Original Perovskite Research Articles

High Performance Perovskite Photodiodes via Molecule-Assisted Interfacial and Bulk Modulations.

Metal halide perovskites have attracted significant attention in photodetection due to their superior photophysical properties and improved stability. However, the performance of their photodiodes is predominantly limited by non-radiative recombination within the perovskite layer or at interfaces. Here, molecular engineering via phenylethylammonium chloride for interfacial modulation and methylenediammonium dichloride for bulk modulation is introduced into vertical perovskite photodiodes to boost the photodetection performance. The responsivity at 635 nm excitation increased from 0.09 to 0.33 AW-1 with interfacial modulation, compared to the original perovskite device, and is further improved to 0.40 AW-1 with the combined effects of interfacial and bulk modulations (i.e., synergistic bimolecular engineering). The optimized photodiodes demonstrated high detectivity of over 1011 Jones, a rapid response time of ≈1 µs, and a linear dynamic range of ≈100 dB. Furthermore, the photocurrent exhibited a U-shaped dependence on temperature ranging from 10 to 300 K, with linearity breaking under strong illumination at low temperatures. These results confirmed that molecular engineering is the promising strategy for achieving high-performance perovskite photodetectors.

Carbon-Based Perovskite Solar Cells: Interface Engineering of 5-AVAI Additive

Perovskite materials have great potential for high efficiencies in photovoltaic devices, with the best performances exceeding 26% in a single junction. We now need to further develop perovskite device architectures that combine ease of industrial development with effective durability. Among the alternatives, mesoporous frameworks based on metal oxide and carbon are promising due to their inherent high stability. In the presented work, two perovskite formulations will be compared: MAPbI3 and (5-AVA)xMA1-xPbI3. Both were infiltrated using drop casting as a final step, which provides a clean industrial process for large scale and stable perovskite devices. The aim was to highlight the differences in behavior between devices based on the traditional MAPbI3 perovskite when fabricated with or without 5-ammonium valeric acid iodide (5-AVAI) as an additive. A detailed study with a large series of characterizations (macroscopic functional properties, LBIC imaging, photoluminescence, UV-visible spectroscopy, X-ray diffraction, impedance spectroscopy) has provided new insights into how carbon-based mesoscopic perovskite solar cells perform and degrade.Perovskites based on AVAI possess higher performances and durability than the original perovskite formulation, however they also demonstrated a higher potential for species diffusion and interface contamination. A special attention will be thus given to the method used to measure performances by analyzing J-V curves at different scan rates. Indeed, this allowed us to define boundary conditions allowing the observation of two different states within our devices (defined as ‘stable’ and ‘metastable’). This behavior was interpreted as a structural transition [1] and can vary according to the perovskite formulation. In addition, the degradation of performance with aging time under damp-heat conditions was found related to a different mechanism in devices formulated with or without AVAI: the critical damage occurring either at the perovskite interfaces or within the perovskite itself.

SrCoNiO3-δ perovskite nanozyme for deep-learning-assisted intelligent detection of dopamine hydrochloride and Cd2+

SrCoO3, SrNiO3, and SrCoNiO3-δ were produced by high-temperature calcination method. Among them, SrCoNiO3-δ trimetallic perovskite exhibited outstanding peroxidase and oxidase activity. Various characterization analyses revealed that the addition of Ni2+ partially replaced Co2+ in the initial perovskite coordination environment, conferring a unique catalytic ability that altered the crystal shape of the original perovskite structure and resulted in a richer electron transfer. This causes the material's surface to exhibit oxygen vacancies (Ovs) and OH radicals, which are the primary source of enzyme activity. Based on the material's excellent enzyme activity, we successfully developed a flexible, intelligent, fast, and instant colorimetry detection platform for the detection of dopamine hydrochloride (DAH) and Cd2+ using a smartphone, assisting in the detection of antibiotic residues in soil and water. The linear ranges of DAH and Cd2+ are 2–20 μM, and their respective detection limits are 0.098 μM and 0.343 μM.

