Oxygen Bulk Diffusion Research Articles

Medium-entropy strategy to inhibit the surface Sr segregation and enhance the stability of Sr2Fe1.5Mo0.5O6-δ cathode for CO2 direct electrolysis

Solid oxide electrolysis cell (SOEC) is a promising solid-state electrochemical device that can convert CO2 into CO with high efficiency. However, the poor catalytic activity and Sr segregation of the cathode diminish the electrode reaction, hindering the large-scale application. Herein, a medium-entropy strategy is proposed to suppress the Sr enrichment while enhancing the catalytic activity for CO2. The surface Sr content on Sr2Fe1.2Ni0.1Cu0.1Co0.1Mo0.5O6-δ (SFNCCM) is significantly reduced after the Ni, Cu, and Co co-doping at Fe-site. Moreover, the oxygen surface exchange and bulk diffusion coefficient at 800 °C for SFNCCM oxide reach 2.42 × 10−4 cm2 s−1 and 2.28 × 10−5 cm2 s−1, which are 1.35 and 1.39 times higher than parent Sr2Fe1.5Mo0.5O6-δ(SFM) oxide. At 850 °C and 1.5 V, single with SFNCCM-Sm0.2Ce0.8O6-δ(SDC) composite exhibits a current density of 2.22 A cm−2 with good stability for up to 100 h. The results suggest that the medium-entropy strategy is a promising method to inhibit Sr segregation and enhance the performance of CO2 direct electrolysis.

Interface engineering of La0.6Sr0.4Co0.2Fe0.8O3−δ/Gd0.1Ce0.9O1.95 heterostructure oxygen electrode for solid oxide electrolysis cells with enhanced CO2 electrolysis performance

For CO2 electrolysis in solid oxide electrolysis cells (SOECs), oxygen evolution reaction in the oxygen electrode limits the electrolysis process due to its slower reaction kinetics. Composite oxygen electrodes with good uniformity and interfacial connectivity are expected to promote the charge carriers' transport effectively and thus increase the electrocatalytic performance of the cell. In this work, interface engineering is applied to promote the conventional La0.6Sr0.4Co0.2Fe0.8O3−δ-Gd0.1Ce0.9O1.95 (LSCF-GDC) composite oxygen electrode to form a heterostructure via co-synthesis method. The results prove that LSCF co-synthesized with 40 wt%GDC (LSCF/40GDC) exhibits higher conductivity and faster oxygen exchange kinetics and bulk diffusion processes. The nickel/yttria stabilized zirconia (Ni-YSZ) supported cell with LSCF/40GDC oxygen electrode could approach an impressive CO2 electrolysis current density of 2.6 A·cm−2 at 1.6 V and 800 °C. Meanwhile the cell can operate at 1.5 V and 750 °C with electrolysis current density of 1.3 A·cm−2 for more than 100 h without apparent degradation. This heterostructure enhances the interfacial bonding strength between LSCF and GDC phases, thereby providing a continuous network structure for electron and ion transport. Such an interface engineering via co-synthesis method offers a straightforward and convenient modification for oxygen electrodes, providing an alternative route for advanced materials development of CO2 electrolysis.

Self-Assembled Nanocomposite Based on SrCo0.7Fe0.2Sc0.1O3-δ as an Efficient Intermediate-to-Low-Temperature SOFC Cathode.

The high performance of intermediate-to-low temperature solid oxide fuel cells (ILT-SOFCs) closely depends on the catalytic activity of the cathode material. However, most high-activity perovskite cathodes are rich in Sr and will arise from Sr segregation during the long-term working, resulting in the decay of activity and stability. Herein, by regulating the calcined way and temperature, a type of self-assembled nanocomposite perovskite cathode is developed, the stoichiometric SrCo0.7Fe0.2Sc0.1O3-δ (SCFSc) powder self-separates into a cubic phase (Pm3̅m, Sc-rich) and a tetragonal phase (P4/mmm, Sc-fewer). Meanwhile, a single cubic phase is prepared with the same formula via calcining the SCFSc pellet. It is found that the nanocomposite cathode shows better oxygen reduction reaction catalytic activity than single cubic SCFSc, caused by lower impedance of oxygen surface exchange and bulk diffusion. Particularly, the nanocomposite SCFSc cathode with the self-assembled heterointerfaces mitigates the Sr segregation and shows a peak power density of 1.17 W cm-2 at 700 °C and excellent stability for ∼101 h at 600 °C. This work provides a strategy for the development of nanocomposite cathodes to mitigate cation segregation and improve catalytic activity and stability.

