Interfacing Manganese Oxide and Cobalt in Porous Graphitic Carbon Polyhedrons Boosts Oxygen Electrocatalysis for Zn-Air Batteries

Atomic Ni-doped ZrO2 with subnanometric Fe clusters for tandem C-C bond cleavage and coupling

The sustainable valorization of lignin β-O-4 compounds into high-value natural products through one-pot tandem catalysis presents an urgent yet scientifically challenging frontier in biomass conversion. Herein, we report a mesoporous Fe3@Ni1-ZrO2 catalyst featuring subnanometric Fe-O clusters anchored on atomic Ni-doped ZrO2 nanosheets. This engineered architecture enables the one-pot tandem conversion of lignin β-O-4 segments to flavones under aerobic and base-free conditions, delivering 56.2% yield with a space-time yield (STY) of 3.3 g gcat -1 h-1 in continuous flow operation. Moreover, the system demonstrates exceptional substrate versatility through efficient conversion of diverse lignin β-O-4 dimers and substituted 2'-phenoxyacetophenones into bioactive flavones. Mechanistic investigations combining controlled experiments and density functional theory (DFT) calculations reveal a cooperative catalytic mechanism, i.e., ZrO2 nanosheets mediate selective oxidative cleavage of C-C bonds in β-O-4 segments, and subnanometric Fe3 clusters activate aldol condensation of cleavage intermediates, while atomic Ni sites suppress competing pathways to govern the selectivity. This synergistic interplay within the Fe3@Ni1-ZrO2 framework establishes a robust catalytic microenvironment to enable a high-efficiency tandem process.

Interwoven MnO/Co-derived N-doped carbon nanotube composites as highly efficient and durable bifunctional oxygen catalysts for zinc-air batteries

Rechargeable zinc-air batteries (ZABs) have emerged as a compelling candidate for advanced electrochemical energy storage and conversion systems, owing to their exceptional theoretical energy density, cost-effectiveness, and environmental compatibility. Despite these advantages, their practical utility is restrained by the intrinsically sluggish kinetics of both the oxygen reduction (ORR) and oxygen evolution (OER) reactions. Herein, we present a novel coordination-assisted ball-milling approach to fabricate MnO/Co-N-CNT composites featuring a unique interwoven carbon nanotube architecture. This rationally designed microstructure not only facilitates more efficient ion diffusion and electron transport, but also exploits the synergistic interaction between cobalt and manganese species to substantially enhance ORR/OER activity and long-term stability. As a result, ZABs incorporating these advanced composites achieve an impressive peak power density of 247.6 mW cm-2 and sustain stable cycling for over 115 hours. These findings offer fresh insights into strategic material design and hold significant potential for guiding the future development of high-performance electrochemical energy devices.

Engineering Triple Phase Interface and Axial Coordination Design of Single-Atom Electrocatalysts for Rechargeable Zn─air Batteries

Bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are highly desirable for rechargeable Zn─air batteries (rZABs). Herein, a space optimized 3D heterostructure Co-N-C@MoS2 catalyst with Co single atom and Co cluster sites is developed by pyrolysis of ZIF-67 and in situ grown ultrathin MoS2 nanosheets. The introduced MoS2 not only has abundant defective structures, but also regulates the Co electronic distribution, thus introducing additional active sites and enhancing Co-Nx activity. In addition, the MoS2 modification leads to an appropriate increase in hydrophilicity which can make a stable liquid/gas/solid triple phase interface, facilitating the approachability of electrolytes into the porous channels and promotes the mass transfer through ensuring a favorite contact among the catalyst, electrolyte and reactants and enhancing utility of active reaction sites. Comprehensive analysis and theoretical simulation indicate that the enhancement of activity stems from the axial coordination of Co cluster over Co single-atom active sites to regulate local electronic structure, thereby optimizing the adsorption of ORR intermediates and enhancing the catalytic activity. Compared with the commercial Pt/C and IrO2, the structurally optimized Co-N-C@MoS2 catalyst displays exceptional bifunctional electrocatalytic activity and long-time stability toward both OER and ORR. Moreover, the Co-N-C@MoS2 catalyst exhibits higher peak power density and superior stability in liquid and flexible ZABs compared to the commercial Pt/C + IrO2 catalyst.

Manganese-Based Metal-Organic Frameworks and Their Derivatives for Electrochemical Water Splitting: Recent Advances and Future Outlook

Metal-organic frameworks (MOFs) and their derivatives have recently attracted significant interest as promising candidates in water splitting due to their well-defined structural and electronic features, three-dimensional architecture, high surface area, abundance of active sites, remarkable stability, and improved capabilities for mass transport and diffusion. Mn-based MOFs and their derivatives have been extensively studied and demonstrated significant potential in water splitting, inspired largely by the natural photosystem-II. Despite the development of numerous Mn-based electrocatalysts, Mn-MOFs stand out due to their strong synergistic interactions, tunable electronic properties, efficient charge and mass transfer, and straightforward synthesis. However, recent reviews on MOFs have largely overlooked the specific advancements in Mn-MOFs and their derivatives for water-splitting applications. By providing an overview of the uses of Mn-MOFs and their materials, this article seeks to close that gap. It looks at their stability, porosity, and structure as well as how they are used in water splitting. This study offers a deeper knowledge of the properties and uses of Mn-MOFs and their related materials by drawing on groundbreaking research. The link between structure, property, and performance is examined, current advancements in the subject are discussed, difficulties faced are addressed, and potential future developments are taken into account.

The Construction of Highly Conductive Framework in Mn3O4@C-MWCNTs Slurry for Aqueous Zinc-Based Semi-Solid Flow Batteries

Aqueous zinc-based semi-solid flow batteries (AZSSFBs) are promising large-scale energy storage devices due to their low cost and superior safety. The formation of a conductive network in the slurry plays an important role in the capacity of active materials and the stability of suspension. Meanwhile, the suspension stability of the slurry will determine the cycle life of AZSSFBs. Herein, metal-organic-framework-derived carbon-coated Mn3O4@C composites are fabricated and dispersed in the aqueous electrolyte to construct a stable 3D conductive carbon framework in slurry by combining multi-walled carbon nanotubes (MWCNTs). The 3D conductive carbon framework can not only facilitate rapid electron transportation, but also enhance the suspension stability of slurry, ensuring stable electron conduction for Mn3O4 in the fluidic semi-solid slurry. Based on Mn3O4@C-MWCNTs semi-solid slurry, AZSSFBs display enhanced electrochemical performance.

