Design Refinement of Catalytic System for Scale-Up Mild Nitrogen Photo-Fixation

Ammonia and nitric acid, versatile industrial feedstocks, and burgeoning clean energy vectors hold immense promise for sustainable development. However, Haber-Bosch and Ostwald processes, which generates carbon dioxide as massive by-product, contribute to greenhouse effects and pose environmental challenges. Thus, the pursuit of nitrogen fixation through carbon-neutral pathways under benign conditions is a frontier of scientific topics, with the harnessing of solar energy emerging as an enticing and viable option. This review delves into the refinement strategies for scale-up mild photocatalytic nitrogen fixation, fields ripe with potential for innovation. The narrative is centered on enhancing the intrinsic capabilities of catalysts to surmount current efficiency barriers. Key focus areas include the in-depth exploration of fundamental mechanisms underpinning photocatalytic procedures, rational element selection, and functional planning, state-of-the-art experimental protocols for understanding photo-fixation processes, valid photocatalytic activity evaluation, and the rational design of catalysts. Furthermore, the review offers a suite of forward-looking recommendations aimed at propelling the advancement of mild nitrogen photo-fixation. It scrutinizes the existing challenges and prospects within this burgeoning domain, aspiring to equip researchers with insightful perspectives that can catalyze the evolution of cutting-edge nitrogen fixation methodologies and steer the development of next-generation photocatalytic systems.

Evolution and Reconstruction of Air-Electrode Surface Composition in Reversible Protonic Ceramic Cells: Mechanisms, Impacts on Catalytic Performance, and Optimization Strategies - A Review

Reversible protonic ceramic cells (R-PCCs) are at the forefront of electrochemical conversion devices, capable of reversibly and efficiently converting chemical energy into electricity at intermediate temperatures (350-700 °C) with zero carbon emissions. However, slow surface catalytic reactions at the air-electrode often hinder their performance and durability. The electrode surface is not merely an extension of the bulk structure, equilibrium reconstruction can lead to significantly different crystal-plane terminations and morphologies, which are influenced by material's intrinsic properties and external reaction conditions. Understanding electrode surface evolution at elevated temperatures in water-containing, oxidative atmospheres presents significant importance. In this review, a comprehensive summary of recent processes in applying advanced characterization techniques for high-temperature electrode surfaces is provided, exploring the correlations between surface evolution and performance fluctuations by examining the structural evolution and reconstruction of various air-electrode surfaces associated with degradation and activation phenomena, offering insights into their impact on electrode performance. Furthermore, reported strategies and recent advances in enhancing the electrochemical performance of R-PCCs through engineering air-electrode surfaces is discussed. This review offers valuable insights into surface evolution in R-PCCs and is expected to guide future developments in high-temperature catalysis, solid-state ionics, and energy materials.

Establishing Quantitative Understanding of Defect-Tuned Properties in Functional Oxides by an Electrochemically-Induced Gradient of Ionic Defect Concentration

Tuning the physical and chemical properties of functional oxides by controlling the amount of ionic point defects has been recognized as a new paradigm of designing oxides with tailored functionality. In order to enable precise tuning of properties, it is important to construct quantitative relationships between properties of interest and concentration of ionic defects, which are conventionally achieved by synthesizing and measuring a large number of samples with varying defect concentration. Compared with this conventional method, which is labor-intensive and susceptible to sample-to-sample variations, this review focuses on a high-throughput method that utilizes an electrochemically induced gradient of defect concentration in one single oxide sample. Combined with spatially resolved characterizations, this method allows establishing a quantitative property-defect concentration relationship. This review will present working principles and case studies that use this method based on graded concentration of ionic defects. Potentials and future extensions of this method will also be discussed.

Status and outlook of solid electrolyte membrane reactors for energy, chemical, and environmental applications

Solid electrolyte membrane reactors (SEMRs) can be operated at high temperatures with distinct reaction kinetics, or at lower temperatures (300-500 °C) for industrially relevant energy applications (such as solid oxide fuel/electrolysis cells, direct carbon fuel cells, and metal-air batteries), chemical (such as alkane dehydrogenation, C-C coupling, and NH3 synthesis), environmental (De-NO x , CO2 utilization, and separation), as well as their combined (one-step coupled CO2/H2O co-electrolysis and methanation reaction, power and chemical cogeneration) applications. SEMRs can efficiently integrate electrical, chemical, and thermal energy sectors, thereby circumventing thermodynamic constraints and production separation issues. They offer a promising way to achieve carbon neutrality and improve chemical manufacturing processes. This review thoroughly examines SEMRs utilizing various ionic conductors, namely O2-, H+, and hybrid types, with operations in different reactor/cell architectures (such as panel, tubular, single chamber, and porous electrolytes). The reactors operate in various modes including pumping, extraction, reversible, or electrical promoting modes, providing multiple functionalities. The discussion extends to examining critical materials for solid-state cells and catalysts essential for specific technologically important reactions, focusing on electrochemical performance, conversion efficiency, and selectivity. The review also serves as a first attempt to address the potential of process-intensified SEMRs through the integration of photo/solar, thermoelectric, and plasma energy and explores the unique phenomenon of electrochemical promotion of catalysis (EPOC) in membrane reactors. The ultimate goal is to offer insight into ongoing critical scientific and technical challenges like durability and operational cost hindering the widespread industrial implementation of SEMRs while exploring the opportunities in this rapidly growing research domain. Although still in an early stage with limited demonstrations and applications, advances in materials, catalysis science, solid-state ionics, and reactor design, as well as process intensification and/or system integration will fill the gaps in current high temperature operation of SEMRs and industrially relevant applications like sustainable clean chemical production, efficient energy conversion/storage, as well as environmental enhancement.

Redesigning protonic ceramic electrochemical cells to lower the operating temperature

Protonic ceramic electrochemical cells (PCECs) can operate at intermediate temperatures (450° to 600°C) for power generation and hydrogen production. However, the operating temperature is still too high to revolutionize ceramic electrochemical cell technology. Lowering the operating temperature to <450°C will enable a wider material choice and reduce system costs. We present approaches to redesigning PCECs via readily fabricated single-grain-thick, chemically homogeneous, and robust electrolytes and a nano-micro positive electrode. At 450°C, the PCECs achieve a peak power density of 1.6 watt per square centimeter on H2 fuel, 0.5 watt per square centimeter on NH3 fuel, and 0.3 watt per square centimeter on CH4 fuel in fuel cell mode. In steam electrolysis mode, a current density of >0.6 ampere per square centimeter with a Faradaic efficiency of >90% is achievable at 1.4 volt and 400°C. In addition, exceptional durability (>2000 hours) has been demonstrated, with a degradation rate of <0.01 millivolt per 100 hours in fuel cell mode at 400°C.

Characterization of high Zr/Ce ratio Ba(Zr,Ce,Y)O3-δ proton conductors: investigating the impact of Y on the properties of materials

Acceptor-substituted Ba(Zr,Ce)O3 proton conducting oxides have attracted significant attention due to their excellent proton conductivity at intermediate temperatures (400-600 °C). A high Zr/Ce ratio is crucial for maintaining stability in humid or other harsh atmospheres. Herein, a systematic study was conducted on the phase composition, microstructure, and the resulting hydration ability and electrochemical performance of high Zr/Ce ratio Ba(Zr,Ce)O3 solid solutions with different Y substitution levels (10 at% to 30 at%). In this substitution range, no apparent secondary phase can be found from XRD, leading to a continuous increase in hydration content. A Y-rich phase was observed in SEM for compositions with high levels of Y substitution. The impact of Y on proton conduction was examined using EIS, with particular attention on elucidating the effects of varying amounts of Y on bulk proton conduction. The increase of proton conductivity was primarily due to the increased charge carrier (proton) concentration caused by Y substitution. Different concentrations of Y have little effect on proton mobility, indicating a compromise between different mechanisms such as the Y trapping effect and the nano-percolation effect. Grain boundary proton conduction was discussed combining the TEM-EDS results to explain the space charge layer effect. Mechanical properties and thermo-chemical stability were also considered to pave the way for real applications.

