Advancements,strategies,and prospects of solid oxide electrolysis cells(SOECs):Towards enhanced performance and large-scale sustainable hydrogen production

Solid oxide electrolysis cells(SOECs)represent a crucial stride toward sustainable hydrogen generation,and this review explores their current scientific challenges,significant advancements,and potential for large-scale hydrogen production.In SOEC technology,the application of innovative fabrication tech-niques,doping strategies,and advanced materials has enhanced the performance and durability of these systems,although degradation challenges persist,implicating the prime focus for future advancements.Here we provide in-depth analysis of the recent developments in SOEC technology,including Oxygen-SOECs,Proton-SOECs,and Hybrid-SOECs.Specifically,Hybrid-SOECs,with their mixed ionic conducting electrolytes,demonstrate superior efficiency and the concurrent production of hydrogen and oxygen.Coupled with the capacity to harness waste heat,these advancements in SOEC technology present signif-icant promise for pilot-scale applications in industries.The review also highlights remarkable achieve-ments and potential reductions in capital expenditure for future SOEC systems,while elaborating on the micro and macro aspects of sOECs with an emphasis on ongoing research for optimization and scal-ability.It concludes with the potential of SOEC technology to meet various industrial energy needs and its significant contribution considering the key research priorities to tackle the global energy demands,ful-fillment,and decarbonization efforts.

Active Cu and Fe Nanoparticles Codecorated Ruddlesden-Popper-Type Perovskite as Solid Oxide Electrolysis Cells Cathode for CO_(2)Splitting

Solid oxide electrolysis cells(SOECs),displaying high current density and energy efficiency,have been proven to be an effective technique to electrochemically reduce CO_(2)into CO.However,the insufficiency of cathode activity and stability is a tricky problem to be addressed for SOECs.Hence,it is urgent to develop suitable cathode materials with excellent catalytic activity and stability for further practical application of SOECs.Herein,a reduced perovskite oxide,Pr_(0.35)Sr_(0.6)Fe_(0.7)Cu_(0.2)Mo_(0.1)O_(3-δ)(PSFCM0.35),is developed as SOECs cathode to electrolyze CO_(2).After reduction in 10%H_(2)/Ar,Cu and Fe nanoparticles are exsolved from the PSFCM0.35 lattice,resulting in a phase transformation from cubic perovskite to Ruddlesden-Popper(RP)perovskite with more oxygen vacancies.The exsolved metal nanoparticles are tightly attached to the perovskite substrate and afford more active sites to accelerate CO_(2)adsorption and dissociation on the cathode surface.The significantly strengthened CO_(2)adsorption capacity obtained after reduction is demonstrated by in situ Fourier transform-infrared(FT-IR)spectra.Symmetric cells with the reduced PSFCM0.35(R-PSFCM0.35)electrode exhibit a low polarization resistance of 0.43Ωcm^(2)at 850℃.Single electrolysis cells with the R-PSFCM0.35 cathode display an outstanding current density of 2947 mA cm^(-2)at 850℃and 1.6 V.In addition,the catalytic stability of the R-PSFCM0.35 cathode is also proved by operating at 800℃with an applied constant current density of 600 mA cm^(-2)for 100 h.

Infiltration of Ce0.8Gd0.2O1.9 nanoparticles on Sr2Fe1.5Mo0.5O6-δ cathode for CO2 electroreduction in solid oxide electrolysis cell

Solid oxide electrolysis cell(SOEC) can electrochemically convert CO2 to CO at the gas-solid interface with a high current density and Faradaic efficiency, which has attracted increasing attentions in recent years.Exploring efficient catalyst for electrochemical CO2 reduction reaction(CO2 RR) at the cathode is a grand challenge for the research and development of SOEC. Sr2Fe1.5Mo0.5O6-δ(SFM) is one kind of promising cathode materials for SOEC, but suffers from insufficient activity for CO2 RR. Herein, Gd0.2Ce0.8O1.9(GDC)nanoparticles were infiltrated onto the SFM surface to construct a composite GDC-SFM cathode and improve the CO2 RR performance in SOEC. The current density over the GDC infiltrated SFM cathode with a GDC loading of 12.8 wt% reaches 0.446 A cm-2 at 1.6 V and 800 °C, which is much higher than that over the SFM cathode(0.283 A cm-2). Temperature-programmed desorption of CO2 measurements suggest that the infiltration of GDC nanoparticles significantly increases the density of surface active sites and three phase boundaries(TPBs), which are beneficial for CO2 adsorption and subsequent conversion. Electrochemical impedance spectroscopy results indicate that the polarization resistance of 12.8 wt% GDCSFM cathode was obviously decreased from 0.46 to 0.30 cm^2 after the infiltration of GDC nanoparticles.

