CaCu3Ti4O12: A Bifunctional Perovskite Electrocatalyst for Oxygen Evolution and Reduction Reaction in 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.

Perovskite Oxides Toward Oxygen Evolution Reaction: Intellectual Design Strategies, Properties and Perspectives

Developing electrochemical energy storage and conversion devices (e.g., water splitting, regenerative fuel cells and rechargeable metal-air batteries) driven by intermittent renewable energy sources holds a great potential to facilitate global energy transition and alleviate the associated environmental issues. However, the involved kinetically sluggish oxygen evolution reaction (OER) severely limits the entire reaction efficiency, thus designing high-performance materials toward efficient OER is of prime significance to remove this obstacle. Among various materials, cost-effective perovskite oxides have drawn particular attention due to their desirable catalytic activity, excellent stability and large reserves. To date, substantial efforts have been dedicated with varying degrees of success to promoting OER on perovskite oxides, which have generated multiple reviews from various perspectives, e.g., electronic structure modulation and heteroatom doping and various applications. Nonetheless, the reviews that comprehensively and systematically focus on the latest intellectual design strategies of perovskite oxides toward efficient OER are quite limited. To bridge the gap, this review thus emphatically concentrates on this very topic with broader coverages, more comparative discussions and deeper insights into the synthetic modulation, doping, surface engineering, structure mutation and hybrids. More specifically, this review elucidates, in details, the underlying causality between the being-tuned physiochemical properties [e.g., electronic structure, metal-oxygen (M-O) bonding configuration, adsorption capacity of oxygenated species and electrical conductivity] of the intellectually designed perovskite oxides and the resulting OER performances, coupled with perspectives and potential challenges on future research. It is our sincere hope for this review to provide the scientific community with more insights for developing advanced perovskite oxides with high OER catalytic efficiency and further stimulate more exciting applications.

Graphical Abstract

CaCu3Ti4O12 Perovskite Materials for Advanced Oxidation Processes for Water Treatment

The many pollutants detected in water represent a global environmental issue. Emerging and persistent organic pollutants are particularly difficult to remove using traditional treatment methods. Electro-oxidation and sulfate-radical-based advanced oxidation processes are innovative removal methods for these contaminants. These approaches rely on the generation of hydroxyl and sulfate radicals during electro-oxidation and sulfate activation, respectively. In addition, hybrid activation, in which these methods are combined, is interesting because of the synergistic effect of hydroxyl and sulfate radicals. Hybrid activation effectiveness in pollutant removal can be influenced by various factors, particularly the materials used for the anode. This review focuses on various organic pollutants. However, it focuses more on pharmaceutical pollutants, particularly paracetamol, as this is the most frequently detected emerging pollutant. It then discusses electro-oxidation, photocatalysis and sulfate radicals, highlighting their unique advantages and their performance for water treatment. It focuses on perovskite oxides as an anode material, with a particular interest in calcium copper titanate (CCTO), due to its unique properties. The review describes different CCTO synthesis techniques, modifications, and applications for water remediation.

High energy storage capabilities of CaCu3Ti4O12 for paper-based zinc-air battery

Zinc–air batteries proffer high energy density and cyclic stability at low costs but lack disadvantages like sluggish reactions at the cathode and the formation of by-products at the cathode. To resolve these issues, a new perovskite material, CaCu₃Ti₄O₁₂ (CCTO), is proposed as an efficacious electrocatalyst for oxygen evolution/reduction reactions to develop zinc–air batteries (ZAB). Synthesis of this material adopted an effective oxalate route, which led to the purity in the electrocatalyst composition. The CCTO material is a proven potential candidate for energy applications because of its high dielectric permittivity (ε) and occupies an improved ORR-OER activity with better onset potential, current density, and stability. The Tafel value for CCTO was obtained out to be 80 mV dec⁻¹. The CCTO perovskite was also evaluated for the zinc–air battery as an air electrode, corresponding to the high specific capacitance of 801 mAh g⁻¹ with the greater cyclic efficiency and minimum variations in both charge/discharge processes. The highest power density (P_max) measured was 127 mW cm⁻². Also, the CCTO based paper battery shows an excellent performance achieving a specific capacity of 614 mAh g⁻¹. The obtained results promise CCTO as a potential and cheap electrocatalyst for energy applications.

