Syngas Production from CO2 and H2O via Solid-Oxide Electrolyzer Cells: Fundamentals, Materials, Degradation, Operating Conditions, and Applications

Highly efficient coelectrolysis of CO2/H2O into syngas (a mixture of CO/H2), and subsequent syngas conversion to fuels and value-added chemicals, is one of the most promising alternatives to reach the corner of zero carbon strategy and renewable electricity storage. This research reviews the current state-of-the-art advancements in the coelectrolysis of CO2/H2O in solid oxide electrolyzer cells (SOECs) to produce the important syngas intermediate. The overviews of the latest research on the operating principles and thermodynamic and kinetic models are included for both oxygen-ion- and proton-conducting SOECs. The advanced materials that have recently been developed for both types of SOECs are summarized. It later elucidates the necessity and possibility of regulating the syngas ratios (H2:CO) via changing the operating conditions, including temperature, inlet gas composition, flow rate, applied voltage or current, and pressure. In addition, the sustainability and widespread application of SOEC technology for the conversion of syngas is highlighted. Finally, the challenges and the future research directions in this field are addressed. This review will appeal to scientists working on renewable-energy-conversion technologies, CO2 utilization, and SOEC applications. The implementation of the technologies introduced in this review offers solutions to climate change and renewable-power-storage problems.

Boosting the Electrocatalytic Activity of Pr0.5Ba0.5FeO3-δ via Ni Doping in Symmetric Solid Oxide Electrolysis Cells

Symmetric solid oxide electrolysis cells (SSOECs) have garnered significant scientific interest due to their simplified cell architecture, robust operational reliability, and cost-effectiveness, for which a highly electrocatalytically active electrode is the decisive main factor. This work evaluates the electrochemical performance of Ni-doped Pr0.5Ba0.5FeO3-δ (PBF) perovskite materials, with a focus on Pr0.5Ba0.5Fe0.8Ni0.2O3-δ (PBFN). The experimental findings herein prove the exceptional electrocatalytic ability of PBFN in facilitating the oxygen evolution and carbon dioxide reduction reaction, surpassing the electrochemical performance of PBF. In addition, the PBFN symmetric cell has excellent performance for CO2 electrolysis, and the cell has a low polarization resistance value of 0.1 Ω·cm2. Moreover, it achieves an impressive current density value of 1.118 A·cm-2 under operating conditions of 2.0 V and 800 °C, which is superior to those of the PBF symmetric cell and the PBFN asymmetric cell. It also has a good structural and performance stability. These results imply a bright development prospect of PBFN as electrodes for SSOECs.

Effect of Steam to Carbon Dioxide Ratio on the Performance of a Solid Oxide Cell for H2O/CO2 Co-Electrolysis

The mixture of H₂ and CO, the so-called syngas, is the value-added product of H₂O and CO₂ co-electrolysis and the feedstock for the production of value-added chemicals (mainly through Fischer-Tropsch). The H₂/CO ratio determines the process in which syngas will be utilized and the type of chemicals it will produce. In the present work, we investigate the effect of H₂O/CO₂ (steam/carbon dioxide, S/C) ratio of 0.5, 1 and 2 in the feed, on the electrochemical performance of an 8YSZ electrolyte-supported solid oxide cell and the H₂/CO ratio in the outlet, under co-electrolysis at 900 °C. The B-site iron doped lanthanum strontium chromite La₀.₇₅Sr₀.₂₅Cr₀.₉Fe₀.₁O_3-δ (LSCF) is used as fuel electrode material while as oxygen electrode the state-of-the art LSM perovskite is employed. LSCF is a mixed ionic-electronic conductor (MIEC) operating both under a reducing and oxidizing atmosphere. The cell is electrochemically characterized under co-electrolysis conditions both in the presence and absence of hydrogen in the feed of the steam and carbon dioxide mixtures. The results indicate that under the same concentration of hydrogen and different S/C ratios, the same electrochemical performance with a maximum current density of approximately 400 mA cm^-2 is observed. However, increasing p(H₂) in the feed results in higher OCV, smaller iV slope and R_p values. Furthermore, the maximum current density obtained from the cell does not seem to be affected by whether H₂ is present or absent from the fuel electrode feed but has a significant effect on the H₂/CO ratio in the analyzed outlet stream. Moreover, the H₂/CO ratio seems to be identical under polarization at different current density values. Remarkably, the performance of the LSCF perovskite fuel electrode is not compromised by the exposure to oxidizing conditions, showcasing that this class of electrocatalysts retains their reactivity in oxidizing, reducing, and humid environments.

