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[Display omitted] The electrocatalytic oxygen reduction reaction (ORR) is crucial for energy conversion systems such as fuel cells and metal-air batteries. Boron carbon nitrogen (BCN) is a novel functional material with a high specific surface area, excellent corrosion resistance, and outstanding electrochemical stability. These properties make BCN an effective ORR catalyst and a promising support for metal catalysts. This study leveraged the strong interaction between BCN and metals to anchor platinum nanoparticles (Pt NPs) onto the BCN surface (Pt/BCN), significantly enhancing the durability of traditional Pt/C catalysts in ORR. The half-wave potential of Pt/BCN is 0.927 V, higher than Pt/XC-72R (0.857 V) and commercial Pt/C (0.879 V). Notably, after 10,000 durability test cycles, the mass activity (MA) of Pt/XC-72R and commercial Pt/C decreased by 67 % and 75 %, respectively. Even after 50,000 cycles, Pt/BCN exhibited only a 54 % decrease in MA. Experimental data and density functional theory calculations confirmed increased electron transfer from Pt to the BCN support, indicating a strong electronic metal-support interaction (EMSI) between Pt and BCN. This strong EMSI effectively anchored the Pt NPs, preventing migration and aggregation during the ORR process. Consequently, our research introduces a novel electrocatalyst support material with significant potential for ORR and broader applications. [ABSTRACT FROM AUTHOR]

The development of efficient and cost-effective catalysts for the oxygen electrocatalysis is crucial for advancing renewable energy technologies, such as fuel cells, electrolyzers and metal-air batteries. Herein, we report the high efficiency of Co nanoclusters generated on porous silicon oxycarbonitride (SiCN(O)) fibre mats towards Oxygen Reduction Reaction (ORR) and Oxygen Evolution Reaction (OER) in alkaline medium. Porous SiCN(O) ceramic fibrous supports were synthesized via electrospinning of a blend of oligosilazane Durazane 1800, polyacrylonitrile and polystyrene followed by an appropriate heat-treatment. Co nanoparticles with a remarkably low mass loading (4 wt%) were immobilized on the SiCN(O) fibres for efficient bifunctional catalytic activity towards OER/ORR. The catalysts exhibited ORR activity (onset potential (E 0) of 0.83 V vs. RHE) and excellent stability (80 h) in alkaline medium. Concomitantly, the catalyst required only 1.67 V to drive a current density of 10 mA cm−2 in 1 M KOH for OER. • Co nanoclusters on SiCN(O) fibre mats for ORR/OER in alkaline medium. • Ultra-low mass loading of Co offers high ORR/OER activity with excellent durability. • Nitrogen-doped carbon layers stabilize Co nanocrystals. • Synergistic Co/CoO and N-doped carbon layer promotes the electron transfer. [ABSTRACT FROM AUTHOR]

Faced with the challenges of energy depletion and environmental pollution, HER/OER/ORR as the main reactions of the water splitting, fuel cells, and metal-air batteries have garnered a lot of attention. In this paper, the Ga 2 XY (X, Y O, S, Se, Te, X≠Y) structure containing single-atom defect is systematically investigated based on the first principles calculation, and its catalytic and electronic properties are also analyzed in depth. The results demonstrated that the catalytic performance is substantially improved by introducing single-atom defect, the Ga 2 OS, Ga 2 OSe, and Ga 2 SeTe defect structures have more excellent performance. Among all the defect structures, the Ga 2 SeTe structure containing Ga atom defect on the Y-side and adsorbed on Y-side Ga atoms (Ga 2 SeTe- V G a Y -Ga Y) has excellent HER, OER, and ORR performances, the overpotentials is 0.20 eV, 0.30 eV, and 0.51 eV, respectively. The origin of the catalytic activity is also described using crystal orbital Hamilton population (COHP) and charge density calculations. It is shown that the p-orbitals of O and the s-orbitals of Ga undergo significant hybridization, which affects the Ga 2 XY defect structure from the structural level. Our work broadens the research scope in the field of multifunctional catalysis and offers novel approaches to the study of multifunctional catalysts. • Studied the HER/OER/ORR electrocatalytic properties of Ga 2 XY defect structures. • The introduction of single atom enhances the electrocatalytic performance. • Intermediates are more likely to attach to Ga atoms. • The Ga 2 SeTe- V G a Y defect structure showed the best HER/OER/ORR catalytic properties. [ABSTRACT FROM AUTHOR]

Trifunctional electrocatalysts, an exciting class of materials that can simultaneously catalyze hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR), can significantly enhance the performance and economic viability of electrochemical energy storage and conversion technologies such as water‐splitting electrolyzers, metal‐air batteries, fuel cells and their integrated devices. Such multifunctional electrocatalysts encompass multiple active sites that can simultaneously catalyze two or more different electrochemical reactions and are feasible routes for addressing global energy and environmental challenges. This review accounts for nanocarbons‐based trifunctional electrocatalysts reported for electrolyzers, metal‐air batteries and integrated electrolyzer‐battery systems, providing a practical perspective. Metal‐free and hybrid (hybrids of nanocarbons and transition metals/compounds) trifunctional electrocatalysts are covered. Given the growing importance of green technologies, we discuss biomass‐derived carbon‐based trifunctional electrocatalysts separately. The collective information provided in the review could help researchers derive more effective and durable trifunctional electrocatalysts suitable for commercial use. [ABSTRACT FROM AUTHOR]

Traditional energy resource, i.e. coal, is converted to value-added electrode materials in electrochemical energy conversion systems. [Display omitted] • Traditional coal energy resource is converted to value-added electrode material for electrochemical energy conversion system. • The intrinsic N- and S-heteroatoms in coal effectively enhance the ORR performance. • The electrode exhibited excellent performance in Zn-air batteries with both liquid and solid electrolytes. Coal-based oxygen electrocatalysts hold immense promise for cost-effective applications in rechargeable Zn-air batteries (ZABs) and the value-added, clean utilization of traditional coal resources. Herein, an electrospun membrane electrode comprising coal-derived carbon nanosheets and directly grown carbon nanotubes (CNS/CMF@CNT) was successfully synthesized. The hierarchical porous structure of the electrode, composed of multiple components, significantly facilitates mass and ion transportation, resulting in exceptional electrochemical performance. Employing Fe as the catalyst for CNT growth, the CNS/CMF@CNT electrode exhibits a remarkable onset potential of 0.96 V and a half-wave potential of 0.87 V in the oxygen reduction reaction (ORR). In-situ surface-enhanced Raman spectroscopy reveals that hydroxyl radical desorption on the surface of CNS/CMF@CNT(Fe) is the rate-determining step of the ORR. Notably, the aqueous ZAB featuring the CNS/CMF@CNT(Fe) electrode achieved a peak power density of 216.0 mW cm−2 at a current density of 414 mA cm−2 and maintained a voltage efficiency of 65.1 % after 2000 charge/discharge cycles at 5 mA cm−2. Furthermore, the all-solid-state ZAB incorporating this electrode displayed an open-circuit voltage of 1.43 V, a peak power density of 70.1 mW cm−2 at a current density of 110 mA cm−2, and a voltage efficiency of 66.5 % after 150 charge/discharge cycles. The utilization of abundant coal as the raw material for electrode fabrication not only brings conceivable economic benefits in ZAB construction, but also commendably advances the effective application of traditional coal resources in a more sustainable manner. [ABSTRACT FROM AUTHOR]

