Ruddlesden-Popper Research Articles

A novel optical sensor for Pb2+ detection based on in-situ formation of Ruddlesden-Popper phase (C4H9NH3)2PbBr4 perovskite

On account of the concentration sensitive photoluminescence (PL) property of the lead-based Ruddlesden-Popper (RP) phase perovskite material, a novel sensing mechanism for highly selective Pb2+ detection based on the in-situ formation of highly emissive luminescence structure matrix (C4H9NH3)2PbBr4 has been demonstrated. The sensor exhibits high sensitivity and selectivity for detecting Pb2+ in complex metal cations mixture solution. This research reports a novel type of sensor mechanism based on the in-situ formation of luminescent lead-based RP phase perovskite. It paves the way for developing highly selective optical sensors for detecting heavy metal cations via their corresponding luminescence structure matrix.

Band alignment engineering of a Ruddlesden–Popper perovskite-based heterostructure constructed using Cs2SnI2Cl2 and α-In2Se3: The effects of ferroelectric polarization switching and electric fields

Ferroelectricity is an important source of the fascinating optoelectronic properties of heterostructures. Interfaces formed between ferroelectrics and oxides or transition metal dichalcogenides have undergone rapid development. However, the integration of ferroelectrics and two-dimensional Ruddlesden–Popper (RP) perovskites has rarely been studied so far. Herein, we use first-principle calculations to investigate ferroelectric polarization and electric field control of band alignments within the RP perovskite-based heterostructure α-In2Se3/Cs2SnI2Cl2. Our calculations demonstrate that the band alignment of heterostructure can be changed from type-II to type-III by switching the ferroelectric polarization direction in the α-In2Se3 layer. Furthermore, application of an external electric field can modulate the band structure of the α-In2Se3/Cs2SnI2Cl2 heterostructure and induce the band alignment transition. These findings highlight the importance of ferroelectric polarization switching in band alignment engineering and suggest the possibility of electric field-tunable multi-band alignment in Ruddlesden–Popper perovskite-based heterostructures.

Over 21% Efficiency Stable 2D Perovskite Solar Cells.

Owing to their insufficient light absorption and charge transport, 2D Ruddlesden-Popper (RP) perovskites show relatively low efficiency. In this work, methylammonium (MA), formamidinum (FA), and FA/MA mixed 2D perovskite solar cells (PSCs) are fabricated. Incorporating FA cations extends the absorption range and enhances the light absorption. Optical spectroscopy shows that FA cations substantially increase the portion of 3D-like phase to 2D phases, and X-ray diffraction (XRD) studies reveal that FA-based 2D perovskite possesses an oblique crystal orientation. Nevertheless, the ultrafast interphase charge transfer results in an extremely long carrier-diffusion length (≈1.98µm). Also, chloride additives effectively suppress the yellow δ-phase formation of pure FA-based 2D PSCs. As a result, both FA/MA mixed and pure FA-based 2D PSCs exhibit a greatly enhanced power conversion efficiency (PCE) over 20%. Specifically, the pure FA-based 2D PSCs achieve a record PCE of 21.07% (certified at 20%), which is the highest efficiency for low-dimensional PSCs (n≤ 10) reported to date. Importantly, the FA-based 2D PSCs retain 97% of their initial efficiency at 85°C persistent heating after 1500h. The results unambiguously demonstrate that pure-FA-based 2D PSCs are promising for achieving comparable efficiency to 3D perovskites, along with a better device stability.

Bimolecular Generation of Excitonic Luminescence from Dark Photoexcitations in Ruddlesden-Popper Hybrid Metal-Halide Perovskites.

