0.2Fe0.8)O3 (LSCF) paste mixed with SDC at 1:1 weight ratio as anode(air electrode) is screen-printed on the SDC layer and heat-treated for desirable adhesion. The single electrolysis cell performances are compared by analyzing AC impedance spectra and product gas composition by GC(gas chromatography)of metal-supported electrolysis cell integrated with metal interconnect and cathode-supported electrolysis cell, and the current-voltage characteristics and cross-sectional microstructure of cathode-supported cell integrated with metal interconnect are tested. The stable long-term performance with co-electrolysis of carbon dioxide (CO2)and steam(H2O) is shown for about 800 h at 800 oC under the constant current density of 300 mA/cm2, 600 mA/cm2, 800 mA/cm2, and 1000 mA/cm2. In the fuel cell mode operation of metal-supported SOEC cell, the maximum power density of 0.8W/cm2 is indicated with hydrogen fuel. The microstructures are analyzed using optical microscope for observing a diffusion of metal ions at the cathode, adhesion layer and metal support(ferritic stainless steel, STS430) with EDAX analysis. In the present work, we have investigated the performance and microstructures of metal-supported SOEC for the co-electrolysis of CO2 and H2O steam. The exemplary works with AC impedance and the composition of product gas are analyzed in the operation of metal-supported co-electrolysis cell.

Producing methane by H2O/CO2 co-electrolysis through solid oxide electrolysis cell (SOEC) is a promising method to store unstable renewable power and reduce CO2 emission simultaneously. Theoretically, methanation reaction is possible to happen in standard condition when temperature is lower than 600oC. Tubular solid oxide electrolysis cell (TSOEC) has great potential for large-scale application due to easily sealing and high strength. Moreover, gradient distribution of temperature in flow direction is beneficial to CH4 production. In this paper, CH4 synthesis characteristics in TSOEC is studied in the temperature range of 500-650oC by combining experiment and simulation. Experiment demonstrates the addition of H2 increases the outlet molar fraction of CH4 from 0 to 2.85% at 600oC, and from 0.01% to 8.77% at 550oC. In addition, it’s found that electricity significantly promotes CH4 production, especially when H2 is added. The applied voltage of 1.5V just increases CH4 production ratio by 2. But when 20% H2 is fed in cathode, CH4 production ratio is improved by 3-4%. Finally, the optimal operating condition, thermal distribution and reaction active zones are simulated by a well validated thermal model. The thermal distribution can be changed by outer boundary condition. CH4production can be further improved by increasing the temperature of upstream zone and reducing that of downstream zone. Fig.1 Methane synthesis schematic in TSOEC Figure 1

The aim of the present work was to illuminate the catholyte-regulated catalytic oxidation performance and mechanism of the FeOOH-catalyzed heterogeneous electro-Fenton (Hetero-EF) system operating in a divided electrolytic cell. Depending on pH evolution with electrolysis time, the effect of the catholyte type on the H2O2 yield and current efficiency was investigated on an anthraquinone@electrochemically reduced grapheme oxide nanohybrid cathode. Based on the physicochemical characterization of the supported FeOOH nanoparticles, it was found that the Hetero-EF system exhibits the synchronous role of coupled adsorption and electrocatalytic oxidation for rhodamine B (RhB) degradation, with a higher apparent rate constant in MgSO4 catholyte and a higher mineralization rate in Na2SO4 catholyte. The catholyte-regulated catalytic oxidation mechanism was proposed according to radical scavenging experiments. In MgSO4 catholyte, the Hetero-EF process follows a classic Haber-Weiss mechanism mediated by

Solid Oxide Electrolysis (SOE) can be used to produce hydrogen with very high efficiencies at remarkable hydrogen production rates. Through microstructural and compositional modification, conventional low cost Solid Oxide Fuel Cell (SOFC) materials have been used to create a Solid Oxide Electrolysis Cell (SOEC) that can achieve remarkable current density at cell voltages allowing higher conversion efficiency than current commercial electrolysers. Current densities in excess of 6 A/cm2 have been achieved at 800°C with a cell voltage of < 1.67 V. This cell shows a more than 3-fold increase in hydrogen production rate at higher efficiency than established commercial electrolysers.

