A perspective on the controlled synthesis of iron-based nanoalloys for the oxygen reduction reaction

The worsening ecological environment is calling for clean energy alternatives, among which hydrogen fuel cells have been one of the hot topics. The commercialized Pt/C catalyst for the oxygen reduction reaction (ORR) in the cathode of fuel cells is suffering from its high cost, serious scarcity and so on. Hence, the exploration on alternative ORR catalysts has attracted much attention. Iron(Fe)-based nanoalloys have shown advantages of low cost, high abundance, and pleasant ORR activity. In this feature, we have summarized Fe-based nanoalloy structures and our recent progress on controllable synthesis as well as their ORR performance, including iron-platinum (Fe-Pt), iron carbide (Fe-C), and iron nitride (Fe-N). Finally, the perspective on this type of ORR electrocatalyst is also discussed.

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.

Noble-Metal-Free Iron Nitride/Nitrogen-Doped Graphene Composite for the Oxygen Reduction Reaction

Considerable effort has been devoted recently to replace platinum-based catalysts with their non-noble-metal counterparts in the oxygen reduction reaction (ORR) in fuel cells. Nitrogen-doped carbon structures emerged as possible candidates for this role, and their earth-abundant metal-decorated composites showed great promise. Here, we report on the simultaneous formation of nitrogen-doped graphene and iron nitride from the lyophilized mixture of graphene oxide and iron salt by high-temperature annealing in ammonia atmosphere. A mixture of FeN and Fe2N particles was formed with average particle size increasing from 23.4 to 127.0 nm and iron content ranging from 5 to 50 wt %. The electrocatalytic oxygen reduction activity was investigated via the rotating disk electrode method in alkaline media. The highest current density of 3.65 mA cm-2 at 1500 rpm rotation rate was achieved in the 20 wt % catalyst via the four-electrode reduction pathway, exceeding the activity of both the pristine iron nitride and the undecorated nitrogen-doped graphene. Since our catalysts showed improved methanol tolerance compared to the platinum-based ones, the formed non-noble-metal system offers a viable alternative to the platinum-decorated carbon black (Pt/CB) ORR catalysts in direct methanol fuel cells.

Fine Co nanoparticles encapsulated in N-doped porous carbon for efficient oxygen reduction

Through the acid pickling of Co@NPC, which was obtained by one-step calcination of ZIF-67 in N₂ and condition optimization of Co nanoparticle sizes, a catalyst of fine Co nanoparticles encapsulated in N-doped porous carbon with excellent ORR performance was prepared.

Metal-organic frameworks-derived core-shell Fe3O4/Fe3N@graphite carbon nanocomposites as excellent non-precious metal electrocatalyst for oxygen reduction

Metal-organic frameworks (MOFs), as precursors for synthesizing new carbon materials, hold promise for applications in the oxygen reduction reaction (ORR) as efficient non-precious metal catalysts. Here, a facile template-assisted strategy was adopted to fabricate a core-shell structure derived from MIL-101(Fe) and polyaniline. MIL-101(Fe) nanoparticles obtained by microwave-assisted synthesis were combined with PAni in different ratios and carbonized at 900 °C under flowing N2. An optimized core-shell Fe3O4/Fe3N@graphite carbon structure was successfully prepared and exhibited attractive ORR activity, with a half-wave potential of 0.916 V vs. RHE and an electron transfer number of 4.0 at 0.4 V vs. RHE. Furthermore, the catalyst displayed excellent stability in an alkaline solution. The superior ORR performance of the catalyst is mainly attributed to its stable core-shell structure, large specific surface area and high content of electrocatalytically active N species.