Dense Perovskite Thick Film Enabled by Saturated Solution Filling for Sensitive X-ray Detection and Imaging.

Thick polycrystalline perovskite films synthesized by using solution processes show great potential in X-ray detection applications. However, due to the evaporation of the solvent, many pinholes and defects appear in the thick films, which deteriorate their optoelectronic properties and diminish their X-ray detection performance. Therefore, the preparation of large area and dense perovskite thick films is desired. Herein, we propose an effective strategy of filling the pores with a saturated precursor solution. By adding the saturated perovskite solution to the polycrystalline perovskite thick film, the original perovskite film will not be destroyed because of the solution-solute equilibrium relationship. Instead, it promotes in situ crystal growth within the thick film during the annealing process. The loosely packed grains in the original thick perovskite film are connected, and the pores and defects are partially filled and fixed. Finally, a much denser perovskite thick film with improved optoelectronic properties has been obtained. The optimized thick film exhibits an X-ray sensitivity of 1616.01 μC Gyair-1 cm-2 under an electric field of 44.44 V mm-1 and a low detection limit of 28.64 nGyair s-1 under an electric field of 22.22 V mm-1. These values exceed the 323.86 μC Gyair-1 cm-2 and 40.52 nGyair s-1 of the pristine perovskite thick film measured under the same conditions. The optimized thick film also shows promising working stability and X-ray imaging capability.

Advancements in perovskite solar cell efficiency through blade coating techniques and post-treatment optimization

Addition of lead chloride (PbCl2) improves the crystallization kinetics of perovskites by suppressing the formation of δ-phase during large-area perovskite film fabrication. However, this addition results in formation and accumulation of lead iodide (PbI2) platelet atop the film, which adversely affects carrier transport. To eliminate the negative effect of PbI2 accumulation and simultaneously obtain a dense, mirror-like perovskite film, a post-treatment method involving blade coating formamidinium iodide (FAI) under air atmosphere is used. Instead of being washed away, as reported in literatures using spin coating process, PbI2 platelets are converted into cesium lead halide perovskites (CsPbX3) through reaction with Cs and halide present in the original perovskite Cs0.22FA0.78Pb(I0.85Br0.15)3. An efficiency enhancement of (>10%) is achieved by FAI treatment, which does not require fast solvent removal or nitrogen (N2) atmospheres, indicating that FAI blade coating is an effective and straightforward method for the post-treatment of excess PbI2.

Achieving improved dielectric energy storage properties and temperature stability in 0.91Na0.5Bi0.5TiO3-0.09K0.7La0.1NbO3 based ferroelectric ceramics by composition design and processing optimization

In this study, a ternary solid solution was designed by incorporating varying concentrations of the B-site composite perovskite Ba(Mg1/3Ta2/3)O3 (BMT) into 0.91Na0.5Bi0.5TiO3-0.09K0.7La0.1NbO3 (NBT-KLN-based) ferroelectric ceramics to optimize their energy storage performance. The introduction of BMT disrupted the long-range ordered state of the A/B site in the original perovskite structure, resulting in increased structural disorder and enhanced relaxor characteristics. The viscous polymer processing (VPP) method was employed to attain a significantly denser structure. The 0.10BMT-vpp ceramic has ultimately achieved optimal energy storage performance, along with exceptional temperature and frequency stability. It boasts a high dielectric breakdown strength (BDS) of 440 kV/cm, an ultra-high effective energy storage density (Wrec) of 6.7 J/cm3, and an energy storage efficiency (η) of 82%. Moreover, the 0.10BMT-vpp ceramic exhibits robust pulse performance, characterized by an ultra-fast discharge time (t0.9) of only 77 ns. Furthermore, within the temperature range of −66 °C–354 °C, the temperature coefficient of capacitance (TCC) of the 0.25BMT ceramics undergoes a variation of no more than ±15%, in compliance with X9R specifications (−55 °C–200 °C). The introduction of BMT endows NBT-KLN-based ceramics with remarkable temperature stability and comprehensive energy storage performance, making it a ceramic material with practical potential for industrial applications.

