Magnetic Array-Aided Visualizing PEMFC Degradation Heterogeneity.

Analyzing degradation heterogeneity of proton exchange membrane fuel cell (PEMFC) while maintaining high practicality is consistently challenging, primarily due to the destructive and costly nature of existing techniques relying on material characterization. In this work, a designed magnetic array integrating 16 sensors within 25 cm2 space is used for direct scanning and imaging of PEMFC performance heterogeneity during its degradation. Results are validated through degradation mechanism analysis and material characterization, confirming its potential in guiding the development of durable materials.

Fe-Doped Ceria-Based Ceramic Cathode for High-Efficiency CO2 Electrolysis in Solid Oxide Electrolysis Cell.

In the quest for sustainable energy solutions, solid oxide electrolysis cell (SOEC) emerges as a key technology for converting CO2 into fuels and valuable chemicals. This work focuses on pure ceramic Fex Sm0.2 Ce0.8 O2- δ (xFe-SDC) as the fuel electrodes, and Sr-free ceria-based ceramic electrodes can be successfully constructed for x ≤ 0.05. The incorporation of Fe into the ceria lattice increases the oxygen vacancy concentration and promotes the formation of catalytic sites crucial for the CO2 reduction reaction (CO2 RR). Density functional theory calculations indicate that Fe enhances electrochemical performance by decreasing the CO2 RR energy barrier and facilitating oxygen ion diffusion. At 800 °C and 1.5 V, single cells with 0.05Fe-SDC cathodes manifest attractive performance, attaining current densities of -1.98 and -2.26 A cm-2 under 50% CO2 /CO and pure CO2 atmospheres, respectively. These results suggest the great potential of xFe-SDC electrodes as promising avenues for high-performance fuel electrodes in SOEC.

A Superior Catalytic Air Electrode with Temperature-Induced Exsolution toward Protonic Ceramic Cells.

Protonic ceramic cells merit extensive exploration, attributed to their innate capabilities for potent and environmentally benign energy conversion. In this work, a temperature-induced exsolution methodology to synthesize SrCo0.5Nb0.5O3-δ (SCN) nanoparticles (NPs) with notably elevated activity on the surface of PrSrCo1.8Nb0.2O6-δ (PSCN) is proposed, directly addressing the extant challenge of restrained catalytic activity prevalent in air electrode materials. In situ assessments reveal that SCN NPs commence exsolution from the matrix at temperatures surpassing 900 °C during straightforward calcination processes and maintain stability throughout annealing. Notably, the resultant SCN-PSCN interface facilitates vapor adsorption and protonation processes, which are poised to enhance surface reaction kinetics pertaining to the proton-involved oxygen reduction and evolution reaction (P-ORR and P-OER). A fuel-electrode-supported protonic ceramic cell leveraging SCN-PSCN as the air electrode manifests compelling performance, attaining a peak power density of 1.30 W·cm-2 in the fuel cell modality and a current density of 1.91 A·cm-2 at 1.3 V in the electrolysis mode, recorded at 650 °C. Furthermore, density functional theory calculations validate that the introduction of SCN NPs onto the PSCN surface conspicuously accelerates electrode reaction rates correlated with P-ORR and P-OER, by significantly mitigating energy barriers associated with surface oxygen and vapor dissociation.

Fe-Doped SDC Solid Solution as an Electrolyte for Low-to-Intermediate-Temperature Solid Oxide Fuel Cells.

Ceria-based oxides, such as samaria-doped ceria (SDC), are potential electrolytes for low-to-intermediate-temperature solid oxide fuel cells (SOFCs). The sinterability of these materials can be improved by adding iron as the sintering aid. This work reveals that Fe is soluble in SDC, forming an Fe-doped SDC solid solution. It is found that the solubility is affected by the sintering temperature. Fe doping has obvious effects on electrolyte properties, including sintering characteristics, thermal expansion behaviors, and electrical conductivities in both air and hydrogen atmospheres. The conductivity obviously increases while the activation energy decreases by doping Fe. Compared with that of the bare SDC electrolyte, the performance of the single cell with the Fe-doped SDC is enhanced; for example, the peak power density is increased by 52.8% to 0.726 W cm-2 at 600 °C when humidified hydrogen is used as the fuel and ambient air is used as the oxidant. The single cell showed stable operation at 600 °C under a constant current density of 0.3 A cm-2 for 150 h. Therefore, the Fe-doped SDC solid solution shows promise as a potential electrolyte for low-to-intermediate-temperature SOFCs.

