NiCo-doped C-N nano-composites for cathodic catalysts of Zn-air batteries in neutral media

High entropy alloy nanoparticles encapsulated into carbon nanotubes enable high performance of zinc air batteries

High entropy alloy nanoparticles encapsulated into nitrogen-doped carbon nanotubes show superior bifunctionality for the ORR and OER, evidenced by a battery performance of 214 mW cm-2, sustained for 200 h.

A superior zinc-air battery performance achieved by CoO/Fe3O4 heterostructured nanosheets

CoO/Fe3O4 nanosheets exhibit a superior rechargeable zinc-air battery (ZAB) performance of 276 mW cm-2 and stability over 600 h. The all-solid-state ZAB also affords a high power density of 107 mW cm-2.

Design Principles and Mechanistic Understandings of Non-Noble-Metal Bifunctional Electrocatalysts for Zinc-Air Batteries

Zinc-air batteries (ZABs) are promising energy storage systems because of high theoretical energy density, safety, low cost, and abundance of zinc. However, the slow multi-step reaction of oxygen and heavy reliance on noble-metal catalysts hinder the practical applications of ZABs. Therefore, feasible and advanced non-noble-metal electrocatalysts for air cathodes need to be identified to promote the oxygen catalytic reaction. In this review, we initially introduced the advancement of ZABs in the past two decades and provided an overview of key developments in this field. Then, we discussed the working mechanism and the design of bifunctional electrocatalysts from the perspective of morphology design, crystal structure tuning, interface strategy, and atomic engineering. We also included theoretical studies, machine learning, and advanced characterization technologies to provide a comprehensive understanding of the structure-performance relationship of electrocatalysts and the reaction pathways of the oxygen redox reactions. Finally, we discussed the challenges and prospects related to designing advanced non-noble-metal bifunctional electrocatalysts for ZABs.

Self-Decoupled Oxygen Electrocatalysis for Ultrastable Rechargeable Zn-Air Batteries with Mild-Acidic Electrolyte

Rechargeable zinc-air batteries (ZABs) have been considered promising as next-generation sustainable energy storage devices; however, their large-scale deployment is hampered by the unsatisfactory cyclic lifespan. Employing neutral and mild-acidic electrolytes is effective in extending the cyclability, but the rapid performance degradation of the bifunctional catalysts owing to different microenvironmental requirements of the alternative oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is still a serious limitation of their cyclic life. Herein, we propose a "self-decoupling" strategy to significantly improve the stability of the bifunctional catalysts by constructing a smart interface in the bifunctional air electrode. This smart interface, containing a resistance-switchable sulfonic acid doped polyaniline nanoarray interlayer, is nonconductive at high potential but conductive at low potential, which enables spontaneous electrochemical decoupling of the bifunctional catalyst for the ORR and OER, respectively, and thus protects it from degradation. The resulting self-decoupled mild-acidic ZAB delivers stable cyclic performances in terms of a negligible energy efficiency loss of 0.015% cycle-1 and 3 times longer cycle life (∼1400 h) compared with the conventional mild-acidic ZAB using a normal bifunctional air electrode and the same low-cost ZnCo phosphide/nitrogen-doped carbon bifunctional catalyst. This work provides an effective strategy for tolerating alternative oxidation-reduction reactions and emphasizes the importance of smart nanostructure design for more sustainable batteries.

Nanostructured Conducting Polymers and Their Applications in Energy Storage Devices

Due to the energy requirements for various human activities, and the need for a substantial change in the energy matrix, it is important to research and design new materials that allow the availability of appropriate technologies. In this sense, together with proposals that advocate a reduction in the conversion, storage, and feeding of clean energies, such as fuel cells and electrochemical capacitors energy consumption, there is an approach that is based on the development of better applications for and batteries. An alternative to commonly used inorganic materials is conducting polymers (CP). Strategies based on the formation of composite materials and nanostructures allow outstanding performances in electrochemical energy storage devices such as those mentioned. Particularly, the nanostructuring of CP stands out because, in the last two decades, there has been an important evolution in the design of various types of nanostructures, with a strong focus on their synergistic combination with other types of materials. This bibliographic compilation reviews state of the art in this area, with a special focus on how nanostructured CP would contribute to the search for new materials for the development of energy storage devices, based mainly on the morphology they present and on their versatility to be combined with other materials, which allows notable improvements in aspects such as reduction in ionic diffusion trajectories and electronic transport, optimization of spaces for ion penetration, a greater number of electrochemically active sites and better stability in charge/discharge cycles.

