Status and outlook of solid electrolyte membrane reactors for energy, chemical, and environmental applications

Abstract

Solid electrolyte membrane reactors (SEMRs) can be operated at high temperatures with distinct reaction kinetics, or at lower temperatures (300-500 °C) for industrially relevant energy applications (such as solid oxide fuel/electrolysis cells, direct carbon fuel cells, and metal-air batteries), chemical (such as alkane dehydrogenation, C-C coupling, and NH₃ synthesis), environmental (De-NO _x , CO₂ utilization, and separation), as well as their combined (one-step coupled CO₂/H₂O co-electrolysis and methanation reaction, power and chemical cogeneration) applications. SEMRs can efficiently integrate electrical, chemical, and thermal energy sectors, thereby circumventing thermodynamic constraints and production separation issues. They offer a promising way to achieve carbon neutrality and improve chemical manufacturing processes. This review thoroughly examines SEMRs utilizing various ionic conductors, namely O^2-, H⁺, and hybrid types, with operations in different reactor/cell architectures (such as panel, tubular, single chamber, and porous electrolytes). The reactors operate in various modes including pumping, extraction, reversible, or electrical promoting modes, providing multiple functionalities. The discussion extends to examining critical materials for solid-state cells and catalysts essential for specific technologically important reactions, focusing on electrochemical performance, conversion efficiency, and selectivity. The review also serves as a first attempt to address the potential of process-intensified SEMRs through the integration of photo/solar, thermoelectric, and plasma energy and explores the unique phenomenon of electrochemical promotion of catalysis (EPOC) in membrane reactors. The ultimate goal is to offer insight into ongoing critical scientific and technical challenges like durability and operational cost hindering the widespread industrial implementation of SEMRs while exploring the opportunities in this rapidly growing research domain. Although still in an early stage with limited demonstrations and applications, advances in materials, catalysis science, solid-state ionics, and reactor design, as well as process intensification and/or system integration will fill the gaps in current high temperature operation of SEMRs and industrially relevant applications like sustainable clean chemical production, efficient energy conversion/storage, as well as environmental enhancement.

Fig. 1. The working principle of a SEMR for versatile energy, chemical, and environmental applications.

Fig. 2. A schematic illustration of outlining the focus of this work.

Fig. 3. The proposed cell structure design for coupling the low temperature F–T process and high temperature co-electrolysis process. Reproduced with permission.

Fig. 4. Thermodynamic calculation of the required energy for CO₂–H₂O co-electrolysis without (a) and with (b) carbon fuel in the anode, (c) comparison of the I–V curves of the electrolysis cell, and (d) temperature-dependence of anode outlet gas composition. Reproduced with permission.

Fig. 5. (a) Schematic illustration of the CH₄-assisted CO₂ electrolysis based on the SOECs with the symmetric electrode, (b) comparison of the CO₂ chemical adsorption at 800 °C using in situ FTIR spectroscopy on Ni and Cu co-doped LSCM materials, (c and d) SEM and TEM images of the NiCu alloy precipitation on the LSCM substrate, (e) comparison of the I–V curves and (f) H₂/CO flowing rate of the outlet gas in FAE with various electrode materials. Reproduced with permission (open access).

Fig. 6. (a) Schematic illustration of the coupling of electrochemical oxidative dehydrogenation of ethane and CO₂ electrolysis into an SOEC and TEM image of the LSCF–SDC anode infiltrated with γ-Al₂O₃, and electrochemical performance of SOEC under different operational conditions: (b) with different anodes at a current of 20 mA and ethane flow rate is 4 mL min⁻¹, (c) at different currents with the ethane flow rate of 4 mL min^—1, (d) at different ethane flow rates and a current of 60 mA on the LSCF–SDC + Al₂O₃ anode and (e) stability test at a current of 20 mA and ethane flow rate of 4 mL min⁻¹. Reproduced with permission.

Fig. 7. (a) Schematic diagram of integrating the CO₂ electrolysis with the OCM process in a successive two-stage reactor design, (b) SOEC performance and (c) durability comparison. Reproduced with permission.

Fig. 8. Schematic illustration of the electrochemical synthesis of NH₃ from NO and H₂O using oxygen-conducting SEMRs and the comparison of NH₃ yield with other studies operated at low to higher temperatures. Reproduced with permission.

Fig. 9. Publication numbers vs. time in Web of Science database by searching for “Cogeneration” and “solid oxide fuel cells” both in “Topic”, up to Jun. 01, 2024.

Fig. 10. (a) Schematics of a Ce_0.90Ni_0.05Ru_0.05O₂ catalytic layer modified classic BZCYYb SOFC, (b) cross-sectional SEM image, (c) the synergistic effect of Ni and Ru element for CH₄ and CO₂ activation using DFT calculations, (d) fuel cell performance, and (e) durability. Reproduced with permission.

Fig. 11. Different strategies for CH₄-fed SEMRs for power and syngas cogeneration: (a) single chamber-SEMR integration with a downstream catalytic partial reformer and (b) thermal and catalytic coupling within the SEMR anode. Reproduced with permission from ref. and .

