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Comprehensive Summary Key Scientists The electrochemical processes of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) play a crucial role in various energy storage and conversion systems. However, the inherently slow kinetics of reversible oxygen reactions present an urgent demand for the development of efficient oxygen electrocatalysts. Recently, metal‐organic framework (MOF) derivatives have attracted extensive attention in electrocatalysis research due to their unique porous structure, abundant active sites, and tunable structural properties. Especially, the optimization of the electronic structure of active sites in MOF derivatives has been proven as an effective strategy to enhance the catalytic activity. In this review, we provide an overview of the electronic structure optimization strategies for active sites in MOF derivatives as advanced catalysts in various O—O bond activation reactions, including the construction of synergistic effects between multiple sites, the development of heterogeneous interfaces, the utilization of metal support interactions, and the precise modulation of organic ligands surrounding catalytic active sites at the atomic level. Furthermore, this review offers theoretical insights into the oxygen activation and catalytic mechanisms of MOF derivatives, as well as the identification of active sites. Finally, the potential challenges and prospects of MOF derivatives in electrocatalysis are discussed. This review contributes to the understanding and advancement of efficient oxygen electrocatalysis in energy systems. [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]

[Display omitted] Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are essential for the development of excellent bifunctional electrocatalysts, which are key functions in clean energy production. The emphasis of this study lies in the rapid design and investigation of 153 MN 4 –graphene (Gra)/ MXene (M 2 NO) electrocatalysts for ORR/OER catalytic activity using machine learning (ML) and density functional theory (DFT). The DFT results indicated that CoN 4 –Gra/Ti 2 NO had both good ORR (0.37 V) and OER (0.30 V) overpotentials, while TiN 4 –Gra/M 2 NO and MN 4 –Gra/Cr 2 NO had high overpotentials. Our research further indicated orbital spin polarization and d-band centers far from the Fermi energy level, affecting the adsorption energy of oxygen-containing intermediates and thus reducing the catalytic activity. The ML results showed that the gradient boosting regression (GBR) model successfully predicted the overpotentials of the monofunctional catalysts RhN 4 –Gra/Ti 2 NO (ORR, 0.39 V) and RuN 4 –Gra/W 2 NO (OER, 0.45 V) as well as the overpotentials of the bifunctional catalyst RuN 4 –Gra/W 2 NO (ORR, 0.39 V; OER, 0.45 V). The symbolic regression (SR) algorithm was used to construct the overpotential descriptors without environmental variable features to accelerate the catalyst screening and shorten the trial-and-error costs from the source, providing a reliable theoretical basis for the experimental synthesis of MXene heterostructures. [ABSTRACT FROM AUTHOR]

In this study, Co/Ni‐NC catalyst with hetero‐diatomic Co/Ni active sites dispersed on nitrogen‐doped carbon matrix is synthesized via the controlled pyrolysis of ZIF‐8 containing Co2+ and Ni2+ compounds. Experimental characterizations and theoretical calculations reveal that Co and Ni are atomically and uniformly dispersed in pairs of CoN4‐NiN4 with an intersite distance ≈0.41 nm, and there is long‐range d–d coupling between Co and Ni with more electron delocalization for higher bifunctional activity. Besides, the in situ grown carbon nanotubes at the edges of the catalyst particles allow high electronic conductivity for electrocatalysis process. Electrochemical evaluations demonstrate the superior ORR and OER bifunctionality of Co/Ni‐NC catalyst with a narrow potential gap of only 0.691 V and long‐term durability, significantly prevailing over the single‐atom Co‐NC and Ni‐NC catalysts and the benchmark Pt/C and RuO2 catalysts. Co/Ni‐NC catalyzed Zn–air batteries achieve a high specific capacity of 771 mAh g−1 and a long continuous operation period up to 340 h with a small voltage gap of ≈0.65 V, also much superior to Pt/C‐RuO2. [ABSTRACT FROM AUTHOR]

[Display omitted] The zinc-air battery (ZAB) performance and stability strongly depend on the structure of bifunctional electrocatalyst for oxygen reduction/evolution reaction (ORR/OER). In this work, we combine the tip and heterogeneous effects to construct cobalt/cobalt oxide heterostructure nanoarrays (Co/CoO-NAs). Due to the formed heterostructure, more oxygen vacancies are found for Co/CoO-NAs resulting in a 1.4-fold higher ORR intrinsic activity than commercial carbon supported platinum electrocatalyst (Pt/C) at 0.8 V versus reversible hydrogen electrode (vs. RHE). Moreover, a fast surface reconstruction is observed for Co/CoO-NAs during OER catalysis evidenced by in-situ electrochemical impedance spectroscopy and Raman tests. In addition, the tip effect efficiently lowers the mass transfer resistance triggering a low overpotential of 347 mV at 200 mA cm−2 for Co/CoO-NAs. The strong electronic interplay between cobalt (Co) and cobalt oxide (CoO) contributes to a stable battery performance during 1200 h galvanostatic charge–discharge test at 5 mA cm−2. This work offers a new avenue to construct high-performance and stable oxygen electrocatalyst for rechargeable ZAB. [ABSTRACT FROM AUTHOR]

A Fe-Co dual-metal co-doped N containing the carbon composite (FeCo-HNC) was prepared by adjusting the ratio of iron to cobalt as well as the pyrolysis temperature with the assistance of functionalized silica template. Fe1Co-HNC, which was formed with 1D carbon nanotubes and 2D carbon nanosheets including a rich mesoporous structure, exhibited outstanding oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalytic activities. The ORR half-wave potential is 0.86 V (vs. reversible hydrogen electrode, RHE), and the OER overpotential is 0.76 V at 10 mA cm−2 with the Fe1Co-HNC catalyst. It also displayed superior performance in zinc–air batteries. This method provides a promising strategy for the fabrication of efficient transition metal-based carbon catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • N -doped carbon nanotube confined CoFe nanoparticles were synthesized using solvothermal and high-temperature calcination methods. • The synergistic effect between CoFe nanoparticles and N -doped carbon nanotubes showed excellent electrocatalytic activity for OER/ORR. • Rechargeable zinc-air battery exhibited high power density, excellent specific capacity and good stability. • This work provides an approach for establishing low-cost and highly active multifunctional electrocatalysts of non-precious metal. Building efficient and stable bifunctional electrocatalysts toward oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is crucial for the advancement of rechargeable zinc-air batteries (ZABs). Here, a convenient in situ strategy is reported to controllably encapsulate CoFe alloy nanoparticles within N -doped carbon nanotubes (CoFe@NCNT). The abundant Co(Fe)-N x active sites and the synergistic interaction between CoFe alloys and carbon nanotubes facilitate mass transfer and interfacial charge transfer, resulting in excellent dual functional electrocatalytic activity of OER/ORR with minor potential difference (ΔE = 0.73 V). Thus, the corresponding rechargeable ZAB displays high power density (194 mW cm−2), excellent specific capacity (795 mAh g Zn -1), and favorable stability (900 cycles@5 mA cm−2). This work provides an approach for establishing low-cost bultifunctional electrocatalysts with excellent performance of non-noble metal nanoalloys. [ABSTRACT FROM AUTHOR]

