Search Results (116)

Zinc–air batteries (ZABs) are crucial for renewable energy conversion and storage due to their cost-effectiveness, excellent safety, and superior cycling stability. However, developing efficient and affordable bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) at the air cathode remains a significant challenge. Manganese (Mn)-based materials, known for their tunable oxidation states, adaptable crystal structures, and environmental friendliness, are regarded as the most promising candidates. This review systematically summarizes recent advances in Mn-based bifunctional catalysts, concentrating on four primary categories: Mn–N–C electrocatalysts, manganese oxides, manganates, and other Mn-based compounds. By examining the intrinsic merits and limitations of each category, we provide a comprehensive discussion of optimization strategies, which include morphological modulation, structural engineering, carbon hybridization, heterointerface construction, heteroatom doping, and defect engineering, aimed at enhancing catalytic performance. Additionally, we critically address existing challenges and propose future research directions for Mn-based materials in rechargeable ZABs, offering theoretical insights and design principles to advance the development of next-generation energy storage systems. Full article

Efficient electrocatalysts for the oxygen reduction reaction (ORR) are essential for numerous energy storage and conversion systems, including zinc–air batteries and fuel cells. Cutting-edge Pt/C catalysts remain the most efficient ORR catalysts to date; however, their high cost and inadequate stability impede their use in commercial devices. Recently, transition metal-based electrocatalysts are being pursued as ideal alternatives for cost-effective and efficient materials with a promising future. This review provides an in-depth analysis of the principles, synthesis, and electrocatalytic assessment of noble metal and transition metal-based catalysts derived from diverse gel precursors, including hydrogels, aerogels, xerogels, metal–organic gels, and metal aerogels. Electrocatalysts derived from gel precursors have garnered significant interest due to their superior physicochemical properties, including an exceptionally high surface area, adjustable porosity, adaptability, and scalability. Catalysts obtained from gel precursors offer numerous advantages over conventional catalyst synthesis methods, including the complete utilization of precursors, precise control over surface area and porosity, and uniform distribution of ORR active sites. Among the various types, metal aerogels are distinguished as the superior catalysts, exceeding the Department of Energy’s (DoE) 2025 targets for the mass and specific activities of ORR catalysts. In contrast, hydrogel- and aerogel-derived catalysts excel in terms of ORR activity, specific surface area, and the potential to incorporate high loadings of single-atom catalysts composed of transition metals. Ultimately, we unequivocally categorized the electrocatalysts into high-, moderate-, and low-performance tiers, identifying the most promising catalyst candidate within each gel classification. Concluding insights, future outlooks, and recommendations were provided for the advancement of cost-effective, scalable electrocatalysts derived from gels for fuel cells and zinc–air batteries. Full article

In this work, the effect of the palladium precursor on the Oxygen Reduction Reaction (ORR) performance of lignin-based electrospun carbon fibers was studied. The fibers were spun from a lignin-ethanol solution free of any binder, where different Pd salts were added at two concentration levels. The system implemented to perform the spinning was a coaxial setup in which the internal flow contains the precursor dispersion with the metallic precursor, and ethanol was used as external flow to help fiber formation and prevent drying before generating the Taylor cone. The obtained cloths were thermostabilized in air at 200 °C and carbonized in nitrogen at 900 °C. The resulting carbon fibers were characterized by physicochemical and electrochemical techniques. The palladium precursor significantly affects nanoparticle distribution and size, fiber diameter, pore distribution, surface area and electrochemical behavior. The fibers prepared with palladium acetylacetonate at high Pd loading and carbonized at 900 °C under a CO₂ atmosphere showed high mechanical stability and the best ORR activity, showing near total selectivity towards the 4-electron path. These features are comparable to those of the commercial Pt/C catalyst but much lower metal loading (10.6 wt.% vs. 20 wt.%). The most promising fibers have been evaluated as cathodes in a zinc–air battery, delivering astonishing stability results that surpassed the performance of commercial Pt/C materials in both charging and discharging processes. Full article

Layered double hydroxides (LDHs), notable for their unique two-dimensional layered structures, have attracted significant research attention due to their exceptional versatility and promising performance in energy storage and conversion applications. This comprehensive review systematically addresses the fundamentals and diverse synthesis strategies for LDHs, including co-precipitation, hydrothermal synthesis, electrochemical deposition, sol-gel processes, ultrasonication, and exfoliation techniques. The synthesis methods profoundly influence the physicochemical properties, morphology, and electrochemical performance of LDHs, necessitating a detailed understanding to optimize their applications. In this paper, the role of LDHs in batteries, supercapacitors, and hydrogen production is critically evaluated. We discuss their incorporation in various battery systems, such as lithium-ion, lithium–sulfur, sodium-ion, chloride-ion, zinc-ion, and zinc–air batteries, highlighting their structural and electrochemical advantages. Additionally, the superior pseudocapacitive behavior and high energy densities offered by LDHs in supercapacitors are elucidated. The effectiveness of LDHs in hydrogen production, particularly through electrocatalytic water splitting, underscores their significance in renewable energy systems. This review paper uniquely integrates these three pivotal energy technologies, outlining current innovations and challenges, thus fulfilling a critical need for the scientific community by providing consolidated insights and guiding future research directions. Full article