The nature of photoexcitations in Ruddlesden-Popper (RP) hybrid metal halide perovskites is still under debate. While the high exciton binding energy in the hundreds of millielectronvolts indicates excitons as the primary photoexcitations, recent reports found evidence for dark, Coulombically screened populations, which form via strong coupling of excitons and the atomic lattice. Here, we use time-resolved mid-infrared spectroscopy to gain insights into the nature and recombination of such dark excited states in (BA)2(MA)n-1PbnI3n+1 (n = 1,2,3) via their intraband electronic absorption. In stark contrast to results in the bulk perovskites, all samples exhibit a broad, unstructured mid-IR photoinduced absorbance with no infrared activated modes, independent of excitonic confinement. Further, the recombination dynamics are dominated by a bimolecular process. In combination with steady-state photoluminescence experiments, we conclude that screened, dark photoexcitations act as a population reservoir in the RP hybrid perovskites, from which nongeminate formation of bright excitons precedes generation of photoluminescence.

Synergistic Effect of Additives on 2D Perovskite Film Towards Efficient and Stable Solar Cell

Recently，layered Ruddlesden–Popper (RP) phase 2D halide perovskites have attracted tremendous attention due to their excellent environment stability and wide tunability on optoelectronic properties. However, the inhibition of out-of-plane charge transport limits the photovoltaic performance of 2D-based perovskite solar cells (PVSCs). To this respect, an orientation control of crystal growth in layered 2D perovskites has been proven to be effective method to manipulate the carrier transport. Here, we report a new approach to achieve orientation regulation of 2D perovskite via the synergistic effect of dimethyl sulfoxide (DMSO) and thio-semicarbazide (TSC) additives. The 2D (BA)2(MA)3Pb4I13 (BA = n-butylammonium, MA = methylammonium) perovskite films treated with DMSO and TSC additives show uniform morphology, increased grain size, intensified crystallinity and vertical orientation, resulting in reduced trap-state density and improved charge transport properties. The PVSCs assembled from these films yield a significant enhancement in PCE from 1.05% to 14.15% and an excellent environment stability. An unsealed device retains 90.3% of its initial PCE after 720 h storage in air atmosphere with relative humidity of 25 ± 5% at 25 °C. This work provides a possibility to fabricate high-quality 2D perovskite films and gives guidance for additive engineering for efficient and stable 2D PVCSs in future.

Anion regulation engineering for efficient Ruddlesden-Popper inverted perovskite solar cells

Recently, many studies have focused on exploiting new spacer cations to boost the power conversion efficiency (PCE) of Quasi-two-dimensional (Q-2D) Ruddlesden-Popper (RP) perovskites solar cells (PSCs). As another essential part of RP perovskite structure, halogen anions have a substantial impact on crystalline quality. However, there are few studies about how halogen anions affect RP PSCs and their possible underlying mechanisms. Here, we investigate different halide anions that impact the optoelectronic properties of RP perovskite films. Specifically, we use PEAI, PEABr, and PEACl (PEA = phenethylammonium) to fabricate RP perovskite films based on PEA 2 MA 3 Pb 4 I 11 X 2 (X = I, Br or Cl, n = 4) for systematical study. Through a series of characterizations and analyses, RP perovskite films with PEACl show a higher proportion of vertical crystal orientation and fewer trap-states, which leads to improved carrier transmission pathways. As a result, the devices based on PEACl (PEA 2 MA 3 Pb 4 I 11 Cl 2 , n = 4) achieve a champion PCE of 12.02%, which is higher than PEAI (6.76%, PEA 2 MA 3 Pb 4 I 13 , n = 4) and PEABr (4.26%, PEA 2 MA 3 Pb 4 I 11 Br 2 , n = 4). • The effect of halogen anions on 2D PSCs is systematically investigated. • The Cl − contributes to the vertical orientation of 2D perovskite film. • The Br − impairs the crystallization quality in 2D perovskite film. • RP PSCs based on PEA 2 MA 3 Pb 4 I 11 Cl 2 achieves a champion PCE of 12.02%. • PSCs of PEA 2 MA 3 Pb 4 I 11 Cl 2 retains 97.1% of its initial PCE after 500 h.