High-temperature electrocatalysis and key materials in solid oxide electrolysis cells

Solid oxide electrolysis cells(SOECs)can convert electricity to chemicals with high efficiency at ~600-900℃,and have attracted widespread attention in renewable energy conversion and storage.SOECs operate in the inverse mode of solid oxide fuel cells(SOFCs)and therefore inherit most of the advantages of SOFC materials and energy conversion processes.However,the external bias that drives the electrochemical process will strongly change the chemical environments in both in the cathode and anode,therefore necessitating careful reconsideration of key materials and electrocatalysis processes.More importantly,SOECs provide a unique advantage of electrothermal catalysis,especially in converting stable low-carbon alkanes such as methane to ethylene with high selectivity.Here,we review the state-of-the-art of SOEC research progress in electrothermal catalysis and key materials and provide a future perspective.

Improving the performance of solid oxide electrolysis cell with gold nanoparticles-modified LSM-YSZ anode

Gold, as the common current collector in solid oxide electrolysis cell(SOEC), is traditionally considered to be inert for oxygen evolution reaction at the anode of SOEC. Herein, gold nanoparticles were loaded onto conventional strontium doped lanthanum manganite-yttria stabilized zirconia(LSM-YSZ) anode, which evidently improved the performance of oxygen evolution reaction at 800 °C. The current densities at 1.2 V and 1.4 V increased by 60.0% and 46.9%, respectively, after loading gold nanoparticles onto the LSM-YSZ anode. Physicochemical characterizations and electrochemical measurements suggested that the improved SOEC performance was attributed to the accelerated electron transfer of elementary process in anodic polarization reaction and the newly generated triple phase boundaries in gold nanoparticles-loaded LSMYSZ anode.

Pulsed electrolysis of carbon dioxide by large-scale solid oxide electrolytic cells for intermittent renewable energy storage

CO_(2) electrolysis with solid oxide electrolytic cells(SOECs)using intermittently available renewable energy has potential applications for carbon neutrality and energy storage.In this study,a pulsed current strategy is used to replicate intermittent energy availability,and the stability and conversion rate of the cyclic operation by a large-scale flat-tube SOEC are studied.One hundred cycles under pulsed current ranging from -100 to -300 mA/cm^(2) with a total operating time of about 800 h were carried out.The results show that after 100 cycles,the cell voltage attenuates by 0.041%/cycle in the high current stage of−300 mA/cm^(2),indicating that the lifetime of the cell can reach up to about 500 cycles.The total CO_(2) conversion rate reached 52%,which is close to the theoretical value of 54.3% at -300 mA/cm^(2),and the calculated efficiency approached 98.2%,assuming heat recycling.This study illustrates the significant advantages of SOEC in efficient electrochemical energy conversion,carbon emission mitigation,and seasonal energy storage.

Enhancing cathode performance for CO2 electrolysis with Ce0.9M0.1O2-δ（M=Fe, Co, Ni） catalysts in solid oxide electrolysis cell

Electrochemical conversion with solid oxide electrolysis cells is a promising technology for CO2 utilization and simultaneously store renewable energy.In this work,Ce0.9M0.1O2-δ(CeM,M=Fe,Co,Ni)catalysts are infiltrated into La0.6Sr0.4Cr0.5Fe0.5O3-δ-Gd0.2Ce0.8O2-δ(LSCr Fe-GDC)cathode to enhance the electrochemical performance for CO2 electrolysis.CeCo-LSCrFe-GDC cell obtains the best performance with a current density of 0.652 A cm^-2,followed by CeFe-LSCrFe-GDC and CeNi-LSCrFe-GDC cells with the value of 0.603 and 0.535 A cm^-2,respectively,about 2.44,2.26 and 2.01 times higher than that of the LSCrFe-GDC cell at1.5 V and 800℃.Electrochemical impedance spectra combined with distributions of relaxed times analysis shows that both CO2 adsorption process and the dissociation of CO2 at triple phase boundaries are accelerated by Ce M catalysts,while the latter is the key rate-determining step.