[Display omitted] The design and development of high-performance and long-life Pt-free catalysts for the oxygen reduction reaction (ORR) is of great important with respect to metal-air batteries and fuel cells. Herein, a new low-cost covalent organic frameworks (COFs)-derived Co N C single-atoms catalyst (SAC) is fabricated and compared with the engineered nanoparticle (NP) counterpart for ORR activity. The ORR performance of the SAC catalyst (Co SA @NC) surpasses the NP counterpart (Co NP -NC) under the same operation condition. Co SA @NC also achieves improved long-term durability and better methanol tolerance compared with the Pt/C. The zinc-air battery assembled by the Co SA @NC cathode delivers a higher power density and energy density than that of commercial Pt/C catalyst. Molecular dynamics (MD) is performed to explain the spontaneous evolution from clusters to single-atom metal configuration and density functional theory (DFT) calculations find that Co SA @NC possesses lower d -band center, resulting in weaker interaction between the surface and the O-containing intermediates. Consequently, the reductive desorption of OH*, the rate-determine step, is further accelerated. [ABSTRACT FROM AUTHOR]

To replace the noble metal catalysts for oxygen reduction reaction (ORR), a Ni@C-supported N-doped carbon material (Ni@C/NC) is in-situ prepared via one-step pyrolyzing the polymerizable ionic liquid of vinyl imidazole combined with Ni(NO 3) 2. Systemic investigations demonstrate that these nanosized Ni particles are tightly wrapped with a thin carbon layer to form the core/shell structure, meanwhile carbon capsules are synchronously yielded on the carbon matrix. As a result, both the carbon shell and the carbon capsule jointly increase the active sites of the Ni@C/NC, while the carbon shell also contributes the fast electron-transfer from Ni particle. Compared with the normal Ni-supported carbon catalyst, the Ni@C/NC shows the respectable ORR performance with the onset and half-wave potentials of 0.96 and 0.84 V RHE. After the long-term electrocatalysis (10 h), the Ni@C/NC is found to possess the great structural and electrocatalytic stabilities, which maintains 93 % of the initial current density and the well-dispersed and uniform Ni@C particles. Subsequently, a Zn-Air battery with the Ni@C/NC cathode is assembled and exhibits a peak power density of 200 mW cm−2. Therefore, the as-obtained Ni@C/NC with the high electroactivity and stability can be expected as an ideal candidate to apply in the metal-air batteries and fuel cells in the future. Ni particles wrapped with a thin carbon layer is in-situ formed and supported on a N-doped carbon with many capsules, fabricating the Ni@C/NC catalyst, which exhibit the superior catalytic performance for oxygen reduction. [Display omitted] • A Ni@C-supported N-doped carbon material is in-situ prepared. • Nanosized Ni particles are wrapped with a thin carbon layer. • Carbon capsules are synchronously yielded on the carbon matrix. • The Ni@C/NC shows the respectable ORR performance. • The Ni@C/NC possesses the great structural and electrocatalytic stabilities. [ABSTRACT FROM AUTHOR]

Uncovering the origin of bifunctional oxygen reduction/evolution reaction (ORR/OER) activity of M-N-C type electrocatalysts is essential for their extensive usage in fuel cells and metal-air batteries. The electrochemical properties of heterogeneous M-N-C catalysts depend on the surface structure, which can be modified via different synthetic methods. Herein, we investigate the effect of structure on the activity of Co–N–C electrocatalyst material derived from an amorphous metal-organic framework TAL-2. Specifically, TAL-2 served as the sole precursor for the synthesis of a range of Co–N–C catalysts via various carbonization and acid-leaching modes. Co–N–C catalysts were prepared by carbonizing TAL-2 at different temperatures (700, 800, 900, and 1000 °C) and subsequent acid-leaching using different acids, namely HCl, H 2 SO 4 , and HNO 3 , either individually or in various combinations. This resulted in the generation of 36 distinct catalyst samples, each exhibiting unique morphological characteristics. By systematically varying these parameters, we aimed to unravel the intricate relationship between post-synthetic treatment and the resulting electrocatalytic properties, shedding light on the rational design of Co–N–C catalysts for enhanced ORR/OER. [Display omitted] • Co–N–C catalysts were derived from TAL-2 MOF by varied post-synthetic treatment. • 36 unique catalysts were studied to understand structure-activity relationships. • Optimized catalysts showed superior ORR/OER performance with low ΔE values. [ABSTRACT FROM AUTHOR]

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[Display omitted] Development of affordable catalysts for the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) represents a central task for advancing electrochemical systems such as fuel cells and metal-air batteries. This study reported the ORR and HER performance of a set of single cluster catalysts (SCCs) with atomically dispersed 3 d /4 d /5 d transition metal cluster (TM 3) embedded in a two-dimensional (2D) defective CrSe 2 substrate. Distinguishing from the conventional SCCs with positive charge active center, the unique electronegativity discrepancy between the metal clusters and the substrate renders the active center controllable charge states from negative to positive. Our investigations indicate that the TM 3 cluster helps tuning the adsorption performance of the intermediates, and therefore enhancing the electrocatalytic activity of the SCCs. Among all the candidates, we demonstrated that the less reported elements of Ir and Ag exhibit the best performance of HER and ORR with low overpotentials of −0.059 and 0.61 V, respectively. Our work provides a prototype to rationally regulate the charge states of catalysts, which could potentially contribute to the development of new kinds of catalysts and serve as a valuable theoretical reference for the experimental rationalization of SCCs. [ABSTRACT FROM AUTHOR]

[Display omitted] Transition metal-based nanoparticles (NPs) are emerging as potential alternatives to platinum for catalyzing the oxygen reduction reaction (ORR) in zinc-air batteries (ZAB). However, the simultaneous coexistence of single-atom moieties in the preparation of NPs is inevitable, and the structural complexity of catalysts poses a great challenge to identifying the true active site. Herein, by employing in situ and ex situ XAS analysis, we demonstrate the coexistence of single-atom moieties and iron phosphide NPs in the N, P co-doped porous carbon (in short, Fe-N 4 -Fe 2 P NPs/NPC), and identify that ORR predominantly proceeds via the atomic-dispersed Fe-N 4 sites, while the presence of Fe 2 P NPs exerts an inhibitory effect by decreasing the site utilization and impeding mass transfer of reactants. The single-atom catalyst Fe-N 4 /NPC displays a half-wave potential of 0.873 V, surpassing both Fe-N 4 -Fe 2 P NPs/NPC (0.858 V) and commercial Pt/C (0.842 V) in alkaline condition. In addition, the ZAB based on Fe-N 4 /NPC achieves a peak power density of 140.3 mW cm−2, outperforming that of Pt/C-based ZAB (91.8 mW cm−2) and exhibits excellent long-term stability. This study provides insight into the identification of true active sites of supported ORR catalysts and offers an approach for developing highly efficient, nonprecious metal-based catalysts for high-energy–density metal-air batteries. [ABSTRACT FROM AUTHOR]

