CO2 Bubble-Assisted Pt Exposure in PtFeNi Porous Film for High-Performance Zinc-Air Battery

Fabrication of Zn-Air Battery with High Output Capacity Under Ultra-Large Current

Zn-air battery (ZAB) is advocated as a more viable option in the new-energy technology. However, the limited-output capacity at a high current density impedes the driving range in power batteries substantially. Here, a novel heterojunction-based graphdiyne (GDY) and Ag29Cu7 alloy quantum dots (Ag29Cu7 QDs/GDY) for constructing a high-performance aqueous ZAB are fabricated. The as-fabricated ZAB achieves discharge at up to 100 mA cm-2 (the highest value ever reported) along with a remarkable output specific capacity of 786.2 mAh g-1 Zn, which is mainly benefitted from the binary-synergistic effect toward a stable triple-phase interface for air electrode induced by the Ag29Cu7 QDs and GDY in harsh base, together with the decreasing reaction energy barrier and polarization. The results outperform the superior reports discharging at low current and will bring breakthrough progress toward the practical applications of ZAB on large power supply facilities.

Advanced Architectures of Air Electrodes in Zinc-Air Batteries and Hydrogen Fuel Cells

The air electrode is an essential component of air-demanding energy storage/conversion devices, such as zinc-air batteries (ZABs) and hydrogen fuel cells (HFCs), which determines the output power and stability of the devices. Despite atom-level modulation in catalyst design being recently achieved, the air electrodes have received much less attention, causing a stagnation in the development of air-demanding equipment. Herein, the evolution of air electrodes for ZABs and HFCs from the early stages to current requirements is reviewed. In addition, the operation mechanism and the corresponding electrocatalytic mechanisms of ZABs are summarized. In particular, by clarifying the air electrode interfaces of ZABs at different scales, several approaches to improve the air electrode in rechargeable ZABs are reviewed, including innovative electrode structures and bifunctional oxygen catalysts. Afterward, the operating mechanisms of proton-exchange-membrane fuel cells (PEMFCs) and anion-exchange-membrane fuel cells (AEMFCs) are explained. Subsequently, the strategies employed to enhance the efficiency of the membrane electrode assembly (MEA) in PEMFCs and AEMFCs, respectively, are highlighted and discussed in detail. Last, the prospects for air electrodes in ZABs and HFCs are considered by discussing the main challenges. The aim of this review is to facilitate the industrialization of ZABs and HFCs.

Sustainable zinc-air battery chemistry: advances, challenges and prospects

Sustainable zinc-air batteries (ZABs) are considered promising energy storage devices owing to their inherent safety, high energy density, wide operating temperature window, environmental friendliness, etc., showing great prospect for future large-scale applications. Thus, tremendous efforts have been devoted to addressing the critical challenges associated with sustainable ZABs, aiming to significantly improve their energy efficiency and prolong their operation lifespan. The growing interest in sustainable ZABs requires in-depth research on oxygen electrocatalysts, electrolytes, and Zn anodes, which have not been systematically reviewed to date. In this review, the fundamentals of ZABs, oxygen electrocatalysts for air cathodes, physicochemical properties of ZAB electrolytes, and issues and strategies for the stabilization of Zn anodes are systematically summarized from the perspective of fundamental characteristics and design principles. Meanwhile, significant advances in the in situ/operando characterization of ZABs are highlighted to provide insights into the reaction mechanism and dynamic evolution of the electrolyte|electrode interface. Finally, several critical thoughts and perspectives are provided regarding the challenges and opportunities for sustainable ZABs. Therefore, this review provides a thorough understanding of the advanced sustainable ZAB chemistry, hoping that this timely and comprehensive review can shed light on the upcoming research horizons of this prosperous area.