Highly dispersed nickel species on iron‐based perovskite for CO_(2) electrolysis in solid oxide electrolysis cell

Feasible construction of cathode materials with highly dispersed active sites can extend the tri‐ple‐phase boundaries,and therefore leading to enhanced electrode kinetics for CO_(2) electrolysis in solid oxide electrolysis cell(SOEC).Herein,highly dispersed nickel species with low loading(1.0 wt%)were trapped within the La_(0.8)Sr_(0.2)FeO_(3)–δ‐Ce_(0.8)Sm_(0.2)O_(2)–δvia a facial mechanical milling ap‐proach,which demonstrated excellent CO_(2) electrolysis performance.The highly dispersed nickel species can significantly alter the electronic structures of the LSF‐SDC without affecting its porous network and facilitate oxygen vacancy formation,thus greatly promote the CO_(2) electrolysis perfor‐mance.The highest current density of 1.53 A·cm^(-2) could be achieved when operated under 800℃ at 1.6 V,which is about 91%higher than the LSF‐SDC counterpart.

Electrochemical conversion of C1 molecules to sustainable fuels in solid oxide electrolysis cells

Stimulated by increasing environmental awareness and renewable-energy utilization capabilities,fuel cell and electrolyzer technologies have emerged to play a unique role in energy storage,conversion,and utilization.In particular,solid oxide electrolysis cells(SOECs)are increasingly attracting the interest of researchers as a platform for the electrolysis and conversion of C1 molecules,such as carbon dioxide and methane.Compared to traditional catalysis methods,SOEC technology offers two major advantages:high energy efficiency and poisoning resistance,ensuring the long-term robustness of C1-to-fuels conversion.In this review,we focus on state-of-the-art technologies and introduce representative works on SOEC-based techniques for C1 molecule electrochemical conversion developed over the past several years,which can serve as a timely reference for designing suitable catalysts and cell processes for efficient and practical conversion of C1 molecules.The challenges and prospects are also discussed to suggest possible research directions for sustainable fuel production from C1 molecules by SOECs in the near future.

Co/Fe oxide and Ce_(0.8)Gd_(0.2)O_(2-δ) composite interlayer for solid oxide electrolysis cell

A composite interlayer comprised of gadolinia doped ceria（GDC） and Co/Fe oxide was prepared and investigated for solid oxide electrolysis cell with yttrium stabilized zirconia（YSZ） electrolyte and LaSrCoFeO（LSCF） anode. The interlayer was constructed of a base layer of GDC and a top layer of discrete CoO/FeCoOparticles. The presence of the GDC layer drastically alleviated the undesired reactions between LSCF and YSZ, and the presence of Co/Fe oxide led to further performance improvement. At 800 °C and 45% humidity, the cell with 70% Co/Fe-GDC interlayer achieved 0.98 A/cmat 1.18 V, 14% higher than the cell without Co/Fe oxide. Electrochemical impedance spectroscopy（EIS） revealed that with higher Co/Fe content, both the ohmic resistance and the polarization resistance of the cell were reduced. It is suggested that Co/Fe oxide can react with the Sr species segregated from LSCF and Sr（Co,Fe）O, a compound with high catalytic activity and electronic conductivity. The Sr-capturing ability of Co/Fe oxide in combination with the Sr-blocking ability of GDC layer can effectively suppress the undesired reaction between LSCF and YSZ, and consequently improve the cell performance.