Decrypting Synergy of Alloy & Metal Nanoparticles Within Nitrogen-Doped Carbon Nanosheets for Zn-Air Batteries with Ultralong Cycling Stability

The exploration of efficient, robust, and low-cost bifunctional electrocatalysts to drive the commercial application of Zn-air batteries (ZABs) is of great significance but still remains a challenge. Herein, a 1D coordination polymer (1D-CP) derived FeNi alloy & Co nanoparticles (NPs) co-implanted N-doped carbon nanosheets (FNC/NCS) is judiciously crafted and employed as a high-performance electrocatalyst for ultralong lifetime ZABs. The key to this strategy is the leveraging of metal-coordinated melamine to direct the pyrolysis of 1D-CP, enabling the in situ formation of well-dispersed FeNi alloy and Co NPs within the carbon matrix. The resulting FNC/NCS exhibits prominent oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity with a small overall oxygen potential difference (ΔE = 0.68 V). Density functional theory (DFT) simulation demonstrates that the synergistic effect between FeNi alloy and Co NPs can reduce energy barriers, promote electron transfer, and optimize the formation of crucial intermediates, thereby largely boost ORR/OER activity of FNC/NCS. The FNC/NCS-assembled ZABs possess high specific capacity, large power density, and ultralong cycling life in both aqueous (> 3300 h) and solid-state (150 h) electrolytes. This work provides a viable strategy for 1D-CP-derived bifunctional electrocatalysts and dissects the synergistic effect between different metal species, affording significant guidance for the development of renewable energy materials.

One-Step Hydrothermal Method Realizing Oxygen Vacancy Construction and P Doping of MnO2 to Optimize Its Oxygen Evolution Performance

MnO2 is considered one of the most potential catalysts for the oxygen evolution reaction, but its activity, which is determined by its electronic structure, crystal phase, and morphology, needs to be improved further. However, it is difficult to realize these multiscale structural regulations of MnO2 simultaneously during the preparation. In this study, α-MnO2 nanomaterial with a lot of oxygen vacancies (OVs) and Mn3+ is prepared by a one-step hydrothermal method, during which the protons of HCl can take the oxygen atom away from MnO2 to form a lot of OVs. The introduction of NH4H2PO4 can realize P doping in MnO2 to stabilize the product in the α-phase. In addition, the OV and P can increase the content of Mn3+ and regulate the Mn-O bond length synergistically to optimize the reaction kinetics. As a result, the product shows obviously enhanced catalytic activity. This study provides a one-step method for multiscale structural regulation of MnO2, which can easily create oxygen vacancies and achieve nonmetallic doping to optimize the oxygen evolution reaction (OER) performance of MnO2.

FeCo Bimetallic ZIF Derivatives Decorated with CoFe-LDH to Promote Bifunctional Oxygen Electrocatalysis Activation

Reasonably screening the targeted oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) constituents and constructing high-efficiency and stabilized ORR/OER bifunctional electrocatalysts are pivotal for the advancement of rechargeable zinc-air batteries (ZABs). Here, CoFe layered double hydroxide (CoFe-LDH) nanosheets are deposited on nitrogen-doped graphite-carbon polyhedra with FeCo alloy nanoparticles (FeCo/LDH-NGCP). Due to the synergic effect between FeCo-NGCP, CoFe-LDH and FeCo/LDH-NGCP, the electrocatalyst with the abundant and accessible active sites can provide good charge/mass transfer, and thus shows wonderful ORR and OER bifunctional electrocatalytic performance. In ORR tests, FeCo/LDH-NGCP catalyst displays larger half-wave potential (E1/2, 0.89 V vs. 0.85 V), higher limiting current density (JL, 5.91 mA/cm2 vs. 5.14 mA/cm2) and better stability than commercial Pt/C. As for OER, FeCo/LDH-NGCP possesses a smaller overpotential (η) of 299.6 mV at a current density of 10 mA/cm2 and more durable stability than commercial RuO2 (330.6 mV). Furthermore, in ZAB tests, the cycling stability of ZAB-FeCo/LDH-NGCP (over 470 h) outperforms the ZAB-Pt/C+RuO2 (92 h) with commercial electrocatalyst (Pt/C+RuO2). Therefore, the FeCo/LDH-NGCP catalyst offers a new perspective to construct ZABs bifunctional catalysts and their commercial application in ZABs.

Achieving advanced hydrogen evolution under large current density using an amorphous/crystalline core-shell electrocatalyst of a-NiCoP/Co2P

Non-precious transition metal-based electrocatalysts with high activities are promising candidates for substituting Pt- or Ru-based electrocatalysts in hydrogen evolution. In this study, we propose core-shell engineering to combine the amorphous NiCoP and crystalline Co2P (a-NiCoP/Co2P@NF), which requires an ultra-low overpotential of only 26 mV to achieve the benchmark current density of 10 mA cm-2. Furthermore, it achieves an industrial-level hydrogen evolution current density of 500 mA cm-2 with excellent stability. The superior catalytic performance and stability can be attributed to the hierarchical amorphous/crystalline interface and the electron-rich interfacial Co sites. The amorphous NiCoP shell can not only protect the internal Co2P from corrosion, but also provide a larger electrochemically active area. Together, the Co2P core provides fast electron transport and promotes H2 emission from the interfacial electron-rich Co sites. This work provides inspiration to the rational design of an advanced core-shell structure between amorphous and crystalline states.

Pyridinic-N Seized Co in Biphasic Nanoarchitecture for Reversible Oxygen Electrocatalysis Enabling Longevous (>1200 h) Aqueous and Dual-Anion Kosmotropic Electrolyte Stabilized High Power Quasisolid-State Zn-Air Battery

Integration of different active sites by heterostructure engineering is pivotal to optimize the intrinsic activities of an oxygen electrocatalyst and much needed to enhance the performance of rechargeable Zn-air batteries (ZABs). Herein, a biphasic nanoarchitecture encased in in situ grown N-doped graphitic carbon (MnO/Co-NGC) with heterointerfacial sites are constructed. The density functional theory model reveals formation of lattice oxygen bridged heterostructure with pyridinic nitrogen atoms anchored Co species, which facilitate adsorption of oxygen intermediates. Consequently, the well-designed catalyst with accessible active sites, abundant oxygen vacant sites, and heterointerfacial coupling effects, simultaneously accelerate the electron/mass transfer and thus promotes the trifunctional electrocatalysis. The assembled aqueous ZAB delivers maximum power density of ≈268 mW cm-2 and a specific capacity of 797.8 mAh gzn -1 along with excellent rechargeability and extremely small voltage gap decay rate of 0.0007 V h-1. Further, the fabricated quasisolid-state ZAB owns a remarkable power density of 163 mW cm-2 and long cycle life, outperforming the benchmark air-electrode and many recent reports, underlining its robustness and suitability for practical utilization in diverse portable applications.