NaCl sealing Strategy-Assisted synthesis CoO-Co heterojunctions as efficient oxygen electrocatalysts for Zn air batteries

Developing highly efficient, low-cost, and stable bifunctional oxygen electrocatalysts is essential for the wide popularization of rechargeable Zn-air batteries. Combining zero-dimensional metal nanoparticles with two-dimensional metal oxide nanosheets is an appealing strategy to balance performance and cost. However, the precise construction of these composites remains a great challenge, and their interaction mechanisms lack thorough study. Herein, a cobalt-oxide-based bifunctional oxygen electrocatalyst comprising a rich Co-CoO heterointerface (CoO/Co@NG) was synthesized via a NaCl sealing-assisted pyrolysis strategy. The NaCl crystals played the role of a closed nanoreactor, which facilitated the formation of a CoO-Co heterojunction. Experimental results and theoretical calculations confirmed that the ingeniously constructed heterojunction expedited the oxygen reduction reaction and oxygen evolution reaction kinetics, which is superior to Pt/C. When serving as the air electrode in an assembled liquid-state Zn-air battery, the battery shows high power density (215 mW cm^-2), specific capacity (710 mAh g_zn^-1), and outstanding durability (720 h at 10 mA cm^-2). This work provides an innovative avenue to design high-performance heterojunction electrocatalysts for perdurable Zn-air batteries.

Recent advances in zinc-air batteries: self-standing inorganic nanoporous metal films as air cathodes

Zinc-air batteries (ZABs) have promising prospects as next-generation electrochemical energy systems due to their high safety, high power density, environmental friendliness, and low cost. However, the air cathodes used in ZABs still face many challenges, such as the low catalytic activity and poor stability of carbon-based materials at high current density/voltage. To achieve high activity and stability of rechargeable ZABs, chemically and electrochemically stable air cathodes with bifunctional oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) activity, fast reaction rate with low platinum group metal (PGM) loading or PGM-free materials are required, which are difficult to achieve with common electrocatalysts. Meanwhile, inorganic nanoporous metal films (INMFs) have many advantages as self-standing air cathodes, such as high activity and stability for both the ORR/OER under highly alkaline conditions. The high surface area, three-dimensional channels, and porous structure with controllable crystal growth facet/direction make INMFs an ideal candidate as air cathodes for ZABs. In this review, we first revisit some critical descriptors to assess the performance of ZABs, and recommend the standard test and reported manner. We then summarize the recent progress of low-Pt, low-Pd, and PGM-free-based materials as air cathodes with low/non-PGM loading for rechargeable ZABs. The structure-composition-performance relationship between INMFs and ZABs is discussed in-depth. Finally, we provide our perspectives on the further development of INMFs towards rechargeable ZABs, as well as current issues that need to be addressed. This work will not only attract researchers' attention and guide them to assess and report the performance of ZABs more accurately, but also stimulate more innovative strategies to drive the practical application of INMFS for ZABs and other energy-related technologies.

Interfacial Engineering of CoN/Co3 O4 Heterostructured Hollow Nanoparticles Embedded in N-Doped Carbon Nanowires as a Bifunctional Oxygen Electrocatalyst for Rechargeable Liquid and Flexible all-Solid-State Zn-Air Batteries

The design of economical, efficient, and robust bifunctional oxygen electrocatalysts is greatly imperative for the large-scale commercialization of rechargeable Zn-air battery (ZAB) technology. Herein, the neoteric design of an advanced bifunctional electrocatalyst composed of CoN/Co₃ O₄ heterojunction hollow nanoparticles in situ encapsulated in porous N-doped carbon nanowires (denoted as CoN/Co₃ O₄ HNPs@NCNWs hereafter) is reported. The simultaneous implementation of interfacial engineering, nanoscale hollowing design, and carbon-support hybridization renders the synthesized CoN/Co₃ O₄ HNPs@NCNWs with modified electronic structure, improved electric conductivity, enriched active sites, and shortened electron/reactant transport pathways. Density functional theory computations further demonstrate that the construction of a CoN/Co₃ O₄ heterojunction can optimize the reaction pathways and reduce the overall reaction barriers. Thanks to the composition and architectural superiorities, the CoN/Co₃ O₄ HNPs@NCNWs exhibit distinguished oxygen reduction reaction and oxygen evolution reaction performance with a low reversible overpotential of 0.725 V and outstanding stability in KOH medium. More encouragingly, the homemade rechargeable liquid and flexible all-solid-state ZABs utilizing CoN/Co₃ O₄ HNPs@NCNWs as the air-cathode deliver higher peak power densities, larger specific capacities, and robust cycling stability, exceeding the commercial Pt/C + RuO₂ benchmark counterparts. The concept of heterostructure-induced electronic modification herein may shed light on the rational design of advanced electrocatalysts for sustainable energy applications.