Enhanced ferromagnetic properties achieved by F-doping in BaFe1-xMnxO3-δ.

Tailoring the crystal structure, spin, and charge state of perovskite oxides through fluorine ion doping is an attractive and effective strategy, which could significantly modify the physical and chemical properties of base oxides. Here, BaFe1-xMnxO3-δ (x = 0, 0.1, 0.2, 0.3) and BaFe1-xMnxO2.9-δF0.1 (x = 0.1, 0.2, 0.3), belonging to 6H-type BaFeO3-δ, are prepared and investigated to evaluate the impact of F- doping. The distortion of crystal structure and the reduced average valence of Mn and Fe confirm the preference for F- substitution in the hexagonal layer, which are found as the key factors for the improved magnetic properties, including ferromagnetic ordering temperature, coercive force, and remanent magnetization. Moreover, the valence reduction of B-site ions and the increased resistance distinctly indicate the expense of electron hole via fluorine doping. This work describes the adjustment of crystal structure, electronic configuration, and ferromagnetic performance by simple F- doping, which provides a prospect for practical magnetic materials.

Surface Self-Assembly Protonation Triggering Triple-Conductive Heterostructure with Highly Enhanced Oxygen Reduction for Protonic Ceramic Fuel Cells.

Triple-conducting (H+ /O2- /e- ) cathodes are a vital constituent of practical protonic ceramic fuel cells. However, seeking new candidates has remained a grand challenge on account of the limited material system. Though triple conduction can be achieved by mechanically mixing powders uniformly consisting of oxygen ion-electron and proton conductors, the catalytic activity and durability are still restricted. By leveraging this fact, a highly efficient strategy to construct a triple-conductive region through surface self-assembly protonation based on the robust double-perovskite PrBaCo1.92 Zr0.08 O5+δ , is proposed. In situ exsolution of BaZrO3 -based nanoparticles growing from the host oxide under oxidizing atmosphere by liberating Ba/Zr cations from A/B-sites readily forms proton transfer channels. The surface reconstructing heterostructures improve the structural stability, reduce the thermal expansion, and accelerate the oxygen reduction catalytic activity of such nanocomposite cathodes. This design route significantly boosts electrochemical performance with maximum peak power densities of 1453 and 992 mW cm-2 at 700 and 650 °C, respectively, 86% higher than the parent PrBaCo2 O5+δ cathode, accompanied by a much improved operational durability of 140 h at 600 °C.

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.

Theoretical and Experimental Investigations on K-doped SrCo0.9 Nb0.1 O3-δ as a Promising Cathode for Proton-Conducting Solid Oxide Fuel Cells.

Improving proton conduction in cathodes is regarded as one of the most effective methods to accelerate the sluggish proton-involved oxygen reduction reaction (P-ORR) for proton-conducting solid oxide fuel cells (P-SOFCs). In this work, K+ dopant was used to improve the proton uptake and migration ability of SrCo0.9 Nb0.1 O3-δ (SCN). K+ -doped SCN (KSCN) demonstrated great potential to be a promising cathode for P-SOFCs. Density functional theory calculations suggested that doping with K+ led to more oxygen vacancies and more negative values of hydration enthalpy, which was helpful for the improvement of proton concentration. Importantly, the proton migration barriers could be depressed, benefiting proton conduction. Electrochemical investigations signified that the cell using KSCN cathode had a peak power density of 967 mW cm-2 at 700 °C, about 54.1 % higher than that using a SCN cathode. This research highlights the K+ -doping strategy to improve electrochemical performance of cathodes for P-SOFCs.