A Sr and Ni doped Ruddlesden−Popper perovskite oxide La1.6Sr0.4Cu0.6Ni0.4O4+δ as a promising cathode for protonic ceramic fuel cells

The performance of a protonic ceramic fuel cell (PCFC) is greatly limited by the oxygen reduction reaction (ORR) activity and durability of cathode under realistic operation conditions. In this study, we report a Sr and Ni dual doped Ruddlesden−Popper (RP) perovskite oxide La 1.6 Sr 0.4 Cu 0.6 Ni 0.4 O 4+δ (LSCN) with an improved electrochemical performance. LSCN demonstrates rich oxygen vacancies on the surface, and a good chemical/thermal compatibility with electrolyte, as confirmed by the analyses of X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetry and thermal expansion coefficient. A Ni–BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3 anode supported cell with LSCN cathode typically demonstrate a peak power density of 1020 mWcm −2 and a polarization resistance of 0.062 Ωcm 2 at 750 °C using wet H 2 (3% H 2 O) as fuel and air as oxidant. In addition, the cells show no observable morphology change or voltage degradation at a constant current density (0.5A cm −2 ) and at 650 °C within a period of 100 h, suggesting that LSCN is a promising cathode material for PCFC. •LSCN has been fabricated and its surface property has been characterized; •PCFCs with LSCN cathode show a P max of 1020 mWcm −2 and a R p of 0.062 Ωcm 2 at 750 °C; •PCFCs with LSCN cathode demonstrate a good electrochemical and structural stability;

A Narrow Bandgap of 2D Ruddlesden-Popper Bilayer Perovskite with Giant Entropy Change and Photoluminescence.

The multifunctional two-dimensional (2D) organic-inorganic hybrid perovskites have potential applications in many fields, such as, semiconductor, energy storage and fluorescent device etc. Here, a 2D Ruddlesden-Popper (RP) perovskite (IPA)2 (FA)Pb2 I7 (1, IPA+ =C3 H9 NI+ , FA+ =CN2 H5 + ) is determined for its photophysical properties. Strikingly, 1 reveals a solid reversible phase transition with Tc of 382 K accompanied by giant entropy change of 40 J mol-1 K-1 . Further optical investigations indicate that 1 reveals a narrow direct bandgap (2.024 eV) attributed to the slight bending of I-Pb-I edge and inorganic [Pb2 I7 ]n layer and a superior photoluminescence (PL) emission with super long lifetime of 0.1607 ms. It is believed that this work will pave an avenue to further design multifunctional semiconductors that combines energy storage and photoelectric materials.

The Performance of Ruddlesden–Popper (R-P) Structured Pr2–xSrxNi0.2Mn0.8O4 for Reversible Single-Component Cells

In view of high catalytic activity and oxygen vacancy concentration, Ruddlesden–Popper (R-P) structure oxide has been widely used as the electrode material for solid oxide fuel cells (SOFCs). Herein, three R-P structure oxides, Pr2–xSrxNi0.2Mn0.8O4 (x = 1, 1.2, and 1.5), are used as the semiconductor materials of single-component cells. The materials for the oxygen side are hybrid oxides consisting of R-P structure oxide and perovskite oxide. The hydrogen side was exposed to the reduction atmosphere before the test, and the perovskite structure disappeared and the lattice parameters of the R-P structure changed, resulting in the formation of a new R-P structure and MnO2 or NiMn alloy. In addition, Pr0.5Sr1.5Ni0.2Mn0.8O4 and reduced Pr0.5Sr1.5Ni0.2Mn0.8O4 exhibit the most content of oxygen vacancy. For a single-component fuel cell (SCFC), the cell performance increased with the decrease in Pr content. The SCFC composed of Pr0.5Sr1.5Ni0.2Mn0.8O4 shows the highest maximum power densities (Pmax), which reached 206.6 mW cm–2 at 700 °C. It is because the reduced Pr0.5Sr1.5Ni0.2Mn0.8O4 has the highest catalytic activity for hydrogen oxidation reaction (HOR). Furthermore, the Pmax at 700 °C can reach a value of 198.1 mW cm–2 in SOFC mode, and in the case of SOEC mode, the current density at 700 °C is as high as −390.8 mA cm–2 with an applied electrolysis voltage of 1.3 V for the reversible single-component cell (RSCC) with Pr0.5Sr1.5Ni0.2Mn0.8O4 as the semiconducting electrocatalyst.