CoFe2O4 with the In-Situ Formed Oxygen Vacancies and Co Particles as an Efficient Bifunctional Catalyst for Rechargeable Zinc-Air Batteries

Rechargeable zinc-air batteries (RZABs) are considered as one of the most promising clean energy device due to their abundant resources, low cost and environmental friendliness. However, their energy efficiency and cycle life are far from satisfactory due to the poor activity and stability of bi-functional electrocatalyst in air cathode. In this work, an efficient bi-functional catalyst (rGO-CoFe2O4/Co) was derived from its precursor (rGO-CoFe2O4) through a simple annealing process. Electrochemical measurements prove that rGO-CoFe2O4/Co with the in-situ formed Co nano particles and rich oxygen vacancies appears excellent oxygen reduction reaction and oxygen evolution reaction catalytic activity compared to its counterpart. Its half-wave potential is 0.81 V (vs RHE) and the OER overpotential is only 310 mV (vs RHE). In addition, rechargeable zinc-air batteries assembled with rGO-CoFe2O4/Co show the highest peak power density (128.9 mW cm-2) and cycling stability compared to rGO-CoFe2O4 and commercial Pt/C-RuO2 catalysts. This work provides a simple strategy for the design of advanced bifunctional catalysts.

PtCo nanoalloy embedded nitrogen-doped carbon nanotube for rechargeable Zn-air batteries

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 RuO2 catalysts.

High-Entropy Prussian Blue Analogue Derived Heterostructure Nanoparticles as Bifunctional Oxygen Conversion Electrocatalysts for the Rechargeable Zinc-Air Battery

In response to energy challenges, rechargeable zinc-air batteries (RZABs) serve as an ideal platform for energy storage with a high energy density and safety. Nevertheless, addressing the sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in RZAB requires highly active and robust electrocatalysts. High-entropy Prussian blue analogues (HEPBAs), formed by mixing diverse metals within a single lattice, exhibit enhanced stability due to their increased mixing entropy, which lowers the Gibbs free energy. HEPBAs innately enable sacrificial templating, an effective way to synthesize complex structures. Impressively, in this study, we successfully transform HEPBAs into exquisite multiphase (multimetallic alloy, metal carbide, and metal oxide) heterostructure nanoparticles through a controlled synthesis process. The elusive multiphase heterostructure nanoparticles manifested two active sites for selective ORR and OER. By integrating CNT into HEPBA-derived nanoparticles (HEPBA/CNT-800), the HEPBA/CNT-800 demonstrates superior activity toward both ORR (E1/2 = 0.77 V) in a 0.1 M KOH solution and the OER (η = 330 mV at 50 mA cm-2) in a 1 M KOH solution. The RZAB with a HEPBA/CNT-based air electrode demonstrated an open-circuit voltage of 1.39 V and provided a significant energy density of 71 mW cm-2. Moreover, the charge and discharge cycles lasting up to 40 h at a current density of 5 mA cm-2 demonstrate its excellent stability. This work provides an alternative avenue for the rational design of HEPBA's derivative for a sustainable rechargeable metal-air battery platform.

Unlocking the Electrocatalytic Behavior of Cu2MnS2 Nanoflake-Anchored rGO for the Oxygen Evolution Reaction in an Alkaline Medium

A catalyst of the oxygen evolution reaction (OER) that is viable, affordable, and active for effective water-splitting applications is critical. A variety of electrocatalysts have been discovered to replace noble metal-based catalysts. Of these, transition metal-based sulfides are essential for incorporating carbonaceous materials to improve electrical conductivity, resulting in better electrocatalytic performance. Our study illustrates the synthesis of Cu2MnS2 (CMS) nanoflakes and their different rGO composites (10 to 40 wt %) via a hydrothermal technique for an effective water oxidation reaction. The X-ray diffraction pattern reveals that the prepared Cu2MnS2 nanoflakes exhibit a cubic crystal structure. The high-resolution scanning electron microscopy and the high resolution transmission electron microscopy images corroborate the formation of the nanoflake-like morphology of Cu2MnS2 with the strong interaction of rGO. The selected area electron diffraction analysis pattern reveals a polycrystalline nature. The Fourier transform infrared spectrum shows the existence of a metal sulfur vibrational band at 590 cm-1, and Raman analysis infers the presence of rGO. The X-ray photoelectron spectroscopy spectra reveal the oxidation states of the elements present in the samples. Using Brunauer-Emmett-Teller analysis, the surface area of CMS-20 is found to be 117.04 m2/g. The measured OER overpotentials using linear sweep volammetry and the values are 380, 370, 340, 376, and 400 mV at 10 mA/cm2 for CMS, CMS-10, CMS-20, CMS-30, and CMS-40, respectively, and the corresponding Tafel slope values are 179, 158, 149, 206, and 240 mV/decade, respectively. The electrochemical active surface area is estimated using cyclic voltammetry for all of the catalysts, where CMS-20 showed a larger surface area. Also, the same catalyst exhibits good stability for ∼24 h at a constant potential, which is confirmed via chronoamperometry. Thus, combining transition metal-based sulfides with carbonaceous materials indicates improved catalytic behavior for the preparation of high-performance OER electrocatalysts. Overall, the prepared CMS-20 performed as an efficient OER electrocatalyst and can be utilized for practical applications in energy conversion.

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

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

General and Facile Synthesis of Co/CoO Nanoparticals Supported by Nitrogen-Doped Graphenic Networks as Efficient Oxygen Electrocatalyst for Zn-Air Batteries

Reasonable design of low-cost, high-efficiency and stable bifunctional oxygen electrocatalysts is of great significance to improve the reaction efficiency of Zn-air batteries, which is still a huge challenge. Here, we report a highly efficient bifunctional oxygen electrocatalyst with three-dimensional (3D) N-doped graphene network-supported cobalt and cobalt oxide nanoparticles (Co/CoO-NG), which can be in situ synthesized by inducing metal ions on metal plates via graphene oxide as an inducer. This 3D network structure and open active center show excellent bifunctional oxygen electrocatalytic activity under alkaline conditions, and can be used as an air electrode in rechargeable Zn-air batteries, with significantly better power density (244.28 mW cm-2) and stability (over 340 h) than commercial Pt/C+RuO2 mixtures. This work is conducive to advancing the practical application of graphene-based materials as air electrodes for rechargeable zinc-air batteries.