A robust fluorine-containing ceramic cathode for direct CO_(2) electrolysis in solid oxide electrolysis cells

Stro ntium-doped lanthanum ferrite(LSF)is a potential ceramic cathode for direct CO_(2) electrolysis in solid oxide electrolysis cells(SOECs),but its application is limited by insufficient catalytic activity and stability in CO_(2)-containing atmospheres.Herein,a novel strategy is proposed to enhance the electrolytic performance as well as chemical stability,achieved by doping F into the O-site of the perovskite LSF.Doping F does not change the phase structure but reduces the cell volume and improves the chemical stability in a CO_(2)-rich atmosphere.Importantly,F doping favors oxygen vacancy formation,increases oxygen vacancy concentration,and enhances the CO_(2) adsorption capability.Meanwhile,doping with F greatly improves the kinetics of the CO_(2) reduction reaction.For example,kchem increases by 78%from3.49×10^(-4) cm s^(-1) to 6.24×10^(-4) cm s^(-1),and Dchem doubles from 4.68×10^(-5) cm^(2) s^(-1) to 9.45×10^(-5)cm^(2) s^(-1).Consequently,doping F significantly increases the electrochemical performance,such as reducing R_(p) by 52.2%from 0.226Ωcm^(2) to 0.108Ωcm^(2) at 800℃.As a result,the single cell with the Fcontaining cathode exhibits an extremely high current density of 2.58 A cm^(-2) at 800℃and 1.5 V,as well as excellent durability over 200 h for direct CO_(2) electrolysis in SOECs.

Novel Perovskite Oxide Hybrid Nanofibers Embedded with Nanocatalysts for Highly Efficient and Durable Electrodes in Direct CO_(2) Electrolysis

The unique characteristics of nanofibers in rational electrode design enable effec-tive utilization and maximizing material properties for achieving highly efficient and sustainable CO_(2) reduction reactions( CO_(2)RRs)in solid oxide elec-trolysis cells(SOECs).However,practical appli-cation of nanofiber-based electrodes faces chal-lenges in establishing sufficient interfacial contact and adhesion with the dense electrolyte.To tackle this challenge,a novel hybrid nanofiber electrode,La_(0.6)Sr_(0.4)Co_(0.15)Fe_(0.8)Pd_(0.05)O_(3-δ)(H-LSCFP),is developed by strategically incorporating low aspect ratio crushed LSCFP nanofibers into the excess porous interspace of a high aspect ratio LSCFP nanofiber framework synthesized via electrospinning technique.After consecutive treatment in 100% H_(2) and CO_(2) at 700°C,LSCFP nanofibers form a perovskite phase with in situ exsolved Co metal nanocatalysts and a high concentration of oxygen species on the surface,enhancing CO_(2) adsorption.The SOEC with the H-LSCFP electrode yielded an outstanding current density of 2.2 A cm^(-2) in CO_(2) at 800°C and 1.5 V,setting a new benchmark among reported nanofiber-based electrodes.Digital twinning of the H-LSCFP reveals improved contact adhesion and increased reaction sites for CO_(2)RR.The present work demonstrates a highly catalytically active and robust nanofiber-based fuel electrode with a hybrid structure,paving the way for further advancements and nanofiber applications in CO_(2)-SOECs.

Analytical Study, 1-D Optimization Modeling, and Testing of Electrode Supported Solid Oxide Electrolysis Cells

This paper presents a straightforward model studying the performance of a solid oxide electrolysis cell at less computational effort while is still comprehensive accounting for details of all physics involved. The model is one dimensional and can be used to optimize SOECs that have composite electrodes. It includes an average mass transfer analysis used to simulate concentration polarization, activation polarization, as well as ohmic loss. The electrochemical reaction that occurs within the electrode functional layers has been accounted for in the calculation of the concentration polarization. This is believed to give a more realistic view of the mass transfer that occurs in SOECs with composite electrodes via a simple and straightforward one dimensional model. Experimental work with SOECs also has been done and some results are reported. The simulation results are compared with experimental data and the agreement is satisfactory. The model can be conveniently used for optimization of the SOEC electrodes and operational conditions.

Operational Robustness Studies of Solid Oxide Electrolysis Stacks

Stacks of solid oxide cells which can be run as both electrolysers and fuel cells have been tested for robustness towards simulations of stress conditions which are likely to occur during operation of solid oxide electrolysis systems, for which the energy supply comes from renewable sources, such as wind mills and solar cells. Such conditions are thermo mechanical stress conditions as well as loss of fuel and air supply. The cells have Ni/YSZ （yttria stabilized zirconia） fuel electrodes, YSZ electrolytes, and LSCF （lanthanum strontium cobalt ferrite） oxygen electrodes with a CGO （cerium gadolinium oxide） barrier layer. In the stacks, the cells are separated by chromium rich steel interconnects. The robustness tests of stacks are one step in the development of a SOEC （solid oxide electrolysis cell） core; the core component in a SOEC system, including one or more SOEC stacks, heaters, heat exchangers, insulation, and feed troughs.