A facile and scalable approach for preparing the monodisperse PtCo nanoalloy anchored on nitrogen-doped carbon nanotubes (PtCo/NCNT) as a superior cathode catalyst to improve the energy conversion efficiency of the zinc-air battery was reported. As a result, the Zn-air battery assembled based on the PtCo/NCNT catalyst demonstrates aremarkable power density of 268 mW cm−2, an outstanding specific capacity of 840 mA h g−1, and extraordinary durability exceeding 500 h. [Display omitted] • PtCo nanoalloy anchored on nitrogen-doped carbon nanotubes (PtCo/NCNT) was reported. • The assembled primary Zn-air battery delivers a higher power density of 268 mW cm−2. • The solid battery exhibits excellent stability under different bending angles. The large-scale application of metal-air batteries strongly depends on the development of cost-effective, highly efficient, and durable bifunctional oxygen catalysts. In this work, a facile approach for preparing the monodisperse PtCo nanoalloy anchored the nitrogen-doped carbon nanotubes (PtCo/NCNT) for zinc-air batteries is reported. The nitrogen-doped carbon shell prevents PtCo nanoalloy from exfoliation, dissolution, and aggregation and enables the accessibility of electrolytes to the alloy surface and the electron transfer. Besides, the strong interaction between PtCo nanoalloy and nitrogen-doped carbon can efficiently modulate the electronic structure of the formed active sites. When used as a cathode catalyst, the constructed rechargeable zinc-air battery presents higher power density (268 mW cm−2), specific capacity (840 mAh g−1), and excellent stability. More importantly, the PtCo/NCNT catalyst allows the all-solid-state cell to exhibit remarkable flexibility and high round-trip efficiency at various bending states, demonstrating a potential possibility to replace the conventional Pt/C and RuO 2 catalysts. [ABSTRACT FROM AUTHOR]

FeN 3 -CoN 3 sites break the symmetric electron distribution of single atom sites optimizing adsorption energies of oxygen intermediates. As a result, FeCo-NC exhibits extraordinary ORR activity with a high half-wave potential of 0.915 V in alkaline electrolyte. [Display omitted] Single-atom catalysts show good oxygen reduction reaction (ORR) performance in metal-air battery. However, the symmetric electron distribution results in discontented adsorption energy of ORR intermediates and a lower ORR activity. Herein, Fe-Co dual-atom catalyst with FeN 3 -CoN 3 configuration was prepared by encapsulating nitrogen-rich ion (triethylenediamine cobalt complex, [Co(en) 3 ]3+) in Fe based MOF cage to greatly enhance ORR performance. Due to the confinement effect of the MOF cage, the encapsulated [Co(en) 3 ]3+ is closer to Fe of MOF, thus easily generating FeN 3 -CoN 3 sites. The FeN 3 -CoN 3 sites can break the symmetric electron distribution of single-atom sites, optimizing adsorption energy of oxygen intermediate. Thus, FeCo-NC exhibits extraordinary ORR activity with a high half-wave potential of 0.915 V and 0.789 V in alkaline and acidic electrolyte, respectively, while it was 0.874 V and 0.79 V for Pt/C. The liquid and solid Zn-air batteries with FeCo-NC as cathode show higher peak power density and specific capacity. DFT results indicate that FeN 3 -CoN 3 site can reduce the reaction energy barrier of the rate-determining step resulting in an excellent ORR performance. [ABSTRACT FROM AUTHOR]

Metal-free nanocarbons with highly editable compositions and well-defined morphologies, and adjustable coordination environments have been considered as promising and inexpensive electrode materials that can be used in the fields of fuel cells and metal-air batteries. Herein, the typical micromorphology of high-output tuber crops potato was examined for the first time by cryo-electron microscopy, and nitrogen-doped spherical carbons with highly curved carbon layers were prepared from potato and sweet potato by hydrothermal and ammonia-activated treatments. The potato-derived carbon (PC) and sweet potato-derived carbon (SPC) with enriched nitrogen dopants on native curved carbon layers exhibit favorable oxygen reduction reaction (ORR) activities in both acidic and alkaline media. The half-wave potential of the curved PC is 60 mV higher than that of commercial Pt/C (20 wt% Pt) in 0.1 M KOH. Impressively, the zinc-air battery using the curved PC displays excellent stability and achieves a peak power density of 116 mW cm−2, surpassing the performance of Pt/C (108 mW m−2). Finite element method (FEM) simulations and molecular dynamics (MD) calculations reveal that the curved carbon surface-enhanced tip electric field on the spherical structure, could further induce charge transfer and accelerate the ORR process. This work elucidates the origin of the catalytic activity of spherically structured metal-free carbons with N-doping, providing meaningful insights into the development of low-cost and highly active catalysts and advancing the field of sustainable energy. [Display omitted] • The morphology of potato abundant spherical starch granules was characterized. • Spherical carbons with doped N were constructed by hydrothermal carbonization. • Zinc-air batteries assembled with catalysts have higher power density than Pt/C. • FEM indicates the curved carbon layer enhanced tip electric field accelerate ORR. [ABSTRACT FROM AUTHOR]

The advancement of economical and readily available electrocatalysts for the oxygen reduction reaction (ORR) holds paramount importance in the advancement of fuel cells and metal‐air batteries. Recently, 2D non‐metallic materials have obtained substantial attention as viable alternatives for ORR catalysts due to their manifold advantages, encompassing low cost, ample availability, substantial surface‐to‐volume ratio, high conductivity, exceptional durability, and competitive activity. The augmented ORR performances observed in metal‐free 2D materials typically arise from heteroatom doping, defects, or the formation of heterostructures. Here, the authors delve into the realm of electrocatalysts for the ORR, pivoting around metal‐free 2D materials. Initially, the merits of metal‐free 2D materials are explored and the reaction mechanism of the ORR is dissected. Subsequently, a comprehensive survey of diverse metal‐free 2D materials is presented, tracing their evolutionary journey from fundamental concepts to pragmatic applications in the context of ORR. Substantial importance is given on the exploration of various strategies for enhancing metal‐free 2D materials and assessing their impact on inherent material performance, including electronic properties. Finally, the challenges and future prospects that lie ahead for metal‐free 2D materials are underscored, as they aspire to serve as efficient ORR electrocatalysts. [ABSTRACT FROM AUTHOR]

Electrochemical transformation processes involving carbon, hydrogen, oxygen, nitrogen, and small‐molecule chemistries represent a promising means to store renewable energy sources in the form of chemical energy. However, their widespread deployment is hindered by a lack of efficient, selective, durable, and affordable electrocatalysts. Recently, grain boundary (GB) engineering as one category of defect engineering, has emerged as a viable and powerful pathway to achieve improved electrocatalytic performances. This review presents a timely and comprehensive overview of recent advances in GB engineering for efficient electrocatalysis. The beneficial effects of introducing GBs into electrocatalysts are discussed, followed by an overview of the synthesis and characterization of GB‐enriched electrocatalysts. Importantly, the latest developments in leveraging GB engineering for enhanced electrocatalysis are thoroughly examined, focusing on the electrochemical utilization cycles of carbon, hydrogen, oxygen, and nitrogen. Future research directions are proposed to further advance the understanding and application of GB engineering for improved electrocatalysis. [ABSTRACT FROM AUTHOR]

The exploration and development of efficient and cost-effective oxygen reduction reaction (ORR) catalysts for non-metallic biomass have emerged as a crucial avenue for synthesizing diverse carbon nanomaterials. We synthesized a nitrogen and sulfur co-doped porous three-dimensional graphene-like carbon nanosheet. The present study employed Ginkgo biloba leaves as the raw material, and a significant number of nanopores were obtained through pre-carbonization treatment followed by high-temperature activation treatment using KOH, along with acidification to eliminate inorganic minerals. The specific surface area of the carbon material was increased to 2219.64 m2 g−1, resulting in enhanced electrocatalytic performance. The results demonstrate that the optimized N,S co-doped carbon material (TKGLC-2) outperformed 20 wt% Pt/C in all key electrochemical performance parameters as an ORR catalyst. The exceptional ORR properties, ease of preparation, and large surface area suggest that the findings offer a promising prototype template for designing and constructing reliable biochar derived from biomass for potential electrochemical energy and storage applications. This highlights its feasibility as an ORR electrocatalyst in potential applications such as fuel cells and metal–air batteries. [ABSTRACT FROM AUTHOR]