Recent Advances in Barium Cobaltite-Based Perovskite Oxides as Cathodes for Intermediate-Temperature Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) are considered as advanced energy conversion technologies due to the high efficiency, fuel flexibility, and all-solid structure. Nevertheless, their widespread applications are strongly hindered by the high operational temperatures, limited material selection choices, inferior long-term stability, and relatively high costs. Therefore, reducing operational temperatures of SOFCs to intermediate-temperature (IT, 500-800 °C) range can remarkably promote the practical applications by enabling the use of low-cost materials and enhancing the cell stability. Nevertheless, the conventional cathodes for high-temperature SOFCs display inferior electrocatalytic activity for oxygen reduction reaction (ORR) at reduced temperatures. Barium cobaltite (BaCoO3-δ)-based perovskite oxides are regarded as promising cathodes for IT-SOFCs because of the high free lattice volume and large oxygen vacancy content. However, BaCoO3-δ-based perovskite oxides suffer from poor structural stability, inferior thermal compatibility, and insufficient ionic conductivity. Herein, an in-time review about the recent advances in BaCoO3-δ-based cathodes for IT-SOFCs is presented by emphasizing the material design strategies including functional/selectively doping, deficiency control, and (nano)composite construction to enhance the ORR activity/durability and thermal compatibility. Finally, the currently existed challenges and future research trends are presented. This review will provide valuable insights for the development of BaCoO3-δ-based electrocatalysts for various energy conversion/storage technologies.

Emerging computational and machine learning methodologies for proton-conducting oxides: materials discovery and fundamental understanding

This review presents computational and machine learning methodologies developed during a 5-year research project on proton-conducting oxides. The main goal was to develop methodologies that could assist in materials discovery or provide new insights into complex proton-conducting oxides. Through these methodologies, three new proton-conducting oxides, including both perovskite and non-perovskites, have been discovered. In terms of gaining insights, octahedral tilt/distortions and oxygen affinity are found to play a critical role in determining proton diffusivities and conductivities in doped barium zirconates. Replica exchange Monte Carlo approach has enabled to reveal realistic defect configurations, hydration behavior, and their temperature dependence in oxides. Our approach 'Materials discovery through interpretation', which integrates new insights or tendencies obtained from computations and experiments to sequential explorations of materials, has also identified perovskites that exhibit proton conductivity exceeding 0.01 S/cm and high chemical stability at 300   ∘ C.

Exploring the Potential of Cold Sintering for Proton-Conducting Ceramics: A Review

Proton-conducting ceramic materials have emerged as effective candidates for improving the performance of solid oxide cells (SOCs) and electrolyzers (SOEs) at intermediate temperatures. BaCeO3 and BaZrO3 perovskites doped with rare-earth elements such as Y2O3 (BCZY) are well known for their high proton conductivity, low operating temperature, and chemical stability, which lead to SOCs' improved performance. However, the high sintering temperature and extended processing time needed to obtain dense BCZY-type electrolytes (typically > 1350 °C) to be used as SOC electrolytes can cause severe barium evaporation, altering the stoichiometry of the system and consequently reducing the performance of the final device. The cold sintering process (CSP) is a novel sintering technique that allows a drastic reduction in the sintering temperature needed to obtain dense ceramics. Using the CSP, materials can be sintered in a short time using an appropriate amount of a liquid phase at temperatures < 300 °C under a few hundred MPa of uniaxial pressure. For these reasons, cold sintering is considered one of the most promising ways to obtain ceramic proton conductors in mild conditions. This review aims to collect novel insights into the application of the CSP with a focus on BCZY-type materials, highlighting the opportunities and challenges and giving a vision of future trends and perspectives.

Interfacial Modification for High-Efficient Reversible Protonic Ceramic Cell with a Spin-Coated BaZr0.1Ce0.7Y0.2O3-δ Electrolyte Thin Film

Slurry spin coating is an effective approach for the fabrication of protonic ceramic electrolyte thin films. However, weak adhesion between the electrode and spin-coated electrolyte layers in electrochemical cells due to the low sinterability of the proton-conducting perovskite materials usually lead to a high interfacial resistance and thus a low performance. Herein, we report a method to improve the interfacial connection and boost the performance of protonic ceramic cells based on a BaZr0.1Ce0.7Y0.2O3-δ (BZCY) electrolyte. Ni-BZCY anode functional layer, BZCY electrolyte layer and La0.6Sr0.4Co0.2Fe0.8O3-δ-BZCY cathode functional layer are all fabricated by slurry spin coating. The electrode functional layers and the components of the electrolyte slurry influence the microstructure of the single cell and the kinetics of the electrochemical processes significantly. A peak power density of 2345 mW cm-2 is achieved at 700 °C in the fuel cell mode, and a current density of -3.0 A cm-2 is obtained at an applied voltage of 1.3 V in the electrolysis mode.

High Temperature Solid Oxide Electrolysis for Green Hydrogen Production

Global warming and energy crises have motivated the development of renewable energy and its energy carriers. Green hydrogen is the most promising renewable energy carrier and will be fundamental to future energy conversion and storage systems. Solid Oxide Electrolysis Cells (SOECs) are a promising green hydrogen production technology featuring high electrical efficiency, no noble metal catalyst usage, and reversible operation. This review provides a timely summary of the latest SOEC progress, covering developments at various levels, from cells to stacks to systems. Cell/stack components, configurations, advanced electrode material/fabrication, and novel characterization methods are discussed. Electrochemical and durable performance for each cell/stack configuration is reviewed, focusing on degradation mechanisms and associated mitigation strategies. SOEC system integration with renewable energy and downstream users is outlined, showing flexibility, robustness, scalability, viability, and energy efficiency. Challenges of cost and durability are expected to be overcome by innovation in material, fabrication, production, integration, and operation. Overall, this comprehensive review identifies the SOEC commercialization bottleneck, encourages further technology development, and envisions a future green hydrogen society with net-zero carbon emissions.

Photovoltaic properties of halide perovskites for solar cell application with efficiency greater than 18

The opto-electronic properties and solar cell efficiency of halide perovskites A2LiInBr6 (A = Rb, Cs) are investigated using density functional theory (DFT) through WEIN2k and SCAPS-1D. The electronic characteristic of A2LiInBr6 (A = Rb, Cs) compounds reveal their direct bandgap semiconductor nature and are active in visible rang. The results indicate that substituting Cs with Rb causes a slight narrowing of the bandgap. According to the optical analysis, these compounds possess dynamic visible-range optical properties that make them ideal for application in opto-electronic devices and solar cells. The A2LiInBr6 (A = Rb, Cs) absorber layer is employed to simulate the solar cell efficiency of these lead free perovskite-based device. The optimized FTO/WS2/A2LiInBr6 (A = Rb, Cs)/Spiro-MeOTAD/Cu solar cells exhibit the best performance with WS2 as the ETL and Spiro-MeOTAD as the HTL having V oc value of 2.27 V and 1.85 V, J sc value is 11.35 and 11.44 mA cm-2, FF is 73.24% and 83.84%, PCE is 18.88% and 17.97%, R s is 9.94 and 4.88 Ω cm2 and R sh is 1.35 and 1.14 Ω cm2 respectively. As a result, this research paves the way for future experiments to create entirely inorganic perovskite photovoltaics, free of lead toxicity and exhibit improved photovoltaic ability.