Preparation and bifunctional properties of the A-site-deficient SrTi0.3Fe0.6Ni0.1O3-δ perovskite

The development of efficient, non-noble metal electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is crucial for their application in energy storage devices, such as fuel cells and metal-air batteries. In this study, SrTi_0.3Fe_0.6Ni_0.1O_3-δ (STFN) perovskite was synthesized using the sol-gel method, and its electrocatalytic activity was evaluated using a rotating disk electrode (RDE) in an alkaline medium. STFN synthesized at the optimum synthesis temperature of 800 °C exhibited good ORR and OER performances. To further improve electrocatalytic activity, a series of Sr_1-x Ti_0.3Fe_0.6Ni_0.1O_3-δ (x = 0, 0.05, and 0.1) perovskites with A-site vacancies were synthesized at 800 °C. Material characterization results showed that the removal of the A-site from the perovskite led to an increase in surface oxygen vacancies, resulting in higher ORR and OER activities. The results of this study indicate that Sr_1-x Ti_0.3Fe_0.6Ni_0.1O_3-δ (x = 0.1) is a promising bifunctional oxygen electrocatalyst for Zn-air batteries.

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.

ZIF-67-derived N-doped double layer carbon cage as efficient catalyst for oxygen reduction reaction

The slow kinetic of oxygen reduction reaction (ORR) hampers the practical application of energy conversion devices, such as fuel cells, metal-air batteries. Here, an efficient ORR electrocatalyst consists of Co, Ni co-decorated nitrogen-doped double shell hollow carbon cage (Ni-Co@NHC) was fabricated by pyrolyzing Ni-doped polydopamine wrapped ZIF-67. During the preparation, polydopamine served as a protective layer can effectively prevent the aggregation of Co and Ni nanoparticles during the pyrolysis process, and at the same time forming a carbon layer to grow a double layer carbon cage. This unique hollow structure endows the catalyst with a high specific surface area as well as more exposed active sites. Also benefited from the synergistic effect between Ni and Co nanoparticles, the Ni-Co@NHC catalyst leads to an outstanding ORR performance of half-wave potential (E_1/2, 0.862 V), outperforms that of commercial Pt/C catalyst. Additionally, when Ni-Co@NHC was used in the cathode for the zinc-air battery, the cell exhibits high power density (108 mW cm^-2) and high specific capacity (806 mAh g^-1) at 20 mA cm^-2outperforming Pt/C. This work offers a promising design strategy for the development of high-performance ORR electrocatalysts.

Mesoporous N-P Codoped Carbon Nanosheets as Superior Cathodic Catalysts of Neutral Metal-Air Batteries

Development of high-efficiency oxygen reduction reaction (ORR) catalysts under neutral conditions has made little research progress. In this work, we synthesized a three-dimensional porous N/P codoped carbon nanosheet composites (CNP@PNS) by high-temperature thermal treatment of dicyandiamide, starch, and triphenylphosphine and subsequent porous structure-making treatment using the NaCl molten salt template. In the neutral solution, the electrocatalytic performance of the CNP@PNS-4 catalyst exhibits an onset potential of 0.98 V (vs reversible hydrogen electrode) and a half-wave potential of 0.91 V for ORR, which greatly surpasses commercial Pt/C (40%). Three kinds of neutral metal-air batteries (Zn-air, Al-air, and Fe-air) using the prepared samples as cathodic catalysts were constructed, corresponding to the maximum power density of 120.2, 78.3, and 18.9 mW·cm^-2, respectively. Also, they reveal outstanding discharge stability under different current densities. The density functional theory calculation depicts the reduction of the free energy of the determining step and subsequent decline of the overpotential for ORR.