Developing efficient and durable non-precious metal catalysts for oxygen electrocatalysis in fuel cells and zinc–air batteries remains an urgent issue to be addressed. Herein, a bimetallic CoCe-NC catalyst is synthesized through pyrolysis of Co/Ce co-doped metal–organic frameworks (MOFs), retaining the inherently high surface area of MOFs to maximize the exposure of Co-N and Ce-N active sites. The electronic interaction between Co and Ce atoms effectively modulates the adsorption/desorption behavior of oxygen-containing intermediates, thereby enhancing intrinsic catalytic activity. In alkaline media, the CoCe-NC catalyst exhibits E_1/2 = 0.854 V electrocatalytic capability comparable to commercial Pt/C, along with superior methanol resistance and durability. Notably, CoCe-NC demonstrates an overpotential 84 mV lower than Pt/C at 300 mA cm⁻² in a GDE half-cell. When the catalyst is employed as a cathode in zinc–air batteries, it demonstrates an open-circuit voltage of 1.47 V, a peak power density of 202 mW cm⁻², and exceptional cycling durability. Full article

Manganese-based oxides, particularly β-MnO₂, have emerged as promising cathode materials for aqueous zinc-ion batteries (ZIBs) due to their high theoretical capacity, low cost, and intrinsic safety. However, their sluggish reaction kinetics, limited active sites, and poor conductivity often lead to suboptimal electrochemical performance. To address these limitations, we propose a facile ethanol-mediated hydrothermal strategy to engineer rod-like β-MnO₂ nanostructures with tailored oxygen vacancies. By precisely adjusting ethanol addition (3–5 mL) during synthesis, oxygen vacancy concentrations were optimized to enhance electronic conductivity and active site exposure. The experimental results demonstrate that β-MnOx-2-5 synthesized with 5 mL of ethanol delivers an exceptional areal capacity of 4.87 mAh cm⁻² (348 mAh g⁻¹, 469.8 Wh kg⁻¹) at 200 mA cm⁻² under a high mass loading of 14 mg cm⁻². Further, a hybrid electrode combining oxygen-deficient β-MnO₂-x-3 (air-calcined) and structurally stable β-Mn₅O₈-y-3 (Ar-calcined) achieves a retained capacity of 3.9 mAh cm⁻² with stable cycling performance, achieving an optimal equilibrium between high capacity and long-term operational durability. Systematic characterizations (XPS, ESR, XANES, FT-EXAFS) confirm vacancy-induced electronic structure modulation, accelerating ion diffusion and redox kinetics. This scalable vacancy engineering approach, requiring only ethanol dosage control, presents a viable pathway toward industrial-scale ZIB applications. Full article

Realistic applications of zinc–air batteries are hindered by the high cost of Pt/C cathode catalysts, necessitating the search for alternative, sustainable electrocatalysts. In this work, we developed a sustainable Fe₃C/Fe-N_x-C cathode catalyst from waste coffee biomass for an oxygen reduction reaction (ORR) in alkaline electrolytes and zinc–air battery applications. The Fe₃C/Fe-N_x-C cathode catalyst was synthesized via a mechanochemical synthesis strategy by using melamine and an EDTA–Fe chelate complex, followed by pyrolysis at 900 °C. The obtained Fe₃C/Fe-N_x-C catalyst was evaluated for detailed ORR activity and stability. The ORR results show that Fe₃C/Fe-N_x-C displayed excellent ORR activity with an E_1/2 of 0.93 V vs. RHE, a Tafel slope of 68 mV dec⁻¹, 3.95 e⁻ transfer for the O₂ molecule, and high ECSA values. In addition, the Fe₃C/Fe-N_x-C catalyst exhibited excellent stability with a loss of 75 mV for 10,000 potential cycles, and a loss of ~14% of relative currents in the chronoamperometric test. When applied as a cathode catalyst in zinc–air battery, the Fe₃C/Fe-N_x-C catalyst delivered a power density of 81 mW cm⁻² and admirable electrochemical stability under galvanostatic discharge conditions. Furthermore, the practical application of the Fe₃C/Fe-N_x-C catalyst was demonstrated by a panel of LEDs illuminated with a dual-cell zinc–air battery connected in a series, clearly validating the practically developed catalysts for use in various energy storage and electronic devices. Full article