Li-O2 batteries are considered a highly promising energy storage solution. However, their practical implementation is hindered by the sluggish kinetics of the oxygen reduction (ORR) and oxygen evolution (OER) reactions at cathodes during discharging and charging, respectively. In this work, we investigated the catalytic performance of Wn+1Cn and Wn+1CnO2 MXenes (n = 1, 2, and 3) as cathodes for Li-O2 batteries using first principles calculations. Both Wn+1Cn and Wn+1CnO2 MXenes show high conductivity, and their conductivity is further enhanced with increasing atomic layers, as reflected by the elevated density of states at the Fermi level. The oxygen functionalization can change the electronic properties of WC MXenes from the electrophilic W surface of Wn+1Cn to the nucleophilic O surface of Wn+1CnO2, which is beneficial for the activation of the Li-O bond, and thus promotes the Li+ deintercalation during the charge–discharge process. On both Wn+1Cn and Wn+1CnO2, the rate-determining step (RDS) of ORR is the formation of the (Li2O)2* product, while the RDS of OER is the LiO2* decomposition. The overpotentials of ORR and OER are positively linearly correlated with the adsorption energy of the RDS LixO2* intermediates. By lowering the energy band center, the oxygen functionalization and increasing atomic layers can effectively reduce the adsorption strength of the LixO2* intermediates, thereby reducing the ORR and OER overpotentials. The W4C3O2 MXene shows immense potential as a cathode catalyst for Li-O2 batteries due to its outstanding conductivity and super-low ORR, OER, and total overpotentials (0.25, 0.38, and 0.63 V). [ABSTRACT FROM AUTHOR]

[Display omitted] Exploring highly active electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) has become a growing interest in recent years. Herein, an efficient pathway for designing MXene-based ORR/OER catalysts is proposed. It involves introducing non-noble metals into Vo (vacancy site), H 1 and H 2 (the hollow sites on top of C and the metal atom, respectively) sites on M 2 CO 2 surfaces, named TM-V O /H 1 /H 2 -M 2 CO 2 (TM = Fe, Co, Ni, M = V, Nb, Ta). Among these recombination catalysts, Co-H 1 -V 2 CO 2 and Ni-H 1 -V 2 CO 2 exhibit the most promising ORR catalytic activities, with low overpotential values of 0.35 and 0.37 V, respectively. Similarly, Fe-H 1 -V 2 CO 2 , Co-V O -Nb 2 CO 2 , and Ni-H 2 -Nb 2 CO 2 possess low OER overpotential values of 0.29, 0.39, and 0.44 V, respectively, suggesting they have enormous potential as effective catalysts for OER. Notably, Co-H 2 -Ta 2 CO 2 possesses the lowest potential gap value of 0.53 V, demonstrating it has an extraordinary bifunctional catalytic activity. The excellent catalytic performance of these recombination catalysts can be elucidated through an electronic structure analysis, which primarily relies on the electron-donating capacity and synergistic effects between transition metals and sub-metals. These results provide theoretical guidance for designing new ORR and OER catalysts using 2D MXene materials. [ABSTRACT FROM AUTHOR]

Bimetallic phosphides are considered as promising electrocatalysts for zinc–air batteries toward oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). To address the semi‐conductor inherent low electronic conductivity and catalytic activity, a polymetal‐chelated strategy is employed to in situ fabricate bimetallic nanophosphides within carbon matrix anchoring by chemical bonding. The employment of biomolecule polydopamine (PDA) efficiently anchors various transition metal ions due to its strong chelating capability via inherent functional groups. Furthermore, the chelation of multi‐metal ion is proved to promote the formation of graphitic nitrogen. The bimetallic FexCoyP phosphides nanoparticles are intimately encapsulated in carbon matrix through in situ carbonization and phosphatization processes. When utilized in Zinc–air batteries, Fe0.20Co0.80P anchored within N, P co‐doped sub‐microsphere (Fe0.20Co0.80P /PNC) exhibit a maximum power density of 167 mW cm−2 and cycle life up to 270 cycles, with a round‐trip voltage of 0.955 V. The mechanisms for catalytic activity passivation are ascribed to the etching of nitrogen and oxidation of phosphorus in carbon matrix, as well as the oxidation of the surface phosphide on the sub‐microspheres. This study presents a promising candidate for advancing the further development of energy conversation catalysis. [ABSTRACT FROM AUTHOR]

Reversible proton‐conducting solid oxide cells (R‐PSOCs) are considered to be one of the most promising devices for efficient power generation and hydrogen production. However, the requirement of high catalytic activity for fast oxygen reduction/evolution reaction (ORR/OER) and durability under high steam concentration of air electrode materials remains the major challenge for the practical application of R‐PSOCs. Here, a series of cobalt‐free Ruddlesden–Popper perovskite of Nd0.8Sr1.2Ni1‐xFexO4±δ are reported with mixed conductivity for enhanced ORR/OER kinetics. The R‐PSOCs with an optimal Nd0.8Sr1.2Ni0.7Fe0.3O4±δ air electrode show a high peak power density of 1.28 W cm−2 in the fuel cell mode and a promising current density of 3.24 A cm−2 at 1.3 V in the electrolysis cell mode at 700 °C. In addition, the R‐PSOCs show favorable stability under the fuel cell, electrolysis, and reversible modes for hundreds of hours. This work demonstrates that the Ruddlesden–Popper materials can be utilized as suitable air electrodes for R‐PSOCs. [ABSTRACT FROM AUTHOR]

The development of efficient, inexpensive, and stable bifunctional non-noble metal catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is of practical significance for the large-scale application of zinc-air batteries. Here, a novel bifunctional Co-based nano-catalyst (Co@C x N y C) is fabricated by complexation-reduction and high-temperature pyrolysis method. Co nanoparticles were loaded in nitrogen-doped hollow irregular carbon nanotubes derived from natural fibers and carbon quantum dots. Remarkably, the unique hollow structure and the Co-N x active site make the screened Co@C 1 N 3 C have efficient ORR&OER catalytic performance. Co@C 1 N 3 C with onset potential (0.90 V) and half-wave potential (0.84 V) exhibited an efficient 4e− transfer path and favorable stability and methanol tolerance. Moreover, the overpotential of Co@C 1 N 3 C needed to achieve 100 mA cm−2 is 625 mV, which is 31 mV better than that of RuO 2. In conclusion, this work not only provides deep insights into the catalytic activity of Co@C x N y C nanocomposite as ORR&OER bifunctional electrocatalysts but also guides the growth of Co-based bifunctional catalysts. • A strategy of combining biomass carbon and carbon quantum dots for fabrication of CoC 1 N 3 C electrocatalyst for ORR and OER. • Hollow N-doped nanotube structure of CoC 1 N 3 C exhibits a high specific surface area. • CoC 1 N 3 C catalyst exhibited excellent bifunctional ORR and OER activity in alkaline media. [ABSTRACT FROM AUTHOR]

Obstacles in the pathway of sustainable energy production basically inspire the researchers to fabricate efficient and stable multifunctional electrocatalysts to speed-up the sluggish kinetics of oxygen reduction reaction (ORR), along with oxygen and hydrogen evolution reactions (OER and HER). For that, we developed a high performing electrocatalyst for ORR, OER, and HER via uniform dispersion of ruthenium nanoparticles on a nitrogen-phosphorous-doped ultrathin carbon matrix (Ru@N–P–C) via pyrolysis. Doped intrinsic heteroatoms (N and P) allowed for the co-existence of graphitic lattice carbons along with amorphous carbon, which aided in the uniform distribution of Ru NPs over the carbon matrix, thereby, facilitating the efficient electron transfer, forming synergistic effect, and suppressing agglomeration of Ru NPs. The constructed Ru@N–P–C heterostructure, prepared at 800 °C, displayed low overpotentials of 45 mV for HER and 327 mV for OER at the current density of 10 mA/cm2, with a Tafel slope value of 115 and 66 mV/dec in alkaline medium, respectively. Furthermore, as-constructed Ru@N–P–C exhibited similar ORR activities to the standard 20% Pt/C catalyst. Besides, Ru@N–P–C heterostructure shows excellent stability during all the ORR, OER, and HER processes, which further suggest its practical applications. Thus, this research paves the way for creating cutting-edge electrocatalysts for energy-related electrocatalysis. • Electrocatalyst (Ru@N–P–C) nanosheets were assembled with Ru particles, followed by pyrolysis. • The fabricated electrode acts as a novel trifunctional catalyst for ORR, OER, and HER in alkaline solution. • The assembled catalyst showed superior open-circuit potential, peak power density, and stability. • Good catalytic activity are primarily attributed to distinct morphology, sufficient graphitization degree, and synergistic effects. [ABSTRACT FROM AUTHOR]

