Monodispersed Co in Mesoporous Polyhedrons: Fine-tuning of ZIF-8 Structure with Enhanced Oxygen Reduction Activity

Multilayer Porous Fe/Co-N-MWCNT Electrocatalyst For Rechargeable Zinc-Air Batteries

The design of efficient, stable, low-cost non-precious metal-based electrocatalysts with enhanced oxygen reduction reaction (ORR) activity has garnered significant attention in the scientific community. This study introduces a novel electrocatalyst, Fe/Co-N-MWCNT, synthesized through the in-situ growth of ZIF-8 and Fe/Co-Phen on multi-walled carbon nanotubes (MWCNTs), followed by pyrolysis at varying temperatures to optimize its properties. The inclusion of Fe and Co during the pyrolysis process facilitated the creation of metal active sites and Fe-Co, enhancing electron transfer and ORR activity. Compared to Pt/C (E1/2=0.854 V, JL=4.90 mA cm-2), Fe/Co-N-MWCNT exhibited a similar half-wave potential (E1/2=0.812 V) and an improved limiting current density (JL=5.37 mA cm-2). Moreover, Fe/Co-N-MWCNT displayed remarkable stability, showing only a 7 mV negative shift in E1/2 after 2000 cycles. Ampere response testing indicated a current decay of only 7.8 % for Fe/Co-N-MWCNT after 10000 s, while Pt/C experienced a decay of about 18.4 %. The exceptional catalytic stability of Fe/Co-N-MWCNT positions it as a promising candidate for rechargeable zinc-air batteries, attributed to its high pyridinic nitrogen content, unique structure, and abundant metal active sites.

A novel metal-organic framework based electrochemical immunosensor for the rapid detection of Salmonella typhimurium detection in milk

Salmonella is one of the most prevalent pathogens causing foodborne diseases. In this study, a novel electrochemical immunosensor was designed for the rapid and accurate detection of Salmonella typhimurium (S. typhimurium) in milk. Platinum nanoparticles and Co/Zn-metal-organic framework @carboxylic multiwalled carbon nanotubes in the immunosensor acted synergistically to enhance the sensing sensitivity and stability. The materials and sensors were characterised using X-ray diffractometry, scanning electron microscopy, Fourier-transform infrared spectroscopy, differential pulse voltammetry, cyclic voltammetry, and other techniques. The optimised immunosensor showed a linear response for S. typhimurium concentrations in the range from 1.3 × 102 to 1.3 × 108 CFU mL-1, with a detection limit of 9.4 × 101 CFU mL-1. The assay also demonstrates good specificity, reproducibility, stability, and practical application potential, and the method can be extended to other foodborne pathogens.

Interfacial Engineering of Leaf-like Bimetallic MOF-Based Co@NC Nanoarrays Coupled with Ultrathin CoFe-LDH Nanosheets for Rechargeable and Flexible Zn-Air Batteries

Exploring high-efficiency, low-cost, and long-life bifunctional self-supporting electrocatalysts is of great significance for the practical application of advanced rechargeable Zn-air batteries (ZABs), especially flexible solid-state ZABs. Herein, ultrathin CoFe-layered double hydroxide (CoFe-LDH) nanosheets are strongly coupled on the surface of leaf-like bimetallic metal-organic frameworks (MOFs)-derived hybrid carbon (Co@NC) nanoflake nanoarrays supported by carbon cloth (CC) via a facile and scalable method for rechargeable and flexible ZABs. This interfacial engineering for CoFe-LDHs on Co@NC improves the electronic conductivity of CoFe-LDH nanosheets as well as achieves the balance of oxygen evolution reduction (OER) and oxygen reduction reaction (ORR) activity. The unique three-dimensional (3D) open interconnected hierarchical structure facilitates the transport of substances during the electrochemical process while ensuring adequate exposure of OER/ORR active centers. When applied as an additive-free air cathode in rechargeable liquid ZABs, CC/Co@NC/CoFe-LDH-700 demonstrates high open-circuit potential of 1.47 V, maximum power density of 129.3 mW cm^-2, and satisfactory specific capacity of 710.7 mAh g^-1_Zn. Further, the flexible all-solid-state ZAB assembled by CC/Co@NC/CoFe-LDH-700 displays gratifying mechanical flexibility and stable cycling performance over 40 h. More significantly, the series-connected flexible ZAB is further verified as a chain power supply for LED strips and performs well throughout the bending process, showing great application prospects in portable and wearable electronics. This work sheds new light on the design of high-performance self-supporting non-precious metal bifunctional electrocatalysts for OER/ORR and air cathodes for rechargeable ZABs.