Reduction-Induced Magnetic Behavior in LaFeO3-δ Thin Films.

The effect of oxygen reduction on the magnetic properties of LaFeO3-δ (LFO) thin films was studied to better understand the viability of LFO as a candidate for magnetoionic memory. Differences in the amount of oxygen lost by LFO and its magnetic behavior were observed in nominally identical LFO films grown on substrates prepared using different common methods. In an LFO film grown on as-received SrTiO3 (STO) substrate, the original perovskite film structure was preserved following reduction, and remnant magnetization was only seen at low temperatures. In a LFO film grown on annealed STO, the LFO lost significantly more oxygen and the microstructure decomposed into La- and Fe-rich regions with remnant magnetization that persisted up to room temperature. These results demonstrate an ability to access multiple, distinct magnetic states via oxygen reduction in the same starting material and suggest LFO may be a suitable materials platform for nonvolatile multistate memory.

Formation mechanism of α-phase CsPbI2Br induced by excessive CsBr without an annealing treatment

For the evaporation preparation of CsPbI2Br films, when the two precursors of CsBr and PbI2 follow the stoichiometric ratio, an additional annealing treatment is necessary to obtain a stable α-phase CsPbI2Br. However, it is found that as the evaporation rate ratio of precursor CsBr to PbI2 is increased, the α-phase CsPbI2Br can be observed in the generated film without an annealing treatment. Adjusting the evaporation rate ratio of Cs to Pb to about 1.2:1, the prepared film has the best morphology and crystallinity. Compared to the α-phase CsPbI2Br films generated by following the stoichiometric ratio and subsequent annealing treatment, the ones prepared here present similar photoelectric properties and even better environmental stability. In addition, photodetectors based on the latter exhibit better optoelectronic performance. To explain the role of excessive CsBr in the formation of α-phase CsPbI2Br, we propose a ‘hollow-perovskite’ structure model. The excessive CsBr is doped into the perovskite structure by replacing the [PbI6]- octahedral structure, and the cubic structure of the original perovskite is not significantly changed. Moreover, the results of DFT calculations also indicate that when Cs (or CsBr) is excessive, the system has lower formation energy, so, is easier to form and has better stability at room temperature. This work is valuable for the study of the preparation and working mechanism of all inorganic perovskite.

Mechanism of the surface-preferred crystal plane of CsPbBr3 single crystals in different solvents

CsPbBr3 single crystals have been grown by using solution method with hydrobromic acid (HBr) and dimethyl sulfoxide (DMSO), respectively. The same orthorhombic phase of crystals grown in these two solvents was confirmed by X-ray powder diffraction (XRD). A very interesting phenomenon is that the surface-preferred crystal plane of the CsPbBr3 single crystal would be (200) in HBr solution, while that would be (101) in DMSO solution. Remarkably, this growth mechanism can be explained effectively by the principle of opposite charges attraction, which would be likely to provide an approach to be extended to the regulation of surface-preferred crystal plane of other perovskite single crystals grown in different solvents, especially using solvent with original perovskite solute ions.

Nb-doped double perovskite Sr2CoFeO6−δ as an efficient and prospective electrode for quasi-symmetrical solid oxide fuel cells

The utilization of identical anode and cathode materials in symmetrical solid oxide fuel cells (SSOFCs) can efficiently reduce their fabrication costs and prolong their operational life. Herein, Nb-doped double perovskite Sr2CoFeO6-δ of a traditional cathode was employed as the electrode material for SSOFCs. Notably, the electrochemical performance and reversibility were improved due to Nb doping. The Nb-doped sample Sr2CoFe0.7Nb0.3O6−δ.5 (SCFN3) was synthesized in air, which decomposed into Co–Fe alloy, SrCoO2.25, and Sr3FeNbO6−δ in H2. Following calcination in air, the sample reverted to the original perovskite structure. The SCFN3 sample exhibited good chemical compatibility with SOFC electrolytes such as La0.8Sr0.2Ga0.8Mg0.2O3−δ (LSGM), Sm0.2Ce0.8O2−δ, and BaZr0.1Ce0.7Y0.1Yb0.1O3−δ. A single cell consisting of 300-μm LSGM electrolyte exhibited maximum power densities of 951, 510, 563, and 397 mW/cm2 at 850℃ when using H2, C3H8, liquid C2H5OH, and solid C as fuels, respectively. These findings adequately demonstrate the fuel-flexible characteristics of SOFCs.

