Investigation of New B-Site-Disordered Perovskite Oxide CaLaScRuO6+δ: An Efficient Oxygen Bifunctional Electrocatalyst in a Highly Alkaline Medium

Strategic Design and Insights into Lanthanum and Strontium Perovskite Oxides for Oxygen Reduction and Oxygen Evolution Reactions

Perovskite oxides exhibit bifunctional activity for both oxygen reduction (ORR) and oxygen evolution reactions (OER), making them prime candidates for energy conversion in applications like fuel cells and metal-air batteries. Their intrinsic catalytic prowess, combined with low-cost, abundance, and diversity, positions them as compelling alternatives to noble metal and metal oxides catalysts. This review encapsulates the nuances of perovskite oxide structures and synthesis techniques, providing insight into pivotal active sites that underscore their bifunctional behavior. The focus centers on the breakthroughs surrounding lanthanum (La) and strontium (Sr)-based perovskite oxides, specifically their roles in zinc-air batteries (ZABs). An introduction to the mechanisms of ORR and OER is provided. Moreover, the light is shed on strategies and determinants central to optimizing the bifunctional performance of La and Sr-based perovskite oxides.

Superior Electrochemical Water Splitting and Energy-Storage Performances of In Situ Fabricated Charge-Separated Metal Organophosphonate Single Crystals

The design and exploration of advanced materials as a durable multifunctional electrocatalyst toward sustainable energy generation and storage development is the most perdurable challenge in the domain of renewable energy research. Herein, a facile in situ solvothermal approach has been adopted to prepare a methylviologen-regulated crystalline metal phosphonate compound, [C12H14N2][Ni(C11H11N2)(H2hedp)2]2•6H2O (NIT1), (H4hedp = 1-hydroxyethane 1,1-diphosphonic acid) and well characterized by several techniques. The as-prepared NIT1 displays excellent bifunctional electrocatalytic activity with dynamic stability toward oxygen evolution reaction (η10 = 288 mV) and hydrogen evolution reaction (η10 = 228 mV) in alkaline (1.0 M KOH) and acidic mediums (0.5 M H2SO4), respectively. Such a low overpotential and Tafel slope (68 mV/dec for OER; 56 mV/dec for HER) along with long-term durability up to 20 h of NIT1 make it superior to benchmark the electrocatalyst and various nonprecious metal-based catalysts under similar experimental condition. Further, the electrochemical supercapacitor measurements (in three-electrode system) reveal that the NIT1 electrode possesses much higher specific capacity of 187.6 C g-1 at a current density of 2 A g-1 (272 C g-1 at 5 mV s-1) with capacitance retention of 75.2% over 10,000 cycles at 14 A g-1 (Coulombic efficiency > 99%) in 6 M KOH electrolyte medium. Finally for a practical application, an asymmetric supercapacitor device (coin cell) is assembled by NIT1 material. The as-fabricated device delivers the maximum energy density of 39.4 Wh kg-1 at a power density of 450 W kg-1 and achieves a wide voltage window of 1.80 V. Notably, the device endures a remarkable cycle performance with cyclic retention of 92% (Coulombic efficiency > 99%) even after 14,000 charge/discharge cycles at 10 A g-1. Nevertheless, the extraordinary electrochemical activities toward OER and HER as well as the high-performance device fabrication for LED illumination of such a noble metal-free lower-dimensional charge-transfer compound are truly path breaking and would be promising for the development of advanced multifunctional materials.

One-Dimensional La0.2Sr0.8Cu0.4Co0.6O3-δ Nanostructures for Efficient Oxygen Evolution Reaction

Producing oxygen and hydrogen via the electrolysis of water has the advantages of a simple operation, high efficiency, and environmental friendliness, making it the most promising hydrogen production method. In this study, La0.2Sr0.8Cu0.4Co0.6O3-δ (LSCC) nanofibers were prepared by electrospinning to utilize non-noble perovskite oxides instead of noble metal catalysts for the oxygen evolution reaction, and the performance and electrochemical properties of LSCC nanofibers synthesized at different firing temperatures were evaluated. In an alkaline environment (pH = 14, 6 M KOH), the nanofibers calcined at 650 °C showed an overpotential of 209 mV at a current density of 10 mA cm-2 as well as good long-term stability. Therefore, the prepared LSCC-650 NF catalyst shows excellent potential for electrocatalytic oxygen evolution.