Role of Polycyclic Aromatic Alkylammonium Cations in Tuning the Electronic Properties and Band Alignment of Two-Dimensional Hybrid Perovskite Semiconductors.

Two-dimensional hybrid organic-inorganic perovskites (HOIPs) have recently drawn intense attention as potential photovoltaic materials. However, n = 1 two-dimensional (2D) HOIPs face the challenge of low conductivity between the inorganic layers, leading to unsatisfactory device performance. Interestingly, 2D HOIPs employing π-conjugated molecules as organic moieties show energy and charge transfers between organic and inorganic layers, indicating potentially efficient carrier transport for photovoltaic applications. Nevertheless, the development of 2D HOIP-based solar cells especially utilizing polycyclic aromatic alkylammonium as cations is in its infancy. Herein, we investigated the electronic structure and band alignment of a series of n = 1 2D Ruddlesden-Popper (RP) phase HOIPs containing different polycyclic aromatic groups and alkyl chains, based on density functional theory calculations. We find that the polycyclic aromatic group plays an important role in controlling the functionality of 2D HOIPs by directly modifying band-edge states, and the band alignment at the organic-inorganic interface can be designed to promote either exciton trapping or dissociation for light-emitting or photovoltaic applications, respectively.

A rational design of FeNi alloy nanoparticles and carbonate-decorated perovskite as a highly active and coke-resistant anode for solid oxide fuel cells

Solid oxide fuel cells (SOFCs) are a kind of clean and efficient device to convert chemical energy in fuels into electricity. However, since anodes with high catalytic activity and carbon tolerance are still underdeveloped, the consequent serious performance degradation of the cells under operational conditions significantly confines their commercial applications. Here we propose a new strategy to remove carbon deposition by in-situ formation of alkali metal carbonate on the anode surface. A multi-phase composite anode, which is composed of an orthorhombic single perovskite main phase, a Ruddlesden-Popper (RP) layered perovskite second phase, and an in-situ exsolved FeNi alloy minor phase, is developed by one-step reduction of La0.65Li0.05Sr0.3Fe0.8Ni0.2O3-δ (LLSFN0.05) at a high temperature. The deficiencies of the RP phase and A-site caused by Li dopant would increase oxygen bulk diffusion, and FeNi nanoparticles would boost the catalytic activity. Moreover, when dealing with carbon fuel, lithium carbonate can be synthesized on the anode surface, serving as a good oxygen ion conductor and an efficient catalyst for coke removal by gasification. A single cell with our reduced LLSFN0.05 anode exhibited maximum power densities of 596, 467, and 424 mW cm−2 at 750 ℃ with H2, CO, and wet C2H6 as the fuel, respectively. In addition, the cells could have a long-term stable operation for over 80 h using CO as the fuel at 200 mA cm−2. This study provides a new material design strategy to develop a highly active and coke-resistant anode.

Phenylformamidinium-enabled quasi-2D Ruddlesden-Popper perovskite solar cells with improved stability