Catalyst-Support Interaction in Polyaniline-Supported Ni3Fe Oxide to Boost Oxygen Evolution Activities for Rechargeable Zn-Air Batteries

Catalyst-support interaction plays a crucial role in improving the catalytic activity of oxygen evolution reaction (OER). Here we modulate the catalyst-support interaction in polyaniline-supported Ni3Fe oxide (Ni3Fe oxide/PANI) with a robust hetero-interface, which significantly improves oxygen evolution activities with an overpotential of 270 mV at 10 mA cm-2 and specific activity of 2.08 mA cmECSA-2 at overpotential of 300 mV, 3.84-fold that of Ni3Fe oxide. It is revealed that the catalyst-support interaction between Ni3Fe oxide and PANI support enhances the Ni-O covalency via the interfacial Ni-N bond, thus promoting the charge and mass transfer on Ni3Fe oxide. Considering the excellent activity and stability, rechargeable Zn-air batteries with optimum Ni3Fe oxide/PANI are assembled, delivering a low charge voltage of 1.95 V to cycle for 400 h at 10 mA cm-2. The regulation of the effect of catalyst-support interaction on catalytic activity provides new possibilities for the future design of highly efficient OER catalysts.

Facile synthesis of MnO/NC nanohybrids toward high-efficiency ORR for zinc-air battery

The development of inexpensive non-precious metal materials as high-efficiency stable oxygen reduction reaction (ORR) catalysts holds significant promise for application in metal-air batteries. Here, we synthesized a series of nanohybrids formed from MnO nanoparticles anchored on N-doped Ketjenblack carbon (MnO/NC) via a facile hydrothermal reaction and pyrolysis strategy. We systematically investigated the influence of pyrolysis temperature (600 to 900 °C) on the ORR activities of the MnO/NC samples. At the optimized pyrolysis temperature of 900 °C, the resulting MnO/NC (referred to as MnO/NC-900) exhibited superior ORR activity (onset potential = 0.85 V; half-wave potential = 0.74 V), surpassing other MnO/NC samples and nitrogen-doped Ketjenblack carbon (NC). Additionally, MnO/NC-900 demonstrated better stability than the Pt/C catalyst. The enhanced ORR activity of MnO/NC-900 was attributed to the synergy effect between MnO and NC, abundant surface carbon defects and surface-active components (N species and oxygen vacancies). Notably, the Zinc-air battery (ZAB) equipped MnO/NC-900 as the cathode catalyst delivered promising performance metrics, including a high peak power density of 146.5 mW cm-2, a large specific capacity of 795 mA h gZn -1, and an excellent cyclability up to 360 cycles. These results underscore the potential of this nanohybrid for applications in energy storage devices.

Ultrathin Ni-Fe MOF Nanosheets: Efficient and Durable Water Oxidation at High Current Densities

Efficient, durable, and economical electrocatalysts are crucial for advancing energy technology by facilitating the oxygen evolution reaction (OER). Here, ultrathin Ni-Fe metal-organic skeleton (MOF) nanosheets were created in situ on nickel foam (NiFe-UMNs/NF). The catalyst exhibited excellent OER catalytical abilities, with only 269 mV overpotentials at 250 mA cm-2. Besides, when integrated with Pt/C/NF, NiFe-UMNs/NF held the potential for application in industrial alkaline water electrolysis with an initial voltage retention of approximately 86% following a continuous operation of 100 h at a current density of 250 mA cm-2. The super performance of the NiFe-UMNs/NF catalyst was attributed to ultrathin morphology, super hydrophilicity, and synergistic effects between Ni and Fe within the MOF. In situ Raman showed that NiFe-UMNs were converted to NiFeOOH as the active species in the OER process. Density functional theory revealed that iron doping accelerated the rate-determining step and reduced the OER reaction energy barrier. This work elucidated a promising electrocatalyst for OER and enriched the practical implementation of MOF materials.

Zn-based batteries for sustainable energy storage: strategies and mechanisms

Batteries play a pivotal role in various electrochemical energy storage systems, functioning as essential components to enhance energy utilization efficiency and expedite the realization of energy and environmental sustainability. Zn-based batteries have attracted increasing attention as a promising alternative to lithium-ion batteries owing to their cost effectiveness, enhanced intrinsic safety, and favorable electrochemical performance. In this context, substantial endeavors have been dedicated to crafting and advancing high-performance Zn-based batteries. However, some challenges, including limited discharging capacity, low operating voltage, low energy density, short cycle life, and complicated energy storage mechanism, need to be addressed in order to render large-scale practical applications. In this review, we comprehensively present recent advances in designing high-performance Zn-based batteries and in elucidating energy storage mechanisms. First, various redox mechanisms in Zn-based batteries are systematically summarized, including insertion-type, conversion-type, coordination-type, and catalysis-type mechanisms. Subsequently, the design strategies aiming at enhancing the electrochemical performance of Zn-based batteries are underscored, focusing on several aspects, including output voltage, capacity, energy density, and cycle life. Finally, challenges and future prospects of Zn-based batteries are discussed.

Construction and mechanistic insights of a novel ZnO functionalized rGO composite for efficient adsorption and reduction of Cr(VI)

A series of ZnO decorated reduced graphene oxide (rGO) (ZnrGOx) with different doping ratios were synthesized by the alkaline hydrothermal method using graphene oxide (GO) and Zn(NO3)2·6H2O as precursors, and subsequently used for the adsorption study of Cr(VI) in water. The morphology, crystalline phase structure, and surface elemental properties of ZnrGOx composites were revealed by XRD, SEM, BET, FT-IR, and XPS characterizations. The results showed that ZnO nanoparticles can be clearly seen on the surface of layered rGO. Meanwhile, as the doping rate increased, the C = C double bonds were broken and more carboxylic acid groups formed in ZnrGOx. In addition, the ZnrGO0.1 composite had the most excellent adsorption performance and good stability, and reusability. The adsorption removal rate of Cr(VI) can reach 99%, and the maximum adsorption amount of Cr(VI) was 68.9655 mg/g in 3 h. The isothermal and kinetic model simulations showed that Cr(VI) adsorption on ZnrGO0.1 composite is a chemical adsorption process, spontaneous and endothermic. Based on the concentrations of different valence states of Cr in the solid and liquid phases, 40% of Cr(VI) was reduced to Cr(III) on the surface of ZnrGO0.1 composite. Moreover, the adsorption-reduction mechanisms of Cr(VI) on ZnrGO0.1 composite were further elucidated. The ZnrGO0.1 composite manifested great potential as an efficient adsorbent for Cr(VI) removal.

Selective Electrocatalytic Conversion of Nitric Oxide to High Value-Added Chemicals

The artificial disturbance in the nitrogen cycle has necessitated an urgent need for nitric oxide (NO) removal. Electrochemical technologies for NO conversion have gained increasing attention in recent years. This comprehensive review presents the recent advancements in selective electrocatalytic conversion of NO to high value-added chemicals, with specific emphasis on catalyst design, electrolyte composition, mass diffusion, and adsorption energies of key intermediate species. Furthermore, the review explores the synergistic electrochemical co-electrolysis of NO with specific carbon source molecules, enabling the synthesis of a range of valuable chemicals with C─N bonds. It also provides in-depth insights into the intricate reaction pathways and underlying mechanisms, offering valuable perspectives on the challenges and prospects of selective NO electrolysis. By advancing comprehension and fostering awareness of nitrogen cycle balance, this review contributes to the development of efficient and sustainable electrocatalytic systems for the selective synthesis of valuable chemicals from NO.