Investigation of Photoelectrocatalytic and Magnetic Properties of Sr2YbRu1-xTaxO6 (x = 0, 0.25, 0.5, 0.75, and 1)

We report the effect of substitution of Ru by Ta in Sr₂YbRuO₆ on its magnetic and photoelectrocatalytic properties. The powder X-ray diffraction data, was satisfactorily refined in the monoclinic space group, P2₁/n. The DC magnetization studies indicated that Sr₂YbRuO₆ shows antiferromagnetic interaction through Yb-O-Ru orbital ordering, with the highest Weiss temperature, among Sr₂YbRu_1-xTa_xO₆ (x = 0, 0.25, 0.5, and 0.75) which have values of -148, -125, -118, and -102 K, respectively. The difference in observed and theoretical magnetic moments was found to increase as x increases. It was also observed that with the increase of Ta concentration in Sr₂YbRu_1-xTa_xO₆, the band gap increased almost linearly, from 1.78(1) eV (x = 0) to 2.08(1) (x = 0.75), and thereafter a sharp increase 2.65(1) eV (x = 1) was observed, with the lowering of energy level of valence band, along with disruption in orbital ordering as x increases. The photoelectrocatalytic oxygen evolution reaction (OER) studies carried out on the series yield a maximum photocurrent density of 17 μA/cm² and photoresponse current of 5.5 μA/cm² at 0.8 V at an onset potential at 0.29 V vs Ag/AgCl for Sr₂YbRuO₆. The XPS analysis showed Ta and Ru to be in +5/+4 oxidation states, with the highest concentration of Ru⁴⁺ ion observed for Sr₂YbRuO₆. The presence of oxygen vacancies was confirmed by XPS as well as EPR studies.

Research progresses on the application of perovskite in adsorption and photocatalytic removal of water pollutants

The problem of global water pollution and scarcity of water resources is becoming increasingly serious. Multifunctional perovskites can well drive adsorption and photocatalytic reactions to remove water pollutants. There are many advantages of perovskites, such as abundant oxygen vacancies, easily tunable structural morphology, stable crystal state, highly active metal sites, and a wide photo response range. However, there are few reviews on the simultaneous application of perovskite to adsorption and photocatalytic removal of water pollutants. Thus, this paper discusses the preparation methods of perovskite, the factors affecting the adsorption of water environmental pollutants by perovskite, and the factors affecting perovskite photocatalytic water pollutants. The particle size, specific surface area, oxygen vacancies, electron-hole trapping agents, potentials of the valence band, and conduction band in perovskites are significant influencing factors for adsorption and photocatalysis. Strategies for improving the performance of perovskites in the fields of adsorption and photocatalysis are discussed. The adsorption behaviors and catalytic mechanisms are also investigated, including adsorption kinetics and thermodynamics, electrostatic interaction, ion exchange, chemical bonding, and photocatalytic mechanism. It summarizes the removal of water pollutants by using perovskites. It provides the design of perovskites as high-efficiency adsorbents and catalysts for developing new technologies.

Facile synthesis of nanostructured perovskites by precursor accumulation on nanocarbons

Perovskite-type oxides have impacted various research fields, including materials and energy science. Despite their vast potential in various applications, general and simple synthesis methods for nano-perovskites remain limited. Herein, various nano-perovskites were synthesized by a facile approach involving the use of nanocarbons. The calcination of the nanocarbon deposited with metal salts yielded nano-perovskites, emulating the morphology of nanocarbons. The accumulation of precursors (i.e., metal salts) on the surface of the nanocarbon during the evaporation of the solvent is the key step in which the precursors are homogeneously mixed prior to calcination. The homogeneity of the precursors facilitated low-temperature calcination that resulted in the formation of nano-perovskites. Various nano-perovskites, including LaMnO3, LaCoO3, LaFeO3, LaNiO3, LaAlO3, LaGaO3, CaMnO3, BaMnO3, SrMnO3, La0.7Sr0.3FeO3, La2CuO4, and Ca2Fe2O5, were successfully synthesized, demonstrating the simplicity and novelty of the method for the general synthesis of nano-perovskites.

Antiferromagnetically Coupled Double Perovskite as an Efficient and Robust Catalyst for Visible Light Driven Water Splitting at Neutral pH

Green and sustainable energy production through renewable sources is enormously an exciting field of research. Herein, we report A-site lanthanum doped oxygen excess ruthenate (predominantly Ru5+-ions) double perovskite system, CaLaScRuO6+δ...

Charge Separated One-Dimensional Hybrid Cobalt/Nickel Phosphonate Frameworks: A Facile Approach to Design Bifunctional Electrocatalyst for Oxygen Evolution and Hydrogen Evolution Reactions

Two new organoamine templated one-dimensional transition metal phosphonate compounds are synthesized, and their bifunctional electrocatalytic activities are examined in highly alkaline and acidic media. Compared with state-of-the-art materials, the cobalt phosphonate system is a new fabrication of sustainable and highly efficient catalysts toward electrochemical water splitting systems.