Deciphering the role of nano-CeO2 morphology on the dry reforming of methane over Ni/CeO2 using transient and isotopic techniques

The effect of ceria morphology, nanorods-NR and nanopolyhedra-NP on important kinetic parameters of the dry reforming of methane (DRM) over Ni/nano-ceria (dNi ∼20 nm) was investigated by transient and isotopic experiments. Transient isothermal reduction by hydrogen evidenced lower activation energy and higher reduction rates of lattice oxygen in the case of CeO2-NR compared to those of CeO2-NP. Transient 16O/18O isotopic exchange provided a lower Eapp of bulk oxygen diffusion (by ∼90 kJ mol−1) for CeO2-NR compared to CeO2-NP. 18O/16O isotopic exchange followed by DRM revealed higher carbon oxidation rates by lattice oxygen to C18O(g) in the case of CeO2-NR compared to those of CeO2-NP, in harmony with the lower amount of carbon accumulated in the former catalyst. The lower Eapp of DRM and carbon oxidation by lattice oxygen confirm the higher DRM activity on Ni/CeO2-NR compared to Ni/CeO2-NP. HAADF-STEM and Raman studies were linked to the observed transient kinetic results.

Ni-doped Fe-based perovskite to obtain multifunctional and highly efficient electrocatalytic active IT-SOFC electrode

This paper systematically studies Ni doping at Fe sites in La0.6Sr0.4Co0.3Fe0.7O3-δ (LSCF) as an intermediate temperature solid oxide fuel cell (IT-SOFC) electrode. The electrocatalytic activity of Ni-doped electrodes in oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) modes was analyzed, rather than individual cathode or anode. The results indicate that Ni doping increases the internal vacancies, ORR activity, and charge transfer ability of La0.6Sr0.4Co0.3Fe0.6Ni0.15O3-δ (LSCFN15). In addition, compared to LSCF, LSCFN15 also reduces the energy barriers for surface oxygen exchange and bulk diffusion, thereby increasing the overall ORR kinetic rate. Combined with the distribution of relaxation time (DRT) analysis, it was confirmed that Ni-doped LSCFN15 increased the adsorption and dissociation rates of oxygen. At 750 ℃, the area-specific resistance (ASR) of LSCFN15 reached 0.045 Ω cm2, which is only 58.4 % of LSCF (0.077 Ω cm2). As a SOFC cathode, the peak power density (PPD) reached 1175 mW cm−2, 1.31 times that of LSCF (898 mW cm−2). As a SOFC anode, the current exchange density of LSCFN15 in OER mode reaches 164 mA cm−2, which is higher than the 125 mA cm−2 of LSCF, indicating that LSCFN15 also has the potential to serve as an anode for SOFC. In addition, Ni doping reduces the thermal expansion coefficient of the electrode and improves its thermal compatibility with traditional electrolytes. As an electrode, LSCFN15 exhibits excellent long-term stability in both SOFC and SOEC modes. Overall, Ni-doped Fe-based perovskite can improve the ORR and OER activities while enhancing the stability of cell operation and is expected to obtain multifunctional SOFC electrode materials.