The Li–CO2 battery often suffers from high overpotential and limited capacity due to the challenges associated with the adsorption of Li+ and CO2 and the decomposition of Li2CO3. Herein, hexagonal rich-stepped NiSe crystals are in situ achieved on a three-dimensional (3D) free-standing porous Ni skeleton with double continuous channel architecture (namely p-Ni@NiSe-50) through an in situ selenization process. Structural characterization and theoretical calculation are applied to demonstrate the synergistic effects of marco/microstructural design and electronic band structure regulation. As a result, the adsorption/desorption of Li+ and CO2 and the formation/decomposition of Li2CO3 are effectively promoted, simultaneously, enabling an enhanced capacity and reversibility of p-Ni@NiSe-50 as the cathode of Li–CO2 battery. An ultra-low overpotential of 0.46 V and a remarkably high energy efficiency of 83.8% (20 μA cm−2) are achieved, along with a high full discharge specific capacity of 8844 μAh cm−2. Excellent long-term cycling stability (cycles up to 1000 h at a voltage gap of 1.14 V) of p-Ni@NiSe-50 is also obtained. The results of this work would provide a new insight and strategy to develop high-performance alkali metal-air batteries. Multi-scale synergistic effect of combining the cathode macroscopic structure design and the microscopic band structure design of NiSe was demonstrated to promote the adsorption of Li+ and CO2, as well as the decomposition of Li2CO3, so as to achieve ultra-low voltage gap and high capacity of Li-CO2 batteries. [ABSTRACT FROM AUTHOR]

Soft robots and wearable technologies benefit significantly from stretchable batteries, yet the rigid nature of high‐capacity electrodes creates large trade‐offs in battery performance and stretchability. This study introduces a new approach for realizing stretchable batteries by allowing the electrodes to slide along a stretchable electrolyte. When the sliding‐electrodes battery is stretched, the forces are transmitted through the hydrogel electrolyte and elastomeric enclosure, while the rigid electrodes slide relative to the hydrogel to maintain interfacial contact. The sliding‐electrodes approach allows 100% of the unstretched battery area to be covered by thick electrodes so that the battery areal capacity and power are improved by up to 10X of prior stretchable designs. Three metal‐air batteries achieve areal capacities of up to 104 mWh cm−2. Further mechanical testing, electrochemical characterization, and integration into soft robotic systems demonstrate the potential of these stretchable batteries in practical applications. The sliding‐electrodes battery can stably power multiple servo motors and sensing circuits under stretching, twisting, bending, and after impact. [ABSTRACT FROM AUTHOR]

Electrochemical energy conversion and storage are playing an increasingly important role in shaping the sustainable future. Differential electrochemical mass spectrometry (DEMS) offers an operando and cost-effective tool to monitor the evolution of gaseous/volatile intermediates and products during these processes. It can deliver potential-, time-, mass- and space-resolved signals which facilitate the understanding of reaction kinetics. In this review, we show the latest developments and applications of DEMS in various energy-related electrochemical reactions from three distinct perspectives. (I) What is DEMS addresses the working principles and key components of DEMS, highlighting the new and distinct instrumental configurations for different applications. (II) How to use DEMS tackles practical matters including the electrochemical test protocols, quantification of both potential and mass signals, and error analysis. (III) Where to apply DEMS is the focus of this review, dealing with concrete examples and unique values of DEMS studies in both energy conversion applications (CO2 reduction, water electrolysis, carbon corrosion, N-related catalysis, electrosynthesis, fuel cells, photo-electrocatalysis and beyond) and energy storage applications (Li-ion batteries and beyond, metal–air batteries, supercapacitors and flow batteries). The recent development of DEMS-hyphenated techniques and the outlook of the DEMS technique are discussed at the end. As DEMS celebrates its 40th anniversary in 2024, we hope this review can offer electrochemistry researchers a comprehensive understanding of the latest developments of DEMS and will inspire them to tackle emerging scientific questions using DEMS. [ABSTRACT FROM AUTHOR]

Electrocatalytic oxygen evolution reaction (OER) is not only a half-reaction of watersplitting to produce hydrogen, but also an important half-reaction of electrocatalytic carbon dioxide reduction, nitrogen reduction, nitrate reduction, organic small molecule reduction, and metal-air batteries. The OER process is driven by a four-electron mechanism. Due to the slow and complex kinetics of the electrocatalytic OER and its strong oxidation characteristics, studying the oxidative reconstruction rules and catalytic mechanisms of electrode materials in the OER process is of great significance to improve the efficiency of the OER. As a kind of metal-free electrode materials, carbon materials are widely used in electrocatalysis, which has become a potential electrocatalyst for OER due to their low price, abundant reserves, and high activity stability. At present, oxygen-containing functional groups on the surface of carbon materials have been proven to be active sites for OER. However, the deactivation mechanism of carbon materials at higher oxidation potentials during the OER process remains unclear due to a lack of understanding of the active site evolution mechanism. Correctly identifying the active sites of carbon materials under oxygen evolution conditions has become a research hotspot in the field. However, ex-situ characterization techniques such as X-ray diffraction (XRD) and scanning electron microscopy (SEM) are difficult to reflect the catalytic behavior of carbon materials under working conditions. In this study, differential electrochemical mass spectrometry (DEMS) was used to monitor the structural changes of carbon material during the OER process with graphite as the model material. The effects of applied voltage and pH value of electrolyte on graphite oxidation were investigated respectively. By changing the applied potential and the pH value of the electrolyte, we found that graphite firstly oxidizes itself to form oxygencontaining functional groups under acidic (pH 0), neutral (pH 7), and alkaline (pH 14) conditions. As the potential increases, the graphite begins to produce CO2 and CO at 1.6 V vs. RHE over the full pH value range, and the content of CO2 gradually augments as the potential increases. The generation potential of O2 is higher than that of CO2 under acidic condition, and the opposite is true under alkaline condition. Therefore, graphite can be used as an OER catalyst under alkaline condition in a certain potential range. This work not only reveals the structural transformation rules and corresponding evolution products of carbon materials in the full pH value range under electrochemical oxidation conditions, but also proposes a feasible potential operating range when carbon materials are used as OER catalysts.kinetics of the electrocatalytic OER and its strong oxidation characteristics, studying the oxidative reconstruction rules and catalytic mechanisms of electrode materials in the OER process is of great significance to improve the efficiency of the OER. As a kind of metal-free electrode materials, carbon materials are widely used in electrocatalysis, which has become a potential electrocatalyst for OER due to their low price, abundant reserves, and high activity stability. At present, oxygen-containing functional groups on the surface of carbon materials have been proven to be active sites for OER. However, the deactivation mechanism of carbon materials at higher oxidation potentials during the OER process remains unclear due to a lack of understanding of the active site evolution mechanism. Correctly identifying the active sites of carbon materials under oxygen evolution conditions has become a research hotspot in the field. However, ex-situ characterization techniques such as X-ray diffraction (XRD) and scanning electron microscopy (SEM) are difficult to reflect the catalytic behavior of carbon materials under working conditions. In this study, differential electrochemical mass spectrometry (DEMS) was used to monitor the structural changes of carbon material during the OER process with graphite as the model material. The effects of applied voltage and pH value of electrolyte on graphite oxidation were investigated respectively. By changing the applied potential and the pH value of the electrolyte, we found that graphite firstly oxidizes itself to form oxygencontaining functional groups under acidic (pH 0), neutral (pH 7), and alkaline (pH 14) conditions. As the potential increases, the graphite begins to produce CO2 and CO at 1.6 V vs. RHE over the full pH value range, and the content of CO2 gradually augments as the potential increases. The generation potential of O2 is higher than that of CO2 under acidic condition, and the opposite is true under alkaline condition. Therefore, graphite can be used as an OER catalyst under alkaline condition in a certain potential range. This work not only reveals the structural transformation rules and corresponding evolution products of carbon materials in the full pH value range under electrochemical oxidation conditions, but also proposes a feasible potential operating range when carbon materials are used as OER catalysts. [ABSTRACT FROM AUTHOR]