Observation of Fast Low-Temperature Oxygen Ion Conduction in CeO2/β"-Al2O3 Heterostructure

Semiconductor ion fuel cells (SIFCs) have demonstrated impressive ionic conductivity and efficient power generation at temperatures below 600 °C. However, the lack of understanding of the ionic conduction mechanisms associated with composite electrolytes has impeded the advancement of SIFCs toward lower operating temperatures. In this study, a CeO2/β″-Al2O3 heterostructure electrolyte is introduced, incorporating β″-Al2O3 and leveraging the local electric field (LEF) as well as the manipulation of the melting point temperature of carbonate/hydroxide (C/H) by Na+ and Mg2+ from β″-Al2O3. This design successfully maintains swift interfacial conduction of oxygen ions at 350 °C. Consequently, the fuel cell device achieved an exceptional ionic conductivity of 0.019 S/cm and a power output of 85.9 mW/cm2 at 350 °C. The system attained a peak power density of 1 W/cm2 with an ultra-high ionic conductivity of 0.197 S/cm at 550 °C. The results indicate that through engineering the LEF and incorporating the lower melting point C/H, there approach effectively observed oxygen ion transport at low temperatures (350 °C), effectively overcoming the issue of cell failure at temperatures below 419 °C. This study presents a promising methodology for further developing high-performance semiconductor ion fuel cells in the low temperature range of 300-600 °C.

Investigation of Water Impacts on Surface Properties and Performance of Air-Electrode in Reversible Protonic Ceramic Cells

Water, being abundant and readily accessible, gains widespread usage as proton source in many catalysis and energy conversion technologies, including applications like reversible protonic ceramic cells (R-PCCs). Revealing the influence of water on the electrode surface and reaction kinetics is critical for further improving their electrochemical performance. Herein, a hydrophilic air-electrode PrBa0.875Cs0.125Co2O5+δ is developed for R-PCC, which demonstrates a remarkable peak power density of 1058 mW cm-2 in fuel cell mode and a current density of 1354 mA cm-2 under 1.3 V in electrolyzing steam at 650 °C. For the first time on R-PCC, surface protons' behavior in response to external voltages is captured using in situ FTIR characterizations. Further, it is shown that contrary to the bulk proton uptake process that is thought to follow hydrogenation reactions and lead to cation reductions. The air-electrode presents enriched surface protons occurring through oxidizing surface cations, as confirmed by depth-profiling XPS results. H/D isotope exchange experiments and subsequent electrochemical characterization analyses reveal that the presence of protons enhances surface reactions. This study fills the knowledge gap between water-containing atmospheres and electrochemical performance by providing insights into the surface properties of the material. These new findings provide guidance for future electrode design and optimization.

Challenges and Advancements in the Electrochemical Utilization of Ammonia Using Solid Oxide Fuel Cells

Solid oxide fuel cells utilized with NH3 (NH3-SOFCs) have great potential to be environmentally friendly devices with high efficiency and energy density. The advancement of this technology is hindered by the sluggish kinetics of chemical or electrochemical processes occurring on anodes/catalysts. Extensive efforts have been devoted to developing efficient and durable anode/catalysts in recent decades. Although modifications to the structure, composition, and morphology of anodes or catalysts are effective, the mechanistic understandings of performance improvements or degradations remain incompletely understood. This review informatively commences by summarizing existing reports on the progress of NH3-SOFCs. It subsequently outlines the influence of factors on the performance of NH3-SOFCs. The degradation mechanisms of the cells/systems are also reviewed. Lastly, the persistent challenges in designing highly efficient electrodes/catalysts for low-temperature NH3-SOFCs, and future perspectives derived from SOFCs are discussed. Notably, durability, thermal cycling stability, and power density are identified as crucial indicators for enhancing low-temperature (550 °C or below) NH3-SOFCs. This review aims to offer an updated overview of how catalysts/electrodes affect electrochemical activity and durability, offering critical insights for improving performance and mechanistic understanding, as well as establishing the scientific foundation for the design of electrodes for NH3-SOFCs.

Unveiling the importance of the interface in nanocomposite cathodes for proton-conducting solid oxide fuel cells

Designing a high-performance cathode is essential for the development of proton-conducting solid oxide fuel cells (H-SOFCs), and nanocomposite cathodes have proven to be an effective means of achieving this. However, the mechanism behind the nanocomposite cathodes' remarkable performance remains unknown. Doping the Co element into BaZrO3 can result in the development of BaCoO3 and BaZr0.7Co0.3O3 nanocomposites when the doping concentration exceeds 30%, according to the present study. The construction of the BaCoO3/BaZr0.7Co0.3O3 interface is essential for the enhancement of the cathode catalytic activity, as demonstrated by thin-film studies using pulsed laser deposition to simulate the interface of the BCO and BZCO individual particles and first-principles calculations to predict the oxygen reduction reaction steps. Eventually, the H-SOFC with a BaZr0.4Co0.6O3 cathode produces a record-breaking power density of 2253 mW cm-2 at 700°C.

Modulating Lattice Oxygen Activity of Iron-Based Triple-Conducting Nanoheterostructure Air Electrode via Sc-Substitution Strategy for Protonic Ceramic Cells

Iron-based perovskite air electrodes for protonic ceramic cells (PCCs) offer broad application prospects owing to their reasonable thermomechanical compatibility and steam tolerance. However, their insufficient electrocatalytic activity has considerably limited further development. Herein, oxygen-vacancy-rich BaFe0.6Ce0.2Sc0.2O3-δ (BFCS) perovskite is rationally designed by a facile Sc-substitution strategy for BaFe0.6Ce0.4O3-δ (BFC) as efficient and stable air electrode for PCCs. The BFCS electrode with an optimized Fe 3d-eg orbital occupancy and more oxygen vacancies exhibits a polarization resistance of ≈ 0.175 Ω cm2 at 600 °C, ≈ 1/3 of the BFC electrode (≈0.64 Ω cm2). Simultaneously, BFCS shows favorable proton uptake with a low proton defect formation enthalpy (- 81 kJ mol-1). By combining soft X-ray absorption spectroscopy and electrical conductivity relaxation studies, it is revealed that the enhancement of Fe4+-O2- interactions in BFCS promotes the activation and mobility of lattice oxygen, triggering the activity of BFCS in both oxygen reduction and evolution reactions (ORR/OER). The single cell achieves encouraging output performance in both fuel cell (1.55 W cm-2) and electrolysis cell (-2.96 A cm-2 at 1.3 V) modes at 700 °C. These results highlight the importance of activating lattice oxygen in air electrodes of PCCs.