Electrochemical performance and stability of Sr-doped LaMnO_(3)-infiltrated yttria stabilized zirconia oxygen electrode for reversible solid oxide fuel cells

Porous Sr-doped lanthanum manganite–yttria stabilized zirconia(LSM–YSZ)oxygen electrode is prepared by an infiltration process for a reversible solid oxide fuel cell(RSOFC).X-ray diffraction and SEM analysis display that perovskite phase LSM submicro particles are evenly distributed in the porous YSZ matrix.Polarization curves and electrochemical impedance spectra are conducted for the RSOFC at 800 and 850C under both SOFC and SOEC modes.At 850℃,the single cell has the maximum power density of~726 mW/cm^(2)under SOFC mode,and electrolysis voltage of 1.35 V at 1 A/cm^(2)under SOEC mode.Fuel cell/water electrolysis cycle shows the cell has good performance stability during 6 cycles,which exhibits the LSM–YSZ oxygen electrode has high electrochemical performance and good stability.The results suggest that netw ork-like LSM–YSZ electrode made by infiltration process could be a promising oxygen electrode for high temperature RSOFCs.

Scientometric analysis of research trends on solid oxide electrolysis cells for green hydrogen and syngas production

Solid oxide electrolysis cell(SOEC)is a promising water electrolysis technology that produces hydrogen or syngas through water electrolysis or water and carbon dioxide co-electrolysis.Green hydrogen or syngas can be produced by SOEC with renewable energy.Thus,SOEC has attracted continuous attention in recent years for the urgency of developing environmentally friendly energy sources and achieving carbon neutrality.Focusing on 1276 related articles retrieved from the Web of Science(WoS)database,the historical development of SOECs are depicted from 1983 to 2023 in this paper.The co-occurrence networks of the countries,source journals,and author keywords are generated.Moreover,three main clusters showing different content of the SOEC research are identified and analyzed.Furthermore,the scientometric analysis and the content of the high-cited articles of the research of different topics of SOECs:fuel electrode,air electrode,electrolyte,co-electrolysis,proton-conducting SOECs,and the modeling of SOECs are also presented.The results show that co-electrolysis and proton-conducting SOECs are two popular directions in the study of SOECs.This paper provides a straightforward reference for researchers interested in the field of SOEC research,helping them navigate the landscape of this area of study,locate potential partners,secure funding,discover influential scholars,identify leading countries,and access key research publications.

Green hydrogen production by intermediate-temperature protonic solid oxide electrolysis cells:Advances,challenges,and perspectives

Protonic solid oxide electrolysis cells(P-SOECs)operating at intermediate temperatures,which have low costs,low environmental impact,and high theoretical electrolysis efficiency,are considered promising next-generation energy conversion devices for green hydrogen production.However,the developments and applications of P-SOECs are restricted by numerous material-and interface-related issues,including carrier mismatch between the anode and electrolyte,current leakage in the electrolyte,poor interfacial contact,and chemical stability.Over the past few decades,considerable attempts have been made to address these issues by improving the properties of P-SOECs.This review comprehensively explores the recent advances in the mechanisms governing steam electrolysis in P-SOECs,optimization strategies,specially designed components,electrochemical performance,and durability.In particular,given that the lack of suitable anode materials has significantly impeded P-SOEC development,the relationships between the transferred carriers and the cell performance,reaction models,and surface decoration approaches are meticulously probed.Finally,the challenges hindering P-SOEC development are discussed and recommendations for future research directions,including theoretical calculations and simulations,structural modification approaches,and large-scale single-cell fabrication,are proposed to stimulate research on P-SOECs and thereby realize efficient electricity-to-hydrogen conversion.