Aluminum‐oxygen batteries (AOBs) own the benefits of high energy density (8.14 kWh kg−1), low cost, and high safety. However, the design of a cathode with high surface area, structure integrity, and good catalytic performance is still challenging for rechargeable AOBs. Herein, the fabrication of a robust self‐supporting cathode using 3D graphene aerogel (3DGA) for rechargeable AOBs is demonstrated. Electroanalysis showed that the 3DGA presented good catalytic activity in both oxygen reduction and evolution reactions, which allowed the AOB to operate for >90 cycles with low overpotentials at a current density of 0.2 mA cm−2, and a high Coulombic efficiency of ca. 99% using ionic liquid as electrolyte. In comparison, the cell with the carbon paper cathode can only cycle for 50 rounds. The excellent cyclic performance can be attributed to the porous structure, large surface area, good electric conductivity, and catalytic activity of the 3DGA, which is prospective to be applied for other metal‐air batteries, fuel cells, and supercapacitors. [ABSTRACT FROM AUTHOR]

Herein, four different metal-free nitrogen containing Covalent Triazine Frameworks (CTFs) based on their applied monomers (DCP, DCBP, m DCB and p DCB) are synthesized via a classical ionothermal synthesis route (ZnCl 2 , 400/600 °C). These materials are fully characterized and their electrochemical activities for ORR are tested and compared to each other including Carbon Super P and Pt black as standards in 0.1 M KOH. While DCP provides similar catalytic activity to Carbon Super P showing mostly a 2eˉ process (n=2.95) with high H 2 O 2 formation of 52.6 %, the other three CTFs (DCBP, m DCB and p DCB) possess higher ORR activities, surprisingly even much higher limiting current densities than Pt black, proving that O 2 is mainly reduced via direct 4eˉ pathway since n values are in the range of 3.52 to 3.62 and the detected H 2 O 2 values are in the range of 19–23.9 %. Among the studied CTFs, m DCB reaches a limiting current density of −5.61 mA cm-2 (1.21 mA cm-2 larger than that for Pt black, −4.40 mA cm-2) with 0.11 V larger onset potential compared to Pt black. The significant electrochemical performances of the CTF materials in ORR via a 4eˉ process are correlated to the high specific surface areas (up to 2500 m2 g-1), large pore volumes (up to 2.05 cm3 g-1) and the largest total N-graphitic/quaternary contents as well as micro-mesoporous structure properties. [Display omitted] • Four N-containing Covalent Triazine Frameworks (CTF) were synthesized via a classical ionothermal route. • Three CTFs provide higher ORR activities, with much larger limiting current densities than Pt black. • O 2 is mostly reduced through a direct 4eˉ process rather than 2eˉ process at three CTFs. • The N-graphitic/quaternary sites are the active sites for oxygen reduction reaction (ORR). [ABSTRACT FROM AUTHOR]

The potential of polyoxometalates (POMs) as alternatives to noble metal-based bifunctional electrocatalysts for air electrode, i.e., for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), was analyzed herein. Five POMs containing transition metal (Mn, Fe, Co, Ni, or Cu) were prepared and combined with reduced graphene oxide (rGO). Kenning structure of POMs with nanolamellae-like morphology and multi-layered graphene sheets of rGO were confirmed by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy with energy dispersive X-ray spectroscopy, transmission electron microscopy and Raman spectroscopy analysis. Different POM:rGO ratios were tested to optimize the composition, and a ratio of 1:5 Ni-POM:rGO was found to be the most electrocatalytically active for OER (Tafel slope as low as 42 mV dec−1, overpotential at 10 mA cm−2 of 354 mV and current density at 400 mV overpotential as high as 83.4 mA cm−2), notably better than IrO 2. As for ORR, Co-POM/rGO carried the lowest Tafel slope of 165 mV dec−1, half-wave potential of 0.711 V and a mixed 2- and 4-electron ORR mechanism. Moreover, these non-precious metal electrocatalysts showed stability in alkaline media with no change in their structure. [Display omitted] • Synergistic effect of transition metal-POM and rGO enhances activity for OER/ORR. • Co-POM/rGO and Ni-POM/rGO outperform IrO 2 as benchmark electrocatalyst for OER. • The price of the catalyst per generated current is lower than in the case of costly IrO 2. • Co-POM/rGO demonstrates the best bifunctional character for ORR/OER. [ABSTRACT FROM AUTHOR]

In response to the escalating environmental impact of fossil fuels, there's a growing demand for clean energy solutions, particularly efficient metal-air batteries. Metal-air batteries are promising for energy storage, boasting abundant materials and low cost. However, their efficiency is hindered by slow oxygen reduction and evolution reactions. Synthesizing effective and stable oxygen electrocatalysts is crucial for enhancing battery performance. Here, this work used a simple solvothermal method to synthesize Iron–Cobalt metal-organic framework (FeCo-MOF), Manganese–Iron–Cobalt metal-organic framework (MnFeCo-MOF), and their composites with (1, 3, and 5) wt% rGO and characterized via using XRD, SEM, FTIR, and Raman spectroscopy. Electrochemical testing was conducted in 1 M KOH solution for both OER and ORR. The 3 wt% rGO MnFeCo-MOF shown the lowest overpotential of 54 mV at 10 mA/cm2 and the lowest Tafel slope of 63.4 mV/dec, with highest current density of 79.42 mA/cm2 at 25 mV/s scan rate for OER indicating excellent electrocatalytic activity superior to already reported in literature due to synergistic effect of Mn, Fe, Co, and rGO facilitating rapid electron transfer and more active sites. The 3 wt% rGO MnFeCo-MOF exhibited the halfwave potential of 0.74 V for ORR showing excellent activity comparable to commercial catalysts Pt/C. The lower potential gap ΔE 0.66 V from the overall combined plot of OER/ORR shows efficient and stable bifunctional activity of the 3 wt% rGO MnFeCo-MOF. These exceptional electrocatalytic properties pave the way for future advancements in metal-air batteries. [Display omitted] • FeCo-MOF, MnFeCo-MOF, and their composites with rGO were synthesized solvothermaly at 120 °C. • 3 wt% rGO MnFeCo-MOF showed lowest TAFEL slope 63.4 mV/dec and overpotential of 54 mV at 10 mA/cm2 for OER. • 3 wt% rGO MnFeCo-MOF for ORR has a halfwave potential of 0.74 V. • Exhibited excellent stability studied via chronopotentiometry experiment. • Synergic effect among rGO and Mn, Fe, Co MOF active sites. [ABSTRACT FROM AUTHOR]