Infiltrated Ni0.08Co0.02CeO2-x@Ni0.8Co0.2 Catalysts for a Finger-Like Anode in Direct Methane-Fueled Solid Oxide Fuel Cells.

Direct utilization of methane in solid oxide fuel cells (SOFCs) is greatly impeded by the grievous carbon deposition and the much depressed catalytic activity. In this work, a promising anode, taking finger-like porous YSZ as the anode substrate and impregnated Ni0.08Co0.02Ce0.9O2-δ@Ni0.8Co0.2O as the novel catalyst, is fabricated via the phase conversion-combined tape-casting technique. This anode shows commendable mechanical strength and excellent catalytic activity and stability toward the methane conversion reactions, which is attributed to the exsolved alloy nanoparticles and the active oxygen species on the reduced Ni0.08Co0.02Ce0.9O2-δ catalyst as well as the facilitated methane transport rooting in the special open-pore microstructure of the anode substrate. Strikingly, this button cell delivers an excellent peak power density of 730 mW cm-2 at 800 °C in 97% CH4/3% H2O fuel, only 9% lower than that in 97% H2/3% H2O. Our work shed new light on the SOFC anode developments.

Interfacial Titanium Diffusion Self-Adapting Layer in Ultrathin Epitaxial MnO2/TiO2 Heterostructures.

The electrochemical performance of supercapacitors is suppressed by a large number of defects in the interface of heterostructure due to lattice mismatch. In this paper, the (001) oriented rutile MnO2 thin films with different thicknesses were grown on rutile TiO2 substrates. The lattice mismatch between film and substrate was minimized through a Ti diffusion self-adapting layer. The energy-dispersive spectroscopy mappings were used to measure the diffusion range of Ti. The results of high-resolution X-ray diffraction confirmed that the dependence of the out-of-plane lattice parameter on the thickness was consistent with the self-adapting interface model, indicating that Ti diffusion can indeed alleviate the lattice mismatch. In addition, the results of the synchrotron soft X-ray absorption spectrum indicated that the capacitance of the thin films with a large proportion of Ti diffusion increased with electrons involved in the reaction. Although the decrease of carrier density and conductivity of the thinner films depressed the electrochemical activity, it is worth mentioning that the film we designed still has considerable specific capacitance even when it is very thin, which can provide a new idea for the development of thinner and larger capacity potential micro-supercapacitors.

A Durable Ruddlesden-Popper Cathode for Protonic Ceramic Fuel Cells.

Protonic ceramic fuel cells (PCFCs) have been proved as an efficient energy converter at intermediate temperatures. To accelerate the kinetics of the proton-involved oxygen reduction reaction (p-ORR), developing efficient and durable cathodes is of great importance for improving PCFCs. In this work, a new triple-layered Ruddlesden-Popper (R-P) structure oxide, Sr3 EuFe2.5 Co0.5 O10-δ (3-SEFC0.5 ), was developed as a potential single-phase cathode for PCFCs, showing high oxygen non-stoichiometry and desirable structural thermal stability. By employing this highly active and stable single-phase cathode, the PCFC demonstrated unprecedented low polarization resistances and exceptionally great peak power densities, which were approximately 0.030â€…Ω cm2 and 900 mW cm-2 measured at 700 °C, respectively. These findings not only manifest the effectiveness of optimal doping in improving the structural stability and electrocatalytic activity in the multi-layered perovskite family, but also highlight the great potential of using multi-layered R-P series oxides as highly active and durable catalysts for PCFCs.

Protonic Ceramic Electrochemical Cell for Efficient Separation of Hydrogen.