Semiconductor Heterostructure (SrFe0.3TiO3-ZnO) Electrolyte with High Proton Conductivity for Low-Temperature Ceramic Electrochemical Cells

In recent years, ceramic cells based on high proton conductivity have attracted much attention and can be employed for hydrogen production and electricity generation, especially at low temperatures. Nevertheless, attaining a high power output and durability is challenging, especially at low operational temperatures. In this regard, we design semiconductor heterostructure SFT-ZnO (SrFe0.3TiO3-ZnO) materials to function as an electrolyte for fuel cell and electrolysis applications. Using this approach, the functional semiconductor heterostructure can deliver a better power output and high ionic and proton conductivity at low operational temperatures. The prepared cell in fuel cell mode has demonstrated excellent performance of 700 mW cm-2 and proton performance of 540 mW cm-2 at the low temperature of 520 °C, suggesting dominant proton conduction. Further, the prepared cell delivers exceptional current densities of 1.18 and 0.38 A cm-2 (at 1.6 and 1.3 V, respectively) at 520 °C in the electrolysis mode. Our electrochemical cell is stable in fuel and electrolysis mode at a low temperature of 500 °C.

Electrocatalysis in Solid Oxide Fuel Cells and Electrolyzers

Interest in energy-to-X and X-to-energy (where X represents green hydrogen, carbon-based fuels, or ammonia) technologies has expanded the field of electrochemical conversion and storage. Solid oxide electrochemical cells (SOCs) are among the most promising technologies for these processes. Their unmatched conversion efficiencies result from favorable thermodynamics and kinetics at elevated operating temperatures (400-900 °C). These solid-state electrochemical systems exhibit flexibility in reversible operation between fuel cell and electrolysis modes and can efficiently utilize a variety of fuels. However, electrocatalytic materials at SOC electrodes remain nonoptimal for facilitating reversible operation and fuel flexibility. In this Review, we explore the diverse range of electrocatalytic materials utilized in oxygen-ion-conducting SOCs (O-SOCs) and proton-conducting SOCs (H-SOCs). We examine their electrochemical activity as a function of composition and structure across different electrochemical reactions to highlight characteristics that lead to optimal catalytic performance. Catalyst deactivation mechanisms under different operating conditions are discussed to assess the bottlenecks in performance. We conclude by providing guidelines for evaluating the electrochemical performance of electrode catalysts in SOCs and for designing effective catalysts to achieve flexibility in fuel usage and mode of operation.

Facile Deficiency Engineering in a Cobalt-Free Perovskite Air Electrode to Achieve Enhanced Performance for Protonic Ceramic Fuel Cells

As a crucial component responsible for the oxygen reduction reaction (ORR), cobalt-rich perovskite-type cathode materials have been extensively investigated in protonic ceramic fuel cell (PCFC). However, their widespread application at a commercial scale is considerably hindered by the high cost and inadequate stability. In response to these weaknesses, the study presents a novel cobalt-free perovskite oxide, Ba0.95La0.05(Fe0.8Zn0.2)0.95O3-δ (BLFZ0.95), with the triple-conducting (H+|O2-|e-) property as an active and robust air electrode for PCFC. The B-site deficiency state contributes significantly to the optimization of crystal and electronic structure, as well as the increase in oxygen vacancy concentration, thus in turn favoring the catalytic capacity. As a result, the as-obtained BLFZ0.95 electrode demonstrates exceptional electrochemical performance at 700 °C, representing extremely low area-specific resistance of 0.04 Ω cm2 in humid air (3 vol.% H2O), extraordinarily high peak power density of 1114 mW cm-2, and improved resistance against CO2 poisoning. Furthermore, the outstanding long-term durability is achieved without visible deterioration in both symmetrical and single cell modes. This study presents a simple but crucial case for rational design of cobalt-free perovskite cathode materials with appreciable performance via B-site deficiency regulation.

High-Temperature Protonic Conduction in La2NiO4+ δ-Based Ruddlesden-Popper Type Oxides: Correlation with Concentration of Interstitial Oxide Ions

Oxygen-excess La2NiO4+ δ (LNO) conducts oxide ions, electron holes, and hydroxide ions simultaneously on exposing to wet oxygen, exhibiting the potential as a cathode material in protonic ceramic fuel cells. Since the incorporation of protons in oxygen-excess LNO is via the hydration reaction assisted by interstitial oxide ions, in this work, the concentration of interstitial oxide ions is reduced and increased by substituting Ni with Cu and Co, respectively. A higher concentration of interstitial oxide ions leads to a high proton concentration, indicating the predominant role of interstitial oxide ions in the hydration reaction, different from that in the oxygen-deficient oxides, where protons are introduced by dissociative absorption of water molecules by oxygen vacancies. The theoretical calculation indicates that protons in Co-doped LNO prefer to locate between the interstitial oxide ions and unshared apical oxide ions. A trapping effect is found between protons and the oxide ions near Cu, leading to decreased proton mobility. Protonic conductivity at 400-575 °C is then directly measured by a Hebb-Wagner direct current polarization method with La0.99Ca0.01NbO4- δ as the blocking electrode, enabling the observation that Co-doped LNO has the highest protonic conductivity among the samples studied in this work.

Reverse Atom Capture on Perovskite Surface Enabling Robust and Efficient Cathode for Protonic Ceramic Fuel Cells

Protonic ceramic fuel cells (PCFCs) hold potential for sustainable energy conversion, yet their widespread application is hindered by the sluggish kinetics and inferior stability of cathode materials. Here, a facile and efficient reverse atom capture technique is developed to manipulate the surface chemistry of PrBa0.5Sr0.5Co1.5Fe0.5O5+ δ (PBSCF) cathode for PCFCs. This method successfully captures segregated Ba and Sr cations on the PBSCF surface using W species, creating a (Ba/Sr)(Co/Fe/W)O3- δ (BSCFW)@PBSCF heterostructure. Benefiting from enhanced kinetics of proton-involved oxygen reduction reaction and strengthened chemical stability, the single cell using the optimized 2W-PBSCF cathode demonstrates an exceptional peak power density of 1.32 W cm-2 at 650 °C and maintains durable performance for 240 h. Theoretical calculations unveil that the BSCFW perovskite delivers lower oxygen vacancy formation energy, hydration energy, and proton transfer energy compared to the PBSCF perovskite. This protocol offers new insights into advanced atom capture techniques for sustainable energy infrastructures.

Synthesis and Characterization of Sol-Gelled Barium Zirconate as Novel MTA Radiopacifiers

Barium zirconate (BaZrO3, BZO), which exhibits superior mechanical, thermal, and chemical stability, has been widely used in many applications. In dentistry, BZO is used as a radiopacifier in mineral trioxide aggregates (MTAs) for endodontic filling applications. In the present study, BZO was prepared using the sol-gel process, followed by calcination at 700-1000 °C. The calcined BZO powders were investigated using X-ray diffraction and scanning electron microscopy. Thereafter, MTA-like cements with the addition of calcined BZO powder were evaluated to determine the optimal composition based on radiopacity, diametral tensile strength (DTS), and setting times. The experimental results showed that calcined BZO exhibited a majority BZO phase with minor zirconia crystals. The crystallinity, the percentage, and the average crystalline size of BZO increased with the increasing calcination temperature. The optimal MTA-like cement was obtained by adding 20% of the 700 °C-calcined BZO powder. The initial and final setting times were 25 and 32 min, respectively. They were significantly shorter than those (70 and 56 min, respectively) prepared with commercial BZO powder. It exhibited a radiopacity of 3.60 ± 0.22 mmAl and a DTS of 3.02 ± 0.18 MPa. After 28 days of simulated oral environment storage, the radiopacity and DTS decreased to 3.36 ± 0.53 mmAl and 2.84 ± 0.27 MPa, respectively. This suggests that 700 °C-calcined BZO powder has potential as a novel radiopacifier for MTAs.