FeNiCo|MnGaOx Heterostructure Nanoparticles as Bifunctional Electrocatalyst for Zn-Air Batteries

Driven by the pressing demand for stable energy systems, zinc-air batteries (ZABs) have emerged as crucial energy storage solutions. However, the quest for cost-effective catalysts to enhance vital oxygen evolution and reduction reactions remains challenging. FeNiCo|MnGaOx heterostructure nanoparticles on carbon nanotubes (CNTs) are synthesized using liquid-phase reduction and H2 calcination approach. Compared to its component, such FeNiCo|MnGaOx/CNT shows a high synergistic effect, low impedance, and modulated electronic structure, leading to a superior bifunctional catalytic performance with an overpotential of 255 mV at 10 mA cm-2 and half-wave potential of 0.824 V (ω = 1600 rpm and 0.1 m KOH electrolyte). Moreover, ZABs based on FeNiCo|MnGaOx/CNT demonstrate notable features, including a peak power density of 136.1 mW cm-2, a high specific capacity of 808.3 mAh gZn -1, and outstanding stability throughout >158 h of uninterrupted charge-discharge cycling. Theoretical calculations reveal that the non-homogeneous interface can introduce more carriers and altered electronic structures to refine intermediate adsorption reactions, especially promoting O* formation, thereby enhancing electrocatalytic performance. This work demonstrates the importance of heterostructure interfacial modulation of electronic structure and enhancement of adsorption capacity in promoting the implementation of OER/ORR, ZABs, and related applications.

Synergistic vacancy engineering of Co/MnO@NC catalyst for superior oxygen reduction reaction in liquid/solid zinc-air batteries

The pursuit of efficient and economically viable catalysts for liquid/solid-state zinc-air batteries (ZABs) is of paramount importance yet presents formidable challenge. Herein, we synthesized a vacancy-rich cobalt/manganese oxide catalyst (Co/MnO@NC) stabilized on a nitrogen-doped mesoporous carbon (NC) nanosphere matrix by leveraging hydrothermal and high-temperature pyrolysis strategy. The optimized Co/MnO@NC demonstrates fast reaction kinetics and large limiting current densities comparable to commercial Pt/C in alkaline electrolyte for oxygen reduction reaction (ORR). Moreover, the Co/MnO@NC serves as an incredible cathode material for both liquid and flexible solid-state ZABs, delivering impressive peak power densities of 217.7 and 63.3 mW cm-2 and robust long-term stability (459 h), outperforming the state-of-the-art Pt/C and majority of the currently reported catalysts. Research indicates that the superior performance of the Co/MnO@NC catalyst primarily stems from the synergy between the heightened electrical conductivity of metallic Co and the regulatory capacity of MnO on adsorbed oxygen intermediates. In addition, the abundance of vacancies regulates the electronic configuration, and superhydrophilicity facilitates efficient electrolyte diffusion, thereby effectively ensuring optimal contact between the active site and reactants. Besides, the coexisting NC layer avoids the shedding of active sites, resulting in high stability. This work provides a viable approach for designing and advancing high-performance liquid/solid-state ZABs, highlighting the great potential of energy storage technology.

Boosted Oxygen Kinetics of Hierarchically Mesoporous Mo2C/C for High-current-density Zn-air Battery

The high-current-density Zn-air battery shows big prospects in next-generation energy technologies, while sluggish O2 reaction and diffusion kinetics barricade the applications. Herein, the sequential assembly is innovatively demonstrated for hierarchically mesoporous molybdenum carbides/carbon microspheres with a tunable thickness of mesoporous carbon layers (Meso-Mo2C/C-x, where x represents the thickness). The optimum Meso-Mo2C/C-14 composites (≈2 µm in diameter) are composed of mesoporous nanosheets (≈38 nm in thickness), which possess bilateral mesoporous carbon layers (≈14 nm in thickness), inner Mo2C/C layers (≈8 nm in thickness) with orthorhombic Mo2C nanoparticles (≈2 nm in diameter), a high surface area of ≈426 m2 g-1, and open mesopores (≈6.9 nm in size). Experiments and calculations corroborate the hierarchically mesoporous Mo2C/C can enhance hydrophilicity for supplying sufficient O2, accelerate oxygen reduction kinetics by highly-active Mo2C and N-doped carbon sites, and facilitate O2 diffusion kinetics over hierarchically mesopores. Therefore, Meso-Mo2C/C-14 outputs a high half-wave potential (0.88 V vs RHE) with a low Tafel slope (51 mV dec-1) for oxygen reduction. More significantly, the Zn-air battery delivers an ultrahigh power density (272 mW cm-2), and an unprecedented 100 h stability at a high-current-density condition (100 mA cm-2), which is one of the best performances.

Atomically Dispersed Fe Sites Regulated by Adjacent Single Co Atoms Anchored on N-P Co-Doped Carbon Structures for Highly Efficient Oxygen Reduction Reaction

Manipulating the coordination environment and electron distribution for heterogeneous catalysts at the atomic level is an effective strategy to improve electrocatalytic performance but remains challenging. Herein, atomically dispersed Fe and Co anchored on nitrogen, phosphorus co-doped carbon hollow nanorod structures (FeCo-NPC) are rationally designed and synthesized. The as-prepared FeCo-NPC catalyst exhibits significantly boosted electrocatalytic kinetics and greatly upshifts the half-wave potential for the oxygen reduction reaction. Furthermore, when utilized as the cathode, the FeCo-NPC catalyst also displays excellent zinc-air battery performance. Experimental and theoretical results demonstrate that the introduction of single Co atoms with Co-N/P coordination around isolated Fe atoms induces asymmetric electron distribution, resulting in the suitable adsorption/desorption ability for oxygen intermediates and the optimized reaction barrier, thereby improving the electrocatalytic activity.