For the advancement of electrochemical energy conversion and storage technologies, bifunctional electrocatalysts are crucial for efficiently driving both the oxygen evolution (OER) and reduction reactions (ORR). Cobalt‐based spinel oxides are a class of promising bifunctional electrocatalysts. However their low electrical conductivity and stability may hinder further improvement. A novel composite material composed of NiCo2O4 nanoparticles integrated with emerging two dimensional MXene nanosheets (NiCo2O4/MXene) was developed. The successful integration of NiCo2O4 with MXene brings about a number of attractive structural features. This includes synergistic effects between NiCo2O4 and MXene, highly accessible surface areas, complete exposure of numerous active sites, and excellent electronic conductivity, all of which collectively contribute to the desirability of composite material for OER and ORR. The synthesized NiCo2O4/MXene composite showed extraordinary OER electrocatalytic activity with a lower overpotential of 360 mV at a current density of 10 mA/cm2, and a small Tafel slope of 64 mV/dec compared to NiCo2O4, MXene and NiCo2O4+MXene (physically mixed). Additionally, NiCo2O4/MXene displays an ORR limiting current density of −4 mA/cm2 and exhibited highest onset potential and half wave potential of 0.92 V and 0.72 V vs. RHE, respectively, for the ORR in alkaline media compared to NiCo2O4, MXene and NiCo2O4+MXene (physically mixed). [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) are crystalline organic porous polymers that can be precisely integrated by building blocks to achieve pre‐designed composition, components, and functions, making them a powerful platform for the development of molecular devices in the field of electrocatalysis. The precise control of channel/dopant positions and highly ordered network structures of COFs provide an ideal material system for the applications of advanced electrocatalysis. In this paper, the topological structure design and synthesis methods of COFs are reviewed in detail, and their design principles are deeply analyzed. In addition, the applications of COFs and their derivatives in the field of electrocatalysis are systematically summarized and the optimization strategies are proposed. Finally, the application prospects of COFs and their derivatives in electrocatalysis and the challenges that may be encountered in the future are prospected, providing helpful guidance for future research. [ABSTRACT FROM AUTHOR]

Challenges in rational designing dual‐atom catalysts (DACs) give a strong motivation to construct coordination‐activity correlations. Here, thorough coordination‐activity correlations of DACs based on how the changes in coordination shells (CSs) of dual‐atom Cu,Co centers influence their electrocatalytic activity in oxygen reduction reaction(ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) is constructed. First, Cu,Co DACs with different CSs modifications are fabricated by using a controlled "precursors‐preselection" approach. Three DACs with unique coordination environments are characterized as secondary S atoms that directly bond to Cu,Co‐N6 in lower CSs, indirectly bond in neighboring CSs, and are doped in higher CSs, respectively. Then, experimentally and theoretically, a coordination correlation resembling a planet‐satellite system, where satellite coordinated atoms (heteroatom N, S) surround Cu‐Co dual‐atom entity in various orbitals CSs. By evaluating electrocatalytic activity indicators, differences are identified in electronic structure and electrocatalytic performance of Cu and Co centers in ORR, OER, and HER. Interestingly, initial CSs modifications for DACs may not always be advantageous for electrocatalysis. This work offers valuable insight for designing DACs for diverse applications. [ABSTRACT FROM AUTHOR]

The emergence of non‐precious metal‐based robust and economic bifunctional oxygen electrocatalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is crucial for the rational design of commercial rechargeable Zn‐air batteries (RZAB) with safe energy conversion and storage systems. Herein, a facile strategy to fabricate a cost‐efficient, bifunctional oxygen electrocatalyst Fe3C/Fe decorated N doped carbon (FeC‐700, the catalyst prepared at carbinization temperature of 700 °C) with a unique structure has been developed by carbonization of a single source precursor, tetrabutylammonium tetrachloroferrate(III) complex. The ORR and OER activity revealed excellent performance (ΔE=0.77 V) of the FeC‐700 electrocatalyst, comparable to commercial Pt/C and RuO2, respectively. The designed temperature‐tuneable structure provided sufficiently accessible active sites for the continuous passage of electrons by shortening the mass transfer pathway, leading to extremely durable electrocatalysts with high ECSA and amazing charge transfer performance. Remarkably, the assembled Zn‐air batteries with the FeC‐700 catalyst as the bifunctional air electrode delivers gratifying charging‐discharging ability with an impressive power density of 134 mW cm−2 with a long lifespan, demonstrating prodigious possibilities for practical application. [ABSTRACT FROM AUTHOR]

Highly active and durable air electrodes are crucial for the commercialization of reversible proton ceramic electrochemical cells (R‐PCECs) for large‐scale energy conversion and storage that may be developed by introducing oxygen ion, electron, and proton triple conducting species into the electrode materials. Here, a new triple conducting nanocomposite is reported as a promising air electrode of R‐PCECs, which consists of a dominated cubic perovskite Ba0.5Sr0.5Co0.72Fe0.18Er0.09O3‐δ and a minor Er2O3 phase, developed by Er doping induced phase separation of Ba0.5Sr0.5(Co0.8Fe0.2)0.9Er0.1O3‐δ precursor. The Er doping stimulates the primary perovskite phase to possess excellent hydration capability and oxygen activation ability, while the Er2O3 minor phase, as a high‐speed proton transport channel, further cooperates with the perovskite main phase to boost the kinetic rate of the electrode for both oxygen reduction and evolution reactions (ORR/OER). As a result, the corresponding R‐PCEC achieves extraordinary electrochemical performance in fuel cell (1.327 W cm−2 at 650 °C) and electrolysis modes (−2.227 A cm−2 at 1.3 V and 650 °C), which exceed the similar cell with a typical Ba0.5Sr0.5Co0.8Fe0.2O3‐δ single‐phase perovskite air electrode by 82.3% and 122.7%, respectively. This Er‐doping induced phase separation provides a new way for new bifunctional electrodes development. [ABSTRACT FROM AUTHOR]

During the past few years, single‐atom catalysts (SACs) have attracted considerable attention in electrolysis due to their outstanding catalytic performance and efficient atomic utilization. SACs exhibit a simple structure, high catalytic activity, consistent scaling relationships for single sites, and low metal content but their practical applications are still limited. Dual single‐atom catalysts (DACs), which feature excellent selectivity, high atomic utilization efficiency, and remarkable stability, are emerging as new frontiers in heterogeneous electrocatalysis. They increase catalytic activity by promoting synergistic effects between metal‐active sites. In this paper, we present a comprehensive overview of the latest developments in dual‐atom catalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). In addition, we explore the differences between homonuclear and heteronuclear configurations, the emergence of single/dual‐site metal catalysts, and the methods currently used for their synthesis. Lastly, this review discusses several perspectives for advancing the development of dual‐atom catalysts for OER and ORR electrocatalysis. [ABSTRACT FROM AUTHOR]

The rational design and exploration of efficient, low‐cost and durable bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are key to the development of rechargeable metal−air batteries. Here, we report a novel approach to in‐situ synthesize Fe0.64Ni0.36 nanoalloy encapsulated in nitrogen‐doped porous carbon nanotubes (FeNi@N−CNTs) as bifunctional electrocatalyst derived from Ni‐modified Prussian blue, on which the ORR/OER can be promoted by the N−CNTs surface due to the electron modulation caused by electron transfer from the inner FeNi nanoalloy to the N−CNTs surface. The abundant wide‐size range of mesopores in N−CNTs can offer rapid mass transport channels to facilitate the catalytic reactions. In addition, the encapsulation structure endows the outer N−CNTs acting as a "shield" to prevent the inner FeNi nanoalloy from corrosion in strong basic medium. Thanks to the synergistic effect between the N−CNTs and FeNi nanoalloy, the obtained FeNi@N−CNTs exhibits excellent bifunctional oxygen catalytic activity together with outstanding performance and cycling durability in rechargeable Zn−air battery. This work will open new avenues for the development of advanced bifunctional electrocatalysts for other metal−air batteries. [ABSTRACT FROM AUTHOR]