Harnessing High-Throughput Computational Methods to Accelerate the Discovery of Optimal Proton Conductors for High-Performance and Durable Protonic Ceramic Electrochemical Cells

The pursuit of high-performance and long-lasting protonic ceramic electrochemical cells (PCECs) is impeded by the lack of efficient and enduring proton conductors. Conventional research approaches, predominantly based on a trial-and-error methodology, have proven to be demanding of resources and time-consuming. Here, this work reports the findings in harnessing high-throughput computational methods to expedite the discovery of optimal electrolytes for PCECs. This work methodically computes the oxygen vacancy formation energy (EV), hydration energy (EH), and the adsorption energies of H2O and CO2 for a set of 932 oxide candidates. Notably, these findings highlight BaSnxCe0.8-xYb0.2O3-δ (BSCYb) as a prospective game-changing contender, displaying superior proton conductivity and chemical resilience when compared to the well-regarded BaZrxCe0.8-xY0.1Yb0.1O3-δ (BZCYYb) series. Experimental validations substantiate the computational predictions; PCECs incorporating BSCYb as the electrolyte achieved extraordinary peak power densities in the fuel cell mode (0.52 and 1.57 W cm-2 at 450 and 600 °C, respectively), a current density of 2.62 A cm-2 at 1.3 V and 600 °C in the electrolysis mode while demonstrating exceptional durability for over 1000-h when exposed to 50% H2O. This research underscores the transformative potential of high-throughput computational techniques in advancing the field of proton-conducting oxides for sustainable power generation and hydrogen production.

An excellent bismuth-doped perovskite cathode with high activity and CO2 resistance for solid-oxide fuel cells operating below 700 °C

Lowering the operating temperatures of solid-oxide fuel cells (SOFCs) is critical, although achieving success in this endeavor has proven challenging. Herein, Bi0.15Sr0.85Co0.8Fe0.2O3-δ (BiSCF) is systematically evaluated as a carbon dioxide (CO2)-tolerant and highly active cathode for SOFCs. BiSCF, which features Bi3+ with an ionic radius similar to Ba2+, exhibits activity (e.g., 0.062 Ω cm2 at 700 °C) comparable to that of Ba0.5Sr0.5Co0.8Fe0.2O3-δ and PrBaCo2O5+δ, while demonstrating a considerable advantage over Bi-doped cathodes. Moreover, BiSCF exhibits long-term stability over a period of 500 h, and an anode-supported cell with BiSCF achieves a power density of 912 mW cm-2 at 650 °C. The CO2-poisoned BiSCF exhibits quick reversibility or slight activation after returning to normal conditions. The exceptional CO2 tolerance of BiSCF can be attributed to its reduced basicity and high electronegativity, which effectively restrict surface Sr diffusion and hinder subsequent carbonate formation. These findings highlight the substantial potential of BiSCF for SOFCs operating below 700 °C.

Multiplying Oxygen Permeability of a Ruddlesden-Popper Oxide by Orientation Control via Magnets

Ruddlesden-Popper-type oxides exhibit remarkable chemical stability in comparison to perovskite oxides. However, they display lower oxygen permeability. We present an approach to overcome this trade-off by leveraging the anisotropic properties of Nd2 NiO4+δ . Its (a,b)-plane, having oxygen diffusion coefficient and surface exchange coefficient several orders of magnitude higher than its c-axis, can be aligned perpendicular to the gradient of oxygen partial pressure by a magnetic field (0.81 T). A stable and high oxygen flux of 1.40 mL min-1  cm-2 was achieved for at least 120 h at 1223 K by a textured asymmetric disk membrane with 1.0 mm thickness under the pure CO2 sweeping. Its excellent operational stability was also verified even at 1023 K in pure CO2 . These findings highlight the significant enhancement in oxygen permeation membrane performance achievable by adjusting the grain orientation. Consequently, Nd2 NiO4+δ emerges as a promising candidate for industrial applications in air separation, syngas production, and CO2 capture under harsh conditions.

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.

Nanotechnologies in ceramic electrochemical cells

Although they are emerging technologies for achieving high-efficiency and green and eco-friendly energy conversion, ceramic electrochemical cells (CECs), i.e. solid oxide electrolysis cells (SOECs) and fuel cells (SOFCs), are still fundamentally limited by their inferior catalytic activities at low temperature, poor thermo-mechanical stability, high material cost, etc. The materials used in electrolytes and electrodes, which are the most important components in CECs, are highly associated with the cell performances. Therefore, rational design of electrolytes and electrodes with excellent catalytic activities and high stabilities at relatively low cost is a meaningful and valuable approach for the development of CECs. Nanotechnology is a powerful tool for improving the material performances in CECs owing to the favourable effects induced by the nanocrystallization of electrolytes and electrodes. Herein, a relatively comprehensive review on the nanotechnologies implemented in CECs is conducted. The working principles of CECs and the corresponding challenges were first presented, followed by the comprehensive insights into the working mechanisms of nanocrystalline materials in CECs. Then, systematic summarization and analyses of the commonly used nano-engineering strategies in the fabrication of CEC materials, including physical and chemical methods, were provided. In addition, the frontiers in the research of advanced electrolyte and electrode materials were discussed with a special emphasis on the modified electrochemical properties derived from nanotechnologies. Finally, the bottlenecks and the promising breakthroughs in nanotechnologies were highlighted in the direction of providing useful references for rational design of nanomaterials for CECs.

Sintering-induced cation displacement in protonic ceramics and way for its suppression

Protonic ceramic fuel cells with high efficiency and low emissions exhibit high potential as next-generation sustainable energy systems. However, the practical proton conductivity of protonic ceramic electrolytes is still not satisfied due to poor membrane sintering. Here, we show that the dynamic displacement of Y3+ adversely affects the high-temperature membrane sintering of the benchmark protonic electrolyte BaZr0.1Ce0.7Y0.1Yb0.1O3-δ, reducing its conductivity and stability. By introducing a molten salt approach, pre-doping of Y3+ into A-site is realized at reduced synthesis temperature, thus suppressing its further displacement during high-temperature sintering, consequently enhancing the membrane densification and improving the conductivity and stability. The anode-supported single cell exhibits a power density of 663 mW cm-2 at 600 °C and long-term stability for over 2000 h with negligible performance degradation. This study sheds light on protonic membrane sintering while offering an alternative strategy for protonic ceramic fuel cells development.

Direct methane protonic ceramic fuel cells with self-assembled Ni-Rh bimetallic catalyst

Direct methane protonic ceramic fuel cells are promising electrochemical devices that address the technical and economic challenges of conventional ceramic fuel cells. However, Ni, a catalyst of protonic ceramic fuel cells exhibits sluggish reaction kinetics for CH4 conversion and a low tolerance against carbon-coking, limiting its wider applications. Herein, we introduce a self-assembled Ni-Rh bimetallic catalyst that exhibits a significantly high CH4 conversion and carbon-coking tolerance. It enables direct methane protonic ceramic fuel cells to operate with a high maximum power density of ~0.50 W·cm-2 at 500 °C, surpassing all other previously reported values from direct methane protonic ceramic fuel cells and even solid oxide fuel cells. Moreover, it allows stable operation with a degradation rate of 0.02%·h-1 at 500 °C over 500 h, which is ~20-fold lower than that of conventional protonic ceramic fuel cells (0.4%·h-1). High-resolution in-situ surface characterization techniques reveal that high-water interaction on the Ni-Rh surface facilitates the carbon cleaning process, enabling sustainable long-term operation.

