High Temperature Co-electrolysis Research Articles

Life Cycle Assessment of Power-to-Syngas: Comparing High Temperature Co-Electrolysis and Steam Methane Reforming

To achieve the European Union's ambitious climate targets, not only the energy system must be transformed, but also other sectors such as industry or transport. Power-to-X (PtX) technologies enable the production of synthetic chemicals and energy carriers using renewable electricity, thus contributing to defossilization of economy. Additionally, they provide storage capacity for renewable energy. Detailed life cycle assessments (LCA) of PtX is required, to prove the environmental advantages to fossil-based benchmark technologies. An emerging PtX technology for syngas production is the high temperature co-electrolysis (HT-co-electrolysis), which produces syngas. Aim of this LCA is the evaluation of syngas production by HT-co-electrolysis at its early stage of development to derive incentives for further research. For comparison, a small-scale steam methane reforming process (SMR) serves as today’s fossil-based benchmark. The required CO2 is obtained via direct air capture (DAC). The by-far most important input for the HT-co-electrolysis is electricity. Hence, several future electricity mixes are considered, representing two different climate protection targets (CPT80, CPT95) for the energy system in 2050. For each CPT, an additional distinction is made regarding full load hours, which depend on the availability of renewable energy. The results show lower global warming potential (GWP) and fossil fuel depletion for HT-co-electrolysis compared to SMR if mostly renewable power is used. Exclusively renewable operated HT-co- electrolysis even achieve negative net GWPs in cradle-to-gate LCA without considering syngas use. If HT-co-electrolysis shall operate continuously (8760 h) additional fossil electricity production is needed. For CPT80, the share of fossil electricity is too high to achieve negative net GWP in contrast to CPT95. Other environmental impacts such as human toxicity, acidification, particulate matter or metal depletion are worse in comparison to SMR. The share of DAC on the total environmental impacts is quite noticeable. Main reasons are high electricity and heat demands. Although plant construction contributes to a minor extent to most impact categories, a considerable decrease of cell lifetime due to higher degradation caused by flexible operation, would change that. Nevertheless, flexibility is one of the most important factors to apply PtX for defossilization successfully and reinforce detailed research to understand its impacts.

Direct Solid Oxide Electrolysis of Carbon Dioxide: Analysis of Performance and Processes

Chemical industries rely heavily on fossil resources for the production of carbon-based chemicals. A possible transformation towards sustainability is the usage of carbon dioxide as a source of carbon. Carbon dioxide is activated for follow-up reactions by its conversion to carbon monoxide. This can be accomplished by electrochemical reduction in solid oxide cells. In this work, we investigate the process performance of the direct high-temperature CO2 electrolysis by current-voltage characteristics (iV) and Electrochemical Impedance Spectroscopy (EIS) experiments. Variations of the operation parameters temperature, load, fuel utilization, feed gas ratio and flow rate show the versatility of the procedure with maintaining high current densities of 0.75 up to 1.5 A·cm−2, therefore resulting in high conversion rates. The potential of the high-temperature carbon dioxide electrolysis as a suitable enabler for the activation of CO2 as a chemical feedstock is therefore appointed and shown.

Coke formation during high-temperature CO2 electrolysis over AFeO3 (A = La/Sr) cathode: Effect of A-site metal segregation

In this study, strontium-doped lanthanum ferrite perovskite oxides (LSF) with different A-site occupancies were used as cathode catalysts for CO2 electrolysis at 800 °C. XRD, EXAFS, XPS, FTIR, and temperature-programmed desorption were used to characterize the properties of the material. Fe K-edge EXAFS indicated that oxygen vacancy concentration and oxidation states of Fe atoms increased with concomitant improvement of electronic and ionic conductivities with a decrease in the A-site occupancy. XPS spectra revealed that Sr atoms segregated on the surface of A-site excess LSF92 to a greater degree than that on the A-site deficient LSF72. These segregated A-site metal oxides, especially SrO, are alkaline in nature and hence strongly bind to acidic CO2 forming stable SrCO3, which consequently facilitates carbon formation. This study highlights the effect of A-site stoichiometric modulation on carbon formation during electrolysis of CO2, which is crucial for improving the long- term performance of an SOEC.