Molecular electrocatalysis requires the immobilization of molecular catalysts on electrode materials for practical uses. Direct adsorption of catalyst molecules on electrode materials is simple, but grafting molecules through chemical bonds can significantly improve electrocatalytic efficiency and durability. However, designing and synthesizing catalyst molecules to simultaneously improve catalytic activities and realize easy grafting on electrodes is challenging. The study herein reports on a one‐pot strategy to graft Co corroles on pyridine‐modified carbon nanotubes (CNTs) for oxygen electrocatalysis. By modifying CNTs with pyridines, the resulting pyridine‐modified CNTs can function as platforms to grab in situ generated Co corroles through the axial pyridine ligation on Co. Such an immobilization strategy combines three effects for the regulation of electrocatalysis, including the axial ligand effect, the electron transfer effect, and the chemical bond effect. The resulting hybrid materials show high efficiency for oxygen electrocatalysis, and the Zn–air battery assembled using these materials displays comparable performance as the Pt/Ir‐based battery. Moreover, the electrocatalytic efficiency of these hybrid materials can be systematically tuned by using different pyridines, highlighting the controllable feature of this strategy. Therefore, this work is significant to present a one‐pot three‐in‐one strategy to immobilize catalyst molecules on CNTs for electrocatalysis. [ABSTRACT FROM AUTHOR]

Cable bacteria are multicellular, filamentous bacteria that use internal conductive fibers to transfer electrons over centimeter distances from donors within anoxic sediment layers to oxygen at the surface. We extracted the fibers and used them as free‐standing bio‐based electrodes to investigate their electrocatalytic behavior. The fibers catalyzed the reversible interconversion of oxygen and water, and an electric current was running through the fibers even when the potential difference was generated solely by a gradient of oxygen concentration. Oxygen reduction as well as oxygen evolution were confirmed by optical measurements. Within living cable bacteria, oxygen reduction by direct electrocatalysis on the fibers and not by membrane‐bound proteins readily explains exceptionally high cell‐specific oxygen consumption rates observed in the oxic zone, while electrocatalytic water oxidation may provide oxygen to cells in the anoxic zone. [ABSTRACT FROM AUTHOR]

Electrochemical water splitting by use of suitable electrocatalysts is an important process to establish water as sustainable energy material. Similarly, the Oxygen reduction reaction is an important step involved in fuel cells. Hence, suitable catalysts are required for low-cost and high-performance activity towards both processes. In this work, we synthesized Cobalt-free Lanthanum-based double Perovskites oxides La 0.5 Sr 0.5 Fe 0.8 Cu 0.2 O 3 and La 0.5 Sr 0.5 Fe 0.8 Zn 0.2 O 3 by sol-gel method followed by calcination at different temperatures (800 °C, 900 °C and 1000 °C). Prepared double Perovskite oxide materials exhibit bifunctional catalytic activity towards both oxygen evolution reaction and oxygen reduction reaction. Calcination temperatures and composition have a significant impact on catalytic performance because of morphological control along with tuning of surface composition. Powder X-ray diffraction study has been performed to characterize the materials and phases/composition of materials was further analyzed by Rietveld refinement. The morphology of the best catalyst was analyzed by SEM, EDS mapping and XPS analysis. The catalytic performances of the catalysts were examined using electrochemical methods such as linear sweep voltammetry, cyclic voltammetry and electrochemical impedance spectroscopy in 0.1 M KOH solution. Preparation of noble-metal/cobalt-free catalysts is important finding towards establishing water as potential source for hydrogen production. • Cobalt-free catalyst of Lanthanum based double perovskites oxides were synthesized and characterized. • Characterization of prepared catalysts was done by SEM, PXRD and XPS analysis. • The atomic and electronic structures of these compounds can be controlled due to compositional differences, which results in high conductivity. • Prepared catalysts were used as bifunctional electrocatalysts in OER and ORR. • Prepared catalysts exhibit bifunctional catalytic activity towards both OER and ORR in an alkaline media. [ABSTRACT FROM AUTHOR]

3D nanostructured Prussian blue analogues (PBA) are promising candidates in the family of metal-organic frameworks (MOFs) for applications as bifunctional electrocatalysts due to their open framework structures, high specific surface areas and variable metal active sites. Due to their facile synthesis approach and unique framework structures, these nanostructures can be easily transformed into different structures/materials having different compositions. Herein, we have synthesized Ni–Fe Prussian blue analogue nanocubes (NiFe-PBA-NC) via a simple precipitation method and converted them into Ni–Fe Prussian blue analogue nanocages (NiFe-PBA-NG) and porous mixed metal oxide (NiFe-oxide). For the conversion of nanocubes to nanocages a very controlled etching process is carried out by using an ammonia solution while for the formation of porous mixed metal oxide, nanocubes are annealed in the presence of air. The transformation of nanocubes to nanocages and mixed metal-oxide is thoroughly characterized by various spectroscopic and microscopic techniques and employed as a bifunctional electrocatalyst for oxygen evolution and oxygen reduction reactions (OER and ORR, respectively) in which NiFe-oxide proved to be the best bifunctional catalyst. This thorough and systematic study reveals the fundamentals of the structure-property co-relation towards engineering novel bifunctional electrocatalysts. • Synthesis of NiFe-PBA-NC nanocubes and their conversion into nanocages and NiFe-oxide. • The prepared catalysts were characterized by XRD, FT-IR, XPS, TGA and FE-SEM techniques. • Investigation of role of morphology on oxygen evolution reaction (OER) and oxygen reduction reactions (ORR). • The Prepared catalysts were employed as bifunctional catalysts for OER and ORR in basic medium. • NiFe-oxide exhibit enhanced catalytic activity due to high electrochemical surface area. [ABSTRACT FROM AUTHOR]

[Display omitted] Exploiting clean, highly efficient energy storage and conversion device like Zn-air battery is of significance for alleviating the energy and environmental crises of this society. Metal organic coordination polymers/frameworks have been regarded as ideal templates to synthesize non-noble metal catalysts for a long time. However, the high density of metal nodes inevitably leads to the heavy aggregation of metal nanoparticles during thermolysis transformation process, which greatly hinders the maximizing of electrochemical performances. Herein, covalent organic framework (COF) has been employed to anchor the quantificational Fe ions (COF-Fe) and then confined into the macropores of g-C 3 N 4 to improve the dispersion of metal active sites and avoid severe aggregation during high temperature pyrolysis. After calcination, the metal nanoparticles highly dispersed Fe-CFN catalysts can be obtained. The optimal Fe-CFN-800 catalysts exhibit excellent ORR and OER performances with the potential difference between ORR and OER of merely 0.723 V. Moreover, experimental way and DFT theoretical calculations are also employed to disclose the reaction mechanism. Finally, the all-solid-state and aqueous Zn-air batteries assembled with the optimized Fe-CFN-800 as cathode present excellent performances with high peak power density, flexible rate performance, strong discharge stability and long-term charge–discharge cycling performance. [ABSTRACT FROM AUTHOR]