In order to develop economical and environment-friendly metal-air batteries, herein, we report aluminium-air batteries (AABs) using low-cost commercially available aluminium (Al) sheets and waste from Al beverage canister as metal anodes and MoSe 2 , NiCo 2 O 4 , and NiCo 2 O 4 –MoSe 2 hybrid nanostructure as cathodes. The electrocatalytic activity of cathode materials have been examined using three-cell electrochemical configuration in 1 M KOH electrolyte, which shows best oxygen reduction behaviour of hybrid nanostructure attributed to large number of active sites, and synergistic effect between NiCo 2 O 4 and MoSe 2. The developed batteries utilize dual electrolyte (KOH-methanol and KOH-water) system to reduce the unwanted corrosion of Al anode and improve the electrocatalytic activity of cathode. Among designed AABs in the present work, AAB with Al canister as anode and NiCo 2 O 4 –MoSe 2 hybrid nanostructure as cathode shows best performance like higher discharging potential of 1.05 V at a current density of 10 mA cm−2 and higher specific capacity of 1304 mAh g−1. The assembled AABs with hybrid electrocatalyst show almost stable performance for more than 50 h by mechanically replacing the Al anode, once consumed. [Display omitted] • Synthesis of NiCo 2 O 4 –MoSe 2 hybrid nanostructure as electrocatalyst. • High specific capacity of 1305 mAh g−1 Al-air battery using NiCo 2 O 4 –MoSe 2 (cathode) and Al beverage canister (anodes). • Dual electrolyte reduces corrosion of Al anode. • Demonstration of mechanically rechargeable Al-air batteries using NiCo 2 O 4 –MoSe 2 as cathode materials. [ABSTRACT FROM AUTHOR]

The sluggish oxygen reduction reaction (ORR) has been one of the most majority bottlenecks of fuel cells and metal-air batteries. It is extremely desirable but challenging to explore low cost, highly active, stable catalysts toward ORR to replace commercial Pt/C catalysts. Herein, a novel hybrid system consisting of trace copper and bi-nonmetallic (N/S) modified the commercial ketjenblack (KB) carbon (Cu–NS–C) has been successfully fabricated by a pyrolysis of Cu–MOF/KB and thiourea to transform crystalline Cu/Cu2O nanoparticles into copper sulfide nanoparticles and the subsequent acid leaching. The optimized Cu–NS–C delivers a half-wave potential of 0.81 V versus RHE and a limiting-current density of 5.0 mA cm−2, which is next to those of commercial 20 wt% Pt/C catalyst. Furthermore, this catalyst demonstrates much better durability and methanol tolerance than Pt/C catalyst. [ABSTRACT FROM AUTHOR]

The effects of B‐site substitution (B═Mn, Fe, and Co) in La‐based perovskite oxides (LPOs); LaMnO3, LaFeO3, LaCoO3, as bifunctional electrocatalysts during oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in metal–air batteries (MABs) under an alkaline electrolyte (pH = 13) are investigated using density functional theory (DFT). It is found that LaMnO3 exhibits higher ORR activity than others with ORR overpotential (ηORR) of 0.57 V, but its OER activity is poor with OER overpotential (ηOER) of 1.12 V. The ηORR (0.59 V) and ηOER (1.13 V) of LaMn0.75Fe0.25O3 closely resemble those of LaMnO3, suggesting that Fe substitution does not yield appreciable enhancements in activity. Fe substitution reduces the ORR and OER activity because the adsorption energies of intermediate species on Fe‐substituted LPOs surfaces are too strong to obtain a potential determining step for ORR and OER. According to Sabatier's principle, the LaMn0.25Co0.75O3 demonstrates superior OER activity compared to the other composition, while ORR activity approximates that of LaMnO3, evidenced by ηORR of 0.65 V and ηOER of 0.53 V. The Co‐terminated LaMn0.25Co0.75O3 shows bifunctional activity higher than Mn/Co termination, indicating that Co is an active site for OER and Mn is a promoter for improved ORR activity. [ABSTRACT FROM AUTHOR]

Polyoxometalates (POMs) with transition metals (Co, Cu, Fe, Mn, Ni) of Keggin structure and lamellar-stacked multi-layer morphology were synthesized. They were subsequently explored as bifunctional electrocatalysts for oxygen electrodes, i.e., oxygen reduction (ORR) and evolution (OER) reaction, for aqueous rechargeable metal-air batteries in alkaline media. The lowest Tafel slope (85 mV dec−1) value and the highest OER current density of 93.8 mA cm−2 were obtained for the Fe-POM electrocatalyst. Similar OER electrochemical catalytic activity was noticed for the Co-POM electrocatalyst. This behavior was confirmed by electrochemical impedance spectroscopy, where Fe-POM gave the lowest charge transfer resistance of 3.35 Ω, followed by Co-POM with Rct of 15.04 Ω, during the OER. Additionally, Tafel slope values of 85 and 109 mV dec−1 were calculated for Fe-POM and Co-POM, respectively, during the ORR. The ORR at Fe-POM proceeded by mixed two- and four-electron pathways, while ORR at Co-POM proceeded exclusively by the four-electron pathway. Finally, capacitance studies were conducted on the synthesized POMs. [ABSTRACT FROM AUTHOR]

The development and synthesis of cathode electrocatalysts with high activity and durable stability for metal-air batteries is an important challenge in the area of electrocatalysis. Herein, we introduce a novel in-situ nitriding and phosphating strategy for producing W3N4 and WP from phosphotungstic acid (HPW)-polyaniline-phytic acid-Fe3+ organic–inorganic hybrid material. The final material has a three-dimensional porous framework with W3N4-WP heterostructures embedded in the carbon matrix (W3N4-WP@NPC). As-made materials exhibit exceptional electrocatalytic performance for the oxygen reduction reaction (ORR), with a diffusion-limiting current density of 6.9 mA·cm−2 and a half-wave potential of 0.82 V. As a Zn-air primary cathode, the W3N4-WP@NPC assembled battery can provide a relatively high peak power density (194.2 mW·cm−2). As a Zn-air secondary air-cathode, it has great cycling stability over 500 h. This work provides a simple and efficient method for rationally designing high-performance air cathodes from copolymer-anchored polyoxometalates. [ABSTRACT FROM AUTHOR]

The development of high-efficient and low-cost oxygen reduction reaction (ORR) electrocatalysts is crucial for the practical applications of metal-air batteries. One promising way is to develop Fe single-atom catalysts. However, the single active center and inherent electronic structure of Fe single-atom catalysts lead to the undesirable adsorption of multiple ORR intermediates. Herein, a charge-asymmetry single-atom alloy (SAA) catalyst with Fe–Cu dual sites supported on nitrogen-doped carbon nanosheet (Fe1Cu SAA/NC) was constructed. Various characterizations manifest the existence of electron interaction between Fe and Cu in Fe1Cu SAA/NC, which facilitates the adsorption of ORR intermediate for fast kinetics. Consequently, the charge-asymmetry Fe1Cu SAA/NC exhibits much faster ORR kinetics with a half-wave potential of 0.917 V vs. reversible hydrogen electrode (RHE), outperforming its counterparts in the references. Furthermore, Fe1Cu SAA/NC still maintains a high half-wave potential with only a drop of 5 mV after 5000 cycles, indicating excellent stability. This work provides a new strategy to design highly active and non-noble metal ORR electrocatalysts, which hold great potential for various catalytic applications. [ABSTRACT FROM AUTHOR]

Metal-free catalysts are made by the elements with infinite reserve in nature and, therefore, show the potential for large-scale applications in energy devices including metal–air batteries. The construction of metal–air batteries prefers using self-supporting catalysts with favorable activity as well as fast kinetics. However, it is challenging due to the limited electropositivity of metal-free catalysts for O–O bond formation in oxygen evolution reaction (OER), scaling relationship restrictions between OER and oxygen reduction reaction, and difficulty in porosity construction on the monolith electrode surface. In this contribution, through developing a facile methodology of quenching high-temperature carbon clothes in liquid nitrogen, a self-supported carbon cloth with bifunctional active graphene skin and fast kinetics is well constructed to serve as the air cathode in metal–air batteries. Regulated oxygen species and three-dimensionally hierarchical porosity are well constructed on the carbon fiber surfaces, contributing high intrinsic activity and prominently enhanced kinetics, which leads to favorable performances in aqueous as well as flexible rechargeable zinc–air batteries. The work proposed a promising strategy in the rational design and smart synthesis of fast-kinetic monolith electrodes, which refreshes concepts and strategies of advanced material fabrication, and also bridges material science and practical energy devices. [ABSTRACT FROM AUTHOR]

