Templating Synthesis of Mesoporous Fe3C-Encapsulated Fe-N-Doped Carbon Hollow Nanospindles for Electrocatalysis

Efficient Synthesis of Fe/N-Doped Carbon Nanotube as Highly Active Catalysts for Oxygen Reduction Reaction in Alkaline Media

It is of significant implication to fabricate high-performance, durable and low-cost catalysts toward to oxygen reduction reaction (ORR) to drive commercial application of fuel cells. In our work, we synthesize the Fe/N-CNT catalyst via one-pot grinding combined with calcination using a mixture of carbamide, CNTs and iron salts as precursors, the as-synthesized catalysts show the structure that Fe nanoparticles are encapsulated in the tube of intertwined CNTs with abundant active sites. The catalyst is synthesized at 800 °C (Fe/N-CNT-800-20) obtain high graphitization degree and high N doped content, especially the high content and proportion of Fe-N and pyridinic-N, exhibiting outstanding ORR activity. Moreover, too high calcination temperature (850 °C) and high Fe content (25%) lead to the agglomeration of Fe during the calcination, which blocked some catalytic sites, leading to poor ORR activity. This facile synergy route will provide new thoughts for the fabrication and optimization of catalysts.

In situ immobilization of Fe/Fe3C/Fe2O3 hollow hetero-nanoparticles onto nitrogen-doped carbon nanotubes towards high-efficiency electrocatalytic oxygen reduction

The rational design of affordable, efficient and robust electrocatalysts towards the oxygen reduction reaction (ORR) is of vital importance for the future advancement of various renewable-energy technologies. Herein, we develop a feasible and delicate synthesis of Fe/Fe3C/Fe2O3 hollow heterostructured nanoparticles in situ immobilized on highly graphitic nitrogen-doped carbon nanotubes (referred to as Fe/Fe3C/Fe2O3@N-CNTs hereafter) via a simple hydrogel-bridged pyrolysis strategy. The simultaneous consideration of interfacial manipulation and nanocarbon hybridization endows the formed Fe/Fe3C/Fe2O3@N-CNTs with sufficiently well-dispersed and firmly immobilized active components, regulated electronic configuration, enhanced electrical conductivity, multidimensional mass transport channels, and remarkable structural stability. Consequently, benefiting from the compositional synergy and architectural superiority, the as-obtained Fe/Fe3C/Fe2O3@N-CNTs exhibit excellent ORR catalytic activity, impressive durability and superior selectivity in an alkaline electrolyte, outperforming the commercial Pt/C catalyst and a majority of the previously reported Fe-based catalysts. Furthermore, the rechargeable Zn-air battery using Fe/Fe3C/Fe2O3@N-CNTs + RuO2 as an air-cathode exhibits a higher power density, larger specific capacity and better cycling stability as compared with the state-of-the-art Pt/C + RuO2 counterpart. The explored hydrogel-bridged pyrolysis strategy enabling the concurrent heterointerface construction, nanostructure engineering and nanocarbon hybridization may inspire the future design of high-efficiency electrocatalysts for diverse renewable energy applications.

Tri-(Fe/F/N)-doped porous carbons as electrocatalysts for the oxygen reduction reaction in both alkaline and acidic media

Developing a low cost, sustainable and high-performance precious-metal free catalyst to replace platinum (Pt)-based catalysts for the oxygen reduction reaction (ORR) in fuel cells has recently attracted significant attention. It is crucial to produce more abundant and more uniformly dispersed ORR active sites for improving the ORR performance of the catalyst. Herein, we synthesized tri-(Fe/F/N)-doped porous carbons as high-efficiency electrocatalysts for the ORR by using Fe-zeolitic imidazolate framework-8 (Fe-ZIF-8) and ammonium fluoride as precursors. The results indicate that the as-prepared FeFNC-5 catalysts exhibit superior ORR activity, methanol tolerance, and long-term stability compared to commercial 20 wt% Pt/C in both alkaline and acidic media because of the abundant and dispersed Fe-N_x and pyridinic-N active sites, high specific surface area, and hierarchical porous structure. This work provides a new method and insights into the synthesis of Fe, F, and N triple-doped porous carbons as high-efficiency ORR electrocatalysts.

Defective S/N co-doped carbon cloth via a one-step process for effective electroreduction of nitrogen to ammonia

The electroreduction of nitrogen (N₂) has gained increasing attention as a promising route to achieve green and sustainable ammonia (NH₃) production.

Formaldehyde-Controlled Synthesis of Multishelled Hollow Mesoporous SiO2 Microspheres

We developed a facile one-pot method to synthesize multishelled hollow mesoporous SiO₂ microspheres (HMSs) with controllable interior structures including one-shell, double-shell, and yolk-shell. Single reagent formaldehyde could fully control the morphology of HMSs, in that formaldehyde was crucial to the SiO₂ precursor's hydrolysis rate and the template pore size.