Insights on MOF-derived metal-carbon nanostructures for oxygen evolution

Electrochemical water splitting has been regarded a promising method for the production of green hydrogen, addressing the need for efficient energy conversion and storage. However, it is severely hindered by the oxygen evolution reaction (OER) because of its multi-step four-electron transfer pathway with sluggish reaction kinetics. Microporous metal-organic-frameworks (MOFs), by virtue of large specific surface area, high porosity, tunable composition and morphology, find widespread use as precursors of metal-carbon nanostructures. The resulting carbon nanomaterials can well inherit the characteristics and advantages of the crystalline MOF precursors, and exhibit versatile application prospects in the fields of environment and energy, particularly in OER. Herein, a meticulous overview of the synthesis strategy for MOF-derived metal-carbon nanostructures and the origins of their enhanced OER properties has been demonstrated. We comprehensively illustrate these aspects across three dimensions: MOF selection, metal introduction, and carbon structures. Finally, the challenges and future prospects for this emerging field will be presented.

Synergistic Niobium Doped Two-Dimensional Zirconium Diselenide: An Efficient Electrocatalyst for O2 Reduction Reaction

The development of high-activity and low-price cathodic catalysts to facilitate the electrochemically sluggish O2 reduction reaction (ORR) is very important to achieve the commercial application of fuel cells. Here, we have investigated the electrocatalytic activity of the two-dimensional single-layer Nb-doped zirconium diselenide (2D Nb-ZrSe2) toward ORR by employing the dispersion corrected density functional theory (DFT-D) method. Through our study, we computed structural properties, electronic properties, and energetics of the 2D Nb-ZrSe2 and ORR intermediates to analyze the electrocatalytic performance of 2D Nb-ZrSe2. The electronic property calculations depict that the 2D monolayer ZrSe2 has a large band gap of 1.48 eV, which is not favorable for the ORR mechanism. After the doping of Nb, the electronic band gap vanishes, and 2D Nb-ZrSe2 acts as a conductor. We studied both the dissociative and the associative pathways through which the ORR can proceed to reduce the oxygen molecule (O2). Our results show that the more favorable path for O2 reduction on the surface of the 2D Nb-ZrSe2 is the 4e- associative path. The detailed ORR mechanisms (both associated and dissociative) have been explored by computing the changes in Gibbs free energy (ΔG). All of the ORR reaction intermediate steps are thermodynamically stable and energetically favorable. The free energy profile for the associative path shows the downhill behavior of the free energy vs the reaction steps, suggesting that all ORR intermediate structures are catalytically active for the 4e- associative path and a high 4e- reduction pathway selectivity. Therefore, 2D Nb-ZrSe2 is a promising catalyst for the ORR, which can be used as an alternative ORR catalyst compared to expensive platinum (Pt).

Rechargeable Zinc-Air Batteries: Advances, Challenges, and Prospects

Rechargeable zinc-air batteries (Re-ZABs) are one of the most promising next-generation batteries that can hold more energy while being cost-effective and safer than existing devices. Nevertheless, zinc dendrites, non-portability, and limited charge-discharge cycles have long been obstacles to the commercialization of Re-ZABs. Over the past 30 years, milestone breakthroughs have been made in technical indicators (safety, high energy density, and long battery life), battery components (air cathode, zinc anode, and gas diffusion layer), and battery configurations (flexibility and portability), however, a comprehensive review on advanced design strategies for Re-ZABs system from multiple angles is still lacking. This review underscores the progress and strategies proposed so far to pursuit the high-efficiency Re-ZABs system, including the aspects of rechargeability (from primary to rechargeable), air cathode (from unifunctional to bifunctional), zinc anode (from dendritic to stable), electrolytes (from aqueous to non-aqueous), battery configurations (from non-portable to portable), and industrialization progress (from laboratorial to practical). Critical appraisals of the advanced modification approaches (such as surface/interface modulation, nanoconfinement catalysis, defect electrochemistry, synergistic electrocatalysis, etc.) are highlighted for cost-effective flexible Re-ZABs with good sustainability and high energy density. Finally, insights are further rendered properly for the future research directions of advanced zinc-air batteries.

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

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

Ni dispersed ultrathin carbon nanosheets as bi-functional oxygen electrocatalyst induced from graphite-like porous supramolecule

Excellent porosity and accessibility are key requirements during carbon-based materials design for energy conversion applications. Herein, a Ni-based porous supramolecular framework with graphite-like morphology (Ni-SOF) was rationally designed as a carbon precursor. Ultrathin carbon nanosheets dispersed with Ni nanoparticles and Ni-Nx sites (Ni@NiNx-N-C) were obtained via in-situ exfoliation during pyrolysis. Due to the hetero-porous structure succeeding from Ni-SOF, the Ni@NiNx-N-C catalyst showed outstanding bifunctional oxygen electrocatalytic activity with a narrow gap of 0.69 V between potential to deliver 10 mA cm-2 oxygen evolution and half-wave potential of oxygen reduction reaction, which even surpassed the Pt/C + IrO2 pair. Therefore, the corresponding zinc-air battery exhibited excellent power output and stability. The multiple Ni-based active sites, the unique 2D structure with a high graphitization degree and large specific surface area synergistically contributed to the excellent bifunctional electrocatalytic activity of Ni@NiNx-N-C. This work provided a novel viewpoint for the development of carbon-based electrocatalyst.

Engineering of heterointerface of ultrathin carbon nanosheet-supported CoN/MnO enhances oxygen electrocatalysis for rechargeable Zn-air batteries

Designing bifunctional electrocatalysts with outstanding reactivity and durability towards the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) has remained a long-term aim for metal-air batteries. Achieving the high level of fusion between two distinct metal components to form bifunctional catalysts with optimized heterointerfaces and well-defined morphology holds noteworthy implications in the enhancement of electrocatalytic activity yet challenging. Herein, the fabrication of numerous heterointerfaces of CoN/MnO is successfully realized within ultrathin carbon nanosheets via a feasible self-templating synthesis strategy. Experimental results and theoretic calculations verify that the interfacial electron transfer from CoN to MnO at the heterointerface engenders an ameliorated charge transfer velocity, finely tuned energy barriers concerning reaction intermediates and ultimately accelerated reaction kinetics. The as-prepared CoN/MnO@NC demonstrates exceptional bifunctional catalytic performance, excelling in both OER and ORR showcasing a low reversible overpotential of 0.69 V. Furthermore, rechargeable liquid and quasi-solid-state flexible Zn-air batteries employing CoN/MnO@NC as the air-cathode deliver remarkable endurance and elevated power density, registering values of 153 and 116 mW cm-2 respectively and exceeding Pt/C + RuO2 counterparts and those reported in literature. Deeply exploring the effect of electron-accumulated heterointerfaces on catalytic activity would contribute wisdom to the development of bifunctional electrocatalysts for rechargeable metal-air batteries.