Li-N2 batteries present a relatively novel approach to N2 immobilization, and an advanced N2/Li3N cycling method is introduced in this study. The low operating overpotential of metal–air batteries is quite favorable to their stable cycling performance, providing a prospect for the development of a new type of battery with extreme voltage. The battery system of Li-N2 uses N2 as the positive electrode, lithium metal as the negative electrode, and a conductive medium containing soluble lithium salts as the electrolyte. In accordance with its voltage-distribution trend, a variety of lithium-nitrogen molecule intermediates are produced during the discharge process. There is a lack of theoretical description of material changes at the microscopic level during the discharge process. In this paper, the first-principles approach is used to simulate and analyze possible material changes during the discharge process of Li-N2 batteries. The discharge process is simulated on a 4N-graphene anode substrate model, and simulations of its electrostatic potential, Density of States (DOS), HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) aspects confirm that the experimentally found Li3N becomes the final stabilized product of the Li-N2 battery. It can also be seen in the density of states that graphene with adsorption of 4N transforms from semiconducting to metallic properties. In addition, the differential charge also indicates that the Li-N2 material has a strong adsorption effect on the substrate, which can play the dual role of electricity storage and nitrogen fixation. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) represents a cornerstone for many clean energy conversion technologies such as fuel cells and metal‐air batteries. Nevertheless, the commercialization of these technologies is largely impeded by the slow kinetics of ORR, for which active, durable and cost‐effective ORR catalysts are needed. In recent years, zeolitic imidazolate framework (ZIF) derived carbon materials emerge as a new class of non‐precious metal catalysts (NPMCs) toward ORR, largely benefiting from their high surface area, abundant porosity, tunable chemical/electronic structure, and superior ORR activity which is comparable or even surpasses those state‐of‐the‐art Pt‐based ORR catalysts. This review offers a comprehensive overview of the recent advances in ZIF‐derived carbons for ORR. The synthesis strategies and the key factors affecting the ORR performance of ZIF‐derived carbon materials are discussed. Future research directions and perspectives on exploring ZIF derived carbons as efficient ORR catalysts are highlighted, with a focus on the principles of rationally engineering the coordination structures of active sites. [ABSTRACT FROM AUTHOR]

Exploration of greatly efficient and steady non‐noble oxygen evolution reaction (OER) electrocatalysts is of great significance in improving the overall efficiency of energy density systems such as regenerative fuel cells, water electrolyzes, and metal‐air batteries. Herein, inspired by hierarchical 3D porous structures with open microchannels of natural wood, CoO@NiFe LDH sandwich‐like nanosheets were anchored on the carbonized wood (CW) via electrodeposition and calcination strategies. The strong interactions between CoO nanosheets and NiFe LDH nanosheets endow CoO@NiFe LDH/CW electrocatalyst with high catalytic properties toward the OER comparable to CoO/CW and NiFe LDH/CW. The optimized CoO@NiFe LDH/CW electrocatalyst demonstrates good OER catalytic performance with an overpotential of 230 mV at 100 mA cm−2. This work presents an innovative approach to utilize renewable resources for constructing advanced free‐standing catalysts. [ABSTRACT FROM AUTHOR]

The oxidation of carbon in conventional gas diffusion electrodes is a limiting factor for the life of secondary metal-air batteries. Replacement of carbon with zeolite is a possible solution to avoid its oxidation in the gas-diffusion electrodes (GDE) and thus to increase the battery lifetime. Due to the fact that the technology provides the required number of charge/discharge cycles, it is applicable for solar energy storage. Zeolites are a large group of natural or synthetic porous aluminosilicate minerals. Their porous structure provides good gas permeability. The gas diffusion layer of the electrode must also have good hydrophobicity. To prevent leakage of electrolyte from the battery, the zeolite was mixed with an appropriate amount of polytetrafluoroethylene, and the electrode was subjected to hot pressing according to a specially developed procedure. The experiments were performed in a specially designed test cell. Its construction ensures measurements of the bifunctional gas-diffusion electrode in a half-cell configuration applying a reference hydrogen electrode. The stationary volt-ampere characteristics and impedance tests were performed on the zeolite electrodes at certain operating points. The cell was subjected to cycling at charge/discharge current ± 2 mA/cm2, respectively. The obtained experimental results show that zeolite is a suitable material for carbon substitution in secondary metal air batteries. The zeolite/polytetrafluoroethylene (PTFE) ratio needs to be optimised in order to improve the gas permeability of the gas diffusion layer without compromising hydrophobicity. [ABSTRACT FROM AUTHOR]

As the kinetic processes of oxygen reduction (ORR) and oxygen evolution reaction (OER) in metal-air batteries are slow, developing bifunctional catalysts with high performances is an essential requirement for boosting metal-air battery application. FeCo alloy is considered an excellent bifunctional active material, its weak corrosion resistance precludes its practical use in bifunctional catalysts. In this work, through dipping and annealing operations, FeCo alloy nanoparticles are doped on the porous carbon spheres (FeCo/PCNs). Strong FeCo nanoparticle-nitrogen-doped porous carbon sphere interaction results in a noticeable improvement in electrocatalytic activity and stability. FeCo/PCNs catalyst shows impressive bifunctional electrocatalytic activity, half-wave potential (E 1/2) of 0.905 V for ORR, and overpotential of 344 mV at a current density of 10 mA cm−2 (E j = 10) for OER, which are better than commercial Pt/C (E 1/2 = 0.865 V) and RuO 2 (E j = 10 = 351 mV) catalysts. Furthermore, the Zinc-air battery (ZABs) prepared by FeCo/PCNs catalyst (ZAB-FeCo/PCNs), exhibits high open circuit voltage (1.53 V), high power density (135 mW cm−2), and good long-term cycle stability, which further proves that FeCo/PCNs has excellent ORR/OER bifunctional activity. Therefore, the unique FeCo/PCNs catalyst provides a new perspective for the construction of ZABs bifunctional catalysts. [Display omitted] • FeCo/PCNs catalyst is prepared via impregnation and pyrolysis processes. • FeCo alloy in FeCo/PCNs catalyst promotes the graphitization the PCNs skeleton. • FeCo alloy and Fe/Co-N x active sites endow catalyst with high OER/ORR activity. • ZABs with FeCo/PCNs catalyst show better property than Pt/C + RuO 2. [ABSTRACT FROM AUTHOR]

Metal–air batteries (MABs) offer exceptional energy density, making them attractive for vehicle electrification and storing intermittent renewable energy. However, several challenges persist, including sluggish oxygen reduction and oxygen evolution reactions, interfacial stability issues, and challenges related to current collectors. Herein, the reasons behind MAB's failures are analyzed, considering their thermodynamic aspects (Gibbs free energy, entropy), electrochemical factors (redox potentials, polarization, and ion concentrations), and kinetic properties (mobility of charges). Strategies for mitigating energy barriers of the electrodes are explored, encompassing insights into the initiation process of the oxygen reduction and determinants of oxygen evolution kinetics. The impact of humidity on the electrolyte is assessed, and effective methods for dendrite prevention are elucidated. Additionally, the utilization of 3D electrodes, oxygen‐selective membranes, solid‐state electrolytes, hybrid polymer electrodes, conductive electrocatalysts, and artificial solid‐electrolyte interfaces, and their effects on addressing the challenges faced by MABs are discussed. The study also emphasizes six critical commercialization aspects for the advancement of MABs. Lastly, the potential prospects and challenges in the field of MAB technology are discussed. [ABSTRACT FROM AUTHOR]