Developments in CO2 Electrolysis of Solid Oxide Electrolysis Cell with Different Cathodes▴

AbstractSolid oxide electrolysis cell (SOEC) is a device that can efficiently convert excessive power of renewable energy, such as wind or solar energy into chemical energy. High temperature CO2 electrolysis based on solid oxide electrolysis cell has been proved as an effective method to produce sustainable fuels and reduce greenhouse emissions. The performance of cathodes as the place where the electrolysis reaction takes place for fuel gas affects the efficiency of SOEC, whereas traditional cathodes show relatively low catalytic activity towards CO2 electrolysis. In recent years, in addition to the optimization of traditional Ni‐based cathodes, the research on perovskite cathodes with better redox stability has been carried out rapidly. In this paper, the development of different cathodes of solid oxide electrolysis cell used for CO2 electrolysis is summarized, from the study of new materials with different doping ratios for CO2 electrolysis, to the microstructure optimization of electrode. It was found, that both durability and catalytic activity for the cathode materials could significantly improve the performance of single cells of SOEC. Finally, more prospects for future research work are put forward.

Integration of water electrolysis for fossil-free steel production

This study investigates the integration of water electrolysis technologies in fossil-free steelmaking via the direct reduction of iron ore followed by processing in an electric arc furnace (EAF). Hydrogen (H2) production via low or high temperature electrolysis (LTE and HTE) is considered for the production of carbon-free direct reduced iron (DRI). The introduction of carbon into the DRI reduces the electricity demand of the EAF. Such carburization can be achieved by introducing carbon monoxide (CO) into the direct reduction process. Therefore, the production of mixtures of H2 and CO using either a combination of LTE coupled with a reverse water-gas shift reactor (rWGS-LTE) or high-temperature co-electrolysis (HTCE) was also investigated. The results show that HTE has the potential to reduce the specific electricity consumption (SEC) of liquid steel (LS) production by 21% compared to the LTE case. Nevertheless, due to the high investment cost of HTE units, both routes reach similar LS production costs of approximately 400 €/tonne LS. However, if future investment cost targets for HTE units are reached, a production cost of 301 €/tonne LS is attainable under the conditions given in this study. For the production of DRI containing carbon, a higher SEC is calculated for the LTE-rWGS system compared to HTCE (4.80 vs. 3.07 MWh/tonne LS). Although the use of HTCE or LTE-rWGS leads to similar LS production costs, future cost reduction of HTCE could result in a 10% reduction in LS production cost (418 vs. 375 €/tonne LS). We show that the use of HTE, either for the production of pure H2 or H2 and CO mixtures, may be advantageous compared to the use of LTE in H2-based steelmaking, although results are sensitive to electrolyzer investment costs, efficiencies, and electricity prices.

Methanol as a carrier of hydrogen and carbon in fossil-free production of direct reduced iron

Abstract Steelmaking is responsible for around 7% of the global emissions of carbon dioxide and new steelmaking processes are necessary to reach international climate targets. As a response to this, steelmaking processes based on the direct reduction of iron ore by hydrogen produced via water electrolysis powered by renewable electricity have been suggested. Here we present a novel variant of hydrogen-based steelmaking incorporating methanol as a hydrogen and carbon carrier together with high-temperature co-electrolysis of water and carbon dioxide and biomass oxy-fuel combustion. The energy and mass balances of the process are analyzed. It is found that this methanol-based direct reduction process may potentially offer a number of process-related advantages over a process based on pure hydrogen, featuring several process integration options. Notably, the electricity and total energy use of the steelmaking process could be reduced by up to 25% and 8% compared to a reference pure-hydrogen process, respectively. The amount of high-temperature (>200 °C) heat that must be supplied to the process could also be reduced by up to approximately 34%, although the demand for medium-temperature heat is substantially increased. Furthermore, the suggested process could allow for the production of high-quality direct reduced iron with appropriate carburization to alleviate downstream processing in an electric arc furnace, which is not the case for a process based on pure hydrogen.