Enhancing Direct Electrochemical CO_(2)Electrolysis by Introducing A-Site Deficiency for the Dual-Phase Pr(Ca)Fe(Ni)O_(3-δ)Cathode

High-temperature CO_(2)electrolysis via solid oxide electrolysis cells(CO_(2)-SOECs)has drawn special attention due to the high energy convention efficiency,fast electrode kinetics,and great potential in carbon cycling.However,the development of cathode materials with high catalytic activity and chemical stability for pure CO_(2)electrolysis is still a great challenge.In this work,A-site cation deficient dual-phase material,namely(Pr_(0.4)Ca_(0.6))_(x)Fe_(0.8)Ni_(0.2)O_(3-δ)(PCFN,x=1,0.95,and 0.9),has been designed as the fuel electrode for a pure CO_(2)-SOEC,which presents superior electrochemical performance.Among all these compositions,(Pr_(0.4)Ca_(0.6))_(0.95)Fe_(0.8)Ni_(0.2)O_(3-δ)(PCFN95)exhibited the lowest polarization resistance of 0.458Ωcm^(2)at open-circuit voltage and 800℃.The application of PCFN95 as the cathode in a single cell yields an impressive electrolysis current density of 1.76 A cm^(-2)at 1.5 V and 800℃,which is 76%higher than that of single cells with stoichiometric Pr_(0.4)Ca_(0.6)Fe_(0.8)Ni_(0.2)O_(3-δ)(PCFN100)cathode.The effects of A-site deficiency on materials'phase structure and physicochemical properties are also systematically investigated.Such an enhancement in electrochemical performance is attributed to the promotion of effective CO_(2)adsorption,as well as the improved electrode kinetics resulting from the A-site deficiency.

Exsolved materials for CO_(2)reduction in high-temperature electrolysis cells

Electrochemical reduction of CO_(2)into valuable fuels and chemicals has become a contemporary research area,where the heterogeneous catalyst plays a critical role.Metal nanoparticles supported on oxides performing as active sites of electrochemical reactions have been the focus of intensive investigation.Here,we review the CO_(2)reduction with active materials prepared by exsolution.The fundamental of exsolution was summarized in terms of mechanism and models,materials,and driven forces.The advances in the exsolved materials used in hightemperature CO_(2)electrolysis were catalogued into tailored interfaces,synergistic effects on alloy particles,phase transition,reversibility and electrochemical switching.

An active and stable hydrogen electrode of solid oxide cells with exsolved Fe-Co-Ni nanoparticles from Sr_(2)FeCo_(0.2)Ni_(0.2)Mo_(0.6)O_(6-δ)double-perovskite

Sr_(2)FeCo_(0.2)Ni_(0.2)Mo_(0.6)O_(6-δ)(SFCNM)and Sr_(2)FeNi_(0.4)Mo_(0.6)O_(6-δ)(SFNM)were prepared as the hydrogen electrode materials for solid oxide cells(SOCs)and comparatively investigated by density function theory(DFT)and experiments to demonstrate the benefit of Co addition.The reduced SFCNM(R-SFCNM)and SFNM(R-SFNM)contain exsolved Fe–Co–Ni and Fe–Ni nanoparticles,respectively.DFT indicates that Fe–Co–Ni has optimized combination of the d-band center(descriptor of catalyst activity)and adsorption behavior for H_(2)O,H_(2),H,and OH.The cell with SFCNM hydrogen electrode,La_(0.8)Sr_(0.2)Ga_(0.8)Mg_(0.2)O_(3-δ)(LSGM)electrolyte,and La_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.8)O_(3-δ)(LSCF)oxygen electrode(Cell-SFCNM)demonstrates a higher performance than that with an SFNM hydrogen electrode(Cell-SFNM)at temperatures between 700 and 850℃in both solid oxide fuel cell(SOFC,3%H_(2)O-97%H_(2)/air)and solid oxide electrolysis cell(SOEC,20%H_(2)O-80%H_(2)/air)modes.At 850 and 700℃,the peak power density is 1.23 and 0.48 W⋅cm^(-2)in SOFC mode,while the current density is 1.25 and 0.37 A⋅cm^(-2)at 1.3 V in SOEC mode,respectively.The performance degradation rates at 750℃are 0.17 mV⋅h^(-1)in SOFC and 0.15 mV⋅h^(-1)in SOEC modes within 150 h,which are improved by Co doping.