Tuning the ORR catalytic activity of LaFeO3-δ-based perovskite cathode for solid oxide fuel cells by doping with alkaline-earth metal elements

Co-based perovskite cathodes have demonstrated impressive catalytic activity for oxygen reduction reaction (ORR) at intermediate temperatures. However, these cathodes face the challenges such as high cost and thermal expansion coefficient (TEC) mismatch. On the other hand, Fe-based perovskite oxides like LaFeO3 exhibit more stable properties and lower TEC, but their ORR activity is not as remarkable as that of Co-based cathodes. In this study, La3+ at the A-site of LaFeO3 was substituted by aliovalent alkaline-earth metal cations. The research findings reveal that the doping of alkaline-earth metal ions induces the formation of structural defects and alters the valence state of Fe. This leads to an increase in the conductivity and oxygen vacancy concentration, which are critical for ORR kinetics in both H–SOFC and O–SOFC. Among the various dopants, Sr doped LaFeO3 (LSrF) exhibits the most outstanding ORR catalytic activity. This can be attributed to its highest total conductivity, O2− conductivity, oxygen surface exchange coefficient, and oxygen bulk diffusion coefficient. At 700 °C, single cell with LSrF cathode achieves peak power densities of 0.781 and 0.894 W cm−2, for O2--conducting solid oxide fuel cell (SOFC) and H+-conducting SOFC, respectively. These performances are essentially twice that of single cell with LaFeO3 cathode. The findings of this study provide valuable insights into doping strategies for Fe-based perovskite cathodes and contribute to the advancement of IT-SOFC cathode research.

Nd-doping-induced perovskite/Ruddlesden-Popper heterointerfaces boost the ORR activity and CO2 tolerance for SrFeO3-δ-based cathode

The development of cathode materials with high oxygen reduction reaction (ORR) activity is crucial to realize the wide application of solid oxide fuel cells. Nd-doped SrFeO3-δ (SNF) two-phase nanocomposite was fabricated by a dopant-induced in situ self-assembly process. The SNF nanocomposite comprises 63.4 wt% perovskite main phase (P–SNF) and 36.6 wt% Ruddlesden-Popper second phase (RP-SNF). The average thermal expansion coefficient (TEC) of SrFeO3-δ is reduced by 36.5 % and down to 13.9 × 10−6 K−1. At 750 °C, SNF demonstrates an impressive output power of 779 mW cm−2, which is twice that of the single-phase SrFeO3-δ. The superior performance stems from the heterointerface effect of the in situ self-assembled two phases. This effect increases the content of oxygen vacancies, thereby enhancing both chemical oxygen surface exchange coefficient and bulk diffusion coefficient. Moreover, the SNF composite exhibits excellent CO2 tolerance than the single-phase SrFeO3-δ. This work presents a promising avenue for exploring multifunctional materials through interface engineering, offering new possibilities for future energy conversion devices.

Ca and Fe co-doped NdBaCo2O5+δ double perovskites as high-performance cathodes for solid oxide fuel cells

For intermediate-temperature solid oxide fuel cells (IT-SOFCs), high electrochemical catalytic activity and a suitable thermal expansion coefficient (TEC) are essential criteria. In this investigation, simultaneous Ca and Fe co-doped NdBa1-xCaxCoFeO5+δ (NBCCF, x = 0, 0.1, and 0.2) double-perovskites were prepared and investigated as SOFC cathode materials. The introduction of Ca and Fe effectively decreased the TECs and improved the oxygen reduction activity of the cathode. The average TEC of NdBa0.9Ca0.1CoFeO5+δ (NBCCF1) at 30–850 °C was 19.1 × 10−6 K−1, which is decreased by 27.1 % compared to the only Fe-doped NdBaCoFeO5+δ (NBCF). According to the distribution of relaxation time (DRT) analysis, the rate-limiting steps of the oxygen reduction reaction (ORR) include bulk diffusion and surface exchange of oxygen, and Ca doping can improve both steps. The maximum power density of the single cell with NBCCF1 as cathode reached 665 mW cm−2 at 750 °C. The polarization resistance decreased from 0.0722 to 0.0482 Ω cm2 at 800 °C. These findings indicate NBCCF1 is a viable cathode candidate for IT-SOFC.