Advancement of a hydrogen economy requires establishment of a whole supply chain including hydrogen production, purification, storage, utilization, and recovery. Nevertheless, it remains challenging to selectively purify hydrogen out of H2-containing streams, especially at low concentrations. Herein, a novel protonic ceramic electrochemical cell is reported that can sustainably separate pure H2 out of H2-diluted streams over the temperature regime of 350-500 °C by mildly controlling the electric voltage. With the Faraday's efficiency above 96%, the measured H2 separation rate at 0.51 V and 500 °C is 3.3 mL cm-2 min-1 out of 10% H2 - 90% N2, or 2.4 mL cm-2 min-1 out of 10% H2 - 90% CH4 taken as an example of renewable hydrogen blended in the natural gas pipelines. Such high hydrogen separation capability at reduced temperatures is enabled by the nanoporous nickel catalysts and well-bonded electrochemical interfaces as produced from well-controlled in situ slow reduction of nickel oxides. These results demonstrate technical feasibility of onsite purification of hydrogen prior to their practical applications such as fuels for fuel cell electric vehicles.

Computational investigation of Zn-doped and undoped SrEu2Fe2O7 as potential mixed electron and proton conductors.

Understanding the electrode properties at the atomistic level is of great benefit to the evaluation of electrode performance and design of better electrode materials in solid oxide fuel cells. In this work, density functional theory (DFT) calculations are employed to investigate the formation and conducting behaviors of oxygen vacancies and proton defects in Ruddlesden-Popper oxide SrEu2Fe2O7 (SEFO), which has been experimentally characterized as a promising cathode. The calculation results suggest both oxygen vacancies and proton defects can be formed in SEFO, and especially, the formation of these defects is largely dependent on oxygen sites in the special crystal structure with alternative stacking of rock-salt layers and double-layered perovskite slabs. The oxygen vacancies within the perovskite slabs have very low formation energies, but demonstrate high energy barriers for migration and low hydration properties; while in the case of those in the rock salt layers, it's contrary. Interestingly, protons have similar migration abilities in the perovskite slabs and rock salt layers. And therefore, increasing the vacancy concentration of the rock salt layer is beneficial to increase the concentration of proton defects and to improve the proton conductivity. DFT calculations also indicate that substituting Zn for Fe in SEFO can largely depress the oxygen vacancy formation energy, which helps to increase the concentration of both defects. Importantly, the energy barriers for migration of both oxygen ions and protons are barely enhanced, implying a negligible trapping effect of the Zn dopant.

A Stable and Efficient Cathode for Fluorine-Containing Proton-Conducting Solid Oxide Fuel Cells.

Substitution of anions such as F- and Cl- can effectively improve the stability of proton-conducting electrolytes at no expense to proton conduction. However, during operation, F- and Cl- in electrolytes can transfer to the cathodes, which reduces the stability of the electrolytes. In this work, F- -doped Ba0.5 Sr0.5 Co0.8 Fe0.2 O3-δ [Ba0.5 Sr0.5 Co0.8 Fe0.2 O2.9-δ F0.1 (F-BSCF)] was prepared as a potential cathode for proton-conducting solid oxide fuel cells with BaCe0.8 Sm0.2 F0.1 O2.85 electrolyte. The incorporation of F- in the cathode depressed F- diffusion from the electrolyte and improved the stability of button cells. Temperature-changing X-ray photoelectron spectroscopy and electronic conductivity relaxation results demonstrated that the incorporation of F- enhanced the oxygen incorporation kinetics at intermediate temperatures and improved the cathode catalytic performance. Moreover, a button cell prepared with this novel cathode was stable for 270 h at a current density of 300 mA cm-2 and 700 °C, which was much superior than those containing a BSCF cathode.

Strain-induced high-temperature perovskite ferromagnetic insulator.

Ferromagnetic insulators are required for many new magnetic devices, such as dissipationless quantum-spintronic devices, magnetic tunneling junctions, etc. Ferromagnetic insulators with a high Curie temperature and a high-symmetry structure are critical integration with common single-crystalline oxide films or substrates. So far, the commonly used ferromagnetic insulators mostly possess low-symmetry structures associated with a poor growth quality and widespread properties. The few known high-symmetry materials either have extremely low Curie temperatures (≤16 K), or require chemical doping of an otherwise antiferromagnetic matrix. Here we present compelling evidence that the LaCoO3 single-crystalline thin film under tensile strain is a rare undoped perovskite ferromagnetic insulator with a remarkably high TC of up to 90 K. Both experiments and first-principles calculations demonstrate tensile-strain-induced ferromagnetism which does not exist in bulk LaCoO3 The ferromagnetism is strongest within a nearly stoichiometric structure, disappearing when the Co2+ defect concentration reaches about 10%. Significant impact of the research includes demonstration of a strain-induced high-temperature ferromagnetic insulator, successful elevation of the transition over the liquid-nitrogen temperature, and high potential for integration into large-area device fabrication processes.

