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In light of the depletion of conventional energy sources, it is imperative to conduct research and development on sustainable alternative energy sources. Currently, electrochemical energy storage and conversion technologies such as fuel cells and metal-air batteries rely heavily on precious metal catalysts like Pt/C and IrO2, which hinders their sustainable commercial development. Therefore, researchers have devoted significant attention to non-precious metal-based catalysts that exhibit high efficiency, low cost, and environmental friendliness. Among them, perovskite oxides possess low-cost and abundant reserves, as well as flexible oxidation valence states and a multi-defect surface. Due to their advantageous structural characteristics and easily adjustable physicochemical properties, extensive research has been conducted on perovskite-based oxides. However, these materials also exhibit drawbacks such as poor intrinsic activity, limited specific surface area, and relatively low apparent catalytic activity compared to precious metal catalysts. To address these limitations, current research is focused on enhancing the physicochemical properties of perovskite-based oxides. The catalytic activity and stability of perovskite-based oxides in Oxygen Reduction Reaction/Oxygen Evolution Reaction (ORR/OER) can be enhanced using crystallographic structure tuning, cationic regulation, anionic regulation, and nano-processing. Furthermore, extensive research has been conducted on the composite processing of perovskite oxides with other materials, which has demonstrated enhanced catalytic performance. Based on these different ORR/OER modification strategies, the future challenges of perovskite-based bifunctional oxygen electrocatalysts are discussed alongside their development prospects. [ABSTRACT FROM AUTHOR]

Solid oxide fuel cells (SOFCs) represent a breed of eco-friendly, weather-independent, decentralized power generation technologies, distinguished for their broad fuel versatility and superior electricity generation efficiency. At present, SOFCs are impeded by a lack of highly efficient oxygen reduction catalysts, a factor that significantly constrains their performance. The double perovskites LnBaCo2O5+δ (Ln = Lanthanide), renowned for their accelerated oxygen exchange and conductivity features, are widely acclaimed as a promising category of cathode catalysts for SOFCs. This manuscript offers a novel perspective on the physicochemical attributes of LnBaCo2O5+δ accumulated over the past two decades and delineates the latest advancements in fine-tuning the composition and nanostructure for SOFC applications. It highlights surface chemistry under operational conditions and microstructure as emerging research focal points towards achieving high-performance LnBaCo2O5+δ catalysts. This review offers a comprehensive insight into the latest advancements in utilizing LnBaCo2O5+δ in the field of SOFCs, presenting a clear roadmap for future developmental trajectories. Furthermore, it provides valuable insights for the application of double perovskite materials in domains such as water electrolysis, CO2 electrolysis, chemical sensors, and metal–air batteries. [ABSTRACT FROM AUTHOR]

Graphene is a well-known two-dimensional material with a large surface area and is used for numerous applications in a variety of fields. Metal-free carbon materials such as graphene-based materials are widely used as an electrocatalyst for oxygen reduction reactions (ORRs). Recently, more attention has been paid to developing metal-free graphenes doped with heteroatoms such as N, S, and P as efficient electrocatalysts for ORR. In contrast, we found our prepared graphene from graphene oxide (GO) by the pyrolysis method under a nitrogen atmosphere at 900 °C has shown better ORR activity in aqueous 0.1 M potassium hydroxide solution electrolyte as compared with the electrocatalytic activity of pristine GO. At first, we prepared various graphene by pyrolysis of 50 mg and 100 mg of GO in one to three alumina boats and pyrolyzed the samples under a N2 atmosphere at 900 °C. The prepared samples are named G50-1B to 3B and G100-1B and G100-2B. The prepared GO and graphenes were also analyzed under various characterization techniques to confirm their morphology and structural integrity. The obtained results suggest that the ORR electrocatalytic activity of graphene may differ based on the pyrolysis conditions. We found that G100-1B (Eonset, E1/2, JL, and n values of 0.843, 0.774, 4.558, and 3.76) and G100-2B (Eonset, E1/2, and JL values of 0.837, 0.737, 4.544, and 3.41) displayed better electrocatalytic ORR activity, as did Pt/C electrode (Eonset, E1/2, and JL values of 0.965, 0.864, 5.222, and 3.71, respectively). These results display the wide use of the prepared graphene for ORR and also can be used for fuel cell and metal–air battery applications. [ABSTRACT FROM AUTHOR]