Biomimetic anti-inflammatory and osteogenic nanoparticles self-assembled with mineral ions and tannic acid for tissue engineering

Bone healing involves complex processes including inflammation, induction, and remodeling. In this context, anti-inflammatory and osteoconductive multi-functional nanoparticles have attracted considerable attention for application in improved bone tissue regeneration. In particular, nanoparticles that promote suppression of inflammatory response after injury and direction of desirable tissue regeneration events are of immense interest to researchers. We herein report a one-step method to prepare multi-functional nanoparticles using tannic acid (TA) and simulated body fluid (SBF) containing multiple mineral ions. Mineral-tannic acid nanoparticles (mTNs) were rapidly fabricated in 10 min, and their size (around 250-350 nm) and chemical composition were controlled through the TA concentration. In vitro analysis using human adipose derived stem cells (hADSCs) showed that mTNs effectively scavenged reactive oxygen species (ROS) and enhanced osteogenesis of hADSCs by inducing secretion of alkaline phosphatase. mTNs also increased osteogenic marker gene expression even in the presence of ROS, which can generally arrest osteogenesis (OPN: 1.74, RUNX2: 1.90, OCN: 1.47-fold changes relative to cells not treated with mTNs). In vivo analysis using a mouse peritonitis model revealed that mTNs showed anti-inflammatory effects by decreasing levels of pro-inflammatory cytokines in blood (IL-6: 73 ± 4, TNF-α: 42 ± 2%) and peritoneal fluid (IL-6: 78 ± 2, TNF-α: 21 ± 6%). We believe that this one-step method for fabrication of multi-functional nanoparticles has considerable potential in tissue engineering approaches that require control of complex microenvironments, as required for tissue regeneration.

Partial deligandation activated ZIF-67 for efficient electrocatalytic oxygen reduction reaction

Removing the blocked molecular groups and fully exposing the intrinsic active sites of metal-organic frameworks (MOFs) could give full play to their advantages of multi-active sites and multi-channel mass transfer, which will benefit the electrocatalytic oxygen reduction reaction (ORR) in fuel cells. Here, the partial diligandation-activated ZIF-67 (named as ZIF-67–400) with excellent ORR performance was obtained by simple low-temperature pyrolysis. The ORR electrocatalytic activity exhibits a half-wave potential of 0.82 V and the stability of maintaining 96% activity after 10 h of operation, which is comparable to commercial Pt/C. Further research studies reveal that the morphology, special dodecahedron configuration, and crystal structure of ZIF-67-400 are maintained well during the pyrolysis, but some hydrocarbon groups in the ligands are eliminated, resulting in the active sites being exposed and coordinated with the intrinsic porosity, improving the catalytic performance. This work may provide an alternative path for activating the electrocatalytic performance of metal-organic frameworks by low-temperature annealing.

Identification of Catalytic Active Sites for Durable Proton Exchange Membrane Fuel Cell: Catalytic Degradation and Poisoning Perspectives