A novel yttrium stabilized zirconia and ceria composite electrolyte lowering solid oxide fuel cells working temperature to 400 °C

Reducing the working temperature and improving the ionic conductivity of electrolytes have been the critical challenges for the gradual development of solid oxide fuel cells (SOFCs) in practical applications. The researchers all over the world attempt to develop alternative electrolyte materials with sufficient ionic conductivity. In this work, YSZ-CeO2 composite material was used as electrolytes in the construction of symmetrical SOFCs. The maximum power densities (Pmax) of YSZ-CeO2 based fuel cell can reach 680 mW cm-2 at 450 °C, 510 mW cm-2 at 430 °C, 330 mW cm-2 at 410 °C and even 200 mW cm-2 as the operational temperature was reduced to 390 °C. A series of characterizations indicates that the activation energy of the YSZ-CeO2 composite is significantly decreased, and the enhancement effect for ion conduction comes from interface transport. Our findings indicate the YSZ-CeO2 composite material can be a highly promising candidate for advanced low-temperature SOFC.

Interface Diffusion and Compatibility of (Ba,La)FeO3-δ Perovskite Electrodes in Contact with Barium Zirconate and Ceria

Ba1-xLaxFeO3-δ perovskites (BLF) capable of conducting electrons, protons, and oxygen ions are promising oxygen electrodes for efficient solid oxide cells (fuel cells or electrolyzers), an integral part of prospected large-scale power-to-gas energy storage systems. We investigated the compatibility of BLF with lanthanum content between 5 and 50%, in contact with oxide-ion-conducting Ce0.8Gd0.2O2-δ and proton-conducting BaZr0.825Y0.175O3-δ electrolytes, annealing the electrode-electrolyte bilayers at high temperature to simulate thermal stresses of fabrication and prolonged operation. By employing both bulk X-ray diffraction and synchrotron X-ray microspectroscopy, we present a space-resolved picture of the interaction between electrode and electrolyte as what concerns cation interdiffusion, exsolution, and phase stability. We found that the phase stability of BLF in contact with other phases is correlated with the Goldschmidt tolerance factor, in turn determined by the La/Ba ratio, and appropriate doping strategies with oversized cations (Zn2+, Y3+) could improve structural stability. While extensive reactivity and/or interdiffusion was often observed, we put forward that most products of interfacial reactions, including proton-conducting Ba(Ce,Gd)O3-δ and mixed-conducting (Ba,La)(Fe,Zr,Y)O3-δ, may not be very detrimental for practical cell operation.

Proton conductivity in multi-component ABO4-type oxides

This work investigates how configurational entropy in oxides could affect proton conductivity. For this purpose, three samples of different elemental compositions are synthesized. Five, six and seven elements were introduced into the A-site of ANbO4, forming La1/5 Nd1/5 Sm1/5Gd1/5 Eu1/5NbO4, La1/6Nd1/6Sm1/6Gd1/6Eu1/6Ho1/6NbO4 and La1/7Nd1/7Sm1/7Gd1/7Eu1/7Ho1/7Er1/7NbO4, respectively. The high configuration disorder changes the local environment, which can have a notable effect on many properties, including proton transport, which is the focus of this work. The conductivity was measured in different atmospheres; dry and wet and in a different temperature range (600-800 °C) to compare the proton transport as well as study the effect of temperature. A homogenous single-phase monoclinic fergusonite was obtained for the three samples. Proton conductivity, measured by means of comparing the conductivity in dry and wet atmospheres, was observed in all samples. La1/5 Nd1/5 Sm1/5Gd1/5 Eu1/5NbO4 exhibited the highest conductivity, about 3.0 × 10-6 S cm-1 at 800 °C in the wet atmosphere, while in the dry atmosphere it was about 2.2 × 10-6 S cm-1 at the same temperature, which implies a modest proton conductivity in this class of materials.

Enhancing the Performance of the p-n Heterostructure Electrolyte for Solid Oxide Fuel Cells via A-Site-Deficiency Engineering

Semiconductor ionic electrolytes are attracting growing interest for developing low-temperature solid oxide fuel cells (LT-SOFCs). Our recent study has proposed a p-n heterostructure electrolyte based on perovskite oxide BaCo0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY) and ZnO, achieving promising fuel cell performance. Herein, to further improve the performance of the heterostructure electrolyte, an A-site-deficiency strategy is used to solely modify BCFZY for regulating the ionic conduction and catalytic activity of the heterostructure. Two new electrolytes, B0.9CFZY-ZnO and B0.8CFZY-ZnO, were developed and systematically studied. The results show that the two samples gain improved ionic conductivity and auxiliary catalytic activity after A-site deficiency as a result of the increment of the surface and interface oxygen vacancies. The single cells with B0.9CFZY-ZnO and B0.8CFZY-ZnO exhibit enhanced peak power outputs at 450-550 °C compared to the cell based on B1.0CFZY-ZnO (typically, 745 and 795 vs 542 mW cm-2 at 550 °C). Particular attention is paid to the impact of A-site deficiency on the interface energy band alignment between BxCFZY and ZnO, which suggests that the p-n heterojunction effect of BxCFZY-ZnO for charge carrier regulation can be tuned by A-site deficiency to enable high proton transport while avoiding fuel cell current leakage. This study thus confirms the feasibility of A-site-deficiency engineering to optimize the performance of the heterostructure electrolyte for developing LT-SOFCs.

A-Site Nonstoichiometric BaxCo0.4Fe0.4Zr0.1Y0.1O3-δ Cathode for Protonic Ceramics Fuel Cells

Highly active triple (proton, oxygen-ion, and electron) conducting materials BaxCo0.4Fe0.4Zr0.1Y0.1O3-δ (BxCFZY, x = 0.9-1.1) were prepared and characterized as potential cathodes for protonic ceramic fuel cells (PCFCs) in this work. The crystal structure, oxygen vacancy concentration, electrical conductivity, oxygen ion transfer properties, and electrochemical performance of BxCFZY oxides were systematically evaluated. The electrical conductivity of BxCFZY decreases but oxygen vacancies increase with increasing Ba content, indicating that the charge compensation was mainly achieved by the production of oxygen vacancy rather than the increase in the valence of transition metal cations. The power density of 1170 mW cm-2 and the polarization resistance of 0.05 Ω cm2 were achieved at 700 °C for the anode-supported single cells with B1.1CFZY cathode, suggesting that the excess A site on the BxCFZY had a positive effect on the catalytic activity for the oxygen reduction reaction. Furthermore, the distribution of relaxation time (DRT) analysis method was adopted to determine the electrochemical processes of the cells with BxCFZY cathodes. The calculated results confirmed that the cell with B1.1CFZY cathode exhibited the optimum performance due to the best oxygen ion transfer properties in BxCFZY cathodes.