Strongly Coupled NiCo2O4 Nanocrystal/MXene Hybrid through In Situ Ni/Co-F Bonds for Efficient Wearable Zn-Air Batteries

Recently, owing to the high energy density and excellent security, wearable Zn-air batteries (ZABs) have been known as one of the most prominent wearable energy storage devices. However, sluggish oxygen reaction kinetics of oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in the air-breathe cathode seriously has limited further practical applications. In this work, we synthesize a NiCo₂O₄ nanocrystal/MXene hybrid with strong Ni/Co-F bonds. The prepared MXene-based hybrid composites show remarkable ORR and OER electrocatalytic activity, which results in the fabricated solid-state ZAB device to achieve an open-circuit voltage of 1.40 V, peak power density of 55.1 mW cm^-2, and energy efficiency of 66.1% at 1.0 mA cm^-2; to the best of our knowledge, this is the record performance among all reported flexible ZABs with MXene-based air cathodes and comparable with some noble metal catalysts. Moreover, even after cutting and suturing, our flexible solid-state ZAB devices are tailorable with high rate of performance.

Fe-based species anchored on N-doped carbon nanotubes as a bifunctional electrocatalyst for acidic/neutral/alkaline Zn-air batteries

Exploring efficient and durable bifunctional catalysts in pH-universal media is critical for versatile fuel cells. Herein, Fe-based species anchored on N-doped carbon nanotubes (Fe/Fe₃C@N-C) are used for bifunctional oxygen electrocatalysts. The composite electrocatalyst exhibits low potential gaps (ΔE, ΔE = E_{j =10} - E _1/2) in a pH-universal environment. The estimated values are about 0.70, 1.07,and 1.10 V in alkaline, neutral, and acidic medias. A neutral Zn-air battery (ZAB) is constructed using an Fe/Fe₃C@N-C composite as the air electrode, which exhibits a favorable performance in energy storage with an open-circuit potential (OCP) of 1.42 V and a high power density of 80 mW cm^-2. The ZAB also has superior cycling stability with only a 0.5% decay after 1200 charge-discharge cycles at 2 mA cm^-2. While the assembled ZAB in acidic media indicates an OCP of 1.40 V, a power density of 23 mW cm^-2, and 612 discharge-charge cycles. The ZAB is rechargeable and has a cycling lifespan of 120 h. This work provides potential applications of Fe/Fe₃C@N-C as air electrodes for advanced pH-universal media based on ZABs for future energy storage devices.

Rechargeable Zinc-Air Battery with Ultrahigh Power Density Based on Uniform N, Co Codoped Carbon Nanospheres

Highly efficient catalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are key to the commercialization of rechargeable zinc-air batteries (ZABs). In this work, a catalyst with uniform nanospherical morphology was prepared from cobalt nitrate, acetylacetone, and hydrazine hydrate. The final catalyst possesses high ORR and OER performances, with a half-wave potential of 0.911 V [vs reversible hydrogen electrode (RHE)] for ORR and a low potential of 1.57 V (vs RHE) at 10 mA cm^-2 for OER in 0.1 M KOH solution. Specially, a ZAB based on the catalyst demonstrates an ultrahigh power density of 479.1 mW cm^-2, as well as excellent stability, and potential in practical applications.

Ultrafine cobalt nitride nanoparticles supported on carbon nanotubes as efficient electrocatalyst for rechargeable zinc-air batteries

Ultrafine (5 nm) cobalt nitride nanoparticles supported on carbon nanotubes (CoN/CNT) are reported as air electrodes for rechargeable zinc-air batteries (ZABs). CoN/CNT exhibits 2.4 fold higher battery performance than commercial Pt/C-IrO₂.