Stable and Efficient Nitrogen-Containing Carbon-Based Electrocatalysts for Reactions in Energy-Conversion Systems

High activity and stability are crucial for the practical use of electrocatalysts in fuel cells, metal-air batteries, and water electrolysis, including the oxygen reduction reaction, hydrogen evolution reaction, oxygen evolution reaction, and oxidation reactions of formic acid and alcohols. Electrocatalysts based on nitrogen-containing carbon (N-C) materials show promise in catalyzing these reactions; however, there is no systematic review of strategies for the engineering of active and stable N-C-based electrocatalysts. Herein, a comprehensive comparison of recently reported N-C-based electrocatalysts regarding both electrocatalytic activity and long-term stability is presented. In the first part of this review, the relationships between the electrocatalytic reactions and selection of the element to modify the N-C-based materials are discussed. Afterwards, synthesis methods for N-C-based electrocatalysts are summarized, and strategies for the synthesis of highly stable N-C-based electrocatalysts are presented. Multiple tables containing data on crucial parameters for both electrocatalytic activity and stability are displayed in this review. Finally, constructing M-N_x moieties is proposed as the most promising engineering strategy for stable N-C-based electrocatalysts.

Functionalization of Graphene Aerogels and their Applications in Energy Storage and Conversion

Functionalized graphene aerogels (GAs) not only own the advantages of the original ones like large specific surface area, three-dimensional porous structures, high specific capacitance and excellent cyclic stability, but also realize the function expansion due to the collective properties endowed via different methods. These characteristics make them advantageous in some promising applications. In this minireview, we focus on the various functionalization methods of GAs and especially their use in the applications of energy storage and conversion like batteries, supercapacitors and fuel cells, etc.

Supramolecular gel assisted synthesis of Co2P nanosheets as an efficient and stable catalyst for oxygen reduction reaction

Co₂P/C, with nanosheet morphology, is prepared through a facile supramolecular-gel assisted strategy which presents excellent electrocatalytic performance for ORR.

Covalent Porphyrin Framework-Derived Fe2P@Fe4N-Coupled Nanoparticles Embedded in N-Doped Carbons as Efficient Trifunctional Electrocatalysts

A new porous covalent porphyrin framework (CPF) filled with triphenylphosphine was designed and synthesized using the rigid tetrakis(p-bromophenyl)porphyrin (TBPP) and 1,3,5-benzenetriboronic acid trivalent alcohol ester as building blocks. The carbonization of this special CPF has afforded coupled Fe₂P and Fe₄N nanoparticles embedded in N-doped carbons (Fe₂P/Fe₄N@N-doped carbons). This CPF serves as an "all in one" precursor of Fe, N, P, and C. The porous property and solid skeleton of the CPF endow Fe₂P/Fe₄N@N-doped carbons with porous structure and a high degree of graphitization. As a result, Fe₂P/Fe₄N@N-doped carbons exhibited highly efficient multifunctional electrocatalytic performance for water splitting and oxygen electroreduction. Typically, Fe₂P/Fe₄N@C-800, obtained at a heat-treatment temperature of 800 °C, showed an ORR half-wave potential of 0.80 V in alkaline media and 0.68 V in acidic media, close to that of commercial Pt/C catalysts. Fe₂P/Fe₄N@C-800 also displayed efficient OER and HER activities, comparable to other phosphide and nitride electrocatalysts. The coupled Fe₄N and Fe₂P nanoparticles embedded in carbons exert unique catalytic efficiency for water splitting and fuel cells.

Retraction: A facile strategy to fabricate nitrogen-doped graphene aerogel supported Fe3N nanoparticles as efficient electrocatalysts for the oxygen reduction reaction

Retraction of ‘A facile strategy to fabricate nitrogen-doped graphene aerogel supported Fe₃N nanoparticles as efficient electrocatalysts for the oxygen reduction reaction’ by Shufeng Wang et al., New J. Chem., 2017, DOI: 10.1039/c6nj04114k.

Ice-templating synthesis of macroporous noble metal/3D-graphene nanocomposites: their fluorescence lifetimes and catalytic study

Porous architectures of 3D-graphene assembled with noble metal (Au, Pd and Pt) nanoparticles were successfully fabricated through a one-step green route using a low-cost freeze-casting method.

Nitrogen doped carbon materials derived from Gentiana scabra Bunge as high-performance catalysts for the oxygen reduction reaction

Gentiana scabraBunge-derived porous carbon materials as high-performance catalysts for the oxygen reduction reaction in both acidic and alkaline solutions were introduced.