High-Temperature Co-Electrolysis

High-temperature Solid Oxide Electrolysis Cells (SOECs) possess the unique property to convert carbon dioxide and/or steam with a faradaic efficiency of 1 into carbon monoxide and/or hydrogen, respectively. High-temperature co-electrolysis of steam and carbon dioxide offers a suitable technology to provide 'white' syngas. Syngas, a mixture of hydrogen and carbon monoxide, as well as pure carbon monoxide are used in chemical industry for the synthesis of many basic chemicals as well as synfuels. Using renewable energy sources and the climate gas CO2 the high-temperature CO2 and co-electrolysis technology presents a sustainable alternative to conventional processes. The technology of co-electrolysis allows the adjustment of the H2 to CO ratio required for various down-stream catalytic processes in one step.Investigations of the high-temperature electrolysis of steam or CO2 and the co-electrolysis of a mixture of both in the feed gas were performed on so-called fuel electrode supported cells consisting of a 8mol% yttria stabilized zirconia (8YSZ) electrolyte, a Ni/8YSZ support and fuel electrode and a (La,Sr)(Co,Fe)O3 air electrode. The experiments showed that the performance of the cell during CO2 electrolysis is lower than for steam and co-electrolysis, as is shown in the Figure. The performance can be characterized by the slope of the current-voltage curve, i.e. the area specific resistance (ASR). For the CO2 electrolysis the ASR at 900 °C and 1.5 A·cm-2 amounts to 410 mΩ·cm-2. For steam and co-electrolysis, the ASR values are nearly the same: 245 mΩ·cm-2. The lower performance for CO2 electrolysis is attributed to the slower kinetics of the CO2 reduction reaction compared to the H2O reduction reaction. Similar observations were made in fuel cell operation, in which the CO oxidation reaction is around a factor 5 slower than the H2 oxidation reaction. The similar ASR values for steam and co-electrolysis are attributed to the occurrence of the reverse water gas shift (RWGS) reaction, in which CO2 and H2 react to CO and H2O during co-electrolysis. The slower kinetics of the CO2 reduction reaction are by-passed in the RWGS reaction using the hydrogen generated through the steam reduction.Further experiments were conducted to investigate the role and importance of the RWGS reaction during co-electrolysis. At the boundary to pure CO2 electrolysis, the performance of feed gas mixtures with low steam contents were investigated. First results show a significant increase of the area specific resistance at a reduced (RWGS) equilibrium steam concentration of about 5 %. Above 15 % steam in the feed gas (in the RWGS equilibrium) the ASR is no longer influenced by the feed gas composition and similar to that of pure steam electrolysis. Experimental results are furthermore compared to theoretical calculations of syngas production on a thermodynamic and partially kinetic level. Figure 1

(Invited) Ruddlesden-Popper-Type Oxides As Air Electrodes for Solid Oxide Electrolyzer Cells

Ruddlesden-Popper-type oxides are promising air electrode materials for solid oxide fuel cells (SOFCs) and electrolyser cells (SOECs). Within the Ruddlesden-Popper (RP) series Lnn+1BnO3n+1, first order (n=1) RP-type rare earth nickelates with Ln=La, Nd, Pr and B=Ni show high oxygen diffusivities, high catalytic activity for the oxygen reduction reaction as well as good electronic and ionic conductivities [1]. In order to further improve the surface oxygen exchange kinetics, the effect of partial substitution of Ni by Co on the B-site in Pr2NiO4+δ was studied, similar to an earlier report for the La2NiO4+δ system [2].Structure-composition-property–relationships were examined for the Pr2NiO4+δ system. The effect of A-site substitution of Pr with La as well as B-site substitution of Ni with Cobalt was investigated with respect to crystal structure, thermodynamic stability, oxygen non-stoichiometry, electronic conductivity as well as oxygen surface exchange and transport properties. Moreover, differences in functional properties between Ruddlesden-Popper phases of different order within the same compositional system were studied. In cases where material characterisation was problematic due to difficulties in obtaining densely sintered samples with high phase purity (including of third-order RP-Phases), electrochemical impedance spectroscopy (EIS) measurements on microelectrodes were applied in order to obtain reliable results for oxygen surface exchange rates. Oxygen surface exchange coefficients kq and kδ could be calculated from surface resistances and chemical capacitances of the thin-film electrodes between 550 and 850°C. Substitution of Ni by 10% of Co in Pr2NiO4+δ results in increased oxygen surface exchange rates expecially at lower oxygen partial pressures [3]. Performance tests with Pr2Ni0.9Co0.1O4+δ SOEC air electrodes for water electrolysis were conducted on anode supported full cells at 800°C at OCV conditions and in electrolyser mode up to current densities of 1000 mA cm-2. For anode supported cells, an electrode-electrolyte composite was used as functional anode layer in order to improve adhesion and avoid delamination issues. Moreover, the long-term stability and resistance against Cr-poisoning was examined by electrochemical impedance spectroscopy and current-voltage measurements on symmetrical cells at 800°C in dry and humid atmospheres. A three-electrode configuration allowed to analyse the time dependence of the air electrode polarization resistance during the SOFC as well as SOEC operation mode. Compared to La2NiO4+δ, a reduced susceptibility for Cr-poisoning was found for Pr2Ni0.9Co0.1O4+δ over a period of 1000 hours in SOEC operation.The development of high-performance SOEC air electrodes is part of the Austrian integrated project HydroMetha. This project combines high-temperature co-electrolysis of CO2 and H2O by solid oxide cells with catalytic methanation in order to enable storage of electrical energy from fluctuating renewable sources with high overall efficiency.