Phase Stability of SrTi1-XFexO3- δ Under Solid Oxide Cell Fuel-Electrode Conditions: Implications for Related Exsolution Electrode Materials

SrTi1-xFexO3-δ (STF) has shown promise as a fuel electrode, and as a basis for fuel electrodes with catalytically active nanoparticle exsolution. This study aims to determine trends in performance and stability of STF in highly reducing environments as Fe-content is varied from x = 0.5 to 0.8. Here we report that, while polarization resistance of STF fuel electrodes decreases with higher Fe-content, this is accompanied with lower stability in highly reducing conditions. For too-reducing conditions and too-high x, partial decomposition of the original perovskite phase is observed with the formation of metallic Fe and a Ruddlesden-Popper STF phase.

Controllable Transformation of 2D Perovskite for Multifunctional Sensing Properties

There is growing demand for convenient and cost-efficient ethanol sensing techniques in daily life and industry. However, the complexity, high cost, and large volume of the equipment hinder the widespread use of conventional ethanol sensing techniques. Here, we introduce a test paperlike visualized label-free ethanol sensing platform by taking advantage of the instability of 2D Ruddlesden–Popper perovskite in ethanol. The photoluminescence of PEA2Csn–1PbnBr3n+1 2D perovskite changes from deep blue to green distinctly when exposed to ethanol. A cheap demo ethanol test paper is fabricated by this 2D perovskite and paper using a simple method, demonstrating interesting rapid and convenient ethanol sensing performance. Crystal analysis, constituent analysis, spectral analysis, and molecular dynamic (MD) simulation reveal the crystal structure transformation from 2D to 3D induced by the migration of PEA+ cations in the original 2D perovskite when exposed to ethanol. In addition, a chemiresistive sensor based on the 2D perovskite and on the 2D–3D phase transformation is developed and demonstrates a high ethanol detection sensitivity with a limit down to 0.7 ppm. The photodetector fabricated by the 2D perovskite also demonstrates tunable sensitivity upon the controllable 2D–3D transformation. This remarkable colorimetric, chemiresistive, and photosensitive perovskite is expected to highlight its future application and be a supplement to the existing ethanol sensing and photodetector techniques.

Energy storage and photoluminescence properties of Sm<sup>3+</sup>-doped 0.94Bi<sub>0.5</sub>Na<sub>0.5</sub>TiO<sub>3</sub>-0.06BaTiO<sub>3</sub> multifunctional ceramics