Design of a highly stable and conductive electrolyte by suppressing barium copper oxide formation at the grain interfaces in Cux-doped BaCe0.7Zr0.1Dy0.2-xO3-δ sintered at a low temperature (1200 °C) for SOFCs

Proton-conducting electrolytes with high conductivity and long-term stability, achievable at low sintering temperatures, are of paramount importance. In this study, we investigate the impact of Cu doping on the sintering mechanism, electrical performance, and stability of BaCe0.7Zr0.1Dy0.2-xO3-δ (BCZD) electrolyte. The morphology, composition, structure, and chemical state of BCZD electrolytes were investigated using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Remarkably, the sintering temperature of BCZD is reduced to 1200 °C through Cu doping Furthermore, the introduction of Cu as a dopant induces Ba exsolution from the BCZD crystal lattice alongside the generation of oxygen vacancies. XPS measurements confirmed that vacancy concentrations increase with increasing Cu doping concentrations. However, as the Cu content surpasses 2 mol%, the exsoluted Cu reacts with Ba, leading to the formation of BaCuO2. Accumulation of BaCuO2 at the grain boundaries adversely affects the conductivity and stability of Cu-doped BCZD, in a humidified atmosphere where it exhibits significant instability. Notably, BCZD with 2 mol% Cu content demonstrates a conductivity of 2.7 × 10-2 S cm-1 and maintains stability for up to 420 h in the H2/3%H2O atmosphere at 600 °C. In contrast, BCZD with 5 mol% Cu content exhibits a conductivity of 1.9 × 10-2 S cm-1 at 600 °C but experiences continuous degradation in a humidified atmosphere, ultimately leading to failure within 30 h. The 2 % Cu-doped BCZD exhibits high conductivity and stability at intermediate temperatures, rendering it highly suitable for solid oxide fuel cell (SOFC) applications.

A Synergistic Three-Phase, Triple-Conducting Air Electrode for Reversible Proton-Conducting Solid Oxide Cells

Reversible proton-conducting solid oxide cells (R-PSOCs) have the potential to be the most efficient and cost-effective electrochemical device for energy storage and conversion. A breakthrough in air electrode material development is vital to minimizing the energy loss and degradation of R-PSOCs. Here we report a class of triple-conducting air electrode materials by judiciously doping transition- and rare-earth metal ions into a proton-conducting electrolyte material, which demonstrate outstanding activity and durability for R-PSOC applications. The optimized composition Ba0.9Pr0.1Hf0.1Y0.1Co0.8O3-δ (BPHYC) consists of three phases, which have a synergistic effect on enhancing the performance, as revealed from electrochemical analysis and theoretical calculations. When applied to R-PSOCs operated at 600 °C, a peak power density of 1.37 W cm-2 is demonstrated in the fuel cell mode, and a current density of 2.40 A cm-2 is achieved at a cell voltage of 1.3 V in the water electrolysis mode under stable operation for hundreds of hours.

Interfacial Disordering and Heterojunction Enabling Fast Proton Conduction

The interfacial disorder is a general method to change the metal-oxygen compatibility and carrier density of heterostructure materials for ionic transport modulation. Herein, to enable high proton conduction, a semiconductor heterostructure based on spinel ZnFe2 O4 (ZFO) and fluorite CeO2 is developed and investigated in terms of structural characterization, first principle calculation, and electrochemical performance. Particular attention is paid to the interfacial disordering and heterojunction effects of the material. Results show that the heterostructure induces a disordered oxygen region at the hetero-interface of ZFO-CeO2 by dislocating oxygen atoms, leading to fast proton transport. As a result, the ZFO-CeO2 exhibits a high proton conductivity of 0.21 S cm-1 and promising fuel cell power output of 1070 mW cm-2 at 510 °C. Based upon these findings, a new mechanism is proposed by focusing on the change of O-O bond length to interpret the diffusion and acceleration of protons in ZFO-CeO2 on the basis of the Grotthuss mechanism. This study provides a new strategy to customize semiconductor heterostructure to enable fast proton conduction.

2 A cm-2 Level Large-Scale Production of Hydrogen Enabled by Constructing Higher Capacity of Interface "Electron Pocket"

The batch production of high-purity hydrogen is a key problem that restricts the progress of fuel cells and the blueprint for achieving carbon neutrality. Transition-metal chalcogenide heterojunctions exhibit certain activity toward electrochemical overall water splitting (EOWS), but their high-current-density catalytic performances are still unsatisfactory due to the slow kinetic progression (H* or *O → *OOH). Inspired by the "electron pocket" theory, we designed a Ni-Mo bimetallic disulfide interface heterojunction electrocatalyst system (NM-IHJ-V) with high electronic storage capacity around the Fermi level (-0.5 eV, +0.5 eV) (e-DFE), which injects more power into the kinetic progression processes of intermediate species in the EOWS process. Consequently, it achieves a superhigh current density of 2 A cm-2 level for EOWS (only 1.98 V voltage is needed), which is 11.23-fold higher than that of the benchmarked Pt/C//IrO2 (178 mA cm-2@1.98 V), as well as an excellent long-term stability of 200 h. Most strikingly, NM-IHJ-V can efficiently produce hydrogen at currents up to 5 A. Our proposed strategy of constructing catalysts to produce hydrogen at superhigh current density through the electron pocket theory will supply valuable insights for the designing other catalytic systems.

Theoretical insight of stabilities and optoelectronic properties of double perovskite Cs2CuIrF6: Ab-initio calculations

CONTEXT

In this study, we predict the stability, elastic, electronic and optical properties of double perovskite (DP) Cs₂CuIrF₆. The detailed investigation of electronic structure and optical properties to find the suitability of DP Cs₂CuIrF₆ for device applications. From the structural optimization results, the stability of DP (Cs₂CuIrF₆) is in cubic order and belongs to the Fm-3 m space group (#225) with a nonmagnetic (NM) state. Additionally, the elastic results show that this DP is mechanically stable in a cubic and ductile manner. Further, we explain in detail the semiconducting nature of the proposed DP with the help of electronic structure and density of states (DOS). The electronic band gap of DP Cs₂CuIrF₆ is 0.72 eV (L_V-X_C). The optical part discussion, like the dielectric function ε, reflectivity R, refractive index n, absorption coefficient α and optical conductivity σ up to 13.00 eV. The studied compound is explored as a potential candidate for optoelectronic applications.

METHODS

The density functional theory (DFT) within generalized gradient approximation (GGA) scheme of Perdew, Burke and Ernzerhof (PBE) as implemented in Wien2k computational code is utilized to achieve stable structure, elastic, electronic and optical properties of this material. The dynamic stability of this material was studied using the finite displacement method implemented in the CASTEP computational code. The elastic results have been computed by the IRelast package implemented in the Wien2k computational code.

Atomic-scale observation of premelting at 2D lattice defects inside oxide crystals

Since two major criteria for melting were proposed by Lindemann and Born in the early 1900s, many simulations and observations have been carried out to elucidate the premelting phenomena largely at the crystal surfaces and grain boundaries below the bulk melting point. Although dislocations and clusters of vacancies and interstitials were predicted as possible origins to trigger the melting, experimental direct observations demonstrating the correlation of premelting with lattice defects inside a crystal remain elusive. Using atomic-column-resolved imaging with scanning transmission electron microscopy in polycrystalline BaCeO₃, here we clarify the initiation of melting at two-dimensional faults inside the crystals below the melting temperature. In particular, melting in a layer-by-layer manner rather than random nucleation at the early stage was identified as a notable finding. Emphasizing the value of direct atomistic observation, our study suggests that lattice defects inside crystals should not be overlooked as preferential nucleation sites for phase transformation including melting.