Pd single site-anchored perovskite cathode for CO2 electrolysis in solid oxide electrolysis cells

Pd single site-anchored La0.5Sr0.5FeO3-δ-Ce0.8Sm0.2O2-x (Pd-LSF(SDC)) cathode is constructed for CO2 electrolysis in solid oxide electrolysis cells. The decoration of Pd species on LSF greatly improves CO2 electrolysis performance with 65.7% enhancement in current density at 1.6 V compared with the LSF counterpart. Electrochemical and density functional theory calculation results suggest that the Pd species are atomically anchored on the LSF phase. The coordinatively unsaturated Pd with oxygen vacancies facilitates the CO2 dissociative adsorption, electron transfer and mass transport, thus greatly decreases the polarization resistance of the cathode and promotes the CO2 electrolysis performance. This work provides an effective strategy to design the supported single site catalyst for high-temperature CO2 electrolysis.

A-site deficient perovskite with nano-socketed Ni-Fe alloy particles as highly active and durable catalyst for high-temperature CO2 electrolysis

The solid oxide electrolysis cell (SOEC) has attracted increased attention in recent years due to its capability to reduce CO2 emissions in a highly efficient and environmentally sustainable fashion. Previous work in our group has fabricated an A-site Ce doped La0.7Sr0.3Cr0.5Fe0.5O3-δ (LSCrF) with gadolinium doped ceria (GDC) as the cathode material in SOEC by the conventional method. This composite cathode presents a satisfying electrochemical performance and good stability due to the presence of excessive oxygen vacancies and strong CO2 adsorption ability. However, its electrochemical catalytic activity is still limited by the catalyst specific area. Hence, the optimization of electrode microstructure is considered as a promising way to further improve the SOEC performance by increasing the active reaction area. In this study, highly active (La0.65Sr0.3Ce0.05)0.9(Cr0.5Fe0.5)0.85Ni0.15O3-δ (Ni-LSCeCrF)/GDC nanostructured cathode was successfully fabricated by incorporating infiltration and in situ exsolution processes. The optimized microstructure contains fine and uniformly distributed perovskite particles on GDC backbone with nano-socketed Ni-Fe alloy nanoparticles. The Ni-LSCeCrF/GDC cathode shows significantly improved electrochemical performance, CO production rate, and Faraday efficiency for CO2 reduction reaction. Furthermore, the density functional theory calculations show that Ni doping could reduce the segregation energy of Fe, revealing a new strategy of multiple elements doping to form active alloy by in situ exsolution.

