Immobilization of iron phthalocyanine on MOF-derived N-doped carbon for promoting oxygen reduction in zinc-air battery.

Functional carbon nanomaterials play a crucial role in the cathodic oxygen reduction reaction (ORR) for sustainable fuel cells and metal-air batteries. In this study, we propose an effective approach to immobilize iron phthalocyanines (FePc) by employing a porous N-doped carbon material, denoted as NC-1000, derived from a sheet-shaped coordination polymer. The resulting NC-1000 possesses substantial porosity and abundant pore defects. The nitrogen sites within NC-1000 not only facilitate FePc adsorption but also optimize the electron distribution at the Fe-N site. The FePc@NC-1000 composite material exhibits a significant number of active centers in the form of Fe-N4 moieties, showcasing satisfactory ORR activity. Specifically, it demonstrates an onset potential of 0.99 V, a positive half-wave potential of 0.86 V, a large limiting current of 5.96 mA cm-2, and a small Tafel slope of 44.41 mV dec-1. Additionally, theoretical calculations and experimental results confirm the favorable performance and durability of zinc-air batteries assembled using FePc@NC-1000, thereby highlighting their considerable potential for practical applications. Overall, this study provides a comprehensive exploration of the enhanced catalytic performance and increased stability of metal-organic framework-derived functional carbon nanomaterials as cost-effective, efficient, and stable catalysts for the ORR.

Metal-Organic Frameworks for Greenhouse Gas Applications.

Using petrol to supply energy for a car or burning coal to heat a building generates plenty of greenhouse gas (GHG) emissions, including carbon dioxide (CO2 ), water vapor (H2 O), methane (CH4 ), nitrous oxide (N2 O), ozone (O3 ), fluorinated gases. These up-and-coming metal-organic frameworks (MOFs) are structurally endowed with rigid inorganic nodes and versatile organic linkers, which have been extensively used in the GHG-related applications to improve the lives and protect the environment. Porous MOF materials and their derivatives have been demonstrated to be competitive and promising candidates for GHG separation, storage and conversions as they shows facile preparation, large porosity, adjustable nanostructure, abundant topology, and tunable physicochemical property. Enormous progress has been made in GHG storage and separation intrinsically stemmed from the different interaction between guest molecule and host framework from MOF itself in the recent five years. Meanwhile, the use of porous MOF materials to transform GHG and the influence of external conditions on the adsorption performance of MOFs for GHG are also enclosed. In this review, it is also highlighted that the existing challenges and future directions are discussed and envisioned in the rational design, facile synthesis and comprehensive utilization of MOFs and their derivatives for practical applications.

Hierarchical N-doped CNTs grafted onto MOF-derived porous carbon nanomaterials for efficient oxygen reduction.

The rational design and preparation of nonprecious metal-based oxygen reduction reaction (ORR) catalysts to facilitate electron and mass transport are of great significance in oxygen-involved energy applications. Herein, a stepwise approach to synthesize a type of hierarchically porous N-doped carbon nanotubes (CNTs) grafted onto zinc-based coordination polymer derived carbon nanomaterials (M-NCNT, M = Fe/Co/Ni) is proposed. At first, an isostructural zinc-based metal-organic framework (MOF) to HKUST-1(Cu) (ZnHKUST-1) is solvothermally prepared, and then under pyrolysis to obtain MOF-derived porous carbon. After the secondary calcination, the in-situ formed N-doped CNTs are efficiently catalyzed by iron group metal-based nanoparticles (Fe/Co/Ni), which are thermally reduced by porous carbon together with additional urea. The synergistic effect between ultrahigh porosity, large surface area, suitable N-doping, high graphitization degree, and ultrafine metal particles prompts M-NCNT series to exhibit satisfactory electrocatalysis in oxygen reduction. Among them, Fe-NCNT owns the optimal ORR activity with high positive onset potential (0.987 V), half-wave potential (0.860 V) and large diffusion-limited current density (4.893 mA cm-2). Meanwhile, it shows a high current retention of 90.7% after the 24-hour stability, and the obtained Zn-air battery by Fe-NCNT with open-circuit voltage of 1.44 V owns moderate capacity and satisfying stability. The demonstrated method to prepare hierarchically porous N-doped carbon nanomaterials stemmed from MOF precursors unfolds a new route for the facile construction of efficient nanocatalysts for advanced energy applications.

Surfactant-Mediated Morphological Evolution of MnCo Prussian Blue Structures.

In the preparation of nanomaterials, the kinetics and thermodynamics in the reaction can significantly affect the structures and phases of nanocrystals. Therefore, people are keen to adopt various synthetic strategies to accurately assemble the target nanocrystals, and reveal the underlying mechanism of the formation of specific structures. In this work, the total reaction time is adjusted to let the prepared MnCo Prussian blue analogous (MnCoPBA) crystals show four evolving morphological changes at different stages with the assistance of sodium dodecyl sulfate. Furthermore, it is clearly observed that the epitaxial growth along the (100) plane on the shell of MnCoPBA nanocrystals is favored, and the thermodynamics and kinetics in the morphology change process are analyzed in detail. Through the simple pyrolysis, MnCoPBA crystals can be successfully converted into the corresponding carbon composites, of which Mn2 Co2 C nanoparticles are evenly distributed in highly graphitized carbon matrix. Among them, PBA-III-700 performs good oxygen reduction reaction performance in alkaline solution with the half-wave potential of 0.801 V and diffusion-limited current density of 5.36 mA cm-2 , and its zinc-air battery exhibits the peak power density of 103.4 mW cm-2 competitive with commercial Pt/C.

A review of recent work on using metal-organic frameworks to grow carbon nanotubes.

Carbon nanotubes (CNTs) have long been known as a class of one-dimensional carbon nanomaterials with sp2-hybridized structures that can be constructed with a very large length-to-diameter ratio, which is significantly larger than that of any other carbon nanomaterials. It is well known that CNTs exhibit many excellent properties in mechanics, electricity, chemistry, optics, etc., and are widely used in various fields, thus attracting scientists' attention. In this context, the development of new strategies for optimizing and synthesizing CNTs has far-reaching significance and demand. On the other hand, most metal-organic frameworks (MOFs) are microporous crystals constructed from ordered and uniform metal ions/clusters and organic linkers to obtain crystalline solids with potential porosity. Using MOF materials as precursors, hierarchical CNT-based composite materials, which are difficult to synthesize through the traditional catalyst-assisted chemical vapor deposition method, can be conveniently synthesized by thermal treatment at high temperature. In the process of converting MOFs into CNTs, MOF crystals are used as both catalysts and carbon sources, which are necessary for the growth of CNTs, and they are also used as templates and/or carriers for additional catalysts. Therefore, there are various possibilities for the thermal conversion of MOFs into CNT-based composite materials. In this review, we mainly summarize the two aspects of catalysts and synthetic strategies for MOF-derived CNT-based composite materials. Despite the rapid development in this area, there is still much space for exploration. In order to accurately control the synthesis of CNTs, we should deeply explore the thermal conversion process and mechanism for the conversion of MOFs into CNTs.