A porous and hollow nanobox catalyst consisting of a nitrogen-doped carbon framework embedded with FeCo alloy and MnO components was successfully prepared, taking into consideration the effects of the intrinsic electric field and hollow/porous support carriers for electrocatalyst design. [Display omitted] • A porous carbon nanobox embedded with FeCo alloy and MnO nanoparticle was prepared. • A built-in electric field expedites charge transfer and enhances ORR-OER activity. • The porous carbon nanobox contributes to rapid mass/charge transport. The advancement of bifunctional oxygen catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is imperative yet challenging for the optimization of Zn-air batteries. In this study, we reported the successful incorporation of a novel Mott-Schottky catalytic site within a MnO-FeCo heterojunction into an N -doping carbon nanobox, taking into consideration the effects of the intrinsic electric field and hollow/porous support carriers for electrocatalyst design. As expected, the resulting heterogeneous catalyst exhibited an encouraging half-wave potential of 0.88 V and an impressive limiting-current density of 5.62 mA/cm2 for the ORR, as well as a minimal overpotential of 271 mV at 10 mA/cm2 for the OER, both in alkaline conditions. Furthermore, the Zn-air battery constructed with the heterojunction nanobox product displayed a decent potential gap of 0.621 V, an outstanding power density of 253 mW/cm2, a considerable specific capacity of 761 mAh/g Zn , and exceptional stability, with up to 336 h of cycling charging and discharging operation. Consequently, this method of modulating the catalyst's surface charge distribution through an internal electric field at the interface and facilitating mass transport offers a novel avenue for the development of robust bifunctional oxygen catalysts. [ABSTRACT FROM AUTHOR]

Rational design of heterogeneous catalysts with unique structural and electronic properties is one of the major challenges to improve the activity toward the reversible oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), the bottleneck in the construction of air cathodes for the next‐generation flexible zinc–air batteries (ZABs). Herein, density functional theory calculations are combined with experimental attempts to exploit the roles of the electronic effects at the interface between Co4N nanoparticles and nitrogen‐doped carbon nanowalls/diamond (d‐NCNWs/D) toward the ORR and OER activities. The vacancy defect‐induced Co‐pyridinic N─C bond optimizes the electronic structure of Co 3d orbitals and balances the adsorption energies of intermediates along the reaction pathways. Consequently, as‐synthesized Co4N@d‐NCNWs/D composites exhibit superior bifunctional oxygen catalytic activity. The overpotential of the OER is as low as 340 mV at 10 mA cm−2 and the high half‐wave potential reaches 0.83 V for the ORR. As a binder‐free and flexible ZABs cathode, this composite exhibits an open circuit voltage of 1.41 V and excellent bendable stability, proving its promising potential for the assembly of wearable devices. This work offers theoretical evidence and a controllable strategy to design high‐performance ZAB cathodes for their application in smart electronic devices. [ABSTRACT FROM AUTHOR]

[Display omitted] Herein, a soft-template strategy involving the cationic surfactants has been successfully applied to size-controlled synthesis of hierarchical porous Fe-N/C for the first time. Specifically, a small amount of Fe and cationic surfactants can be uniformly doped into the zinc-based zeolite imidazole framework (ZIF-8) crystal particles and the cationic surfactants play a critical role in the formation of hierarchically porous Fe-ZIF-8@surfactant precursors. When the Fe-ZIF-8@surfactant is subsequently pyrolyzed, atomically dispersed Fe-N x coordination structures can be in-situ converted to Fe-N/C, while the cationic surfactants decompose to form a carbon matrix to encapsulate the active sites, thereby preventing the aggregation of nanoparticles to a certain extent. As a result, the combined Fe nanocrystals and atomically dispersed Fe-N x in the graphitic carbon matrix generate a synergistic effect to boost the electrocatalytic behaviors with a more positive half-wave potential (0.92 V) for oxygen reduction reaction (ORR) and a lower overpotential (420 mV at 10 mA cm−2) for oxygen evolution reaction (OER). As a proof of concept, the Fe-N/C@TTAB based zinc-air batteries (ZABs) present an outstanding peak power density (107.9 mW cm−2) and a superior specific capacity (706.3 mAh g−1) with robust cycling stability over 900 cycles for 150 h, which are better than the commercial Pt/C + IrO 2 based ZABs. [ABSTRACT FROM AUTHOR]

Multifunctional electrocatalysts are desirable for overall water splitting and zinc-air batteries. In this work, N, S co-doped carbon nanotubes (CNT-NS) with a plentiful of defects were obtained through a novel molecular-level codoped and lattice defect construction method. Thiamine hydrochloride and thiocarbamide were adopted as new precursors in situ doping N and S into multi-walled CNTs surfaces, and lattice defects were constructed by in situ chemical etching using ammonium chloride and ammonium bicarbonate. These surface defects and N,S biatom co-doping synergistic effects can accumulate the CNT-NS to exhibit the superior behavior for electrocatalysis of water splitting and zinc-air batteries. The overpotential for overall water splitting was 1.61 V and the specific capacity for zinc-air batteries was 781 mA h g−1, which was superior to previous works. According to the Operando Raman spectroscopy measurements, the S atoms can serve as the intrinsic catalytic sites for HER and OER, and the defective CNT structures could enhance the catalytic kinetics by the electron-transfer process. Further, density functional theory (DFT) results also indicated the contribution of binary atoms co-doping for low ΔG H∗ values. Therefore, this work provides the valuable reference for rational design/construction for metal-free catalysts of overall water splitting. [Display omitted] • CNT-550-NS were successfully prepared through a molecular-level codoped and lattice defect construction method. • CNT-550-NS exhibited a plentiful of defective structure on the carbon nanotubes surfaces. • CNT-550-NS possessed a high contents of heteroatoms of N and S. • CNT-550-NS executed a remarkable performance for HER, OER and ORR. [ABSTRACT FROM AUTHOR]

In light of the depletion of conventional energy sources, it is imperative to conduct research and development on sustainable alternative energy sources. Currently, electrochemical energy storage and conversion technologies such as fuel cells and metal-air batteries rely heavily on precious metal catalysts like Pt/C and IrO2, which hinders their sustainable commercial development. Therefore, researchers have devoted significant attention to non-precious metal-based catalysts that exhibit high efficiency, low cost, and environmental friendliness. Among them, perovskite oxides possess low-cost and abundant reserves, as well as flexible oxidation valence states and a multi-defect surface. Due to their advantageous structural characteristics and easily adjustable physicochemical properties, extensive research has been conducted on perovskite-based oxides. However, these materials also exhibit drawbacks such as poor intrinsic activity, limited specific surface area, and relatively low apparent catalytic activity compared to precious metal catalysts. To address these limitations, current research is focused on enhancing the physicochemical properties of perovskite-based oxides. The catalytic activity and stability of perovskite-based oxides in Oxygen Reduction Reaction/Oxygen Evolution Reaction (ORR/OER) can be enhanced using crystallographic structure tuning, cationic regulation, anionic regulation, and nano-processing. Furthermore, extensive research has been conducted on the composite processing of perovskite oxides with other materials, which has demonstrated enhanced catalytic performance. Based on these different ORR/OER modification strategies, the future challenges of perovskite-based bifunctional oxygen electrocatalysts are discussed alongside their development prospects. [ABSTRACT FROM AUTHOR]

Rechargeable Zn–air batteries (ZABs) can play a significant role in the transition to a cleaner and more sustainable energy system due to their high theoretical energy density, high cell voltage, and environmental friendliness. ZAB's air cathode is the principal determinant in predicting the battery's overall performance, as it is responsible for catalyzing the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) during the discharging and charging process, respectively. In this work, a detailed optimization study of the architecture of the air cathode was carried out using the benchmark bifunctional oxygen electrocatalyst (Pt/C-RuO2). The air cathode composition and architecture were optimized regarding the choice of the commercial gas diffusion layer (GDL), the effect of hot pressing the catalyst layer (CL), and the optimum pore size of the current collector. The best cathode from this study shows a maximum power density (PDmax) of 167 mW/cm2, with a round trip efficiency and a voltage gap (Egap) of 59.8% and 0.78 V, respectively, indicating the air cathodes preparation approach proposed in this work as a promising strategy for the improvement of the overall performance of ZABs. [ABSTRACT FROM AUTHOR]