Optimal system layout and locations for fully renewable high temperature co-electrolysis

High temperature co-electrolysis can be a promising technology for the transformation of energy systems as it enables sector coupling and carbon dioxide utilization. In this article, we analyze the optimal layout and operation of distributed electrolysis sites powered exclusively by local renewable energy sources and a local battery storage device for current techno-economic parameters. For this purpose an energy system model with a spatial resolution of 277 regions within Europe is set up, which facilitates the analysis of intermittent renewable electricity generation, a battery storage device and the innovative high temperature co-electrolysis. We discuss the techno-economic competitiveness and analyze potential leverage points for improvement such as an enhanced flexibility. The lowest costs are found in Lincolnshire with 0.24 €/kWh and the highest costs in Central Slovakia with 0.49 €/kWh differing by more than a factor of two. Remarkably, several locations with vastly different resources and layouts lead to a similar techno-economic performance of the investigated system. We compare the techno-economic performance of high temperature co-electrolysis with steam methane reforming as the conventional synthesis gas production route.

Insight into high electrochemical activity of reduced La0·3Sr0·7Fe0·7Ti0·3O3 electrode for high temperature CO2 electrolysis

Electrochemical reduction of CO2 under the high temperature electrolysis condition with favored kinetics is a promising method to utilize and convert CO2 to valuable chemicals and to reduce its environmental impact. In this work, the electrochemical performance of perovskite-type La0·3Sr0·7Fe0·7Ti0·3O3 (LSFT) oxide was thoroughly investigated as a cathode for high temperature solid oxide electrochemical reduction under practical CO2 electrolysis conditions of various current densities, partial pressures, and different CO–CO2 mixtures. The rate-limiting step of CO2 reduction on the LSFT surface was determined by the electrochemical impedance spectroscopy technique with a three-electrode configuration. The exceptional performance of LSFT cathode is confirmed as reflected by the low polarization resistance and the extremely low activation energy. Moreover, improved electrode performance is also obtained on the reduced LSFT sample under reducing atmosphere with CO, while the rate-determining step is not changed. It is also confirmed that the reduced LSFT cathode gives increased surface oxygen vacancy concentration which is believed to serve as accommodation for chemical adsorption and consequently the active sites for electrochemical activation of CO2, leading to the improved electrochemical performance.

Scaling up syngas production with controllable H2/CO ratio in a highly efficient, compact, and durable solid oxide coelectrolysis cell unit-bundle

High-temperature coelectrolysis of H2O and CO2 by using solid oxide coelectrolysis cells (SOC) is considered to be among the most efficient processes for CO2 conversion as these SOCs can efficiently utilize both heat and renewable electrical energy. One of the key components is the development of highly efficient, modular SOC cells and stacks to further scale up the CO2 conversion process towards industrial applications. In this study, we developed highly efficient and durable flat-tubular solid oxide coelectrolysis cells (FT-SOCs) and investigated the electrochemical performance (I-V, EIS, long-term galvanostatic test) of single cells and a 6-cell bundle for CO2-H2O coelectrolysis to produce syngas with controllable H2/CO ratios. The FT-SOC with an active area of 40 cm2 reached a maximum current density of −3.2A/cm2 at 1.6 V at 800 °C and an H2O/CO2 ratio of 2. In the 6-cell FT-SOC bundle, 90% CO2 conversion was achieved by producing high-quality syngas with flexible H2/CO ratios and stable long-term operation for continuous 500 h. The results of this study show that by using an FT-SOC bundle, scalable and controllable syngas quality could be produced and integrated with the multitude of downstream processes.

Study of CO2 and H2O direct co-electrolysis in an electrolyte-supported solid oxide electrolysis cell by aqueous tape casting technique

High temperature co-electrolysis based on Solid Oxide Electrolysis Cell (SOEC) is a very promising method to produce sustainable fuels and reduce greenhouse emissions. In this paper, the electrolyte-supported LSCM-GDC/SSZ/LSCF-GDC (LSCM: La0.75Sr0.25Cr0.5Mn0.5O3+δ) single cells are prepared and evaluated for high temperature steam and carbon dioxide direct co-electrolysis. And the fabrication of electrolyte layer is used with aqueous tape casting technique, which contributes to form a flat electrolyte layer with lower ohmic resistance in an eco-friendly way. LSCM fuel electrode exhibits good properties of redox stability and catalytic performance. During the experiment, different temperatures and volume ratios of H2O/CO2 are introduced into the cell to evaluate the electrochemical performance. In order to further verify the long-term performance of the cell, durability constant current SOEC test is carried out and the cell showed a stable voltage of 1.5 V for more than 100 h and throughout the duration of co-electrolysis. The results show that the electrolyte-supported SOEC using aqueous tape casting technique has good electrochemical performance and stability.