Two-dimensional (2D)/quasi-2D perovskite solar cells (PSCs) incorporating organic spacer cations exhibit appealing ambient stability in comparison with their 3D analogs. Most reported organic spacer cations are based on ammonium, whereas formamidinium (FA+) has been seldom applied despite that FA has been extensively used in high-efficiency 3D PSCs. Herein, a novel FA-based organic spacer cation, 4-chloro-phenylformamidinium (CPFA+), is applied in quasi-2D Ruddlesden-Popper (RP) PSCs for the first time, and methylammonium chloride (MACl) is employed to promote crystal growth and orientation of perovskite film, resulting in high power conversion efficiency (PCE) with improved stability. Upon incorporating CPFA+ organic spacer cation and MACl additive, high-quality quasi-2D CPFA2MAn−1Pbn(I0.857Cl0.143)3n+1 (n = 9) perovskite film forms, exhibiting improved crystal orientation, reduced trap state density, prolonged carrier lifetime and optimized energy level alignment. Consequently, the CPFA2MAn−1Pbn(I0.857Cl0.143)3n+1 (n = 9) quasi-2D RP PSC devices deliver a highest PCE of 14.78%. Moreover, the un-encapsulated CPFA-based quasi-2D RP PSC devices maintain ∼ 80% of its original PCE after exceeding 2000 h storage under ambient condition, whereas the 3D MAPbI3 counterparts retain only ∼ 45% of its original PCE. Thus, the ambient stability of quasi-2D RP PSC devices is improved obviously relative to its 3D MAPbI3 counterpart.

Pressure-Induced Phase Transition, Jahn-Teller Suppression, Optical and Electronic Property Evolutions in Ruddlesden-Popper Perovskites Rb2 CuCl4-x Brx.

Transition-metal containing halides with Ruddlesden-Popper (RP) perovskite structures have received extensive attention owing to their emerging and anisotropic photoelectric functionalities. Among them, A2 CuX4 (A=alkali metal or organic cations, X=Cl, Br, I) series are particular, because of the Jahn-Teller distortion of Cu2+ sensitive to external stimuli such as temperature and pressure. In this article, we report the structure evolution and physical property responses of RP perovskites Rb2 CuCl4-x Brx (x=1, 2) to external pressure. Dramatic structural phase transitions from orthorhombic to monoclinic occur around 3.0 GPa in both materials regardless of their distinct compositions. Structure analyses reveal the suppression and final vanishing of the Jahn-Teller distortion of Cu2+ cations under compression and crossing the phase transition, respectively. Rb2 CuCl4-x Brx perovskites exhibit abrupt bandgap narrowing (from reddish-brown to black) along with the structural phase transition, and an overall bandgap narrowing of 75% up to ∼27 GPa but still keeping semiconductive. During the compression processes, the resistances of Rb2 CuCl4-x Brx have been greatly reduced by 5-orders of magnitude. Moreover, all of the pressure-induced phenomena in Rb2 CuCl4-x Brx perovskites are reversible upon decompression and no obvious difference is observed for the pressure responses between [CuCl4 Br2 ] and [CuCl4 (Cl,Br)2 ] coordination environments. The impact of pressure on the structural and physical properties in two-dimensional Rb2 CuCl4-x Brx provides in-depth understanding on the structure design of functional halide perovskites at ambient conditions.

Integrated Quasi‐2D Perovskite/Organic Solar Cells with Efficiency over 19% Promoted by Interface Passivation

AbstractIntegrated perovskite/organic solar cells (IPOSCs) have shown great potential in broadening the light absorption range and improving the photovoltaic performance. However, the severe interface charge recombination and unmatched energy levels between perovskite and organic photoactive layers hinder their performance improvement. Here, an efficient interface passivation strategy for IPOSCs based on a layered Ruddlesden–Popper (RP) perovskite and high photovoltaic performance is successfully demonstrated. It is found that an ultrathin conjugated polymer (PM6) layer could passivate the surface defects of perovskite film, tuning the energy level and suppress the nonradiative recombination loss, leading to efficient interface contact between RP perovskite and organic photoactive layers, boosting the open‐circuit voltage from 1.06 to 1.12 V and the efficiency from 17.23% to 19.15%. Importantly, the optimized device shows extended photocurrent response to 930 nm with a peak intensity close to 50% from 800 to 931 nm. The results indicate that interface passivation using a functionalized polymer could be an efficient strategy to improve the photovoltaic performance of integrated devices.

Structure, Magnetism, and Thermal Stability of La2NiO2.5F3: A Ruddlesden-Popper Oxyfluoride Crystallizing in Space Group P42/nnm.

