A Review of Rechargeable Zinc-Air Batteries: Recent Progress and Future Perspectives

Zinc-air batteries (ZABs) are gaining attention as an ideal option for various applications requiring high-capacity batteries, such as portable electronics, electric vehicles, and renewable energy storage. ZABs offer advantages such as low environmental impact, enhanced safety compared to Li-ion batteries, and cost-effectiveness due to the abundance of zinc. However, early research faced challenges due to parasitic reactions at the zinc anode and slow oxygen redox kinetics. Recent advancements in restructuring the anode, utilizing alternative electrolytes, and developing bifunctional oxygen catalysts have significantly improved ZABs. Scientists have achieved battery reversibility over thousands of cycles, introduced new electrolytes, and achieved energy efficiency records surpassing 70%. Despite these achievements, there are challenges related to lower power density, shorter lifespan, and air electrode corrosion leading to performance degradation. This review paper discusses different battery configurations, and reaction mechanisms for electrically and mechanically rechargeable ZABs, and proposes remedies to enhance overall battery performance. The paper also explores recent advancements, applications, and the future prospects of electrically/mechanically rechargeable ZABs.

Tunable Metal-Free Imidazole-Benzimidazole Electrocatalysts for Oxygen Reduction in Aqueous Solutions

A series of metal-free imidazole-benzimidazole catalysts (ImBenz-H, ImBenz-NO2 , ImBenz-OCH3 ) for oxygen reduction reaction (ORR) were prepared. We demonstrate that the electrocatalytic O2 reduction by ImBenz-NO2 with the electron-withdrawing group showed high selectivity toward H2 O with the number of electrons transferred (n=3.7) in a neutral aqueous solution. The highest ORR selectivity toward H2 O2 was achieved using ImBenz-H (n=2.4) in an alkaline solution. Electrochemical studies of reaction kinetics disclosed that the highest turnover frequencies were obtained from ImBenz-H in both neutral and alkaline aqueous solutions. The results prove that the ORR selectivity is tunable by modulating the substituent of the ImBenz catalysts. Furthermore, DFT calculations suggested that the ORR mechanism of ImBenz-H involves the electron transfer from imidazole-benzimidazole to O2 resulting in the formation of H2 O2 which supports the redox active properties of the catalysts ImBenz.

Application of response surface methodology for optimization of the test condition of oxygen evolution reaction over La0.8Ba0.2CoO3 perovskite-active carbon composite

The Experimental Design was applied to optimize the electrocatalytic activity of La0.8Ba0.2CoO3 perovskite oxide/Active Carbon composite material in the alkaline solution for the Oxygen Evolution Reaction. After the preparation of La0.8Ba0.2CoO3, and structural characterizations, the experimental design was utilized to determine the optimal amount of the composite material and testing conditions. The overpotential was defined as the response variable, and the mass ratio of perovskite/active carbon, Potassium hydroxide (KOH) concentration, and Poly(vinylidene fluoride) (PVDF) amount were considered effective parameters. The significance of model terms is demonstrated by P-values less than 0.0500. The proposed prediction model determined the optimal amounts of 0.665 mg of PVDF, a KOH concentration of 0.609 M, and A perovskite/Active Carbon mass ratio of 2.81 with 308.22 mV overpotential (2.27% greater than the actual overpotential). The stability test of the optimized electrode material over 24 h suggests that it could be a good candidate electrocatalyst for OER with reusability potential.

Electrodeposition of nickel–iron on stainless steel as an efficient electrocatalyst coating for the oxygen evolution reaction in alkaline conditions

Significant amount of effort has been devoted in the development of water electrolysis technology as the prime technology for green hydrogen production. In this paper, we investigate nickel–iron-based electrocatalytic coatings on stainless-steel substrates for commercial alkaline water electrolysers. Stainless steel electrodes for water electrolysis have received attention lately, showing that they can be a low-cost substrate for water electrolysis. Coating stainless steel with low-cost electrocatalysts can prove beneficial to lower overpotential for the oxygen evolution reaction (OER), thereby reducing the overall energy consumption of water electrolysis at an affordable cost. We show that NiFe-deposited substrates have an overpotential of 514 mV at 10 mA cm−2 current. The substrates also exhibited excellent stability in strong alkaline condition for 60 h under continuous 1.2 V working potential vs SCE. The results in full-cell electrolysers demonstrate that the electrolyser with the NiFe-coated anode could generate nearly six times as much current density compared with the bare stainless-steel substrate.

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Recent Progress of Non-Noble Metal Catalysts for Oxygen Electrode in Zn-Air Batteries: A Mini Review

Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) play crucial roles in energy conversion and storage devices. Particularly, the bifunctional ORR/OER catalysts are core components in rechargeable metal–air batteries, which have shown great promise in achieving "carbon emissions peak and carbon neutrality" goals. However, the sluggish ORR and OER kinetics at the oxygen cathode significantly hinder the performance of metal–air batteries. Although noble metal-based catalysts have been widely employed in accelerating the kinetics and improving the bifunctionality, their scarcity and high cost have limited their deployment in the market. In this review, we will discuss the ORR and OER mechanisms, propose the principles for bifunctional electrocatalysts design, and present the recent progress of the state-of-the-art bifunctional catalysts, with the focus on non-noble metal-based materials to replace the noble metal catalysts in Zn–air batteries. The perspectives for the future R&D of bifunctional electrocatalysts will be provided toward high-performance Zn–air batteries at the end of this paper.