Selective high-temperature CO2 electrolysis enabled by oxidized carbon intermediates

High-temperature CO2 electrolysers offer exceptionally efficient storage of renewable electricity in the form of CO and other chemical fuels, but conventional electrodes catalyse destructive carbon deposition. Ceria catalysts are known carbon inhibitors for fuel cell (oxidation) reactions; however, for more severe electrolysis (reduction) conditions, catalyst design strategies remain unclear. Here we establish the inhibition mechanism on ceria and show selective CO2 to CO conversion well beyond the thermodynamic carbon deposition threshold. Operando X-ray photoelectron spectroscopy during CO2 electrolysis—using thin-film model electrodes consisting of samarium-doped ceria, nickel and/or yttria-stabilized zirconia—together with density functional theory modelling, reveal the crucial role of oxidized carbon intermediates in preventing carbon build-up. Using these insights, we demonstrate stable electrochemical CO2 reduction with a scaled-up 16 cm2 ceria-based solid-oxide cell under conditions that rapidly destroy a nickel-based cell, leading to substantially improved device lifetime. CO2 electrolysers store electricity as CO or other chemical fuels, but can suffer from carbon deposition at the electrodes. Skafte et al. identify a mechanistic route to inhibiting carbon build-up in ceria-based electrolysers and build a cell that operates beyond the thermodynamic carbon deposition threshold.

White Syngas by Co-Electrolysis for Industrial Chemistry

White syngas is produced by co-electrolysis of carbon dioxide and water. As syngas is one of the essential petrochemical foundations of industrial chemistry, the high temperature co-electrolysis can induce a possibility for the defossilization process in conventional petro chemistry. Therefore, it is necessary to discuss the proper technological framework in the scopes of supply of CO2, electrochemical performance of Solid Oxide Electrolysis Cells (SOEC) and products of white syngas. In future Power-to-X scenarios with a 100 % share of renewable energy, it is fundamentally important to calculate process-related carbon dioxide emissions from the total CO2 emissions. Also, we show the superior performance of co-electrolysis to different electrolysis technologies. As a standard of comparison, we introduce the Fossil Carbon Equivalent (FCE) to clarify the impact of white syngas on industrial chemistry by matching energy demand, need of installed electrolysis capacities, consumption of carbon dioxide and substitutable amount of fossil resources.

Synthesis and Evaluation of the A-Site Deficient Perovskite La0.65Sr0.3Cr0.85Ni0.15O3-δ as Fuel Electrode for High Temperature Co-Electrolysis Enhanced by In Situ Exsolution of Ni Nanoparticles

Lanthanum strontium chromite (LSC) perovskite partially doped with 15% of Ni on the B-site as reducible transition metal was investigated with the aim to perform in situ exsolution under reducing conditions. A-site deficient compounds were formulated to enhance the exsolution of the electrocatalyst. Single phase is achieved with the formulation La0.65Sr0.3Cr0.85Ni0.15O3-δ (L65SCN) and has been characterized by X-ray diffraction (XRD), Rietveld refinement and scanning electron microscopy (SEM). Exsolution was investigated under reducing conditions in which Ni exsolution was confirmed. Such electrocatalyst was implemented into an electrolyte-supported-cell (ESC) for early electrochemical investigation. Cells were manufactured by screen printing of composite L65SCN/CGO as fuel electrode and La0.58Sr0.4Fe0.8Co0.2O3-δ (LSCF) as air electrode on CGO-3YSZ-CGO substrates. These cells were characterized in steam electrolysis at 930°C by Electrochemical Impedance Spectroscopy (EIS). Further microstructural engineering and fine tuning of the manufacturing parameters are essential for a practical use of this electroctalyst for H2O/CO2 co-electrolysis operation.

High-Temperature CO2 Electrolysis in Solid Oxide Electrolysis Cells: Developments, Challenges, and Prospects.