Efficient removal of bromate from contaminated water using electrochemical membrane filtration with metal heteroatom interface

Efficient utilization of atomic hydrogen (H*) is of great importance for achieving efficient bromate reduction using electrochemical technologies. Herein, an electrochemical membrane with metal heteroatom interface of Ru and Ni was developed to enhance the utilization efficiency of H* via the membrane filtration process. The RuNi membrane demonstrated 91.3% of bromate removal at 5 mA cm^-2 under the flow-through operation (40 L m^-2 h^-1). Cyclic voltammetry (CV) curves and electron spin resonance (ESR) spectra elucidated that the bromate reduction was mainly attributed to H* -mediated reduction rather than the direct electron transfer between bromate and RuNi active layer. The quenching experiments revealed a significant contribution of adsorbed H* to the bromate removal during the membrane filtration. Based on X-ray photoelectron spectrometry and X-ray diffraction analyses, we found that the resultant Ru⁰Ni⁰ structure on the electrochemical membrane could facilitate the generation of H* during the bromate reduction reaction. Besides, the higher pH might suppress the formation of H* and increase the energy barrier for breaking the Br-O bond, resulting in dramatic increase of energy consumption for removing bromate. Our work highlights the potential of utilizing H* in electrochemical membrane for removing bromate in water treatment and remediation.

Interface synergism and engineering of Pd/Co@N-C for direct ethanol fuel cells

Direct ethanol fuel cells have been widely investigated as nontoxic and low-corrosive energy conversion devices with high energy and power densities. It is still challenging to develop high-activity and durable catalysts for a complete ethanol oxidation reaction on the anode and accelerated oxygen reduction reaction on the cathode. The materials' physics and chemistry at the catalytic interface play a vital role in determining the overall performance of the catalysts. Herein, we propose a Pd/Co@N-C catalyst that can be used as a model system to study the synergism and engineering at the solid-solid interface. Particularly, the transformation of amorphous carbon to highly graphitic carbon promoted by cobalt nanoparticles helps achieve the spatial confinement effect, which prevents structural degradation of the catalysts. The strong catalyst-support and electronic effects at the interface between palladium and Co@N-C endow the electron-deficient state of palladium, which enhances the electron transfer and improved activity/durability. The Pd/Co@N-C delivers a maximum power density of 438 mW cm^-2 in direct ethanol fuel cells and can be operated stably for more than 1000 hours. This work presents a strategy for the ingenious catalyst structural design that will promote the development of fuel cells and other sustainable energy-related technologies.

Hierarchically hollow N-doped carbon-cobalt nanoparticle heterointerface for efficient bifunctional oxygen electrocatalysis

The rational design and fabrication of high-performance and durable bifunctional non-noble-metal electrocatalysts for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are still a great challenge in the practical applications of rechargeable zinc-air (Zn-air) batteries. Herein, we report a simple yet robust route to synthesize cobalt nanoparticles rooted in the hierarchically hollow nitrogen-doped carbon frameworks (Co@HNCs). This strategy employs the pyrolysis of nanostructured hollow Co-based metal-organic framework (ZIF-67) precursors produced by selective linker cleaving with pyrazino(2,3-f)(1,10)phenanthroline-2,3-dicarboxylic acid molecules (H₂PPDA). The designed hierarchically architecture is favorable for the accessibility of the active sites in the catalyst, which affords enhanced bifunctional performance for ORR and OER. Moreover, when used as a cathode in liquid and all-solid-state Zn-air batteries, the resultant Co@HNCs delivers high efficiency and outstanding durability, even outperforming the benchmark Pt/C + RuO₂. This work provides a feasible design avenue to achieve advanced dual-phasic oxygen electrocatalyst and promotes the development of rechargeable Zn-air batteries.