Expanding the application scenarios of wood-derived biochar guided by the conversion of traditional energy to new energy shows great promise as a field. As thrilling energy conversion apparatus, zinc-air batteries (ZABs) require cathode catalysts with high oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities and stability. Herein, two-dimensional nickel-iron hydroxide nanosheets were creatively assembled in N-doped wood-derived biochar (NiFe-LDH@NC) by an in-situ growth method. The categorized porous organization in wood-derived biochar facilitates the rapid seepage of electrolytes and rapid diffusion of reaction gases. The unique interfacial structure of biochar and NiFe-LDH accelerates electron transfer during oxygen electrocatalysis, and endows NiFe-LDH@NC with first-class catalytic activity and durability for ORR and OER. The ZAB derived from NiFe-LDH@NC showed elevated discharge productivity and cycle endurance, making it promising for viable applications. This work provided a convenient way for the conversion of wood-derived biochar to high-value added electrocatalysts. Article Highlights: Heteroatom-doped wood-derived biochar was assisted in situ growth of NiFe-LDH. NiFe-LDH@NC exhibited excellent bifunctional activity and stability toward ORR/OER. The ZAB achieved a peak power density of 123 mW cm−2 and a cycling stability of 270 h. [ABSTRACT FROM AUTHOR]

The proper utilization of renewable energy sources has emerged as a major challenge in our pursuit of a sustainable and carbon‐neutral energy landscape. Small molecule activation is a key component for proper utilization of renewable energy resources, where O2/H2O redox couple is reckoned to be a potential game changer. In this regard, electrocatalytic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) have become the prime interest of catalyst designers. Typically, these ORR and OER electrocatalysts are developed distinctly; however, very soon, the requirement of a bidirectional ORR/OER electrocatalyst becomes obvious for practical applicability and rapid energy transduction purposes. A bidirectional catalyst is defined as a catalyst capable of driving a redox reaction in opposing directions. This review has portrayed the development of enzyme structure‐inspired design of molecular bidirectional ORR/OER catalysts. The strategic incorporation of secondary and outer coordination sphere features has significantly enhanced the performance of these catalysts, which can be monitored via the key catalytic parameters. These bifunctional OER/ORR catalysts are vital for metal‐air battery and fuel cell applications and appropriately poised to lay the foundation for an efficient, economical, and eco‐friendly pathway for sustainable energy usage with the rational assembly of energy converting and storage devices. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial electrochemical reactions that play vital roles in energy conversion and storage technologies, such as fuel cells and metal–air batteries. Typically, noble-metal-based catalysts are required to enhance the sluggish kinetics of the ORR and OER, but their high costs restrict their practical commercial applications. Thus, highly active and strong non-noble metal catalysts are essential to address the cost and durability challenge. Based on previous research, carbon-based catalysts may present the best alternatives to these precious metals in the future owing to their affordability, very large surface areas, and superior mechanical and electrical qualities. In particular, carbon aerogels prepared using biomass as the precursors are referred to as biomass-derived carbon aerogels. They have sparked broad attention and demonstrated remarkable performance in the energy conversion and storage sectors as they are ecologically beneficial, affordable, and have an abundance of precursors. Therefore, this review focuses on various nanostructured materials based on biomass-derived carbon aerogels as ORR/OER catalysts, including metal atoms, metal compounds, and alloys. [ABSTRACT FROM AUTHOR]

Co 4 N@NCNTs with superior ORR and OER activity and stability were prepared by triazole -assisted in-situ pyrolysis of MOF-74/TZ. [Display omitted] • Co 4 N@NCNTs were prepared by triazole -assisted in-situ pyrolysis of MOF-74/TZ. • The possible structure outward contract evolution mechanism of Co 4 N@NCNTs was investigated. • Co 4 N@NCNT-900 showed superior ORR and OER catalytic activity and stability. • A ZAB with Co 4 N@NCNT-900 air cathode delivers higher power density and specific capacity. The design of high-performance oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) dual-functional catalysts is not only important for the further applications of zinc-air batteries (ZABs) but also a major challenge in the field of energy conversion. The cheap 1,2,4-triazole (1,2,4-TZ) can be decomposed easily by heat, making it a high research value in carbon catalysts derived from metal-organic frameworks (MOFs). Here, Co 4 N particles encapsulated at the top of N -doped carbon nanotubes (Co 4 N@NCNTs) were conveniently prepared by 1,2,4-TZ-assisted pyrolysis of Co-MOF-74 for the first time. Owing to the excellent activity of Co 4 N particles and the highly graphitized N -doped carbon nanotubes (NCNTs), Co 4 N@NCNTs obtained at 900 °C (Co 4 N@NCNT-900) exhibited astonishing catalytic performance in both ORR and OER, and high reversible oxygen bifunctional activity (ΔE = 0.685 V). Moreover, Co 4 N@NCNT-900 displayed a larger discharge power density (122 mW cm−2), a better specific capacity (811.8 mAh g−1), and more excellent durability during the ZAB test, implying that Co 4 N@NCNT-900 can act as a bifunctional high active catalyst in ZABs. [ABSTRACT FROM AUTHOR]

Porous cobalt (III) oxide (Co 3 O 4) and mixed cobalt (III) oxide - tin oxide (Co 3 O 4 /SnO 2) were prepared by a novel template-based hydrothermal method resulting in their spherical morphology as confirmed by thorough physico-chemical characterisation. Two oxides were systematically examined as bifunctional electrocatalysts for oxygen reduction (ORR) and evolution (OER) reaction in alkaline media by voltammetry with rotating disk electrode, electrochemical impedance spectroscopy, and chronoamperometry. Low-cost Co 3 O 4 and Co 3 O 4 /SnO 2 electrocatalysts showed excellent ORR performance with low onset and half-wave potential, low Tafel slope, and the number of exchange electrons near 4, comparable to the commercial Pt/C electrocatalyst. Low OER onset potential of 1.52 and 1.57 V was observed for Co 3 O 4 and Co 3 O 4 /SnO 2 , respectively, with low charge transfer resistance under anodic polarization conditions. Finally, to test bifunctional activity and durability of the two electrocatalyst, switch OER/ORR test was carried out. [Display omitted] • Spherical Co 3 O 4 and Co 3 O 4 /SnO 2 were synthesized by the hydrothermal method. • Both electrocatalysts showed excellent ORR performance comparable with Pt/C. • OER at Co 3 O 4 electrocatalyst starts ca. 50 mV earlier than at Co 3 O 4 /SnO 2. • Co 3 O 4 /SnO 2 gave comparable OER current densities to Co 3 O 4. • Co 3 O 4 and Co 3 O 4 /SnO 2 could be promising candidates for metal-air batteries. [ABSTRACT FROM AUTHOR]

The oxygen reduction and evolution reactions are considered the bottleneck in many electrochemical devices, i. e. fuel cells, water electrolyzers, and metal‐air batteries. The continuous focus has been on inventing and exploring cost‐effective and robust electrocatalysts. Few developed non‐precious metal/metal‐free materials, in fact, outperformed state‐of‐the‐art catalysts during the half‐cell study. However, most of these materials show limited activity during the full cell demonstration, restricting their deployment in commercial energy devices. In this direction, transition metal nitrides (TMNs) have emerged as a potential alternative with peculiar electronic properties and the ease of tuning their intrinsic as well as extrinsic properties. High hardness, refractory nature, d‐band modulation ability and comparatively lower energy for the nitride formation are the other motivations to explore their effectiveness in oxygen electrocatalysis. Considering this, the minireview attempts first to present the properties of catalytic interest, followed by the most viable synthesis approaches in nanoengineering of the TMNs. Next, we provide key trends toward catalytic property modulation for oxygen electrocatalysis, the role of TMNs as potential catalytic support, followed by the effect of TMNs′ in situ autoxidation on the performance. Finally, we state the current limitations of TMNs toward oxygen electrocatalysis, followed by our vision for further advancements. [ABSTRACT FROM AUTHOR]