Nanoscale Structural Modulation and Low-temperature Magnetic Response in Mixed-layer Aurivillius-type Oxides.

Nanoscale structural modulation with different layer numbers in layer-structured complex oxides of the binary Bi4Ti3O12-BiFeO3 system can give rise to intriguing phenomena and extraordinary properties, originating from the correlated interfaces of two different phases with different strain states. In this work, we studied the nanoscale structural modulation induced by Co-substitution in the Aurivillius-type oxide of Bi11Fe3Ti6O33 with a unique and naturally occurred mixed-layer structure. Nanoscale structural evolution via doping occurred from the phase-modulated structure composed of 4- and 5-layer phases to a homogeneous 4-layer structure was clearly observed utilizing x-ray diffraction and electron micro-techniques. Significantly, magnetic response for the samples under various temperatures was recorded and larger magnetic coercive fields (e.g. H c ∼ 10 kOe at 50 K) were found in the phase-modulated samples. Analyses of the x-ray absorption spectra and magnetic response confirmed that the low-temperature magnetic behaviour should be intrinsic to the phase-modulated structure inside the structural transformation region, mainly arising from structural distortions at the correlated interfaces.

Superlattice-like structure and enhanced ferroelectric properties of intergrowth Aurivillius oxides.

Aurivillius oxides with an intergrowth structures have been receiving increasing interest because of their special structures and potential outstanding ferroelectric properties. In this work, Bi3LaTiNbFeO12-Bi5Ti3FeO15 and Bi3TiNbO9-Bi3LaTiNbFeO12 compounds were successfully synthetised using a simple solid-state reaction method. X-Ray diffraction patterns and scanning transmission electron microscopy high angle annular dark field (STEM-HAADF) images confirm the 2-3 and the 3-4 intergrowth structures in Bi3TiNbO9-Bi3LaTiNbFeO12 and Bi3LaTiNbFeO12-Bi5Ti3FeO15 compounds, respectively. A superlattice-like distortion in these oxides was proposed resulting from the combination of sub-lattices with different a and b parameters, which was validated by XRD refinements and Raman spectra. Polarization-electric field tests and pulsed polarization positive-up negative-down measurements demonstrate that such superlattice-like structures can effectively enhance the intrinsic ferroelectric polarization and coercive field of these oxides, especially when compared with their component oxides Bi3TiNbO9, Bi3LaTiNbFeO12 and Bi5Ti3FeO15. Simultaneously, ferroelectric Curie temperatures of Bi3TiNbO9-Bi3LaTiNbFeO12 and Bi3LaTiNbFeO12-Bi5Ti3FeO15 oxides are lowered because of the internal stress in the superlattice-like structure. Nevertheless, the paramagnetism of the samples is hardly influenced by their structure, while mainly related to their iron content, in which iron has a similar effective magnetic moment around 3.4-3.9.

New, Efficient, and Reliable Air Electrode Material for Proton-Conducting Reversible Solid Oxide Cells.