High-temperature CO2 electrolysis in solid-oxide electrolysis cells (SOECs) could greatly assist in the reduction of CO2 emissions by electrochemically converting CO2 to valuable fuels through effective electrothermal activation of the stable CO bond. If powered by renewable energy resources, it could also provide an advanced energy-storage method for their intermittent output. Compared to low-temperature electrochemical CO2 reduction, CO2 electrolysis in SOECs at high temperature exhibits higher current density and energy efficiency and has thus attracted much recent attention. The history of its development and its fundamental mechanisms, cathode materials, oxygen-ion-conducting electrolyte materials, and anode materials are highlighted. Electrode, electrolyte, and electrode-electrolyte interface degradation issues are comprehensively summarized. Fuel-assisted SOECs with low-cost fuels applied to the anode to decrease the overpotential and electricity consumption are introduced. Furthermore, the challenges and prospects for future research into high-temperature CO2 electrolysis in SOECs are included.

Active and stable Ni/Cr2O3-δ cathodes for high temperature CO2 electrolysis

To reduce greenhouse effects, reduction of CO2 in solid oxide electrolyser has attracted considerable attentions. Herein, a series of metallic nickel cathodes with in situ grown Cr2O3-δ nano-islands are developed for CO2 electrolysis at high temperature. Enhanced CO2 chemisorption is observed with distributed Cr2O3-δ nanoparticles on porous nickel backbone while the adsorption mechanism is discussed. The optimal current density of 2.07 A cm−2 is harvested when using Ni/12.20% Cr2O3-δ as cathode in CO2/CO atmosphere at 800 °C and 1.6 V. Long-term stability is achieved for either CO2/CO or pure CO2 electrolysis even after high-temperature operation of 50 h, indicating that the Ni/Cr2O3-δ would be an attractive cathode for CO2 electrolysis at high temperature.

CO2 and H2O Electrolysis Using Solid Oxide Electrolyzer Cell (SOEC) with La and Cl- doped Strontium Titanate Cathode

The average CO2 concentration in atmosphere increased by 25 ppm in the last decade, and during the same period, the average global surface level temperature rose by 0.3 °C. CO2, one of the biggest contributors to climate change, is a greenhouse gas that traps the energy emitted by the earth’s surface, causing an increase in the temperature. Because of the greenhouse effect of CO2, a growing area of research is trying to find ways to minimize CO2 emission and decrease the CO2 concentration in the atmosphere. Besides reducing the CO2 emission, it is also important to develop technologies to convert CO2 into valuable products. One such product is syngas, a mixture of carbon monoxide and hydrogen that can be used as fuel, as well as for synthesis of hydrocarbons through Fischer–Tropsch synthesis. Intermediate and high temperature co-electrolysis of CO2 and water using Solid Oxide Electrolyzer Cell (SOEC) is a promising method to produce syngas from CO2. This work focuses on the use of La0.2Sr0.8TiO3±δClσ as an SOEC cathode for CO2 and H2O co-electrolysis, and its activity compared with conventional SOFC electrode material, Ni/NiO-YSZ. Electrocatalytically, it was found that Ni/NiO-YSZ outperforms La0.2Sr0.8TiO3±δClσ when only CO2 is reduced, however, La0.2Sr0.8TiO3±δClσ shows higher activity for co-electrolysis of CO2 and H2O. Post-reaction temperature-programmed oxidation testing performed on the co-electroylsis cells demonstrated less coking associated with La0.2Sr0.8TiO3±δClσ than Ni/NiO-YSZ, although both materials showed relatively lower levels of coking when H2O was not present. Interactions between the surfaces of these materials and CO2 were characterized using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and Raman spectroscopy. These showed that CO2 interacts more strongly with La0.2Sr0.8TiO3±δClσ than Ni/NiO-YSZ, forming carbonate species on the surface. The electrical conductivity of the materials was also compared, and while Ni/NiO-YSZ showed slightly higher values, the electrical conductivity of La0.2Sr0.8TiO3±δClσ increased more rapidly with temperature and was in the same order of magnitude as that of Ni/NiO-YSZ.