Fe/Co/N co-doped multi-channel interpenetrating three-dimensional graphene catalyst (FeCo–N-3D-HG) with good oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalytic performances is prepared by a facile method, using poly (2,5-benzimidazole) (ABPBI), iron salt, cobalt salt and nanometer CaCO 3 (template). ABPBI forms a complex with iron and cobalt ions and the complex is coated on the surface of CaCO 3. The pyrolysis process is carried out in an Ar gas protection, the template is removed by acid to obtain FeCo–N-3D-HG. The results show that FeCo–N-3D-HG is three-dimensional multi-layered graphene structure with multi-channels. The catalytic performance of ORR (E 1/2 = 0.860 V vs RHE) is better than 20 wt% Pt/C in O 2 saturated 0.1 M KOH electrolyte. The catalyst also shows similar OER performance with the RuO 2 in 1 M KOH solution. The prepared zinc-air battery exhibits outstanding peak power density (261.7 mW cm−2), preeminent specific capacity (760.1 mAh g−1), and good cycle durability (150 h). High nitrogen-containing Fe/Co/N co-doped three-dimensional graphene bifunctional oxygen catalysts is prepared by one-step pyrolysis for zinc air battery. The bimetallic synergistic effect, three-dimensional porous structure of graphene and the high nitrogen content greatly improve the catalytic performance. [Display omitted] • FeCo–N-3D-HG with multistage perforated is prepared by nano CaCO 3. • High N, Fe and Co content is achieved by complex of ABPBI with Fe3+ and Co3+. • The synergistic effect of FeCo–N-3D-HG can enhance the catalytic performance. • The zinc air battery with this catalyst shows high power density and durability. [ABSTRACT FROM AUTHOR]

[Display omitted] A flexible solid rechargeable Zn-air battery for advanced energy conversion and storage has extensive applications in portable electric sources, wildlife rescue and flexible wearable systems. Herein, the CoSe 2 nanoparticles anchored on cobalt-embedded N -doping carbon nanoplates (CoSe 2 /CoNC) is developed as a highly active bifunctional catalyst via pyrolysis and selenization of bimetallic zeolitic imidazolate frameworks containing Zn and Co. The introduction of inactive Zn generates strong electrochemically active surface areas due to the synergistic effect between CoSe2 nanoparticles and CoNC matrix. Further, CoSe2/CoNC exhibits prominent Zn–air battery performance and even outperforms the commercially available noble-metal catalysts. Notably, a high-rate flexible Zn-air battery enabled by an alkaline composite polyacrylic acid-carboxymethyl cellulose electrolyte delivers the open-circuit potential of 1.51 V. The battery offers high wearability and performs very well under various conditions, such as soaking, drilling and sewing. [ABSTRACT FROM AUTHOR]

Multifunctional electrocatalysts play an increasingly crucial role in various practical electrochemical energy conversion devices. Especially, on the air cathode of rechargeable zinc–air batteries (ZABs), oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), requiring efficient bifunctional electrocatalysts, are switched during discharging and charging process. Here, supported by the theoretical computations, a facile strategy for the in situ assembly of NiFe‐MOFs nanosheets on heteroatoms‐doped porous activated carbon spheres is developed. The newly designed electrocatalyst (NP‐ACSs@NiFe‐MOFs) shows excellent performance toward bifunctional oxygen electrocatalysis. Specifically, a remarkable low value of potential gap (ΔE = 0.61 V), which is the difference between the potential to reach an OER current density of 10 mA cm−2 and ORR half‐wave potential, is achieved in 0.1 m KOH. Notably, the aqueous ZAB based on NP‐ACSs@NiFe‐MOFs shows super cycle stability with small voltage gap of only 0.79 V when cycled for 450 h at 10 mA cm−2. Also, the quasi‐solid‐state ZAB indicates excellent flexibility and cycling stability. This study presents a facile strategy for the rational integration of different catalytically active components, and can be extended to prepare other strongly competitive multifunctional electrocatalysts. [ABSTRACT FROM AUTHOR]

Rechargeable zinc-air batteries (RZAB) have gained significant attention as potential energy storage devices due to their high energy density, cost-effectiveness, and to the fact that they are environmentally safe. However, the practical implementation of RZABs has been impeded by challenges such as sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), including poor cyclability. Herein, we report the preparation of cobalt- and nitrogen-doped porous carbon derived from phloroglucinol-formaldehyde polymer networks with 2-methyl imidazole and cobalt phthalocyanine as precursors for nitrogen and cobalt. The CoN-PC-2 catalyst prepared in this study exhibits commendable electrocatalytic activity for both ORR and OER, evidenced by a half-wave potential of 0.81 V and Ej=10 of 1.70 V. Moreover, the catalyst demonstrates outstanding performance in zinc-air batteries, achieving a peak power density of 158 mW cm−2 and displaying excellent stability during charge-discharge cycles. The findings from this study aim to provide valuable insights and guidelines for further research and the development of hierarchical micro-mesoporous carbon materials from polymer networks, facilitating their potential commercialisation and widespread deployment in energy storage applications. [ABSTRACT FROM AUTHOR]

Ce-based materials have been widely used in photocatalysis and other fields because of their rich redox pairs and oxygen vacancies, despite research on the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) remaining scare. However, most pristine cerium-based materials, such as CeO2, are non-conductive materials. Therefore, how to obtain highly conductive and stable OER/ORR electrocatalysts is currently a hot research topic. To overcome these limitations, researchers have proposed a variety of strategies to promote the development of Ce-based electrocatalysts in recent years. This progress report focuses on reviewing new strategies concerning three categories of Ce-based electrocatalysts: metal–organic framework (MOF) derivatives, structure tuning, and polymetallic doping. It also puts forward the main existing problems and future prospects. The content of cerium in the crust is about 0.0046%, which is the highest among the rare earth elements. As a low-cost rare earth material, Ce-based materials have a bright future in the field of electrocatalysis due to replacing precious metal and some transition metals. [ABSTRACT FROM AUTHOR]

Catalysts with FeNC moieties have demonstrated remarkable activity toward oxygen reduction reaction (ORR), but precise synthesis and configuration regulation of FeNC to achieve bi‐functional catalytic sites for ORR and oxygen evolution reaction (OER) remain a great challenge. Herein, a pomegranate‐like catalyst with optimized FeN4 configuration is designed. The unique framework affords a large surface area for sufficient active site exposure and abundant macroporous channels for mass transport. By twisting chemical bonds, the electronic structure of FeN4 is regulated, and the adsorption/desorption of oxygen species is facilitated. Compared to noble metal‐based catalysts (Pt/C+IrO2), the optimized FeNC exhibits impressive onset potential (0.96 V versus reversible hydrogen electrode), larger limiting current density (5.85 mA cm−2), and better long‐term life for ORR, as well as, lower OER overpotential. When integrated into Zn‐air batteries, it demonstrates a respectable peak power density (71.6 mW cm−2) and ideal cycling stability (30 h), exceeding that of commercial Pt/C+IrO2. The exploration offers a guideline for designing advanced bi‐functional electrocatalysts. [ABSTRACT FROM AUTHOR]

Bifunctional oxygen electrocatalysts constructed with the separate active sites of ORR and OER have shown excellent performance in rechargeable zinc-air battery. [Display omitted] High activity, excellent durability, and low-cost oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) bifunctional catalysts are highly required for rechargeable zinc (Zn)-air batteries. Herein, we designed an electrocatalyst by integrating the ORR active species of ferroferric oxide (Fe 3 O 4) and the OER active species of cobaltous oxide (CoO) into the carbon nanoflower. By well regulating and controlling the synthesis parameters, Fe 3 O 4 and CoO nanoparticles were uniformly inserted into the porous carbon nanoflower. This electrocatalyst can reduce the potential gap between the ORR and OER to 0.79 V. The Zn-air battery assembled with it exhibited an open-circuit voltage of 1.457 V, a stable discharge of 98 h, a high specific capacity of 740 mA h g−1, a large power density of 137 mW cm−2, as well as good charge/discharge cycling performance, exceeding the performance of platinum/carbon (Pt/C). This work provides references for exploring highly efficient non-noble metal oxygen electrocatalysts by tuning ORR/OER active sites. [ABSTRACT FROM AUTHOR]