Isolating Contiguous Fe Atoms by Forming a Co-Fe Intermetallic Catalyst from Spent Lithium-Ion Batteries to Regulate Activity for Zinc-Air Batteries

The recycling of spent lithium-ion batteries (LIBs) has become a necessity for recovering valuable resources and protecting the environment to support sustainable development. We report the design of a highly efficient CoFe/C catalyst by combining the Co and Fe wastes from spent LIBs with sawdust-derived carbon, which were cathode materials in zinc-air batteries (ZABs). As a result of the electrostatic attraction between the Co³⁺/Fe³⁺ cations and the hydroxyl groups in sawdust, CoFe nanoparticles are uniformly dispersed in the CoFe/C catalyst after annealing. The Fe atoms in the CoFe nanoparticles are all isolated into single sites by the Co atoms, which redistribute the electrons in the CoFe/C catalyst. The catalyst produced a Pt-like dissociative mechanism, contributing to an excellent oxygen reduction reaction performance. After assembly in ZABs, the CoFe/C catalyst cathode exhibits a long cycling stability of 350 h and an impressive power density of 199.2 mW cm^-2. The CoFe/C catalyst cathode has also been used in flexible ZABs to power LEDs or charge a mobile phone. The work combines spent LIBs with sawdust to fabricate high-performance catalysts, which could reduce environmental pollution and realize high economic value.

Robust Oxygen Reduction Electrocatalysis Enabled by Platinum Rooted on Molybdenum Nitride Microrods

Robust oxygen reduction electrocatalysis is central to renewable fuel cells and metal-air batteries. Herein, Pt nanoparticles (NPs) rooted on porous molybdenum nitride microrods (Pt/Mo₂N MRs) are rationally constructed toward the oxygen reduction reaction (ORR). Owing to the desired composition with strong electronic metal-support interactions (EMSIs) and a porous one-dimensional structure supporting ultrafine NPs, the developed Pt/Mo₂N MRs possess much higher ORR mass and specific activities than commercial Pt/C. In situ Raman and density functional theory calculations reveal that the EMSI weakens the adsorption of intermediates over Pt/Mo₂N MRs via an associative mechanism. Moreover, the porous Mo₂N support stabilizes these high activities. Impressively, a homemade zinc-air battery driven by Pt/Mo₂N MRs delivers excellent performance including a peak power density of 167 mW cm^-2 and a high rate capability that ranged from 5 to 50 mA cm^-2. This work highlights the role of EMSI in promoting robust ORR electrocatalysis, thus providing a promising approach for efficient and robust cathode materials for advanced metal-air batteries.

Tailoring the Electronic Structure of an Atomically Dispersed Zinc Electrocatalyst: Coordination Environment Regulation for High Selectivity Oxygen Reduction

Accurately regulating the selectivity of the oxygen reduction reaction (ORR) is crucial to renewable energy storage and utilization, but challenging. A flexible alteration of ORR pathways on atomically dispersed Zn sites towards high selectivity ORR can be achieved by tailoring the coordination environment of the catalytic centers. The atomically dispersed Zn catalysts with unique O- and C-coordination structure (ZnO₃ C) or N-coordination structure (ZnN₄ ) can be prepared by varying the functional groups of corresponding MOF precursors. The coordination environment of as-prepared atomically dispersed Zn catalysts was confirmed by X-ray absorption fine structure (XAFs). Notably, the ZnN₄ catalyst processes a 4 e^- ORR pathway to generate H₂ O. However, controllably tailoring the coordination environment of atomically dispersed Zn sites, ZnO₃ C catalyst processes a 2 e^- ORR pathway to generate H₂ O₂ with a near zero overpotential and high selectivity in 0.1 M KOH. Calculations reveal that decreased electron density around Zn in ZnO₃ C lowers the d-band center of Zn, thus changing the intermediate adsorption and contributing to the high selectivity towards 2 e^- ORR.