Li-ion batteries (LIBs) are one of the most deployed energy storage technologies worldwide, providing power for a wide range of applications—from portable electronic devices to electric vehicles (EVs). The growing demand for LIBs, coupled with a shortage of critical battery materials, has prompted the scientific community to seek ways to improve material utilization through the recycling of end-of-life LIBs. While valuable battery metals are already being recycled on an industrial scale, graphite—a material classified as a critical resource—continues to be discarded. In this study, graphite waste recovered from the recycling of LIBs was successfully upcycled into an active graphite/rGO (reduced graphene oxide) composite oxygen electrocatalyst. The precursor graphite for rGO synthesis was also extracted from LIBs. Incorporating rGO into the graphite significantly enhanced the specific surface area and porosity of the resulting composite, facilitating effective doping with residual metals during subsequent nitrogen doping via pyrolysis. These composite catalysts enhanced both the oxygen reduction and oxygen evolution reactions, enabling their use as air electrode catalyst materials in zinc–air batteries (ZABs). The best-performing composite catalyst demonstrated an impressive power density of 100 mW cm⁻² and exceptional cycling stability for 137 h. This research further demonstrates the utilization of waste fractions from LIB recycling to drive advancements in energy conversion technologies. Full article

The development of efficient, sustainable, and cost-effective catalysts is crucial for energy storage technologies, such as zinc–air batteries (ZABs). These batteries require bifunctional catalysts capable of efficiently and selectively catalyzing oxygen redox reactions. However, the high cost and low selectivity of conventional catalysts hinder the large-scale integration of ZABs into the electric grid. This study presents binder-free Fe-based bifunctional electrocatalysts synthesized via a sol–gel method, followed by thermal treatment under ammonia flow. Supported on nickel foam, the catalyst exhibits enhanced activity for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), essential for ZAB operation. This work addresses two critical challenges in the development of ZABs: first, the replacement of costly cobalt or platinum-group-metal (PGM)-based catalysts with an efficient alternative; second, the achievement of prolonged battery performance under real conditions without passivation. Structural analysis confirms the integration of iron nitrides, oxides, and carbon, resulting in high conductivity and catalytic stability without relying on precious or cobalt-based metals. Electrochemical tests reveal that the catalyst calcined at 800 °C delivers superior performance, achieving a four-electron ORR mechanism and prolonged operational life compared to its 900 °C counterpart. Both catalysts outperform conventional Pt/C-RuO₂ systems in stability and selective bifunctionality, offering a more sustainable and cost-effective alternative. The innovative combination of nitrogen, carbon, and iron compounds overcomes limitations associated with traditional materials, paving the way for scalable, high-performance applications in renewable energy storage. This work underscores the potential of transition metal-based catalysts in advancing the commercial viability of ZABs. Full article

The development of bifunctional air electrodes with high activity and durability is essential for advancing flexible zinc–air batteries. Herein, a hierarchical electrode structure is designed by growing N-doped carbon nanotubes (CNTs) on copper foam, where CNTs serve as highly active oxygen reduction reaction (ORR) sites. The controlled deposition of NiFeCo-layered double hydroxide (LDH) nanosheets, optimized to maintain ORR activity while enhancing oxygen evolution reaction (OER) performance, enables a finely tuned bifunctional catalyst. This architecture achieves outstanding electrochemical properties, requiring only 0.897 V vs. RHE and 1.446 V vs. RHE to reach 10 mA cm⁻² in 1 M KOH, thereby minimizing overpotentials. When implemented as an air electrode in a quasi-solid-state zinc–air battery, the system demonstrates remarkable cycling stability, sustaining performance for over 300 h. Furthermore, a 16 cm² pouch-type zinc–air battery delivers a high discharge capacity of 0.62 Ah, highlighting the scalability of this design. This work presents a robust and scalable strategy for developing high-performance bifunctional air electrodes, offering a promising route for next-generation flexible energy storage systems. Full article

Solid polymer electrolytes (SPEs) are gaining attention as viable alternatives to traditional aqueous electrolytes in zinc–air batteries (ZABs), owing to their enhanced performance and stability. In this study, anion-exchange solid polymer electrolytes (A-SPEs) were synthesized via electrophilic aromatic substitution and substitution reactions. Thin films were prepared using the solvent casting method and characterized using proton nuclear magnetic resonance (¹H-NMR), Fourier-transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA). The ion-exchange capacity (IEC), KOH uptake, ionic conductivity, and battery performance were also obtained by varying the degree of functionalization of the A-SPEs (30 and 120%, denoted as PSf30/PSf120, respectively). The IEC analysis revealed that PSf120 exhibited a higher quantity of functional groups, enhancing its hydroxide conductivity, which reached a value of 22.19 mS cm⁻¹. In addition, PSf120 demonstrated a higher power density (70 vs. 50 mW cm⁻²) and rechargeability than benchmarked Fumapem FAA-3-50 A-SPE. Postmortem analysis further confirmed the lower formation of ZnO for PSf120, indicating the improved stability and reduced passivation of the zinc electrode. Therefore, this type of A-SPE could improve the performance and rechargeability of all-solid-state ZABs. Full article