In recent years, inorganic multifunctional ferroelectric ceramics have been widely utilized in various fields, including aerospace, optical communication, and capacitors, owing to their high stability, easy synthesis, and flexibility. Rare-earth doped ferroelectric materials hold immense potential as a new type of inorganic multifunctional material. This work focuses on the synthesis of <i>x</i>%Sm<sup>3+</sup>-doped 0.94Bi<sub>0.5</sub>Na<sub>0.5</sub>TiO<sub>3</sub>-0.06BaTiO<sub>3</sub> (BNTBT:<i>x</i>%Sm<sup>3+</sup> in short) ceramics by using the conventional solid-state sintering method, aiming to comprehensively investigate their ferroelectric, energy storage, and photoluminescence (PL) properties. The X-ray diffraction analysis reveals that the introduction of Sm<sup>3+</sup> does not trigger off the appearing of secondary phases or changing of the original perovskite structure. The scanning electron microscope (SEM) images demonstrate that Sm<sup>3+</sup> incorporation effectively restrains the grain growth in BNTBT, resulting in the average grain size decreasing from 1.16 to 0.95 μm. The reduction in remanent polarization (<i>P</i><sub>r</sub>) and coercive field (<i>E</i><sub>c</sub>) can be attributed to both the grain size refinement and the formation of morphotropic phase boundaries (MPBs). Under an applied field of 60 kV/cm, the maximum value of energy storage density (<i>W</i><sub>rec</sub>) reaches to 0.27 J/cm<sup>3</sup> at an Sm<sup>3+</sup> doping concentration of 0.6%. The energy storage efficiency (<i>η</i>) gradually declines with electric field increasing and stabilizes at approximately 45% for Sm<sup>3+</sup> doping concentrations exceeding 0.6%. This result can be ascribed to the decrease in Δ<i>P</i> (<i>P</i><sub>max</sub><sub> </sub>– <i>P</i><sub>r</sub>) due to the growth of ferroelectric domains as the electric field increases. Additionally, all Sm<sup>3+</sup>-doped BNTBT ceramics exhibit outstanding PL performance upon being excited with near-ultraviolet (NUV) light at 408 nm, without peak position shifting. The PL intensity peaks when the Sm<sup>3+</sup> doping concentration is 1.0%, with a relative change (Δ<i>I/I</i>) reaching to 700% at 701 nm (<sup>4</sup>G<sub>5/2</sub>→<sup>6</sup>H<sub>11/2</sub>). However, the relative change in PL intensity is minimum at 562 nm (<sup>4</sup>G<sub>5/2</sub>→<sup>6</sup>H<sub>5/2</sub>) due to the fact that the <sup>4</sup>G<sub>5/2</sub>→<sup>6</sup>H<sub>5/2</sub> transition represents a magnetic dipole transition, and the PL intensity remains relatively stable despite variations in the crystal field environment surrounding Sm<sup>3+</sup>. Our successful synthesis of this novel ceramic material, endowed with both energy storage and PL properties, offers a promising avenue for developing inorganic multifunctional materials. The Sm<sup>3+</sup>-doped BNTBT ceramics hold considerable potential applications in optical memory and multifunctional capacitors.

In-situ organic-inorganic ferroelectric layer growth for efficient perovskite solar cells with high photovoltage

Halide perovskite solar cells (PSCs) have shown outstanding performance, which can be further improved through enhancing the built-in electric field (Vbi) and reducing non-radiative recombination pathways. Here we in-situ grow an organic-inorganic ferroelectric layer on the perovskite film, which can be easily and quickly processed even at room-temperature within one minute. The in-situ process endows intimate growth of ferroelectric layer on the original perovskite grains, which can reduce the formation of grain boundaries and thus minimize the recombination of electron and hole at grain boundaries. The Vbi of the PSCs is enhanced from 1.02 V to 1.28 V due to the widened space charge depletion region after the formation of ferroelectric layer. Finally, an output photovoltage up to 1198 mV is achieved with a champion efficiency of 22.45% and a low voltage deficit of 352 mV. The strategy offers a new platform of growing intimate ferroelectric layers on perovskite photoactive films for integration between ferroelectrics and PSCs.

Low pressure assisted thin film growth for high performance perovskite solar cells

• Simple thin film manufacturing process. • Improved the perovskite film quality. • Enhanced PCE and environment stability. Perovskite solar cells (PSCs) have been the most promising candidate for next generation commercial solar cells after silicon cells. However, the original perovskite films always present defects showing pinholes and uneven particles causing low performance and stability during operation. Here, we prepared high quality and outstanding performance perovskite films through low pressure assisted (LPA, −1 bar) thin film growth strategy to control morphology and crystallinity form precursor perovskite solution. Consequently, the PSCs (target) showed a maximum power conversion efficiency (PCE) of 20.33% based on LPA growth perovskite films, while the PCE for normal annealing devices (control) was only 19.47%. The target devices also showed superior stability at a humidity range of 20%-30% compared with control devices. After 1000 h, 66.50% initial PCE was remained for target devices (20.33% to 13.52%), only 45.45% for control devices (19.47% to 8.85%).