Recent progress in synthetic strategies, analysis techniques, and computational modeling assist researchers to develop more active catalysts including metallic clusters to single-atom active sites (SACs). Metal coordinated N-doped carbons (M-N-C) are the most auspicious, with a large number of atomic sites, markedly performing for a series of electrochemical reactions. This perspective sums up the latest innovative and computational comprehension, while giving credit to earlier/pioneering work in carbonaceous assembly materials towards robust electrocatalytic activity for proton exchange membrane fuel cells via inclusive performance assessment of the oxygen reduction reaction (ORR). M-N_x -C_y are exclusively defined active sites for ORR, so there is a unique possibility to intellectually design the relatively new catalysts with much improved activity, selectivity, and durability. Moreover, some SACs structures provide better performance in fuel cells testing with long-term durability. The efforts to understand the connection in SACs based M-N_x -C_y moieties and how these relate to catalytic ORR performance are also conveyed. Owing to comprehensive practical application in the field, this study has covered very encouraging aspects to the current durability status of M-N-C based catalysts for fuel cells followed by degradation mechanisms such as macro-, microdegradation, catalytic poisoning, and future challenges.

Fe/Co/N-C/graphene derived from Fe/ZIF-67/graphene oxide three dimensional frameworks as a remarkably efficient and stable catalyst for the oxygen reduction reaction

The development of non-noble metal catalysts with high-performance, long stability and low-cost is of great importance for fuel cells, to promote the oxygen reduction reaction (ORR). Herein, Fe/Co/N-C/graphene composites were easily prepared by using Fe/ZIF-67 loaded on graphene oxide (GO). The Fe/Co/porous carbon nanoparticles were uniformly dispersed on graphene with high specific surface area and large porosity, which endow high nitrogen doping and many more active sites with better ORR performance than the commercial 20 wt% Pt/C. Therefore, Fe/Co/N-C/graphene composites exhibited excellent ORR activity in alkaline media, with higher initial potential (0.91 V) and four electron process. They also showed remarkable long-term catalytic stability with 96.5% current retention after 12 000 s, and outstanding methanol resistance, compared with that of 20 wt% Pt/C catalysts. This work provides an effective strategy for the preparation of non-noble metal-based catalysts, which could have significant potential applications, such as in lithium-air batteries and water-splitting devices.

Recent Advances in Synthesis and Applications of Single-Atom Catalysts for Rechargeable Batteries

The rapid development of flexible and wearable optoelectronic devices, demanding the superior, reliable, and ultra-long cycling energy storage systems. But poor performances of electrode materials used in energy devices are main obstacles. Recently, single-atom catalysts (SACs) are considered as emerging and potential candidates as electrode materials for battery devices. Herein, we have discussed the recent methods for the fabrication of SACs for rechargeable metal-air batteries, metal-CO₂ batteries, metal-sulfur batteries, and other batteries, following the recent advances in assembling and performance of these batteries by using SACs as electrode materials. The role of SACs to solve the bottle-neck problems of these energy storage devices and future perspectives are also discussed.

Nanostructure Engineering of Metal-Organic Derived Frameworks: Cobalt Phosphide Embedded in Carbon Nanotubes as an Efficient ORR Catalyst

Heteroatom doping is considered an efficient strategy when tuning the electronic and structural modulation of catalysts to achieve improved performance towards renewable energy applications. Herein, we synthesized a series of carbon-based hierarchical nanostructures through the controlled pyrolysis of Co-MOF (metal organic framework) precursors followed by in situ phosphidation. Two kinds of catalysts were prepared: metal nanoparticles embedded in carbon nanotubes, and metal nanoparticles dispersed on the carbon surface. The results proved that the metal nanoparticles embedded in carbon nanotubes exhibit enhanced ORR electrocatalytic performance, owed to the enriched catalytic sites and the mass transfer facilitating channels provided by the hierarchical porous structure of the carbon nanotubes. Furthermore, the phosphidation of the metal nanoparticles embedded in carbon nanotubes (P-Co-CNTs) increases the surface area and porosity, resulting in faster electron transfer, greater conductivity, and lower charge transfer resistance towards ORR pathways. The P-Co-CNT catalyst shows a half-wave potential of 0.887 V, a Tafel slope of 67 mV dec⁻¹, and robust stability, which are comparatively better than the precious metal catalyst (Pt/C). Conclusively, this study delivers a novel path for designing multiple crystal phases with improved catalytic performance for energy devices.