Role of the Metal Precursor in Preparing Dual-Atom Catalysts for the Oxygen Reduction Reaction

Dual-atom catalysts (DACs) have arisen as a novel type of heterogeneous catalyst that extends from single-atom catalysts (SACs) by incorporating two kinds of metals. These materials have demonstrated enhanced performance when compared to SACs. The choice of metal precursors plays an important role in the synthesis of DACs. Here, we choose Fe and Co as DAC models and study types, contents, molar ratios of two precursors, and oxygen reduction reaction (ORR) activity. The Fe,Co DACs were synthesized by an adsorption-annealing approach, using nitrogen-doped graphitic carbon (NC) as the support. As a result, the adsorption ability of metal precursors on the support determines the metal loadings in Fe and Co DACs, leading to differences in ORR performance. The Fe precursors win the adsorption competitions in most cases, resulting in a much higher loading than that of Co precursors. Importantly, it is difficult to increase the precursor content by simply increasing the initial amount. Choosing the right combination of metal precursors, such as ferrocene and cobalt chloride, can yield Fe,Co DACs with enhanced ORR performance..

Open-Mouthed Hollow Carbons: Systematic Studies as Cobalt- and Nitrogen-Doped Carbon Electrocatalysts for Oxygen Reduction Reaction

Although hollow carbon structures have been extensively studied in recent years, their interior surfaces are not fully utilized due to the lack of fluent porous channels in the closed shell walls. This study presents a tailored design of open-mouthed particles hollow cobalt/nitrogen-doped carbon with mesoporous shells (OMH-Co/NC), which exhibits sufficient accessibility and electroactivity on both the inner and outer surfaces. By leveraging the self-conglobation effect of metal sulfate in methanol, a raspberry-structured Zn/Co-ZIF (R-Zn/Co-ZIF) precursor is obtained, which is further carbonized to fabricate the OMH-Co/NC. In-depth electrochemical investigations demonstrate that the introduction of open pores can enhance mass transfer and improve the utilization of the inner active sites. Benefiting from its unique structure, the resulting OMH-Co/NC exhibits exceptional electrocatalytic oxygen reduction performance, achieving a half-wave potential of 0.865 V and demonstrating excellent durability.

Recycling cobalt in spent lithium ion batteries to design CoN/HPCF/CoN electrocatalysts for advanced zinc-air batteries

Cobalt (Co) in spent lithium ion batteries was recycled to design a hollow and porous CoN/HPCF/CoN bifunctional electrocatalyst. It reveals superior rechargeable zinc-air battery performance (peak power density is 161.6 mW cm-2) with excellent stability.

Engineering Molecular Heterostructured Catalyst for Oxygen Reduction Reaction

Introducing a second metal species into atomically dispersed metal-nitrogen-carbon (M-N-C) catalysts to construct diatomic sites (DASs) is an effective strategy to elevate their activities and stabilities. However, the common pyrolysis-based method usually leads to substantial uncertainty for the formation of DASs, and the precise identification of the resulting DASs is also rather difficult. In this regard, we developed a two-step specific-adsorption strategy (pyrolysis-free) and constructed a DAS catalyst featuring FeCo "molecular heterostructures" (FeCo-MHs). In order to rule out the possibility of the two apparently neighboring (in the electron microscopy image) Fe/Co atoms being dispersed respectively on the top/bottom surfaces of the carbon support and thus forming "false" MHs, we conducted in situ rotation (by 8°, far above the critical angle of 5.3°) and directly identified the individual FeCo-MHs. The formation of FeCo-MHs could modulate the magnetic moments of the metal centers and increase the ratio of low-spin Fe(II)-N4 moiety; thus the intrinsic activity could be optimized at the apex of the volcano-plot (a relationship as a function of magnetic moments of metal-phthalocyanine complexes and catalytic activities). The FeCo-MHs catalyst displays an exceptional ORR activity (E1/2 = 0.95 V) and could be used to construct high-performance cathodes for hydroxide exchange membrane fuel cells and zinc-air batteries.

Biomass-Derived Bifunctional Cathode Electrocatalyst and Multiadaptive Gel Electrolyte for High-Performance Flexible Zn-Air Batteries in Wide Temperature Range

High-efficiency and low-cost bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), as well as gel electrolytes with high thermal and mechanical adaptability are required for the development of flexible batteries. Herein, abundant Setaria Viridis (SV) biomass is selected as the precursor to prepare porous N-doped carbon tubes with high specific surface area and the 900 °C calcination product of SV (SV-900) shows the optimum ORR/OER activities with a small EOER -EORR of 0.734 V. Meanwhile, a new multifunctional gel electrolyte named C20E2G5 is prepared using cellulose extracted from another widely distributed biomass named flax as the skeleton, epichlorohydrin as the cross-linker and glycerol as the antifreezing agent. C20E2G5 possesses high ionic conductivity from -40 to + 60 °C, excellent tensile and compressive resistance, high adhesion, strong freezing and heat resistance. Moreover, the symmetrical cell assembled with C20E2G5 can significantly inhibit Zn dendrite growth. Finally, flexible solid-state Zn-air batteries assembled with SV-900 and C20E2G5 show high open circuit voltage, large energy density, and long-term operation stability between -40 and + 60 °C. This biomass-based approach is generic and can be used for the development of diverse next-generation electrochemical energy conversion and storage devices.

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

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

Engineering work functions of cobalt-doped manganese oxide based electrocatalysts for highly efficient oxygen evolution reaction

The crystalline and electronic structures are two important factors for the design of electrocatalysts. In this work, Co-doped MnO electrocatalysts grown on nickel foam (NF) were prepared by a facile hydrothermal reaction, followed by H₂ treatment process. The electrocatalytic performance of MnO was significantly improved after doping with Co and the Co_0.1Mn_0.9O-NF sample achieved excellent oxygen evolution reaction (OER) performance with low overpotential (370 mV at 10 mA cm^-2) and reasonable Tafel slope (85.6 mV dec^-1). Significantly, the low work function was obtained in the Co_0.1Mn_0.9O-NF sample (4.37 eV), which could accelerate the charge transfer process of the OER activity. The excellent OER performance of the Co_0.1Mn_0.9O-NF sample is also attributed to the rich active sites, which improved electrical conductivity and enlarged electrochemical surface areas.

Stabilization of transition metal heterojunctions inside porous materials for high-performance catalysis

Transition metal-based heterostructural materials are a class of very promising substitutes for noble metal-based catalysts for high-performance catalysis, due to their inherent internal electric field at the interface in the heterojunctions, which could induce electron relocalization and facilitate charge carrier migration between different metal sites at heterostructural boundaries. However, redox-active metal species suffer from reduction, oxidation, migration, aggregation, leaching and poisoning in catalysis, which results in heavy deterioration of the catalytic properties of transition metal-based heterojunctions and frustrates their practical applications. To improve the stability of transition metal-based heterojunctions and sufficiently expose redox-active sites at the heterosurfaces, many kinds of porous materials have been used as porous hosts for the stabilization of non-precious metal heterojunctions. This review article will discuss recently developed strategies for encapsulation and stabilization of transition metal heterojunctions inside porous materials, and highlight their improved stability and catalytic performance through the spatial confinement effect and synergistic interaction between the heterojunctions and the host matrices.