Enhancement in energy storage performance of La-modified bismuth-ferrite-based relaxor ferroelectric ceramics by defect compensation and process optimization

In this investigation, La2O3 was doped into 0.85(0.65BF-0.35BT)-0.15Sr0.7Bi0.2TiO3 (BF-BT-SBT) to form a solid solution with relaxation ferroelectric properties. The dielectric breakdown strength (BDS) of 1% mole of La doping was 220 kV/cm, the maximum recoverable energy storage (Wrec) was 2.35 J/cm3, and the energy storage efficiency (η) was 71%. The relationship between ceramic properties and microstructure was investigated in detail. Doping with La has the following main features: (1) The dissolution of La3+ ions in the A position of the original perovskite structure reduced the concentration of oxygen vacancies in the lattice and played a role of compensating the defects. (2) The dielectric loss of ceramics was reduced, the impedance was greatly increased, and the specimen exhibited a high-temperature stability: a maximum Wrec of 4.04 ± 1.7% J/cm3 in 30–130 °C. (3) The core–shell–like with single phase structure in La-doped ceramics had been successfully observed, which may become a strategy for preparing high-performance ceramics. Higher BDS and denser structures were obtained in 0.01 La ceramics by further optimizing the preparation of the above compositions by the viscous polymer process (VPP). The BDS of 0.01La ceramics prepared by VPP reached 480 kV/cm, the effective energy storage density reached 6.15 J/cm3, and the η was about 81%. This made La-doped 15SBT (chemical composition of BF-BT-SBT + La2O3) ceramics become a potential candidate material for energy storage devices.

Analysis of Perovskite Solar Cell Degradation over Time Using NIR Spectroscopy—A Novel Approach

In recent years, there has been a dynamic development of photovoltaic materials based on perovskite structures. Solar cells based on perovskite materials are characterised by a relatively high price/performance ratio. Achieving stability at elevated temperatures has remained one of the greatest challenges in the perovskite solar cell research community. However, significant progress in this field has been made by utilising different compositional engineering routes for the fabrication of perovskite semiconductors such as triple cation-based perovskite structures. In this work, a new approach for the rapid analysis of the changes occurring in time in perovskite structures was developed. We implemented a quick and inexpensive method of estimating the ageing of perovskite structures based on an express diagnosis of light reflection in the near-infrared region. The possibility of using optical reflectance in the NIR range (900–1700 nm) to observe the ageing of perovskite structures over time was investigated, and changes in optical reflectance spectra of original perovskite solar cell structures during one month after PSC production were monitored. The ratio of characteristic pikes in the reflection spectra was determined, and statistical analysis by the two-dimensional correlation spectroscopy (2D-COS) method was performed. This method allowed correctly detecting critical points in thermal ageing over time.

Formula omitted] perovskites as electrode materials for SOFCs

In this work, the Pechini method was used to synthesize La0.7−xLnxCa0.3MnO3,(Ln=ProrSm)-La1−xLnxCa0.3MnO3 type perovskites, evaluating the effect of the type of cation and composition on the structural, morphological and textural properties. The use of similar rare earth cations was studied to promote weak bonds between the reactive surface and adsorbed oxygen species that could facilitate the oxygen reduction reaction and thus improve electrochemical performance of SOFC devices. To achieve this goal, different compositions of Pr or Sm ions (x = 0.1, 0.3, 0.5 or 0.6) were used for the partial substitution of lanthanum at the A site. The results indicated that the substitution of La by Pr or Sm did not modify the original orthorhombic perovskite structure of Ca-doped lanthanum manganites. However, a shift in the main reflections can be obtained as the content of both cations increases due to cell distortion. Rietveld refinement confirms that the crystal structure belongs to the Pnma space group with a large distortion along the b-axis but no secondary phase formation. The compensated charge neutrality of the Mn3+/Mn4+ ratio influences the octahedral sites of MnO6 and cell volume. Orthorhombic distortion (c2<a<b) occurs through Jahn-Teller mechanism promoting a hole-doped system for electrical conductivity. The adsorption-desorption isotherms reveal that in any composition of Pr, a mesoporous isotherm (type IV) is obtained. In contrast, the isotherms changed from micro- to meso-porous features depending on the amount of Sm substitution at the A-site. All the prepared samples showed a soft granular structure with agglomerates ranging between 200 and 300 nm with well-interconnected pores. Comparing the La substitution by Pr or Sm, it was found that Sm can form perovskites that can better promote oxygen vacancies and triple boundary phase formation, which is essential in SOFC devices.