[Display omitted] • Co/CoFeNC@N-CNF displays efficient catalytic performance for ORR, OER and HER. • The assembled mold battery can provide a power density of 292 mW cm−2. • The DFT calculations indicate that the synergistic effect between Co/CoFe bimetal. In this work, a three-dimensional (3D) multifunctional Co/CoFeNC@N-CNF electrocatalyst was first synthesized by the pyrolysis of a CoFe bimetal-centred metal-organic framework (MOF) and bacterial cellulose (BC). The initial potential and half-wave potential of Co/CoFeNC@N-CNF can reach 0.99 V and 0.8 V. Low overpotentials of 320 mV and 155 mV are purely required for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) at a current density of 10 mA cm−2, respectively. The electrochemical performance of Co/CoFeNC@N-CNF exceeds most bimetal-MOF-derived electrocatalysts reported to date. The superior electrochemical performance is mainly due to abundant active sites, high-efficiency electrochemical performance, and high electron transport efficiency. In addition, the theoretical calculation results show that the synergistic effect of the CoFe bimetal can optimize the adsorption energy for intermediates of the oxygen reduction reaction (ORR), OER and HER. Furthermore, we assembled a mold and solid Zn-air battery using the catalyst as an air cathode catalyst, demonstrating the maximum power densities of 292 mW cm−2 and 178 mW cm−2. The 3D structure electrocatalysts derived from the MOF and bacterial cellulose provide an innovative and instructive approach for the design of diverse energy nanomaterials. [ABSTRACT FROM AUTHOR]

In this paper, a waxberry‐like MnS/Ni3S4 composite catalyst was designed and synthesized. In this coating structure, MnS is located inside and Ni3S4 is wrapped on the surface to form a spherical structure. This structure makes the material show excellent stability in the electrocatalytic process. The diffusion staggered region structure formed at the two‐phase interface greatly enhances the synergistic interaction between MnS and Ni3S4. At the same time, the defects and vacancies formed by the diffusion mechanism at the interface of the two phases increase the active site and improve the interfacial electron transfer kinetics. Therefore, MnS/Ni3S4 composites showed good catalytic performance for ORR/OER. At 10 mA cm−2, the overpotential of it is only 320 mV, and the half‐wave potential can reach 0.81 V. The catalyst also exhibited extraordinary cycle stability and small voltage gap when used as cathode of Zn‐air batteries. When the current density is 3 mA cm−2, the cyclic discharge can be stable for 400 h and the voltage difference between the front and back does not increase more than. When the current density increases to 5 mA cm−2, the cyclic charge and discharge can be stable for more than 300 h. [ABSTRACT FROM AUTHOR]

Electrocatalytic water splitting is one of the most efficient ways of producing green hydrogen energy. The design of stable, active, and efficient electrocatalysts plays a crucial role in water splitting for achieving efficient energy conversion from electrical to hydrogen energy, aimed at solving the lingering energy crisis. In this work, CNT composites modified with CoP-V4P3 composites (CoVO-10-CNT-450P) were formed by carbonising a pencil-like precursor (Co3V2O8-H2O) and growing carbon nanotubes in situ, followed by in situ phosphorylation on the carbon nanotubes. In the HER electrocatalytic process, an overpotential of only 124 mV was exhibited at a current density of 10 mA cm−2. In addition, as an OER catalyst, a low overpotential of 280 mV was attained at a current density of 10 mA cm−2. Moreover, there was no noticeable change in the performance of the catalyst over a 90 h test in a continuous total water splitting experiment. The unique electronic structure and hollow carbon nanotube structure of CoVO-10-CNT-450P effectively increased the catalytic active sites, while also significantly improving the electrocatalytic activity. This work provides theoretical guidance for the design and synthetic route of high-performance non-precious metal electrocatalysts, and actively promotes the commercial application of electrochemical water splitting. [ABSTRACT FROM AUTHOR]

It is of significance to search non-noble metal OER/ORR catalysts with perfect performance. The introduction of carbon into perovskite can significantly enhance oxygen electrocatalytic activity. Herein, nanofiber-based Sm 0.5 Sr 0.5 Co 0.2 Fe 0.8 O 3-δ /rGO (SSCF28/rGO) and Sm 0.5 Sr 0.5 Co 0.2 Fe 0.8 O 3-δ /N-MWCNT (SSCF28/N-MWCNT) hybrids with various mass ratios were synthesized successfully by a facile ultrasonic mixing method and their oxygen evolution reaction (OER)/oxygen reduction reaction (ORR) properties were compared and studied. In 0.1 M KOH, SSCF28/N-MWCNT = 1.3 with optimal mass ratio shows better OER/OER bifuntional catalytic activity than SSCF28/rGO = 2:1. After 1000 CV cycles, SSCF28/N-MWCNT = 1.3 remains stable. Compared to SSCF28/rGO = 2:1, SSCF28/N-MWCNT = 1:3 shows promising practical applicability in metal-air batteries. The excellent OER/ORR activity of SSCF28/N-MWCNT = 1:3 can be attributed to the component optimization of perovskite and carbon and the synergistic effect between nanofiber-structured SSCF28 and N-functionalized MWCNT (N-MWCNT). • SSCF28/rGO and SSCF28/N-MWCNT were first synthesized via a facile method. • SSCF28/N-MWCNT reveals a low overpotential of 53 mV in 0.1 M KOH. • SSCF28/N-MWCNT shows excellent bifunctional activity with a low ΔE of 1.077 V. • SSCF28/N-MWCNT has superior OER stability. [ABSTRACT FROM AUTHOR]

The electrochemical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are the most critical processes in renewable energy-related technologies, such as fuel cells, water electrolyzers, and unitized regenerative fuel cells. N-doped carbon composites have been demonstrated to be promising ORR/OER catalyst candidates because of their excellent electrical properties, tunable pore structure, and environmental compatibility. In this study, we prepared porous N-doped carbon nanocomposites (NC) by combining mussel-inspired polydopamine (PDA) chemistry and transition metals using a solvothermal carbonization strategy. The complexation between dopamine catechol groups and transition metal ions (Fe, Ni, Co, Zn, Mn, Cu, and Ti) results in hybrid structures with embedded metal nanoparticles converted to metal–NC composites after the carbonization process. The influence of the transition metals on the structural, morphological, and electrochemical properties was analyzed in detail. Among them, Cu, Co, Mn, and Fe N-doped carbon nanocomposites exhibit efficient catalytic activity and excellent stability toward ORR. This method improves the homogeneous distribution of the catalytically active sites. The metal nanoparticles in reduced (MnO, Fe3C) or metallic (Cu, Co) oxidation states are protected by the N-doped carbon layers, thus further enhancing the ORR performance of the composites. Still, only Co nanocomposite is also effective toward OER with a potential bifunctional gap (ΔE) of 0.867 V. The formation of Co-N active sites during the carbonization process, and the strong coupling between Co nanoparticles and the N-doped carbon layer could promote the formation of defects and the interfacial electron transfer between the catalyst surface, and the reaction intermediates, increasing the bifunctional ORR/OER performance. [ABSTRACT FROM AUTHOR]

A set of platinum (Pt) and earth-abundant transition metals (M = Ni, Fe, Cu) on graphene nanoplatelets (sqPtM/GNPs) was synthesised via sequential deposition to establish parallels between the synthesis method and the materials' electrochemical properties. sqPtM/GNPs were assessed as bifunctional electrocatalysts for oxygen evolution (OER) and reduction (ORR) reactions for application in unitised regenerative fuel cells and metal-air batteries. sqPtFe/GNPs showed the highest catalytic performance with a low potential difference of ORR half-wave potential and overpotential at 10 mA cm−2 during OER, a crucial parameter for bifunctional electrocatalysts benchmarking. A novel two-stage synthesis strategy led to higher electrocatalytic performance by facilitating the reactants' access to the active sites and reducing the charge-transfer resistance. [ABSTRACT FROM AUTHOR]