Designed Concave Octahedron Heterostructures Decode Distinct Metabolic Patterns of Epithelial Ovarian Tumors

Epithelial ovarian cancer (EOC) is a polyfactorial process associated with alterations in metabolic pathways. A high-performance screening tool for EOC is in high demand to improve prognostic outcome but is still missing. Here, a concave octahedron Mn₂ O₃ /(Co,Mn)(Co,Mn)₂ O₄ (MO/CMO) composite with a heterojunction, rough surface, hollow interior, and sharp corners is developed to record metabolic patterns of ovarian tumors by laser desorption/ionization mass spectrometry (LDI-MS). The MO/CMO composites with multiple physical effects induce enhanced light absorption, preferred charge transfer, increased photothermal conversion, and selective trapping of small molecules. The MO/CMO shows ≈2-5-fold signal enhancement compared to mono- or dual-enhancement counterparts, and ≈10-48-fold compared to the commercialized products. Subsequently, serum metabolic fingerprints of ovarian tumors are revealed by MO/CMO-assisted LDI-MS, achieving high reproducibility of direct serum detection without treatment. Furthermore, machine learning of the metabolic fingerprints distinguishes malignant ovarian tumors from benign controls with the area under the curve value of 0.987. Finally, seven metabolites associated with the progression of ovarian tumors are screened as potential biomarkers. The approach guides the future depiction of the state-of-the-art matrix for intensive MS detection and accelerates the growth of nanomaterials-based platforms toward precision diagnosis scenarios.

Supporting Trimetallic Metal-Organic Frameworks on S/N-Doped Carbon Macroporous Fibers for Highly Efficient Electrocatalytic Oxygen Evolution

Hybrid materials, integrating the merits of individual components, are ideal structures for efficient oxygen evolution reaction (OER). However, the rational construction of hybrid structures with decent physical/electrochemical properties is yet challenging. Herein, a promising OER electrocatalyst composed of trimetallic metal-organic frameworks supported over S/N-doped carbon macroporous fibers (S/N-CMF@Fe_x Co_y Ni_1-x-y -MOF) via a cation-exchange strategy is delicately fabricated. Benefiting from the trimetallic composition with improved intrinsic activity, hollow S/N-CMF matrix facilitating exposure of active sites, as well as their robust integration, the resultant S/N-CMF@Fe_x Co_y Ni_1-x-y -MOF electrocatalyst delivers outstanding activity and stability for alkaline OER. Specifically, it needs an overpotential of 296 mV to reach the benchmark current density of 10 mA cm^-2 with a small Tafel slope of 53.5 mV dec^-1 . In combination with X-ray absorption fine structure spectroscopy and density functional theory calculations, the post-formed Fe/Co-doped γ-NiOOH during the OER operation is revealed to account for the high OER performance of S/N-CMF@Fe_x Co_y Ni_1-x-y -MOF.

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

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

Hollow Carbon Nanopillar Arrays Encapsulated with Pd-Cu Alloy Nanoparticles for the Oxygen Evolution Reaction

Delicate design and bottom-up synthesis of hollow nanostructures for oxygen evolution electrocatalysts is a promising way to accelerate the reaction kinetics of overall water splitting. Herein, an efficient and versatile strategy for the controllable preparation of Pd-Cu alloy nanoparticles encapsulated in carbon nanopillar arrays (PD-Cu@HPCN) is developed. Core-shell structured MOF@imidazolium-based ionic polymers (ImIPs) have been prepared and adopted as a template, along with the decomposition of the inner Cu-MOFs when an anion exchange occurs between sodium tetrachloropalladate in solution and bromides in the external ImIP shell. Pd nanoparticles will be highly dispersed in the resulting Pd-Cu@HO-ImIP array, and subsequent topotactic transformation generates Pd-Cu@HNPC. No hazardous reagents or tedious steps are used to remove the inner Cu-MOF templates in contrast to the traditional top-down methods. Remarkably, the Pd-Cu@HPCN catalyst possesses outstanding oxygen evolution reaction (OER) activity, including small overpotential with 10 mA cm^-2 at an overpotential of 188 mV, a large double layer capacitance (73.8 mF cm^-2), and high stability (20 h). This simple, green, and efficient synthesis methodology represents a new way to design metal alloys for OER electrocatalysts or other electrocatalytic devices.

Enhancing the oxygen reduction activity by constructing nanocluster-scaled Fe2O3/Cu interfaces

Interface engineering is a promising strategy to enhance the catalytic performance of electrocatalysts for the oxygen reduction reaction (ORR). However, it is still a challenge to modulate the size into a suitable range (e.g., nanocluster-scale) to make the most of the interface. Moreover, the explicit mechanism of the interface for enhancing catalytic performance is still elusive. Herein, a model catalyst (FeCu@NC) loaded with nanocluster-scaled Fe₂O₃/Cu interfaces was prepared by modulating the metal components of the precursor to explore the enhancement of interface engineering for the ORR. Benefiting from the synergistic effect of the strong interfacial coupling effects of Fe₂O₃/Cu and optimized microstructure, FeCu@NC exhibited superior ORR activity and zinc-air battery performance. Experimental and theoretical calculations revealed that the presence of the Fe₂O₃/Cu interface breaks the traditional cognition to endow the Cu atoms (intrinsically inferior for the ORR) with a slight positive charge, which serves as the active sites for the ORR. This study provides a novel insight into the design of advanced electrocatalysts for the ORR by interface engineering.

Construction of a Co/MnO Mott-Schottky Heterostructure to Achieve Interfacial Synergy in the Oxygen Reduction Reaction for Aluminum-Air Batteries

The rational design of non-noble metal-based electrocatalysts for an efficient oxygen reduction reaction (ORR) is an important research topic to promote the advancement of aluminum-air batteries. In this work, heterostructural Co/MnO nanoparticles encapsulated in a N-doped carbon electrocatalyst were prepared via one-step pyrolysis utilizing different reduction potentials of Co and Mn ions, and the heterointerface between the two phases was confirmed. The prepared catalyst displays Pt/C competitive ORR performance because of the interfacial synergy of a Co/MnO Mott-Schottky (M-S) heterostructure, which leads to boosted conductivity, formation of an M-S barrier, and a reduced oxygen reduction energy barrier for excited electrons. Furthermore, the Co/MnO-based aluminum-air battery displays good discharge performance, demonstrating good feasibility for practical application.