Developing efficient bifunctional oxygen reduction (ORR) and oxygen evolution (OER) electrocatalysts is critical for renewable energy technologies. Noble metal catalysts face limitations in cost, scarcity, and bifunctional compatibility. Herein, we report the synthesis of nickel nanoparticles encapsulated in nitrogen-doped carbon nanosheets (Ni@NC-T) via a solvothermal polymerization and pyrolysis process using a Ni-hexamine coordination framework (NiHMT) as a precursor. The Ni@NC-900 catalyst exhibits superior ORR and OER activity under alkaline conditions, with an ORR performance (half-wave potential = 0.86 V) comparable to commercial Pt/C and an OER overpotential of only 430 mV at 10 mA cm⁻². Structural analysis indicates that the hierarchical porous structure and high specific surface area (409 m² g⁻¹) of Ni@NC-900 facilitate the exposure of active sites and enhance mass transport. The surface-doped nitrogen species, predominantly in the form of pyridinic N and graphitic N, promote electron transfer during the ORR. Furthermore, its application as a bifunctional cathode in rechargeable zinc-air batteries results in a high power density of 137 mW cm⁻², surpassing the performance levels of many existing carbon-based bifunctional catalysts. This work highlights a facile strategy for the fabrication of transition metal-based catalysts encapsulated in MOF-derived carbon matrices, with promising potential for energy storage and conversion devices. Full article

Aqueous zinc batteries, mainly including Zn-ion batteries (ZIBs) and Zn–air batteries (ZABs), are promising energy storage systems, but challenges exist at their current stage. For instance, the zinc anode in aqueous electrolyte is impacted by anodic dendrites, hydrogen and oxygen precipitation, and some other harmful side reactions, which severely affect the battery’s lifespan. As for traditional cathode materials in ZIBs, low electrical conductivity, slow Zn²⁺ ion migration, and easy collapse of the crystal structure during ion embedding and migration bring challenges. Also, the slower critical oxygen reduction reaction (ORR), for example, in ZABs shows unsatisfactory results. All these issues greatly hindered the development of zinc batteries. Aerogel materials, characterized by their high specific surface area, unique open-pore structure formed by nanoporous structures, and excellent physicochemical properties, have a positive role in cathode modification, electrode protection, and catalytic reactions in zinc batteries. This manuscript provides a systematic review of aerogel materials, highlighting advancements in their preparation and application for zinc batteries, aiming to promote the future progress and development of aerogel nanomaterials and zinc batteries. Full article

Metal–air batteries represent a category of energy storage system that leverages the reaction between metal and oxygen from the atmosphere to produce electricity. These batteries, known for their high energy density, have attracted considerable attention as potential solutions for extending the range of electric vehicles. Understanding the capabilities and limitations of metal-air batteries as range extenders is crucial for advancing electric vehicle technology, as these batteries could offer the additional energy needed to overcome current range limitations. This review paper provides a detailed overview of various metal-air battery technologies, delving into their design, functionality, and inherent challenges. By analyzing key theoretical and practical parameters, the study highlights how these factors influence overall battery performance. Additionally, the review addresses critical cost considerations, particularly the relationship between vehicle cost and driving range, uncovering the significant trade-offs involved in adopting metal-air batteries. Through an examination of nearly all the existing metal-air batteries, this paper sheds light on their potential to serve as effective range extenders, thereby facilitating the transition to a cleaner, more sustainable transportation landscape. Full article

Developing low-cost, efficient alternatives to catalysts for bifunctional oxygen electrode catalysis in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is critical for advancing the practical applications of alkaline fuel cells. In this study, Co particles and single atoms co-loaded on nitrogen-doped carbon (CoNC) were synthesized via pyrolysis of a C₃N₄ and cobalt nitrate mixture at varying temperatures (900, 950, and 1000 °C). The pyrolysis temperature and precursor ratios were found to significantly influence the ORR/OER performance of the resulting catalysts. The optimized CoNC-950 catalyst demonstrated exceptional ORR (E_1/2 = 0.85 V) and OER (E_j10 = 320 mV) activities, surpassing commercial Pt/C + RuO₂-based devices when used in a rechargeable zinc–air battery. This work presents an effective strategy for designing high-performance non-precious metal bifunctional electrocatalysts for alkaline environments. Full article