CoxFe1-xFeAlO4-δ as highly active oxygen carriers for enhanced chemical looping hydrogen production

The oxygen carrier is a key factor to enable efficient and high-quality chemical looping hydrogen production. Here, we prepared several oxygen vacancies engineered CoxFe1-xFeAlO4-δ spinel by tuning Co loading of and investigated the performance for hydrogen production through chemical looping. The results show that Co0.4Fe0.6FeAlO4-δ displays a high hydrogen yield of 10.56 mmol.g−1 with a stable trend for 100 cycles at 600 °C. Mechanism studies demonstrate that doping Co decreases the energy barriers for oxygen vacancy formation, resulting in a high oxygen vacancy concentration on the surface. The high oxygen vacancy concentration accelerates the bulk oxygen diffusion, which is the rate-limiting step of the redox reaction. The enhanced bulk oxygen diffusion improves the oxygen release and redeposition of the lattice oxygen during redox cycles, thus promoting the chemical looping hydrogen production performance. No obvious phase separation can be found for Co0.4Fe0.6FeAlO4-δ during 100 cycles. The observed doping effect can pave way to developing more advanced oxygen carriers with high reactivity and stability for chemical looping applications.

Oxidation kinetics of Fe-(2-10)Mn-xSb alloys during annealing

The selective oxidation kinetics of a series of Fe-(2-10)Mn-(0.00/0.01/0.03)Sb (at. pct) were determined and a model was proposed for analyzing oxide growth during intercritical annealing prior to galvanizing. The annealing conditions (temperature and isothermal holding time) affected the thickness and depth of the oxidation zone, which in turn influenced the MnO growth rate. Increasing the alloy bulk Mn content increased the Mn elemental flux to the external surface, thereby increasing the oxidation parabolic rate constant and decreasing the oxidation activation energy. Micro-additions of Sb to the Fe-Mn alloys reduced the parabolic rate constant, which was attributed to the reduction of oxygen permeability at the surface and interfaces by Sb segregation at both the external and internal oxide interfaces. This reduction was more significant in the Fe-10Mn alloys due to higher Sb segregation at the interfaces. The average activation energy of internal oxidation for the Fe-2Mn, Fe-6Mn and Fe-10Mn alloys were determined to be 216 ± 15 kJ/mol, 178 ± 18 kJ/mol and 152 ± 10 kJ/mol, respectively, which are consistent with the activation energy of oxygen diffusion through MnO interfaces and the bulk diffusion of oxygen in austenite. Furthermore, the average activation energy for external oxide growth was ∼113 ± 18 kJ/mol, which was attributed to the diffusion of Mn cations along the grain boundaries of the external Mn oxides.

F-doped LiNi0.8Co0.15Al0.05O2-δ cathodes with enhanced ORR catalytic activity for LT-SOFCs

Developing highly effective catalysts for oxygen reduction reaction (ORR) is crucial to enable the low-temperature operation of solid oxide fuel cells (SOFCs). Recent studies have proposed a promising O2-/H+/e- conducting oxide, LiNi0.8Co0.15Al0.05O2-δ (LNCA) with good ORR catalytic activity for SOFC cathode uses. Herein, to further optimize the cathode functionality of LNCA, a fluorine anion (F-) doping strategy is applied to develop highly active LNCAF0.1 and LNCAF0.2 cathodes for Sm-doped ceria (SDC) electrolyte-based SOFCs. It is found the successful doping of F- in the oxygen site of LNCA leads to improved oxygen ionic conductivity and facilitated surface exchange and bulk diffusion of oxygen in LNCAF0.1 and LNCAF0.2, which thus gain distinctly promoted ORR catalytic activity at 450–550 °C, as confirmed by the decreased area specific resistances (ASR) and activation energy on symmetrical cells. The as-fabricated two SDC-based SOFCs with LNCAF0.1 and LNCAF0.2 cathodes exhibit peak power densities of 497 and 591 mW cm-2 at 550 °C, respectively, which are higher than that of the cell with LNCA cathode. Furthermore, the single cell with the best-performing LNCAF0.2 cathode demonstrates a good stability for 110 h at 550 °C. The present study thus provides a feasible strategy of F anion doping to promote the ORR catalytic activity of LNCA cathode for developing low-temperature SOFCs.