Novel Mn-/Co-Nx Moieties Captured in N-Doped Carbon Nanotubes for Enhanced Oxygen Reduction Activity and Stability in Acidic and Alkaline Media

Fe-N-C-based electrocatalysts have been developed as an encouraging substitute compared to their expensive Pt-containing equivalents for the oxygen reduction reaction (ORR). However, they still face major durability challenges from the in- situ production of Fenton radicals. Therefore, the synthesis of Fe-free ORR catalysts is among the emerging concerns. Herein, we have precisely applied a multistep heating strategy to produce mesoporous N-doped carbon nanostructures with Mn-/Co-N_x dual moieties from mixed-metal zeolitic imidazolate frameworks (ZIFs). It is found that their unique structure, with dual-metallic active sites, not only offers a high electrochemical performance for the ORR (E_1/2 = 0.83 V vs reversible hydrogen electrode (RHE) in acid media), but also enhances the operational durability of the catalyst after 20 000 cycles with 97% of retention and very low H₂O₂ production (<5%) in 0.1 M HClO₄. In addition, the catalyst performs well toward the ORR also in alkaline solution (exhibiting E_1/2 = 0.90 V and 30 000 cyclic stability).

MOF-derived Co/Cu-embedded N-doped carbon for trifunctional ORR/OER/HER catalysis in alkaline media

In this report, we demonstrate a bimetallic Co/Cu-embedded N-doped carbon structure for trifunctional catalysis of oxygen reduction, oxygen evolution and hydrogen evolution reactions in alkaline media. A hybrid catalyst synthesized through a metal-organic framework-based process (M-NC-CoCu) enables an active trifunctional catalysis due to its multi-faceted favorable characteristics. It is believed that a range of catalytically active sites are formed through the approach including well-dispersed tiny CuCo2O4 phases, a high concentration of pyridinic and graphitic N, and Cu-Ox, Cu-Nx and Co-Nx moieties. In addition, a high-surface-area morphology with a high concentration of sp2 bonding, which is beneficial for facilitated electron conduction, further contributes to the performance as an electrocatalyst.

ZIF67@MFC-Derived Co/N-C@CNFs Interconnected Frameworks with Graphitic Carbon-Encapsulated Co Nanoparticles as Highly Stable and Efficient Electrocatalysts for Oxygen Reduction Reactions

Development of nonprecious metal catalysts for oxygen reduction reaction (ORR) to reduce or eliminate Pt-based electrocatalysts is of great importance for fuel cells. Herein, Co/N-codoped carbon with carbon nanofiber (CNF) interconnected three-dimensional (3D) frameworks and graphitic carbon-encapsulated Co nanoparticles were designed and successfully prepared via the in situ growth of zeolitic imidazolate framework-67 (ZIF67) with biomass nano-microfibrillar cellulose (MFC) and then pyrolysis. The catalyst (Co/N-C@CNFs) exhibited outstanding long-term catalytic durability with 92.7% current retention after 70 000 s, which was much higher than that of commercial Pt/C in alkaline media. The support and connection of CNFs to Co/N-C frameworks and the protection of Co nanoparticles by graphite layers contribute to their impressive long-term catalytic stability. Meanwhile, Co/C-N@CNFs displayed excellent ORR catalytic performance (E₀ = 0.952 V vs RHE, E_1/2 = 0.852 V vs RHE, and n: 4.2) in alkaline media. This strategy provides new insights into developing advanced nonprecious metal carbon-based catalysts for ORR.