Fig. 12. Schematic illustration of electricity–gas cogeneration in DCFC: (a) single cell and (b) the corresponding exhausted gas composition and power response to the operating time of 2-cell stack operated at 2 A, at 800 °C and (c) electrical efficiency and overall conversion efficiency of the cells operated with different current at 800 °C. Reproduced with permission from ref. .

Fig. 13. (a) Cell structure, working principle and cycling performance with different anode fuel materials at U_Fe = 50% and 0.2C (10 mA cm⁻²) at 550 °C (b) and 500 °C (c) of a solid oxide iron–air battery. Reproduced with permission (open access).

Fig. 14. (a) Schematic illustration of an RSOC, comparison of (b) voltage and (c) impedance spectra responses of an SOC during a constant-current electrolysis test, and a reversible cycling test. Reproduced with permission.

Fig. 15. The different working principles of H-SEMRs: (a) fuel cell, (b) electrolyzer cell, (c) CO₂/H₂O co-electrolysis, and (d) co-electrolysis reactor based on co-ionic conductor. Reproduced with permission.

Fig. 16. Co-ionic conductive SEMRs for CH₄ to aromatics conversion: (a) tubular cell configuration and material system, (b) SEM image of MEA based on BZCY electrolyte, (c) percentage of H₂ extracted and O₂ injected versus current density at 700 °C, (d) aromatic yields vs. time and (e) CH₄ conversion. Reproduced with permission.

Fig. 17. (a) Schematic preparation procedures of NiCo/PBM catalyst selectively loading on BZCYYb in the porous nickel cermet anode, (b) the role of PBM nanocatalyst and Ni in cermet, (c) electrochemical performance of PCFCs fed with 50 ppm H₂S–CH₄/CO₂ fuel using different fuel electrodes and (d) the exhaust gas compositions of FC-NiCo/PBM during continuous 36 h testing. Reproduced with permission.

Fig. 18. Ethane dehydrogenation using H-SEMRs. (a) Schematic of applied reactors and cell components, (b) a cross-sectional SEM image of an actual electrochemical cell, (c) the corresponding voltage and (d) durability test at a current density of 1 A cm⁻² as a function of time, and a comparison of the (e) process energies and (f) carbon footprint for ethylene production from ethane based on electrochemical and industrial steam cracker processes. Reproduced with permission.

Fig. 19. (a) Schematic illustration of the possible electrochemical and chemical reactions during electrolysis and upgrading CO₂–H₂O into CH₄ in the PCEC (b), (c–e) one pass CO₂ conversion, CH₄ selectivity, and CH₄ yields at 400–550 °C, and (f) with H₂ recycling at 450 °C. Reproduced with permission.

Fig. 20. Schematic diagrams of the working principles of (a) O-SOEC, (b) H-SOEC, (c) hybrid-SOEC, and (d–f) electrochemical performance and comparison with the literature work and other electrolysis systems. Reproduced with permission.

Fig. 21. Different SEMR design based on SC-SOFCs with/without catalyst components in tubular structures: (a) all flow-through mode, (b) first cathode chamber then anode chamber, (c) similar to mode b but with catalyst at the inlet of anode chamber and (d) similar to mode c with additional catalyst at the outlet of the anode chamber. Reproduced with permission.

Fig. 22. Novel SEMR (SOFC) design: (a) the micro–monolithic anode support incorporating 6 sub-channels with droplet shapes, (b) full structure simulation, (c) utilizing LCVGs with reactions at triple-phase boundaries, and (d) power density/voltage–current density characteristics with various LCVGs fed as fuels. With permission (open access) from ref. .

Fig. 23. Process-intensified SEMRs using different external energy sources: (a) light-induced cell voltage increase in solid oxide photo-electrochemical cells, (b) thermoelectric SOFCs, (c) SEMRs intensified by H₂ energy storage in the anode and (d) plasma intensified SEMRs for N₂ activation and NH₃ synthesis. Reproduced with permission from individual reference-related publishers.

Fig. 24. (a) Schematic illustration of H-SEMRs integrated with an electro-chemical H₂ compression process, (b) energy balance and system micro-integration for operation at 800 °C for a feed inlet of one mole CH₄, (c) tabular SEMRs with Ni catalyst loaded inside the ceramic tube (insets are SEM cross-section images of the overall cell and electrode reactions), (d) H₂ production rate versus current density compared with the theoretical value and (d) conversion, yield of CO₂ and CO versus hydrogen recovery at 800 °C, 10 bar, S/C = 2.5. Steam pressure on the hydrogen side inlet was 0–2.0 bar. Reproduced with permission from ref. .

Fig. 25. (a) Schematic representation of the tubular SOFC reactor with reactions at each electrode under OCV and short-circuit conditions, (b) power generation characteristics, and (c) temperature dependence under steady-state conditions on the Λ and ρ. P_H2 = 7 kPa, P_CO2 = 1 kPa, FT = 200 cm³ min⁻¹. Reproduced with permission from ref. .

Fig. 26. (A) Schematic of the basic principle of EPOC when ions (oxide ions or cations) are moved to the catalyst of the working electrode and (B) CH₄ and CO production rates when CO₂ hydrogenation is carried out over a range of negative and positive polarization. Reproduced with permission from ref. and .

Liangdong Fan

Te-Wei Chiu

Peter D. Lund