Research Progress in Metal-Organic Framework Based Nanomaterials Applied in Battery Cathodes

Metal-Organic Frameworks have attracted profound attention the latest years for use in environmental applications. They can offer a broad variety of functions due to their tunable porosity, high surface area and metal activity centers. Not more than ten years ago, they have been applied experimentally for the first time in energy storage devices, such as batteries. Specifically, MOFs have been investigated thoroughly as potential materials hosting the oxidizing agent in the cathode electrode of several battery systems such as Lithium Batteries, Metal-Ion Batteries and Metal-Air Batteries. The aim of this review is to provide researchers with a summary of the electrochemical properties and performance of MOFs recently implemented in battery cathodes in order to provide fertile ground for further exploration of performance-oriented materials. In the following sections, the basic working principles of each battery system are briefly defined, and special emphasis is dedicated to MOF-based or MOF-derived nanomaterials, especially nanocomposites, which have been tested as potential battery cathodes.

Microwave-assisted synthesis of iridium oxide and palladium nanoparticles supported on a nitrogen-rich covalent triazine framework as superior electrocatalysts for the hydrogen evolution and oxygen reduction reaction

Iridium oxide (IrOx-NP) and palladium nanoparticles (Pd-NP) were supported on a 2,6-dicyanopyridine-based covalent-triazine framework (DCP-CTF) by energy-saving and sustainable microwave-assisted thermal decomposition reactions in propylene carbonate and in the ionic liquid [BMIm][NTf2]. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) confirm well-distributed NPs with sizes from 2 to 13 nm stabilized on the CTF particles. Metal contents between 10 and 41 wt% were determined by flame atomic absorption spectroscopy (AAS). Nitrogen sorption measurements of the metal-loaded CTFs revealed Brunauer–Emmett–Teller (BET) surface areas between 904 and 1353 m2 g−1. The composites show superior performance toward the hydrogen evolution reaction (HER) with low overpotentials from 47 to 325 mV and toward the oxygen reduction reaction (ORR) with high half-wave potentials between 810 and 872 mV. IrOx samples in particular show high performances toward HER while the Pd samples show better performance toward ORR. In both reactions, electrocatalysts can compete with the high performance of Pt/C. Exemplary cyclic voltammetry durability tests with 1000 cycles and subsequent TEM analyses show good long-term stability of the materials. The results demonstrate the promising synergistic effects of NP-decorated CTF materials, resulting in a high electrocatalytic activity and stability.

The effect of cobalt on morphology, structure, and ORR activity of electrospun carbon fibre mats in aqueous alkaline environments

An innovative approach for the design of air electrodes for metal-air batteries are free-standing scaffolds made of electrospun polyacrylonitrile fibres. In this study, cobalt-decorated fibres are prepared, and the influence of carbonisation temperature on the resulting particle decoration, as well as on fibre structure and morphology is discussed. Scanning electron microscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, elemental analysis, and inductively coupled plasma optical emission spectrometry are used for characterisation. The modified fibre system is compared to a benchmark system without cobalt additives. Cobalt is known to catalyse the formation of graphite in carbonaceous materials at elevated temperatures. As a result of cobalt migration in the material the resulting overall morphology is that of turbostratic carbon. Nitrogen removal and nitrogen-type distribution are enhanced by the cobalt additives. At lower carbonisation temperatures cobalt is distributed over the surface of the fibres, whereas at high carbonisation temperatures it forms particles with diameters up to 300 nm. Free-standing, current-collector-free electrodes assembled from carbonised cobalt-decorated fibre mats display promising performance for the oxygen reduction reaction in aqueous alkaline media. High current densities at an overpotential of 100 mV and low overpotentials at current densities of 333 μA·cm-2 were found for all electrodes made from cobalt-decorated fibre mats carbonised at temperatures between 800 and 1000 °C.

Bifunctional oxygen evolution and supercapacitor electrode with integrated architecture of NiFe-layered double hydroxides and hierarchical carbon framework

Layered double hydroxide with exchangeable interlayer anions are considered promising electro-active materials for renewable energy technologies. However, the limited exposure of active sites and poor electrical conductivity of hydroxide powder restrict its application. Herein, bifunctional integrated electrode with a 3D hierarchical carbon framework decorated by nickel iron-layered double hydroxides (NiFe-LDH) is developed. A conductive carbon nanowire array is introduced not only to provide enough anchoring sites for the hydroxide, but also affords a continuous pathway for electron transport throughout the entire electrode. The 3D integrated architecture of NiFe-hydroxide and hierarchical carbon framework possesses several beneficial effects including large electrochemical active surfaces, fast electron/mass transport, and enhanced mechanical stability. The as-prepared electrode affords a current density of 10 mA cm^-2 at a low overpotential of 269 mV for oxygen evolution reaction (OER) in 1 M of KOH. It also offers excellent stability with negligible current decline even after 2000 cycles. Besides, density functional theory calculations revealed that the (110) surface of NiFe-LDH is more active than the (003) surface for OER. Furthermore, the electrode possesses promising application prospects in alkaline battery-supercapacitor hybrid devices with a capacity of 178.8 mAh g^-1 (capacitance of 1609.6 F g^-1) at a current density of 0.2 A g^-1. The viability of the as-prepared bifunctional electrode will provide a potential solution for wearable electronics in the near future.