The Effect of Ni-Modified LSFCO Promoting Layer on the Gas Produced through Co-Electrolysis of CO2 and H2O at Intermediate Temperatures

The co-electrolysis of CO2 and H2O at an intermediate temperature is a viable approach for the power-to-gas conversion that deserves further investigation, considering the need for green energy storage. The commercial solid oxide electrolyser is a promising device, but it is still facing issues concerning the high operating temperatures and the improvement of gas value. In this paper we reported the recent findings of a simple approach that we have suggested for solid oxide cells, consisting of the addition of a functional layer coated to the fuel electrode of commercial electrochemical cells. This approach simplifies the transition to the next generation of cells manufactured with the most promising materials currently developed, and improves the gas value in the outlet stream of the cell. Here, the material in use as a coating layer consists of a Ni-modified La0.6Sr0.4Fe0.8Co0.2O3, which was developed and demonstrated as a promising fuel electrode for solid oxide fuel cells. The results discussed in this paper prove the positive role of Ni-modified perovskite as a coating layer for the cathode, since an improvement of about twofold was obtained as regards the quality of gas produced.

Activity of La0.75Sr0.25Cr0.5Mn0.5O3−δ, Ni3Sn2 and Gd-doped CeO2 towards the reverse water-gas shift reaction and carburisation for a high-temperature H2O/CO2 co-electrolysis

LSCrM_, Ni₃Sn₂ and GDC₂₀ powders show high activity and selectivity for the RWGS reaction.

Sustainable Conversion of Carbon Dioxide: An Integrated Review of Catalysis and Life Cycle Assessment

CO₂ conversion covers a wide range of possible application areas from fuels to bulk and commodity chemicals and even to specialty products with biological activity such as pharmaceuticals. In the present review, we discuss selected examples in these areas in a combined analysis of the state-of-the-art of synthetic methodologies and processes with their life cycle assessment. Thereby, we attempted to assess the potential to reduce the environmental footprint in these application fields relative to the current petrochemical value chain. This analysis and discussion differs significantly from a viewpoint on CO₂ utilization as a measure for global CO₂ mitigation. Whereas the latter focuses on reducing the end-of-pipe problem "CO₂ emissions" from todays' industries, the approach taken here tries to identify opportunities by exploiting a novel feedstock that avoids the utilization of fossil resource in transition toward more sustainable future production. Thus, the motivation to develop CO₂-based chemistry does not depend primarily on the absolute amount of CO₂ emissions that can be remediated by a single technology. Rather, CO₂-based chemistry is stimulated by the significance of the relative improvement in carbon balance and other critical factors defining the environmental impact of chemical production in all relevant sectors in accord with the principles of green chemistry.

Synthesis of mesoporous nanocomposites for their application in solid oxide electrolysers cells: microstructural and electrochemical characterization

Fabrication routes for new SOEC mesoporous nanocomposite materials as electrodes are presented in this paper. NiO-CGO and SDC-SSC are described as possible new materials and their synthesis and the cell fabrication are discussed. The obtained materials are microstructurally characterised by SEM, TEM and XRD, where the mesoporous structures are observed and analysed. The obtained samples are electrochemically analysed by I-V polarisation curves and EIS analysis, showing a maximum current density of 330 mA cm(-2) at 1.7 V. A degradation of the cell performance is evidenced after a potentiostatic test at 1.4 V after more than 40 hours. Oxygen electrode delaminating is detected, which is most probably the main cause of ageing. Even taking into account the lack of durability of the fabricated cells, the mesoporous electrodes do not seem to be altered, opening the possibility for further studies devoted to this high stability material for SOEC electrodes.