A sponge-templated sandwich-like cobalt-embedded nitrogen-doped carbon polyhedron/graphene composite as a highly efficient catalyst for Zn-air batteries

Non-noble metal materials are regarded as the most promising catalysts for the oxygen reduction reaction (ORR) to overcome the inherent defects of Pt-based catalysts, like high cost, limited availability and insufficient stability. Here, we fabricate sandwich-like Co encapsulated nitrogen doped carbon polyhedron/graphene (s-Co@NCP/rGO) via a facile and scalable strategy by loading Co-based zeolitic imidazolate framework (ZIF-67) and graphene oxide (GO) layers individually on a polyurethane (PU) sponge template. The 3D sandwich structure is maintained with the assistance of the sponge template, which promotes the uniform dispersion of ZIF-67-derived Co embedded nitrogen doped carbon polyhedra (Co@NCP) and prevents the graphene plates from agglomerating during the annealing process. The final product demonstrates considerable catalytic performance for the ORR with a half-wave potential of 0.85 V, preferable stability and increased poisoning tolerance by comparison to 20 wt% Pt/C, which stems from the 3D sandwich-like structure, N/Co-doping effect, large accessible surface area and hierarchical porous structures. The excellent ORR performance of the catalysts means that they can be utilised in a Zn-air battery as cathode catalysts. During such a demonstration, s-Co@NCP/rGO shows a high open-circuit voltage of 1.466 V, remarkable long-term durability and an outstanding peak power density of 186 mV cm-2, which shows its high potential as a prospective alternative for widespread practical application in the field of non-noble metal ORR catalysts.

Structure and electrochemical properties of hierarchically porous carbon nanomaterials derived from hybrid ZIF-8/ZIF-67 bi-MOF coated cyclomatrix poly(organophosphazene) nanospheres

Hierarchically porous carbon nanostructures with intrinsically doped heteroatoms and metal elements are attractive for electrochemical energy storage applications.

Electro- and photoelectro-catalysts derived from bimetallic amorphous metal–organic frameworks

It is developed a synthesis method for the design of new bimetallic amorphous MOFs. Such frameworks serve as precursors to prepare high-performance electro- and photoelectro-catalysts for ORR, OER and HER in both acidic and alkaline media.

Hierarchical "tube-on-fiber" carbon/mixed-metal selenide nanostructures for high-performance hybrid supercapacitors

This work reports hierarchical "tube-on-fiber" nanostructures, composed of carbon nanotubes (CNTs) on carbon nanofibers (CNFs), impregnated with mixed-metal selenide nanoparticles (Co-Zn-Se@CNTs-CNFs), as high performance supercapacitors. Co-Zn hybrid zeolitic imidazolate framework-67 (Co-Zn ZIF-67) was electrospun with polyacrylonitrile (PAN) to form nanofibers that were sequentially thermally treated and subjected to selenylation. The "tube-on-fiber" structure is designed to confine the Co-Zn mixed-metal selenide nanoparticles and prevents their agglomeration. Extruded CNTs rooting in carbon nanofibers further improve the electronic conductivity. The mixed-metal selenide allows more accommodation space and faradic reactions compared to single metal selenide. Based on these merits, the hierarchical Co-Zn-Se@CNTs-CNFs exhibit a high specific capacity of 1040.1 C g^-1 (1891 F g^-1) at 1 A g^-1 with impressive rate performance in supercapacitors. Furthermore, a hybrid supercapacitor with Co-Zn-Se@CNTs-CNFs as the cathode and porous carbon nanofibers as the anode (denoted as Co-Zn-Se@CNTs-CNFs//PCNFs) is fabricated. It delivers a superior energy and power density of 61.4 W h kg^-1 and 754.4 W kg^-1, respectively, and meanwhile retains 31.7 W h kg^-1 of the energy density with 15 421.6 W kg^-1 of the working power. In addition, the assembled supercapacitor device displays an excellent capacity retention of 88.6% after 8000 cycles at 5 A g^-1.

Comparison of new metal organic framework-based catalysts for oxygen reduction reaction

In this article, we collected the most significant and recent data in brief in the field of metal organic frameworks oxygen reduction reaction catalysts, obtained from some of the most recent research papers in the field. We present lists of materials and their key parameters that are relevant to the cathode catalysts in polymer electrolyte membrane fuel cells. All the materials listed in this paper are composed of metal organic frameworks, zeolitic imidazolate frameworks, or their derivatives. These are divided into two main groups: pristine MOFs and MOF-derived materials. The data in this article is a summary of more extensive review (Gonen and Elbaz, 2018) [1].