We report on the new Ruddlesden-Popper (RP) oxyfluoride La2NiO2.5F3 containing an unprecedented high amount of fluorine and Ni2+. This oxyfluoride was prepared by topochemical low-temperature fluorination of La2NiO4, which was obtained by a soft chemistry synthesis, with poly(vinylidene difluoride) (PVDF) as fluorinating agent. La2NiO2.5F3 is the first n = 1 RP compound crystallizing in the tetragonal space group P42/nnm (a = 5.7297(6) Å and c = 13.0106(2) Å). The crystal structure shows a unique tilting scheme of the NiO4F2 octahedra that has so far been only theoretically predicted. Combined neutron and X-ray powder diffraction experiments together with bond-valence-sum and DFT+U calculations reveal an unusual anion ordering with fluoride being located on the apical anion sites of the NiO4F2 octahedra. Excess fluorine ions were found to populate two of the four interstitial anion sites in an ordered fashion. A third interstitial anion position is occupied by oxygen ions while the fourth site remains unoccupied. This hitherto unobserved ordering scenario in RP oxyfluorides promotes a strong layerwise alternating tilting of the NiO4F2 octahedra. Magnetic measurements show strong antiferromagnetic interactions with a high Néel temperature of about 225 K and a pronounced ZFC/FC splitting most likely as the result of a small ferromagnetic moment arising from spin canting. The electronic structure was characterized by DFT and UV-vis spectroscopy, and a strong increase of Eg was found compared to La2NiO4 (3.4 eV vs 1.3 eV).

Ru/Nb co-doped perovskite anode: Achieving good coking resistance in hydrocarbon fuels via core-shell nanocatalysts exsolution

Ru/Nb co-doped (Pr0.5Sr0.5)0.9Fe0.8Ru0.1Nb0.1O3-δ (PSFRN) cubic perovskite oxide was fabricated and used as the solid oxide fuel cell (SOFC) anode material. After treated in wet H2 at 900 °C for 2 h, the PSFRN was partially transformed into Ruddlesden-Popper (RP) layered perovskite PrSrFe0.8Ru0.1Nb0.1O4+δ (RP-PSFRN), and Fe0.7Ru0.3 alloy-FeOx oxide (FRA@FO) core-shell nanoparticles were in-situ exsolved on the reduced-PSFRN (R-PSFRN) substrate surface. The phase transition and the exsolution of the nanoparticles were investigated using X-ray diffraction, transmission electron microscope and X-ray photoelectron spectroscopy. Modified by the in-situ exsolved FRA@FO core-shell nanoparticles, the R-PSFRN anode material showed high catalytic activity for hydrogen and hydrocarbon fuels. The power density of SOFC reached 0.683 and 0.537 W cm−2 with wet H2 and C3H8 as fuel at 800 °C, respectively. Moreover, the SOFC showed a stable output under a constant current load of 0.15 A cm−2 in C3H8, demonstrating a high resistance to carbon deposition and coking.

Inorganic Ruddlesden-Popper Faults in Cesium Lead Bromide Perovskite Nanocrystals for Enhanced Optoelectronic Performance.

While the layered hybrid Ruddlesden-Popper (RP) halide perovskites have already established themselves as the frontrunners among the candidates in optoelectronics, their all-inorganic counterparts remain least explored in the RP-type perovskite family. Herein, we study and compare the optoelectronic properties of all-inorganic CsPbBr3 perovskite nanocrystals (PNCs) with and without RP planar faults. We find that the RP-CsPbBr3 PNCs possess both higher exciton binding energy and longer exciton lifetimes. The former is ascribed to a quantum confinement effect in the PNCs induced by the RP faults. The latter is attributed to a spatial electron-hole separation across the RP faults. A striking difference is found in the up-conversion photoluminescence response in the two types of CsPbBr3 PNCs. For the first time, all-inorganic RP-CsPbBr3 PNCs are tested in light-emitting devices and shown to significantly outperform the non-RP CsPbBr3 PNCs.