Driven by the demand to minimize fluctuation in common renewable energies, reversible solid oxide cells (RSOCs) have drawn increasing attention for they can operate either as fuel cells to produce electricity or as electrolysis cells to store electricity. Unfortunately, development of proton-conducting RSOCs (P-RSOCs) faces a major challenge of poor reliability because of the high content of steam involved in air electrode reactions, which could seriously decay the lifetime of air electrode materials. In this work, a very stable and efficient air electrode, SrEu2Fe1.8Co0.2O7-δ (SEFC) with layer structure, is designed and deployed in P-RSOCs. X-ray diffraction analysis and High-angle annular dark-filed scanning transmission electron microscopy images of SEFC reveal that Sr atoms occupy the center of perovskite slabs, whereas Eu atoms arrange orderly in the rock-salt layer. Such a special structure of SEFC largely depresses its Lewis basicity and therefore its reactivity with steam. Applying the SEFC air electrode, our button switches smoothly between both fuel cell and electrolysis cell (EC) modes with no obvious degradation over a 135 h long-term test under wet H2 (∼3% H2O) and 10% H2O-air atmospheres. A record of over 230 h is achieved in the long-term stability test in the EC mode, doubling the longest test that had been previously reported. Besides good stability, SEFC demonstrates great catalytic activity toward air electrode reactions when compared with traditional La0.6Sr0.4Co0.2Fe0.8O3-δ air electrodes. This research highlights the potential of stable and efficient P-RSOCs as an important part in a sustainable new energy power system.

A first-principles study on divergent reactions of using a Sr3Fe2O7 cathode in both oxygen ion conducting and proton conducting solid oxide fuel cells.

Exploring mechanisms for sluggish cathode reactions is of great importance for solid oxide fuel cells (SOFCs), which will benefit the development of suitable cathode materials and then accelerate cathode reaction rates. Moreover, possible reaction mechanisms for one cathode should be different when operating in oxygen ion conducting SOFCs (O-SOFC) and in proton conducting SOFCs (P-SOFCs), and therefore, they lead to different reaction rates. In this work, a Ruddlesden-Popper (R-P) oxide, Sr3Fe2O7 (SFO), was selected as a promising cathode for both O-SOFCs and P-SOFCs. Using the first-principles approach, a microscopic understanding of the O2 reactions over this cathode surface was investigated operating in both cells. Compared with La0.5Sr0.5Co0.25Fe0.75O3 (LSCF), the low formation energies of oxygen vacancies and low migration energy barriers for oxygen ions in SFO make oxygen conduction more preferable which is essential for cathode reactions in O-SOFCs. Nevertheless, a large energy barrier (2.28 eV) is predicted for oxygen dissociation reaction over the SFO (001) surface, while there is a zero barrier over the LSCF (001) surface. This result clearly indicates that SFO shows a weaker activity toward the oxygen reduction, which may be due to the low surface energies and the specific R-P structure. Interestingly, in P-SOFCs, the presence of protons on the SFO (001) surface can largely depress the energy barriers to around 1.46-1.58 eV. Moreover, surface protons benefit the oxygen adsorption and dissociation over the SFO (001) surface. This result together with the extremely low formation energies and migration energy barriers for protons seem to suggest that SFO could work more effectively in P-SOFCs than in O-SOFCs. It's also suggested that too many protons at the SFO surface will lead to high energy barriers for the water formation process, and thus that over-ranging steam concentrations in the testing atmosphere may have a negative effect on cell performances. Our study firstly and clearly presents the different energy barriers for one cathode performing in both O- and P-SOFCs according to their different working mechanisms. The results will be helpful to find the constraints for using cathodes toward oxygen reduction reactions, and to develop effective oxide cathode materials for SOFCs.

Engineering the exchange bias and bias temperature by modulating the spin glassy state in single phase Bi9Fe5Ti3O27.

Exchange anisotropy is normally observed at ferromagnetic (FM)/anti-ferromagnetic (AFM) interfaces and also usually at low temperatures. An effective way to find new single-phase materials with strong exchange bias (EB) and high operation temperatures is required for making them useful in practical applications of future spintronic devices. In this work, the exchange bias behaviors of single phase Bi9Fe5Ti3O27 (BFT) were found able to be manipulated by altering its spin glassy state, when the material was intentionally prepared in the nanobelt format. A core-shell model has been proposed to explain the controllable behavior of both exchange bias and bias temperature, in which the AFM domain could be effectively reduced within the nanobelts when changing their particle sizes. A direct observation of two spin glassy behaviors corresponding to two distinct peaks in the zero field cooling (ZFC) curves manifests the validity of the proposed core-shell model.