Chemical looping oxidative propane dehydrogenation controlled by oxygen bulk diffusion over FeVO4 oxygen carrier pellets

The oxygen distribution and evolution within the oxygen carrier exert significant influence on chemical looping processes. This paper describes the influence of oxygen bulk diffusion within FeVO4 oxygen carrier pellets on the chemical looping oxidative propane dehydrogenation (CL-ODH). During CL-ODH, the oxygen concentration at the pellet surface initially decreased and then maintained stable before the final decrease. At the stage with the stable surface oxygen concentration, the reaction showed a stable C3H6 formation rate and high C3H6 selectivity. Therefore, based on Fick’s second law, the oxygen distribution and evolution in the oxygen carrier at this stage were further analyzed. It was found that main reactions of selective oxidation and over-oxidation were controlled by the oxygen bulk diffusion. C3H8 conversion rate kept decreasing during this stage due to the decrease of the oxygen flux caused by the decline of oxygen gradient within the oxygen carrier, while C3H6 selectivity increased due to the decrease of over-oxidation. In addition, reaction rates could increase with the propane partial pressure due to the increase of the oxygen gradient within the oxygen carrier until the bulk transfer reached its limit at higher propane partial pressure. This study provides fundamental insights for the diffusion-controlled chemical looping reactions.

Enhanced oxygen bulk diffusion of La0.6Sr0.4FeO3-δ fuel electrode by high valence transition metal doping for direct CO2 electrolysis in solid oxide electrolysis cells

Solid oxide electrolysis cell (SOEC) is a promising energy conversion device for the efficient conversion of CO2 into valuable chemicals by using renewable energy sources. Fe-based perovskite oxides are highly active for CO2 electrochemical reduction as fuel electrodes in SOECs. Herein, high valence cations doped La0.6Sr0.4FeO3-δ oxides (La0.6Sr0.4FeO3-δ, La0.6Sr0.4Fe0.9Sc0.1O3-δ, La0.6Sr0.4Fe0.9Ta0.1O3-δ, La0.6Sr0.4Fe0.9W0.1O3-δ) are used as fuel electrodes in SOECs for CO2 electrolysis, and the crystal structure, electrical conductivity, chemical surface exchange coefficient (Kchem), chemical bulk diffusion coefficient (Dchem) and electrolysis performance are investigated for CO2 electrolysis. In addition, we determine the electrochemical processes on half cells and single cells with La0.6Sr0.4FeO3-δ series fuel electrodes by distribution of relaxation times (DRT) analysis, respectively. The results show that W-doping introduces more highly oxidative oxygen species O22−/O− and decreases the activation energy of lattice oxygen diffusion, thus accelerating the oxygen ion diffusion kinetics. The value of Dchem for La0.6Sr0.4Fe0.9W0.1O3-δ reaches to 4.671 × 10−4cm2 S−1 at 800 °C, and this value is 3.8 times than that of La0.6Sr0.4FeO3-δ (1.216 × 10−4cm2 S−1). DRT analysis indicates the different rate-limiting steps for CO2 reduction reaction (CO2RR) on half cells and single cells, which are the dissociation of carbonate intermediate process on half cells, and the exchange and diffusion of oxygen ions process on single cells. W-doping remarkably improves the oxygen ion transport property, thus enhancing the single cell performance for CO2 electrolysis. The single cell with La0.6Sr0.4Fe0.9W0.1O3-δ fuel electrode demonstrates a high current density of 1.48 A cm−2 at 800 °C and 1.5 V, with the polarization resistance (Rp) of 0.527 Ω cm2 at open circuit voltage (OCV). Meanwhile, the single cell exhibits good stability for 50 h at an applied voltage of 1.2 V. This work reveals the difference in electrochemical processes on half cells and single cells, and provides a strategy to accelerate the CO2RR kinetics of La0.6Sr0.4FeO3-δ-based materials.