An Efficient High-Entropy Perovskite-Type Air Electrode for Reversible Oxygen Reduction and Water Splitting in Protonic Ceramic Cells

Reversible protonic ceramic electrochemical cells (R-PCECs) are emerging as ideal devices for highly efficient energy conversion (generating electricity) and storage (producing H₂ ) at intermediate temperatures (400-700 °C). However, their commercialization is largely hindered by the development of highly efficient air electrodes for oxygen reduction and water-splitting reactions. Here, the findings in the design of a highly active and durable air electrode are reported: high-entropy Pr_0.2 Ba_0.2 Sr_0.2 La_0.2 Ca_0.2 CoO_{3- δ} (HE-PBSLCC), which exhibits impressive activity and stability for oxygen reduction and water-splitting reactions, as confirmed by electrochemical characterizations and structural analysis. When used as an air electrode of R-PCEC, the HE-PBSLCC achieves encouraging performances in dual modes of fuel cells (FCs) and electrolysis cells (ECs) at 650 °C, demonstrating a maximum power density of 1.51 W cm^-2 in FC mode, and a current density of -2.68 A cm^-2 at 1.3 V in EC mode. Furthermore, the cells display good operational durabilities in FC and EC modes for over 270 and 500 h, respectively, and promising cycling durability for 70 h with reasonable Faradaic efficiencies. This study offers an effective strategy for the design of active and durable air electrodes for efficient oxygen reduction and water splitting.

Deforming lanthanum trihydride for superionic conduction

With strong reducibility and high redox potential, the hydride ion (H-) is a reactive hydrogen species and an energy carrier. Materials that conduct pure H- at ambient conditions will be enablers of advanced clean energy storage and electrochemical conversion technologies1,2. However, rare earth trihydrides, known for fast H migration, also exhibit detrimental electronic conductivity3-5. Here we show that by creating nanosized grains and defects in the lattice, the electronic conductivity of LaHx can be suppressed by more than five orders of magnitude. This transforms LaHx to a superionic conductor at -40 °C with a record high H- conductivity of 1.0 × 10-2 S cm-1 and a low diffusion barrier of 0.12 eV. A room-temperature all-solid-state hydride cell is demonstrated.

High-Entropy Perovskites for Energy Conversion and Storage: Design, Synthesis, and Potential Applications

Perovskites have shown tremendous promise as functional materials for several energy conversion and storage technologies, including rechargeable batteries, (electro)catalysts, fuel cells, and solar cells. Due to their excellent operational stability and performance, high-entropy perovskites (HEPs) have emerged as a new type of perovskite framework. Herein, this work reviews the recent progress in the development of HEPs, including synthesis methods and applications. Effective strategies for the design of HEPs through atomistic computations are also surveyed. Finally, an outlook of this field provides guidance for the development of new and improved HEPs.

Protonic Ceramic Electrochemical Cells for Synthesizing Sustainable Chemicals and Fuels

Protonic ceramic electrochemical cells (PCECs) have been intensively studied as the technology that can be employed for power generation, energy storage, and sustainable chemical synthesis. Recently, there have been substantial advances in electrolyte and electrode materials for improving the performance of protonic ceramic fuel cells and protonic ceramic electrolyzers. However, the electrocatalytic materials development for synthesizing chemicals in PCECs has gained less attention, and there is a lack of systematic and fundamental understanding of the PCEC reactor design, reaction mechanisms, and electrode materials. This review comprehensively summarizes and critically evaluates the most up-to-date progress in employing PCECs to synthesize a wide range of chemicals, including ammonia, carbon monoxide, methane, light olefins, and aromatics. Factors that impact the conversion, selectivity, product yield, and energy efficiencies are discussed to provide new insights into designing electrochemical cells, developing electrode materials, and achieving economically viable chemical synthesis. The primary challenges associated with producing chemicals in PCECs are highlighted. Approaches to tackle these challenges are then offered, with a particular focus on deliberately designing electrode materials, aiming to achieve practically valuable product yield and energy efficiency. Finally, perspectives on the future development of PCECs for synthesizing sustainable chemicals are provided.

Exceptional Hydrogen Diffusion Rate over Ru Nanoparticle-Doped Polar MgO(111) Surface

Hydrogen (H) conductivity on oxide-based materials is crucially important in fuel cells and related catalysis. Here, this work measures the diffusion rate of H generated from Ru nanoparticles loaded on polar MgO(111) facet particles under H₂ at elevated temperatures without moisture and compares it to conventional nonpolar MgO(110) for the first time by in situ quasielastic neutron scattering (QENS). The QENS reveals an exceptional diffusion rate on the polar facet via a proton (H⁺ ) hopping mechanism, which is an order of magnitude superior to that of typical H⁺ -conducting oxides. This work attributes this to the unique atomic arrangement of alternate layers of Mg cations and O anions of the polar MgO(111) where the strong electrostatic field of terminal oxygen anions facilitates protonic migration with a lower degree of local covalency.

Anhydrous Superprotonic Conductivity in the Zirconium Acid Triphosphate ZrH5 (PO4 )3

The development of solid-state proton conductors with high proton conductivity at low temperatures is crucial for the implementation of hydrogen-based technologies for portable and automotive applications. Here, we report on the discovery of a new crystalline metal acid triphosphate, ZrH₅ (PO₄ )₃ (ZP3), which exhibits record-high proton conductivity of 0.5-3.1×10^-2  S cm^-1 in the range 25-110 °C in anhydrous conditions. This is the highest anhydrous proton conductivity ever reported in a crystalline solid proton conductor in the range 25-110 °C. Superprotonic conductivity in ZP3 is enabled by extended defective frustrated hydrogen bond chains, where the protons are dynamically disordered over two oxygen centers. The high proton conductivity and stability in anhydrous conditions make ZP3 an excellent candidate for innovative applications in fuel cells without the need for complex water management systems, and in other energy technologies requiring fast proton transfer.

A multicomponent equimolar proton-conducting quadruple hexagonal perovskite-related oxide system

Since the high configurational entropy-driven structural stability of multicomponent oxide system was proposed Rost et al. in 2015, many experiments and simulations have been done to develop new multicomponent oxides. Although many notable findings have shown unique physical and chemical properties, high configurational entropy oxide systems that have more than 3 distinct cation sites are yet to be developed. By utilizing atomic-scale direct imaging with scanning transmission electron microscopy and AC-impedance spectroscopy analysis, we demonstrated for the first time that a multicomponent equimolar proton-conducting quadruple hexagonal perovskite-related Ba₅RE₂Al₂ZrO₁₃ (RE = rare earth elements) oxide system can be synthesized even when adding eight different rare earth elements. In particular, as the number of added elements was increased, i.e., as the configurational entropy was increased, we confirmed that the chemical stability toward CO₂ was improved without a significant decrement of the proton conductivity. The findings in this work broaden the use of the crystal structure to which the multicomponent model can be applied, and a systematic study on the correlation between the configurational entropy and proton conductivity and/or chemical stability is noteworthy.

Multilayered Ceramic Membrane with Ion Conducting Thin Layer Induced by Interface Reaction for Stable Hydrogen Production

Conventional methods for fabricating multilayered ceramic membranes with ion conducting dense thin layers are often cumbersome, costly, and limited by poor adhesion between layers. Inspired by the architectural structure of the rooted grasses in soil, here, we report an interface-reaction-induced reassembly approach for the direct fabrication of Ce_0.9 Gd_0.1 O_2-δ (CGO) thin layers rooted in the parent multilayered ceramic membranes by only one firing step. The CGO dense layers are very thin, and adhered strongly to the parent support layer, ensuring low ionic transport resistance and structural integrity of the multilayered membranes. When using as an oxygen permeable membrane for upgrading fossil-fuel-derived hydrogen, it shows very long durability in harsh conditions containing H₂ O, CH₄ , H₂ , CO₂ and H₂ S. Furthermore, our approach is highly scalable and applicable to a wide variety of ion conducting thin layers, including Y_0.08 Zr_0.92 O_2-δ , Ce_0.9 Sm_0.1 O_2-δ and Ce_0.9 Pr_0.1 O_2-δ .