Fuel cells and metal‐air batteries are examples of renewable energy technologies that depend on having highly effective electrocatalysts for the oxygen evolution reaction (OER). In this study, a mesoporous nanostructure composed of Fe3O4‐Carbon nanocomposites was synthesised using a simple and economically viable approach at a relatively low temperature. The observed catalytic activity of the prepared defected Fe3O4‐Carbon nanocomposites mesoporous nanostructure was found to be remarkable. Additionally, the nanostructure exhibited a high tolerance to methanol and demonstrated durability towards the oxygen evolution reaction (OER) in alkaline media. In the course of the experiment, it was observed that the catalyst exhibited noteworthy activity in the Oxygen Evolution Reaction (OER) when compared to the commercially available RuO2 catalyst. This was evident through a more overpotential value of 325 mV at current density of 10 mA/cm2. The catalyst's notable capacity for high oxygen reaction activity may potentially enhance the synergistic effect resulting from the combination of defect sites and the porous structure of Fe3O4‐Carbon nanocomposites. The findings of this study indicate that the Fe3O4‐Carbon nanocomposites nanostructures exhibit promising attributes as an electrocatalyst for the oxygen evolution reaction (OER) in real‐world scenarios. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) is the bottleneck of metal‐air batteries and fuel cells. Strain regulation can change the geometry and adjust the surface charge distribution of catalysts, which is a powerful strategy to optimize the ORR activity. The introduction of controlled strain to the material is still difficult to achieve. Herein, we present a temperature‐pressure‐induced strategy to achieve the controlled lattice strain for metal coordination polymers. Through the systematic study of the strain effect on ORR performance, the relationship between geometric and electronic effects is further understood and confirmed. The strained Co‐DABDT (DABDT=2,5‐diaminobenzene‐1,4‐dithiol) with 2 % lattice compression exhibits a superior half‐wave potential of 0.81 V. Theoretical analysis reveals that the lattice strain changes spin‐charge densities around S atoms for Co‐DABDT, and then regulates the hydrogen bond interaction with intermediates to promote the ORR catalytic process. This work helps to understand the catalytic mechanism from the atomic level. [ABSTRACT FROM AUTHOR]

Driven by the goal of establishing a fossil‐fuel‐free and nuclear‐power‐free economy based on renewable energy, metal‐air batteries are regarded as promising energy conversion and storage devices. Developing efficient oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) bifunctional electrocatalysts for the air electrode of metal‐air batteries is becoming increasingly important. In this work, 36 transition metal (TM) single‐atom catalysts are designed based on MXenes Ti2CT2 with different surface terminal atoms (T = O, S, Cl), and their ORR/OER catalytic activity and stability are evaluated by the density functional theory. Ni@Ti2CO2, Pd@Ti2CS2, and Co@Ti2CCl2 are found to exhibit good catalytic activity with ORR/OER overpotentials of.54 V/.62 V,.59 V/.29 V,.44 V/.40 V. The aggregation behavior of three catalysts is estimated by comparing the average binding energy of one, two, three, and four TM atoms anchored on Ti2CT2. This work cannot only provide a theoretical guide to develop bifunctional single‐atom catalysts, but also help us understand the effect of terminal atoms on the electronic structures and catalytic activity of TM@Ti2CT2. [ABSTRACT FROM AUTHOR]

Out of practicality, ambient air rather than oxygen is preferred as a fuel in electrochemical systems, but CO2 and H2O present in air cause severe irreversible reactions, such as the formation of carbonates and hydroxides, which typically degrades performance. Herein, we report on a Na-air battery enabled by a reversible carbonate reaction (Na2CO3·xH2O, x = 0 or 1) in Nasicon solid electrolyte (Na3Zr2Si2PO12) that delivers a much higher discharge potential of 3.4 V than other metal-air batteries resulting in high energy density and achieves > 86 % energy efficiency at 0.1 mA cm−2 over 100 cycles. This cell design takes advantage of moisture in ambient air to form an in-situ catholyte via the deliquescent property of NaOH. As a result, not only reversible electrochemical reaction of Na2CO3·xH2O is activated but also its kinetics is facilitated. Our results demonstrate the reversible use of free ambient air as a fuel, enabled by the reversible electrochemical reaction of carbonates with a solid electrolyte. Metal-air batteries, operated in ambient air, suffer from irreversible redox reactions, limiting their energy density. Herein, the authors present a solid electrolyte-based sodium-air battery with a reversible carbonate reaction, facilitated by the in-situ formed catholyte enabled by moisture. [ABSTRACT FROM AUTHOR]

Nowadays, self‐charging devices using clean energy have raised the potential of portable and wearable power generators. Herein, a novel moisture‐induced self‐powered device based on metal–air redox reaction has been designed which can work under normal humidity conditions. Through bridging two asymmetric electrodes including a carbon nanotube/polyaniline composite electrode and a metal electrode by filter paper with CaCl2, the 1D planar device can be simply fabricated. A single device can provide an open‐circuit voltage of over 1.3 V under normal humidity (40%) within 5 min (the maximum can be up to 1.42 V at 80% humidity) and the harvesting energy can be stored effectively. The device possesses great circularity and stability which can maintain steady and consistent output over at least 6 months. Due to the microelectrolyte, this device can prevent harmful leakage or deformation of the electrolyte completely. What is more, the device shows good extendibility. Three single devices in series using common electrodes can light up two light‐emitting diodes. Besides its application potential in self‐powered portable and wearable electronics, this device can provide a reference for utilization in medical devices due to the response signals under breath with different frequencies. [ABSTRACT FROM AUTHOR]

The expensiveness of oxygen reduction reaction (ORR) catalyst materials especially Pt has hindered the commercialization of next-generation energy conversion devices including metal–air batteries and polymer electrolyte membrane fuel cells. Fe– N –C has drawn attention as a nonprecious metal catalyst owing to its high but commercially unsatisfactory ORR performance; nevertheless, additional heteroatom co-doping could help augment its ORR activity. Here we report nitrogen/fluorine-coordinated iron-co-doped carbon (Fe@NFC) catalysts with improved ORR performance in alkaline media. The annealing temperature affects the nitrogen/fluorine doping and functional group formation, as ascertained by an analysis of control samples annealed at various temperatures. To assess the synergy between the doped fluorine and nitrogen-coordinated iron, we compare the catalyst annealed at 700 °C (Fe@NFC700) with control samples containing different heteroatom dopants but annealed at 700 °C (Fe@NC, Fe@FC). Fe@NFC700 shows improved ORR kinetics and onset potential than those of Fe@NC and commercial Pt/C, respectively, in alkaline media. • The most optimal annealing temperature of the Fe@NFC is found at 700 °C for the ORR. • F-doping increases the ORR favorable N -functional group ratio like Fe-N x. • The high ECSA from N -functional groups enhances the ORR performance. • F-functional groups like semi-ionic C –F bonds provide remarkable ORR kinetics. • The Fe@NFC700 catalyst exhibits higher onset potential than Pt/C in 0.1 M KOH. [ABSTRACT FROM AUTHOR]