2D/3D Heterojunction perovskite light-emitting diodes with tunable ultrapure blue emissions

High performance blue light-emitting diodes are indispensable for solid-state lighting and full-color displays. Recently, tremendous efforts have been dedicated to boost the performance for blue perovskite light-emitting diodes (PeLEDs). In this work, we construct an ingenious 2D/3D heterostructure perovskite by long-chain organic halide salt post-treatment in blue perovskites for the first time. Organic halide salt post-treatment can form a 2D capping layer on the original 3D perovskite surface, thus to passivate defects and improve exciton radiative recombination rate. As a result, 2D/3D PeLEDs with tunable blue emissions (465, 475, and 486 nm), ultra-low turn-on voltages (3.0, 2.7, and 2.7 V), high brightness (928, 6727, and 9242 cd m−2), and excellent EQEs (2.11%, 6.29%, and 8.57%) are demonstrated. Moreover, due to the high phase homogeneity, the optimized PeLEDs exhibit ultrapure blue emissions (FWHM < 15 nm), in which the PeLED (465 nm) achieve ≈ 98% coverage of the Rec. 2020 standard.

Deciphering the Interaction of Single-Phase La0.3Sr0.7Fe0.7Cr0.3O3-δ with CO2/CO Environments for Application in Reversible Solid Oxide Cells.

A detailed study aimed at understanding and confirming the reported highly promising performance of a La0.3Sr0.7Fe0.7Cr0.3O3-δ (LSFCr) perovskite catalyst in CO2/CO mixtures, for use in reversible solid oxide fuel cells (RSOFCs), is reported in this work, with an emphasis on chemical and performance stability. This work includes an X-ray diffraction (XRD), thermogravimetric analysis (TGA), and electrochemical study in a range of pO2 atmospheres (pure CO2, CO alone (balance N2), and a 90-70% CO2/10-30% CO containing mixture), related to the different conditions that could be encountered during CO2 reduction at the cathode. Powdered LSFCr remains structurally stable in 20-100% CO2 (balance N2, pO2 = 10-11-10-12 atm) without any decomposition. However, in 30% CO (balance N2, pO2 ∼ 10-26 atm), a Ruddlesden-Popper phase, Fe nanoparticles, and potentially some coke are observed to form at 800 °C. However, this can be reversed and the original perovskite can be recovered by heat treatment in air at 800 °C. While no evidence for coke formation is obtained in 90-70% CO2/10-30% CO (pO2 = 10-17-10-18 atm) mixtures at 800 °C, in 70 CO2/30 CO, minor impurities of SrCO3 and Fe nanoparticles were observed, with the latter potentially beneficial to the electrochemical activity of the perovskite. Consistent with prior work, symmetrical two-electrode full cells (LSFCr used at both electrodes), fed with the various CO2/CO gas mixtures at one electrode and air at the other, showed excellent electrochemical performance at 800 °C, both in the SOFC and in SOEC modes. Also, LSFCr exhibits excellent stability during CO2 electrolysis in medium-term potentiostatic tests in all gas mixtures, indicative of its excellent promise as an electrode material for use in symmetrical solid oxide cells.