Transition metal (TM) single atomic catalysts (MSAC-N-C) derived from doped zeolite imidazolate frameworks (ZIF-8) are considered attractive oxygen reduction reaction (ORR) catalysts for fuel cells and metal-air batteries due to their advantages of high specific surface area, more active catalytic sites, adjustable pore size, and coordination topology features. This review provides an updated overview of the latest advances of MSAC-N-C catalysts derived from ZIF-8 precursors in ORR electrocatalysis. Particularly, some key challenges, including coordination environments regulation of catalysis center in MSAC-N-C, the active sites loading optimization and synergistic effects between TM nanoclusters/nanoparticles and the single atoms on MSAC-N-C catalysis activity, as well as their adaptability in various devices, are summarized for improving future development and application of MSAC-N-C catalysts. In addition, this review puts forward future research directions, making it play a better role in ORR catalysis for fuel cells and metal air batteries. [ABSTRACT FROM AUTHOR]

Opening up electrocatalysts for oxygen reduction reaction (ORR) is essential for practical application in fuel cells and metal-air batteries; however, how to make the catalysts with both good performance and low cost is difficult. Recently, research on the ORR of molybdenum disulfide-based catalysts in alkaline electrolytes has been on the rise. However, the development of MoS2 catalyst for acidic ORR is still in its infancy. Herein, without using reductant and morphology control reagent, we firstly obtained flowerball-like MoS2/Vulcan XC-72R (VC) nanocomposites via hydrothermal method. The designed composite exhibits a nearly 4e− ORR process with 0.78 and 0.92 V onset potentials in 0.1 M KOH and HClO4, respectively. Furthermore, the flowerball-like composite shows utmost electrochemical stability judging by 87 and 80% current retention for about 5.5 h either in alkaline or acid media, long term durability for continuous 10,000 cycles, and stronger resistance to methanol than the commercial Pt/C catalyst. The abundant Mo edges as catalytic active centers of flowerball-like structure, high electron conductivity, and enhanced mass transport in either alkaline or acidic electrolyte are favorable for catalytic performance. The prepared catalyst provides great potential for the substitution of noble metal based catalysts in fuel cells and metal-air batteries. [ABSTRACT FROM AUTHOR]

The high activity of non-platinum electrocatalysts for oxygen reduction reaction (ORR) in alkaline media is necessary for applications in energy conversion devices such as fuel cells and metal-air batteries. Herein, we present the electrocatalytic activity of TaOx/carbon black (CB) nanoparticles for the ORR in an alkaline atmosphere as well as in an acidic electrolyte. Ultrafine TaOx nanoparticles 1–2 nm in size and uniformly dispersed on CB supports were prepared by potentiostatic electrodeposition in a nonaqueous electrolyte and subsequent annealing treatment in an H2 flow. The TaOx/CB nanoparticles largely catalyzed the ORR with an onset potential of 1.03 VRHE in an O2-saturated 0.1 M KOH solution comparable to that of a commercial Pt/CB catalyst. ORR activity was also observed in 0.1 M H2SO4 solution. According to the rotating ring disk electrode measurement results, the oxide nanoparticles partly produced H2O2 during the ORR in 0.1 M KOH, and the ORR process was dominated by both the two- and four-electron reductions of oxygen in a diffusion-limited potential region. The Tafel slope of −120 mV dec−1 in low and high current densities revealed the surface stability of the oxide nanoparticles during the ORR. Therefore, these results demonstrated that the TaOx/CB nanoparticles were electroactive for the ORR in both acidic and alkaline electrolytes. [ABSTRACT FROM AUTHOR]

The development of efficient and cost-effective electrocatalysts for oxygen reduction reactions (ORR) is one of the most crucial goals in the field of energy conversion devices such as fuel cells or metal-air batteries. Until now, the platinum-based catalyst has been considered the gold standard electrocatalyst and is widely used for ORR. In recent times, transition metal-nitrogen (N)-carbon (C)-based electrocatalysts have verified ORR performances comparable to novel metal-based catalysts. However, due to the complex production methods and low yield, their high price is their one major disadvantage compared to platinum-based catalysts. Herein, we present a transition metal-N-C electrochemical catalyst prepared by simple electrospinning and heat treatment. The metal- and nitrogen-embedded carbon nanofiber represents considerably enhanced activity for oxygen reduction reactions compared to pristine carbon nanofiber. [ABSTRACT FROM AUTHOR]