Preconstructing Asymmetric Interface in Air Cathodes for High-Performance Rechargeable Zn-Air Batteries

Rechargeable zinc-air batteries afford great potential toward next-generation sustainable energy storage. Nevertheless, the oxygen redox reactions at the air cathode are highly sluggish in kinetics to induce poor energy efficiency and limited cycling lifespan. Air cathodes with asymmetric configurations significantly promote the electrocatalytic efficiency of the loaded electrocatalysts, whereas rational synthetic methodology to effectively fabricate asymmetric air cathodes remains insufficient. Herein, a strategy of asymmetric interface preconstruction is proposed to fabricate asymmetric air cathodes for high-performance rechargeable zinc-air batteries. Concretely, the asymmetric interface is preconstructed by introducing immiscible organic-water diphases within the air cathode, at which the electrocatalysts are in situ formed to achieve an asymmetric configuration. The as-fabricated asymmetric air cathodes realize high working rates of 50 mA cm^-2 , long cycling stability of 3400 cycles at 10 mA cm^-2 , and over 100 cycles under harsh conditions of 25 mA cm^-2 and 25 mAh cm^-2 . Moreover, the asymmetric interface preconstruction strategy is universal to many electrocatalytic systems and can be easily scaled up. This work provides an effective strategy toward advanced asymmetric air cathodes with high electrocatalytic efficiency and significantly promotes the performance of rechargeable zinc-air batteries.

Sm0.5Sr0.5Co1−xNixO3−δ—A Novel Bifunctional Electrocatalyst for Oxygen Reduction/Evolution Reactions

The development of non-precious metal catalysts with excellent bifunctional activities is significant for air–metal batteries. ABO3-type perovskite oxides can improve their catalytic activity and electronic conductivity by doping transition metal elements at B sites. Here, we develop a novel Sm0.5Sr0.5Co1−xNixO3−δ (SSCN) nanofiber-structured electrocatalyst. In 0.1 M KOH electrolyte solution, Sm0.5Sr0.5Co0.8Ni0.2O3−δ (SSCN82) with the optimal Co: Ni molar ratio exhibits good electrocatalytic activity for OER/ORR, affording a low onset potential of 1.39 V, a slight Tafel slope of 123.8 mV dec−1, and a current density of 6.01 mA cm−2 at 1.8 V, and the ORR reaction process was four-electron reaction pathway. Combining the morphological characteristic of SSCN nanofibers with the synergistic effect of cobalt and nickel with a suitable molar ratio is beneficial to improving the catalytic activity of SSCN perovskite oxides. SSCN82 exhibits good bi-functional catalytic performance and electrochemical double-layer capacitance.

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.

High-Efficiency of Bi-Functional-Based Perovskite Nanocomposite for Oxygen Evolution and Oxygen Reduction Reaction: An Overview

High efficient, low-cost and environmentally friendly-natured bi-functional-based perovskite electrode catalysts (BFPEC) are receiving increasing attention for oxygen reduction/oxygen evolution reaction (ORR/OER), playing an important role in the electrochemical energy conversion process using fuel cells and rechargeable batteries. Herein, we highlighted the different kinds of synthesis routes, morphological studies and electrode catalysts with A-site and B-site substitution co-substitution, generating oxygen vacancies studies for boosting ORR and OER activities. However, perovskite is a novel type of oxide family, which shows the state-of-art electrocatalytic performances in energy storage device applications. In this review article, we go through different types of BFPECs that have received massive appreciation and various strategies to promote their electrocatalytic activities (ORR/OER). Based on these various properties and their applications of BFPEC for ORR/OER, the general mechanism, catalytic performance and future outlook of these electrode catalysts have also been discussed.

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.

Recent Advances of First d-Block Metal-Based Perovskite Oxide Electrocatalysts for Alkaline Water Splitting

First d-block metal-based perovskite oxides (FDMPOs) have garnered significant attention in research for their utilization in the water oxidation reaction due to their low cost, earth abundance, and promising activities. Recently, FDMPOs are being applied in electrocatalysis for the hydrogen evolution reaction (HER) and overall water splitting reaction. Numerous promising FDMPO-based water splitting electrocatalysts have been reported, along with new catalytic mechanisms. Therefore, an in-time summary of the current progress of FDMPO-based water splitting electrocatalysts is now considered imperative. However, few reviews have focused on this particular subject thus far. In this contribution, we review the most recent advances (mainly within the years 2014–2020) of FDMPO electrocatalysts for alkaline water splitting, which is widely considered to be the most promising next-generation technology for future large-scale hydrogen production. This review begins with an introduction describing the fundamentals of alkaline water electrolysis and perovskite oxides. We then carefully elaborate on the various design strategies used for the preparation of FDMPO electrocatalysts applied in the alkaline water splitting reaction, including defecting engineering, strain tuning, nanostructuring, and hybridization. Finally, we discuss the current advances of various FDMPO-based water splitting electrocatalysts, including those based on Co, Ni, Fe, Mn, and other first d-block metal-based catalysts. By conveying various methods, developments, perspectives, and challenges, this review will contribute toward the understanding and development of FDMPO electrocatalysts for alkaline water splitting.