Formation of needle-like porous CoNi2S4-MnOOH for high performance hybrid supercapacitors with high energy density

Seeking for suitable electrode materials and designing rational porous structures are great challenges for developing high performance supercapacitors. Herein, needle-like porous CoNi₂S₄-MnOOH (denoted as NCS-MO) were prepared via a simple two steps solvothermal method and used as battery-type electrode of supercapacitor for the first time. Owing to the multiple oxidation states of needle-like porous NCS-MO and the inherent porous structure, the electrode delivers outstanding electrochemical capacitive properties with a high gravimetric specific capacitance of 1267.7 F g^-1 at the scan rate of 1 mV s^-1. To further assess the practical electrochemical performances, we assembled a hybrid supercapacitor using the as-synthesized porous NCS-MO as cathode and active carbon as anode. The device exhibits excellent performance with a high energy density of 47.1 Wh kg^-1 at the power density of 998 W kg^-1 in an extended voltage range of 1.6 V and outstanding cycling stability. These results demonstrate that the needle-like porous NCS-MO could be promising potential electrode material for high performance supercapacitor.

Sandwiching Defect-Rich TiO2-δ Nanocrystals into a Three-Dimensional Flexible Conformal Carbon Hybrid Matrix for Long-Cycling and High-Rate Li/Na-Ion Batteries

Developing flexible power sources is crucially important to fulfill the need for wearable electronic devices, but state-of-the-art flexible electrodes cannot meet the requirements of practical applications because of their heavy weight and unsatisfactory mechanical properties. Here, we highlight a design strategy for constructing a novel robust three-dimensional (3D) flexible electrode with a unique sandwichlike N-doped carbon sponge/TiO_2-δ/reduced graphene oxide (NCS/TiO_2-δ/RGO) configuration. In this electrode architecture, ultrafine defect-rich TiO_2-δ nanocrystals are spatially sandwiched by a 3D conformal carbon hybrid matrix, where the 3D porous NCS provides an interconnected open diffusion channel for efficient ionic accessibility while the conformal RGO coating layer serves as an additional upper current collector, resulting in a double continuous conductive network for fast electronic transport and guaranteeing excellent electrochemical reaction kinetics. Hence, the as-built NCS/TiO_2-δ/RGO flexible electrodes exhibit high-rate capabilities and long-cycling life in lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), and they also exhibit outstanding thermal stability under cycling at 55 °C. More remarkably, a flexible soft-package full battery based on a NCS/TiO_2-δ/RGO anode and a LiNi_1/3Co_1/3Mn_1/3O₂ (for LIBs) or Na_0.67Fe_0.3Mn_0.3Co_0.4O₂ (for SIBs) cathode shows stable electrochemical characteristics under bending and folding, holding great potential for flexible energy storage devices.

Designing Robust Support for Pt Alloy Nanoframes with Durable Oxygen Reduction Reaction Activity

Polymer electrolyte membrane fuel cells are appealing to resolve the environmental and energy issues but are still heavily inhibited by the dilemma of fabricating effective and durable electrocatalysts for oxygen reduction reaction (ORR). In this work, highly open Pt₃Cu nanoframes and one-dimensional, hollow titanium nitride architectures are both successfully explored and implemented as the new system to replace the traditional Pt-carbon motif. The ORR performance of the obtained electrocatalyst shows specific and mass activities of 5.32 mA cm^-2 and 2.43 A mg_Pt^-1, respectively, which are 14.4 and 11.6 times higher than those of the commercial Pt/C. Notably, the novel catalyst also exhibits high stability and a much slower performance degradation than that of the benchmarked Pt₃Cu/C with the same durability testing procedures. The comprehensive data confirm that the new type of catalyst possesses a high charge transfer during the ORR process, and the unique structure and synergistic effects between anchored Pt and the support mainly contributes to the high stability. This work provides a strategic method for designing an effective ORR electrocatalyst with desirable stability.

Polymer-derived Co/Ni–SiOC(N) ceramic electrocatalysts for oxygen reduction reaction in fuel cells

For the first time, the oxygen reduction reaction on transition metal and nitrogen doped SiOC-based electrocatalysts is studied.