Perovskite and related oxide based electrodes for water splitting

Water splitting for renewable energy technologies necessitates the creation of low-cost, highly active, and stable electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), which remains a challenging issue. Oxide-based catalysts, especially perovskites (ABO3), ruddlesden–popper perovskite (A2BO4) and pyrochlore-type oxides (A2B2O7), have attracted gotten much interest as electrocatalysts for water splitting because of their distinctive physical, chemical, and electronic properties. In this work, a scientometric analysis is conducted on developing various oxide-based catalysts for water splitting to explore further developments. Up to now, a total of 29,761 publications (between the years 1990–2020) have been obtained from the Web of Science (WoS) website by searching for these written documents on this subject with a variety of linking keywords. The derived documents were subjected to a scientometric study, which included a look at the contributing authors, publications, contributing countries, top citation bursts, and topic categories. Based on the information obtained, in this research area, the publications started to increase dramatically since 2012. In terms of scientific output on oxide-based catalysts for water splitting, China and the United States were discovered to be the world leaders.

Nanocomposites: A New Opportunity for Developing Highly Active and Durable Bifunctional Air Electrodes for Reversible Protonic Ceramic Cells

AbstractReversible protonic ceramic cells (RePCCs) can facilitate the global transition to renewable energy sources by providing high efficiency, scalable, and fuel‐flexible energy generation and storage at the grid level. However, RePCC technology is limited by the lack of durable air electrode materials with high activity toward the oxygen reduction/evolution reaction and water formation/water‐splitting reaction. Herein, a novel nanocomposites concept for developing bifunctional RePCC electrodes with exceptional performance is reported. By harnessing the unique functionalities of nanoscale particles, nanocomposites can produce electrodes that simultaneously optimize reaction activity in both fuel cell/electrolysis operations. In this work, a nanocomposite electrode composed of tetragonal and Ruddlesden–Popper (RP) perovskite phases with a surface enriched by CeO2 and NiO nanoparticles is synthesized. Experiments and calculations identify that the RP phase promotes hydration and proton transfer, while NiO and CeO2 nanoparticles facilitate O2 surface exchange and O2‐ transfer from the surface to the major perovskite. This composite also ensures fast (H+/O2‐/e‐) triple‐conduction, thereby promoting oxygen reduction/evolution reaction activities. The as‐fabricated RePCC achieves an excellent peak power density of 531 mW cm‐2 and an electrolysis current of −364 mA cm‐2 at 1.3 V at 600 °C, while demonstrating exceptional reversible operation stability of 120 h at 550 °C.

K2NiF4 type oxides, Ln2-xSrxNiO4+δ (Ln = La and Pr; x = 0–1.4) as an oxygen electrocatalyst for aqueous lithium–oxygen rechargeable batteries

The structural and electrochemical characteristics of the Ln2-xSrxNiO4+δ (Ln = La and Pr; x = 0–1.4) system were investigated to clarify the relationship between the electrocatalytic activity and various characteristics such as the structure, composition, electrical conductivity, and oxygen content. Rietveld analysis of the powder X-ray diffraction (XRD) data showed that the tetragonal distortion of the NiO6 octahedra decreased monotonically with an increase of x, while the Ln (Sr)–O (//c-axis) in the rock-salt block was expanded with an increase in x, although the tetragonality, c/a showed a maximum at x = 0.6. Cyclic voltammetry (CV) measurements showed that the activity for the oxygen evolution reaction (OER) increased with x, while that of the oxygen reduction reaction (ORR) was independent of x. The characteristic peak due to oxygen insertion into the lattice was observed at ca. 1.45 V vs. RHE, the intensity of which increased with the Sr content, which reflects the increase in the internal chemical diffusion of oxygen species. X-ray photoelectron spectroscopy (XPS) measurements for the constituent elements confirmed the presence of OH− groups inside the catalyst particles, especially in the Sr-rich region. It is suggested that the reversible intercalation ability of the OH− group into the rock-salt layer in the Ruddlesden-Popper (RP) phase (An+1BnO3n+1) contributes significantly to the improvement of the OER activity.