(Digital Presentation) Understanding the Rate Limiting Process in a Pulse Laser Deposited Thin-Film Double Perovskite Electrode for Oxygen Reduction Reaction

Oxygen reduction reaction (ORR) in a double perovskite material is considered to be the most sluggish reaction in the intermediate temperature operation of a solid oxide fuel cell (SOFC). ORR is often inhibited by poor oxygen surface exchange rates or bulk diffusion in the material. In order to understand the rate-limiting process of the material, we have fabricated a dense thin-film double perovskite of composition Sr2CoNbO6- δ. The pulse laser deposition (PLD) method is employed to fabricate geometrically well-defined symmetric electrodes of SCN on an electrolyte substrate for accurate assessment of electrode impedance. Electrode thickness is varied from 40 nm to 80 nm by changing the deposition parameters in PLD. On increasing the thickness, the electrode impedance is observed to increase, suggesting bulk diffusion of oxygen anions limiting the electrochemical performance in the electrode material.

Enhanced performance of chemical looping methane oxidative coupling by the synergistic effect of TiO2 doped Na2WO4/Mn2O3/SiO2 oxygen carriers

Chemical looping methane oxidative coupling is a promising method to directly convert methane to C2 products but is limited by the trade-off between CH4 conversion and C2 selectivity. Here, we develop a series of TiO2 doped Na2WO4/Mn2O3/SiO2 for chemical looping methane oxidative coupling and investigate the underline mechanism for the enhanced performance. The results show that 5 wt% TiO2 doped Na2WO4/Mn2O3/SiO2 exhibited 31.2% CH4 conversion, which is 1.68 times as large as that of Na2WO4/Mn2O3/SiO2, without significantly decreasing C2 selectivity (~70.3%). Pulse experiments show that TiO2 improves the bulk oxygen diffusion, providing more surface oxygen to convert methane, thus leading to enhanced CH4 conversion. O 1 s spectra manifests that the active oxygen content on the surface was not significantly increased by TiO2 dopant, thus TiO2 dopant has little effect on C2 selectivity. Therefore, 5 wt% TiO2 doped Na2WO4/Mn2O3/SiO2 shows high chemical looping methane oxidative coupling performance. The explored mechanism in this work can be extended to design more oxygen carriers to enhance the chemical looping reactions.

Oxidation kinetics of La and Yb incorporated Zr-doped ceria for solar thermochemical fuel production in the context of dopant ionic radius and valence

The influence of ionic radii and valence of dopants in Ce0.9LaxYbyZr0.1−x−yO2−δ (x = 0, 0.05, 0.1, y = 0, 0.05, 0.1) on the oxidation kinetics were investigated by thermogravimetric analysis in synthetic air and were compared to undoped ceria. Samples co-doped with Zr–La and Zr–Yb exhibited moderate oxidation kinetics that were slower than undoped ceria, but much faster than 10mol% Zr-doped ceria. The extrinsic oxygen vacancy induced by the trivalent dopants improves the kinetics at oxidation temperatures below 700 °C, where the diffusion, and not the surface exchange reaction is the limiting factor. A smaller ionic radius of the substituent (i.e. r(Yb3+) < r(La3+)) in the co-doped ceria tends to facilitate lower activation energy resulting in slightly faster oxidation kinetics at temperatures below 700 °C. In contrast, additional extrinsic vacancies are rather obstructive at high temperatures (i.e. T> 700 °C) due to a change of rate limiting mechanism from bulk oxygen diffusion to surface exchange reaction. Overall, the valence of the dopant rather than the ionic radius seems to determine the oxidation kinetics primarily, and additional La or Yb doping on Zr-doped ceria is appealing especially when the applications are focused on low temperature reactions.

An electrochemical assessment of pristine SrCoO3‐δ using the distribution of relaxation times analysis

AbstractStrontium cobalt oxide is an important perovskite‐type material in the research of solid oxide fuel cells (SOFCs), since a great number of derived cathode materials can be obtained through composition modification against SrCoO3‐δ (SCO). In this work, pristine SCO without any additional dopants was synthesized, and its electrochemical properties were evaluated according to the electrochemical impedance spectroscopies (EIS) analyses through the distribution of relaxation times (DRT) method on the symmetrical cells. The undoped SCO displayed low polarization resistances as well as a high oxygen transport ability, even comparable to the famous cathode, Sm0.5Sr0.5CoO3‐δ (SSC). Oxygen surface and bulk diffusion were found to be the dominating processes in the oxygen reduction reaction (ORR) of SCO. These results could broaden our knowledge about the ionic transport behavior of SCO‐based perovskite materials.