A Hydrangea-Like Superstructure of Open Carbon Cages with Hierarchical Porosity and Highly Active Metal Sites

Carbon micro-/nanocages have attracted great attention owing to their wide potential applications. Herein, a self-templated strategy is presented for the synthesis of a hydrangea-like superstructure of open carbon cages through morphology-controlled thermal transformation of core@shell metal-organic frameworks (MOFs). Direct pyrolysis of core@shell zinc (Zn)@cobalt (Co)-MOFs produces well-defined open-wall nitrogen-doped carbon cages. By introducing guest iron (Fe) ions into the core@shell MOF precursor, the open carbon cages are self-assembled into a hydrangea-like 3D superstructure interconnected by carbon nanotubes, which are grown in situ on the Fe-Co alloy nanoparticles formed during the pyrolysis of Fe-introduced Zn@Co-MOFs. Taking advantage of such hierarchically porous superstructures with excellent accessibility, synergetic effects between the Fe and the Co, and the presence of catalytically active sites of both metal nanoparticles and metal-N_x species, this superstructure of open carbon cages exhibits efficient bifunctional catalysis for both oxygen evolution reaction and oxygen reduction reaction, achieving a great performance in Zn-air batteries.

Pyrolysis of self-assembled hemin on carbon for efficient oxygen reduction reaction

The employment of inexpensive metallomacrocycles to create non-precious metal electrocatalysts (NPMEs) with high performance remains a challenge. Herein, we report the self-assembly of low-cost and abundant hemin on carbon black (EC600) under hydrothermal conditions in combination with subsequent pyrolysis, leading to a new NPME. Our NPME exhibits a half-wave potential of 0.89 V vs. reversible hydrogen electrode (RHE), an onset potential of 1.0 V vs. RHE and an average HO[Formula: see text] yield below 2% as well as high durability toward oxygen reduction reactions (ORR) in alkaline electrolytes, ranking at the top of all reported NPMEs derived from hemin.

Temperature-directed synthesis of N-doped carbon-based nanotubes and nanosheets decorated with Fe (Fe3O4, Fe3C) nanomaterials

The coupling of N-doped carbon materials with transition-metal-based materials shows great promise for electrochemical energy conversion and storage. However, it is still a big challenge to achieve high-performance carbon-based composites with a simplified preparation process and a general synthesis strategy. Herein, a facile and efficient one-pot synthetic strategy was developed for the simultaneous preparation of N-doped one-dimensional carbon nanotube-based hybrids and two-dimensional carbon nanosheet-based hybrids through temperature-directed fabrication. A mixture containing dicyandiamide (DCDA), glucose, and FeCl3·6H2O as precursors was used. C3N4, derived from the pyrolysis of DCDA, acted not only as the self-sacrificing template to guide the formation of the distinct shape and structure of the hybrids, but also as the N and C sources for N-doped carbon materials. Meanwhile, FeCl3·6H2O served both as the catalyst to induce the transformation of the structure and as the reactive template affording an Fe reservoir to generate various Fe species. Effects of temperature on the structure and morphology as well as on the corresponding electrochemical performance of the hybrids were further studied in detail. Moreover, the as-prepared products demonstrated good capacitive performance. This work provides good guidance for the facile and efficient preparation of N-doped carbon-based materials with a distinct shape and structure.

Templated Growth of Crystalline Mesoporous Materials: From Soft/Hard Templates to Colloidal Templates

Mesoporous non-siliceous materials, in particular mesoporous transition metal oxides (m-TMOs), are of interest due to their fascinating electronic, redox, and magnetic properties for a wide range of applications in catalysis and energy storage. Control of the porosity (e.g., pore size, wall thickness, and surface area) and the crystalline degree (e.g., phase composition, crystallinity, and crystal grain size) of m-TMOs are critical for those applications. To crystallize TMOs, high temperature annealing is often needed to remove the amorphous defects and/or tune the compositions of different crystalline phases. This has brought many challenges to surfactant or block copolymer templates used in the process of evaporation-induced-self-assembly to prepare m-TMOs. In this review, we summarize the most recent achievements including the findings in our own laboratory on the use of organosilicate-containing colloids for the templated growth of mesoporous materials. We review a few key examples of preparing crystalline mesoporous oxides using different templating methods. The colloidal templating method by which mesoporous nanostructures can be stabilized up to 1,000°C is highlighted. The applications of m-TMOs and meso metal-oxide hybrids synthesized using organosilicate-containing colloidal templates in photocatalysis and high-temperature catalysis are also discussed.

A robust iron catalyst for the selective hydrogenation of substituted (iso)quinolones

By applying N-doped carbon modified iron-based catalysts, the controlled hydrogenation of N-heteroarenes, especially (iso)quinolones, is achieved. Crucial for activity is the catalyst preparation by pyrolysis of a carbon-impregnated composite, obtained from iron(ii) acetate and N-aryliminopyridines. As demonstrated by TEM, XRD, XPS and Raman spectroscopy, the synthesized material is composed of Fe(0), Fe3C and FeN x in a N-doped carbon matrix. The decent catalytic activity of this robust and easily recyclable Fe-material allowed for the selective hydrogenation of various (iso)quinoline derivatives, even in the presence of reducible functional groups, such as nitriles, halogens, esters and amides. For a proof-of-concept, this nanostructured catalyst was implemented in the multistep synthesis of natural products and pharmaceutical lead compounds as well as modification of photoluminescent materials. As such this methodology constitutes the first heterogeneous iron-catalyzed hydrogenation of substituted (iso)quinolones with synthetic importance.