Development of Perovskite Oxide-Based Electrocatalysts for Oxygen Evolution Reaction

Perovskite oxides are studied as electrocatalysts for oxygen evolution reactions (OER) because of their low cost, tunable structure, high stability, and good catalytic activity. However, there are two main challenges for most perovskite oxides to be efficient in OER, namely less active sites and low electrical conductivity, leading to limited catalytic performance. To overcome these intrinsic obstacles, various strategies are developed to enhance their catalytic activities in OER. In this review, the recent developments of these strategies is comprehensively summarized and systematically discussed, including composition engineering, crystal facet control, morphology modulation, defect engineering, and hybridization. Finally, perspectives on the design of perovskite oxide-based electrocatalysts for practical applications in OER are given.

GdFeO3 Perovskite Oxide Decorated by Group X Heterometal Oxides and Bifunctional Oxygen Electrocatalysis

Bifunctional electrocatalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are necessary in the renewable energy systems. However, the kinetically slow and large energy-demanding procedures of oxygen electrocatalysis make the preparation of bifunctional catalysts difficult. In this work, we report a novel hierarchical GdFeO₃ perovskite oxide of a spherelike nanostructure and surface modification with the group X heterometal oxides. The nanostructured GdFeO₃ layer behaved as a bifunctional electrocatalyst in the oxygen electrocatalysis of OER and ORR. Moreover, the surface decoration with catalytically active PtO_x + Ni/NiO nanoparticles enhanced the electrocatalytic performances substantially. Incorporation of mesoporous PtO_x + Ni/NiO nanoparticles into the porous GdFeO₃ nanostructure enlarged the electrochemically active surface area and provided the interconnected nanostructures to facilitate the OER/ORR. The nanostructures were visualized by scanning electron microscopy and transmission electron microscopy images, and the surface area and pore size of nanoparticles were analyzed from N₂ adsorption/desorption isotherms. Tafel analysis indicates that surface modification effectively improves the kinetics of oxygen reactions and accordingly increases the electrocatalytic efficiency. Finally, the 2 wt % PtO_x + NiO|GdFeO₃ (x = 0, 1, and 2) electrode achieved the enhanced OER performance with an overpotential of 0.19 V at 10 mA/cm² in an alkaline solution and a high turnover frequency of 0.28 s^-1 at η = 0.5 V. Furthermore, the ORR activity is observed with an onset potential of 0.80 V and a half-wave potential (E_1/2) of 0.40 V versus reversible hydrogen electrode.

Recent advances of noble-metal-free bifunctional oxygen reduction and evolution electrocatalysts

Bifunctional oxygen reduction and evolution constitute the core processes for sustainable energy storage. The advances on noble-metal-free bifunctional oxygen electrocatalysts are reviewed.

Sr2NiWO6 Double Perovskite Oxide as a Novel Visible-Light-Responsive Water Oxidation Photocatalyst

Screening of stable visible-light-responsive water oxidation semiconductor photocatalysts is highly desired for the development of photocatalytic water splitting systems. Herein, a visible-light-absorbing Sr₂NiWO₆ double perovskite oxide photocatalyst was successfully prepared via a conventional solid-state reaction method. The intrinsic Sr₂NiWO₆ shows photocatalytic oxygen evaluation reaction (OER) activity of 60 μmol h^-1 g^-1, even without loading any cocatalysts. The DFT calculation indicates that the Ni species on the surface is the active site for the OER. The photocatalytic OER activity was further improved by loading Pt and RuO₂ dual redox cocatalysts on the surface of Sr₂NiWO₆ to achieve a photocatalytic OER activity of 420 μmol h^-1 g^-1, which corresponds to a remarkable apparent quantum efficiency (AQE) of 8.6% (λ ≈ 420 nm). The result indicates that Sr₂NiWO₆ is one of the best double perovskite oxide-based photocatalysts for the photocatalytic OER, and the activity is even comparable to the benchmark BiVO₄-based photocatalyst. The improvement of the photocatalytic OER activity is due to the provision of more active redox sites as well as the synergetic effect of the dual redox cocatalysts in facilitating charge separation and transfer. This work demonstrates that double perovskite oxides may serve as a novel class of efficient and stable oxide-based semiconductor photocatalysts for water splitting.

Solvent and additive-free efficient aerobic oxidation of alcohols by a perovskite oxide-based heterogeneous catalyst

A perovskite oxide has been utilized for the solvent and additive-free heterogeneous oxidation of various alcohols.