Tuning the Phase Transition of SrFeO3-δ by Mn toward Enhanced Catalytic Activity and CO2 Resistance for the Oxygen Reduction Reaction.

Developing high-performance cathodes with sufficient stability against CO2 rooting in ambient atmosphere is crucial to realizing the practical application of solid-oxide fuel cells. Herein, the Mn dopant is investigated to regulate the phase structure and cathode performance of SrFeO3-δ perovskites through partially replacing the B-site Fe. Compared with parent SrFeO3-δ, Mn-doped materials, SrFe1-xMnxO3-δ (x = 0.05 and 0.1), show stabilized cubic perovskites at room temperature. Meanwhile, doping Mn accelerates the oxygen reduction reaction process, showing a reduced polarization resistance of 0.155 Ω·cm2 at 700 °C for SrFe0.95Mn0.05O3-δ, which is less than 30% of SrFeO3-δ. In addition, the Mn dopant improves the chemical oxygen surface exchange and bulk diffusion coefficients. Furthermore, Mn enhances the tolerance toward CO2 corrosion in various CO2 atmospheres. Density functional theory calculations also reveal that Mn can strengthen the structural stability and increase the activity for the oxygen reduction reaction.

A Strategy to Enhance the Catalytic Activity of Electrode Materials by Doping Bismuth for Symmetrical Solid Oxide Electrolysis Cells

Lanthanum chromate-based perovskites are potential ceramic electrodes for symmetrical solid oxide electrolysis cells (Sym-SOECs). In order to improve its electrochemical activity for CO2 reduction reaction (CO2RR), bismuth is introduced into the A-site. While all the components are stable in the anode atmosphere, the cathode application limits the doping content to 0.2, below which bismuth has the suboxidation state between 0 and +3. As revealed with experimental investigations and density functional theory calculations, doping bismuth could effectively increase the physicochemical properties for CO2RR, including oxygen vacancy concentration, CO2 adsorption capacity, conductivities in CO–CO2 atmospheres, oxygen bulk diffusion coefficient, as well as surface exchange coefficient. Consequently, Rp for CO2RR is reduced by 82% to 1.07 Ω cm2 at 800 °C. And the Sym-SOEC performance for CO2 electrolysis is increased by 46% to 0.79 A cm–2 at 800 °C, 1.5 V, indicating that bismuth-doped material is an excellent ceramic electrode material for Sym-SOECs.

Boosting CO2 directly electrolysis by electron doping in Sr2Fe1.5Mo0.5O6-δ double perovskite cathode

Commercialization of solid oxide electrolysis cell (SOEC) depends on the development of cathode materials with outstanding catalytic activity for CO2 electroreduction. Herein, Pure La-doped Sr2-xLaxFe1.5Mo0.5O6-δ double perovskite oxide is prepared via the citric acid-glycine method and used as a cathode to evaluate its electrochemical performance for CO2 electrolysis. La substitution at Sr-site promotes the oxygen surface exchange and bulk diffusion in Sr2-xLaxFe1.5Mo0.5O6-δ oxide, leading to higher CO2 electrolysis performance compared to Sr2Fe1.5Mo0.5O6-δ parent oxide. At 850 °C and 1.5 V, a current density of −2760 mA cm−2 is obtained on an LSGM-supported single cell with Sr1.9La0.1Fe1.5Mo0.5O6-δ cathode. In addition, the electrolysis cell displays excellent stability under a constant voltage of 1.2 V, suggesting that Sr1.9La0.1Fe1.5Mo0.5O6-δ oxide is a promising SOEC cathode material for pure CO2 electrolysis.