1. Introduction Solid oxide electrolysis cells (SOECs) are devices which can generate hydrogen from high temperature steam by electrolysis techniques. For a micro-tubular SOEC, a current collector position affects the temperature and the reactive current distributions, and these distributions affect performance and durability. Understanding the distributions is important, however, researching the distributions by only experimental methods is difficult because of thin components, small radius and high operating temperature. Therefore, combining the experiment and numerical analysis is better way to understand phenomena in the SOEC. In this study, the latter method is mainly reported. the two-dimensional tubular model of micro-tubular SOEC based on heat, mass and electric charge transfers was developed. The results of numerical analysis were compared with experimental data of micro-tubular SOEC. In addition, the conditions of co-flow and counter-flow were calculated and compared for the temperature distributions. Here, the co-flow means electron current flow is in parallel with gas flow. The counter-flow means electron current flow face gas flow. In this report, the anode gas flow is in parallel with the cathode gas flow. 2. Numerical model and analytic conditions In the model, heat, mass and electric charge transfers were calculated simultaneously. Heat and mass transfers were calculated as two-dimensional models. On the other hand, the electronic charge transfer in anode electrode (the outside of the cylinder) and all ionic charge transfer were calculated as quasi-two-dimensional models to reduce computation time. The quasi-two-dimensional models mean that one-dimensional models for radius direction were lined up to direction of length. Electronic charge transfers in the cathode electrode (the inside of the cylinder) were calculated as two-dimensional models. The anode electrode was mixed material of nickel (Ni) and yttrium stabilized zirconium (YSZ). The electrolyte was YSZ. The cathode electrode was mixed material of lanthanum strontium manganite (LSM) and YSZ. Current collectors were platinum (Pt). The thicknesses of anode electrode, electrolyte and cathode electrode were 200um, 20um and 20um, respectively. Supplied anode gas was mixed gas of hydrogen and steam (hydrogen/steam ratio = 1). Supplied cathode gas was air. The operating temperature was 1123K. Experiments for micro-tubular SOEC were carried out under the similarly conditions. 3. Results and discussions Fig. 1 shows the relationship between current density and overpotential. Fig. 2 shows the relationship between overpotential and temperature change. In Fig. 1 and 2, both experimental data and results of numerical analysis are shown. In Fig. 2, experimental data and the results of numerical analysis is different, however, tendency of temperature changes was similar. In the part of lower overpotential, temperature changes were negative because of heat absorption with electrolysis reaction. On the other hand, in the part of higher overpotential, temperature changes were positive because amount of heat generation from overpotential was higher than that of heat absorption. Fig. 3 is temperature distributions in a micro-tubular SOEC. Fig. 3(a) is positions of SOEC’s components. The current collector at the cathode was located at z = 4.0cm. Fig. 3(b) shows the distribution with co-flow condition. Fig.3(c) shows the distributions with counter-flow conditions. The maximum temperature change of co-flow condition was larger than that of counter-flow because the reactive current of the cathode was concentrated to the current collector side of the reactive area. The reactive area is range that z position is from 1.0cm to 3.0cm.

Solid oxide electrolysis cells (SOECs) have already proven their ability to electrolyze steam (H2O). Recently, the attention has been drawn towards the electrolysis of carbon dioxide (CO2). In this paper, the electrochemical reduction of CO2 over Ni–Ce0.8Sm0.2O1.9 (SDC) and Ni–8 mol% Y2O3–ZrO2(YSZ) electrodes was studied on SOEC device. Cells used in this work consist of Ni–SDC or Ni–YSZ cermet electrodes, YSZ electrolyte, and (La0.8Sr0.2)0.97MnO3 (LSM) electrode. Electrochemical properties of SOEC were evaluated by impedance spectroscopy and current–voltage (I–V) curves with a supply of CO2/H2 and pure O2 gases to the cathode and anode sides, respectively, at 1000 oC. The results of preliminary experiments indicated that in CO2/H2 mixture, CO2 reduction proceeds indirectly via kinetically fast reverse water-gas shift reaction (RWGSR, CO2 + H2 ⇌ CO + H2O). The impact of cathode material on CO2 reduction was studied as depicted in Fig. 1 (a) and (b), which shows I–V curves of single button cells employing Ni–SDC and Ni–YSZ electrodes, respectively. The cell with Ni–SDC electrode exhibited relatively high current density compared with Ni–YSZ electrode. The better performance of Ni–SDC electrode depends on the conductivity of doped ceria; it exhibits higher ionic conductivity than YSZ and shows electronic conductivity under a reducing atmosphere. These two factors are most likely extended the effective triple phase boundary (TPB) region and improved the electrochemical reactions at electrode/electrolyte interface.

Electrochemical surface finishing is a highly scalable manufacturing process that traditionally uses viscous, non-aqueous and/or highly acidic electrolytes to achieve the desired surface profiles on metallic parts, with the addition of aggressive, hazardous chemical species to remove the oxide film on strongly passive materials. An emerging approach applies pulse and pulse reverse electric fields to control current distribution, mitigate oxide film formation and achieve the desired surface finish, in the presence of environmentally benign and simple chemistries. This approach lowers the cost of the manufacturing process, and improves process robustness. After a brief discussion of electrochemical surface finishing processes, case studies that describe deburring of automotive gears and electropolishing of semiconductor valves and superconducting radio frequency cavities are presented in this article. Conventional Electrochemical Surface Finishing Processes Electrochemical surface finishing removes metal in a selective manner from the surface of the workpiece by converting the metal into ions by means of an applied electric field. This is accomplished in an electrolytic cell by applying a positive (anodic) potential to the workpiece and a negative (cathode) potential to the tool used to shape the workpiece. While fundamental investigations of electrochemical metal removal processes typically employ a 3-electrode system, a manufacturing environment is typically not conducive to the use of reference electrodes. Therefore, most electrochemical manufacturing systems are based on a two-electrode cell. Conventional electrochemical surface finishing relies heavily on the “art” of chemical mediation for process control. Under the influence of a constant electric field and controlled electrolyte flow, aggressive chemical species diffuse to the electrochemical interface and control the preferential dissolution of asperities from a surface via an electrolytic reaction, which may be generally represented as