Topochemical pyrolytic synthesis of quasi-Mxene hybrids via ionic liquid-iron phthalocyanine as a self-template

A novel quasi-Mxene structure hybrid is first realized through topochemical pyrolysis with the assistance of an ionic liquid.

Iron encapsulated in 3D N-doped carbon nanotube/porous carbon hybrid from waste biomass for enhanced oxidative activity

Novel iron encapsulated in nitrogen-doped carbon nanotubes (CNTs) supported on porous carbon (Fe@N-C) 3D structured materials for degrading organic pollutants were fabricated from a renewable, low-cost biomass, melamine, and iron salt as the precursors. SEM and TEM micrographs show that iron encapsulated bamboo shaped CNTs are vertically standing on carbon sheets, and thus, a 3D hybrid was formed. The catalytic activities of the prepared samples were thoroughly evaluated by activation of peroxymonosulfate for catalytic oxidation of Orange II solutions. The influences of some reaction conditions (pH, temperature, and concentrations of reactants, peroxymonosulfate, and dye) were extensively evaluated. It was revealed that the adsorption could enrich the pollutant which was then rapidly degraded by the catalytically generated radicals, accelerating the continuous adsorption of residual pollutant. Remarkable carbon structure, introduction of CNTs, and N/Fe doping result in promoted adsorption capability and catalytic performances. Due to the simple synthetic process and cheap carbon precursor, Fe@N-C 3D hybrid can be easily scaled up and promote the development of Fenton-like catalysts.

A hybrid composite catalyst of Fe3O4 nanoparticles-based carbon for electrochemical reduction of oxygen

We report an Fe₃O₄ nanoparticles-based carbon catalyst with good electrical conductivity, abundant active sites and efficient catalytic ORR activity.

Porous Core-Shell Fe3C Embedded N-doped Carbon Nanofibers as an Effective Electrocatalysts for Oxygen Reduction Reaction

The development of nonprecious-metal-based electrocatalysts with high oxygen reduction reaction (ORR) activity, low cost, and good durability in both alkaline and acidic media is very important for application of full cells. Herein, we developed a facile and economical strategy to obtain porous core-shell Fe3C embedded nitrogen-doped carbon nanofibers (Fe3C@NCNF-X, where X denotes pyrolysis temperature) by electrospinning of polyvinylidene fluoride (PVDF) and FeCl3 mixture, chemical vapor phase polymerization of pyrrole, and followed by pyrolysis of composite nanofibers at high temperatures. Note that the FeCl3 and polypyrrole acts as precursor for Fe3C core and N-doped carbon shell, respectively. Moreover, PVDF not only plays a role as carbon resources, but also provides porous structures due to hydrogen fluoride exposure originated from thermal decomposition of PVDF. The resultant Fe3C@NCNF-X catalysts, particularly Fe3C@NCNF-900, showed efficient electrocatalytic performance for ORR in both alkaline and acidic solutions, which are attributed to the synergistic effect between Fe3C and N-doped carbon as catalytic active sites, and carbon shell protects Fe3C from leaching out. In addition, the Fe3C@NCNF-X catalyst displayed a better long-term stability, free from methanol crossover and CO-poisoning effects than those of Pt/C, which is of great significance for the design and development of advanced electrocatalysts based on nonprecious metals.

Superior oxygen reduction electrocatalysis enabled by integrating hierarchical pores, Fe3C nanoparticles and bamboo-like carbon nanotubes

Hierarchical porous carbon nanostructures doped with nitrogen or other active elements have been demonstrated to be of importance in enhancing the oxygen reduction reaction (ORR) activity. However, their intrinsic limited active sites usually make them exhibit lower ORR activity than commercial Pt/C. In order to solve well this challenging issue, herein we develop a simple method for encapsulating more electrochemically active Fe3C nanoparticles (NPs) into the channels of bamboo-like carbon nanotubes (bCNTs) with interesting 3D hierarchical micro-, meso- and macropores by impregnating the bCNTs with a Fe(NO3)3 solution, followed by the calcination of the composite under a N2 atmosphere. The resulting bCNT/Fe3C hybrid electrocatalysts with much more active sites exhibit excellent ORR activity in acidic media with the half-wave potential of 0.710 V comparable to the commercial Pt/C catalyst (0.782 V). Furthermore, they show very high ORR activity in 0.10 M KOH with the half-wave potential of 0.879 V, 67 mV more positive than that of the Pt/C catalyst. Most importantly, the as-prepared new catalysts are very stable for ORR in both acidic and alkaline solutions with almost no ORR polarization curve shift after 3000 cycles, much better than that of the Pt/C catalyst. To the best of our knowledge, our new bCNT/Fe3C catalyst is the best non-noble-metal catalyst ever reported for ORR under both acidic and alkaline conditions. The present work highlights the important roles of introducing more stable Fe3C NPs and hierarchical micro-, meso- and macropores as much more active sites in maximizing the ORR electrocatalysis performance.

Towards high-efficiency nanoelectrocatalysts for oxygen reduction through engineering advanced carbon nanomaterials

We summarize and discuss recent developments of different-dimensional advanced carbon nanomaterial-based noble-metal-free high-efficiency oxygen reduction electrocatalysts, including heteroatom-doped, transition metal-based nanoparticle-based, and especially iron carbide (Fe₃C)-based carbon nanomaterial composites.

High Performance Heteroatoms Quaternary-doped Carbon Catalysts Derived from Shewanella Bacteria for Oxygen Reduction

A novel heteroatoms (N, P, S and Fe) quaternary-doped carbon (HQDC-X, X refers to the pyrolysis temperature) can be fabricated by directly pyrolyzing a gram-negative bacteria, S. oneidensis MR-1 as precursors at 800 °C, 900 °C and 1000 °C under argon atmosphere. These HQDC-X catalysts maintain the cylindrical shape of bacteria after pyrolysis under high temperatures, while heteroatoms including N, P, S and Fe distribute homogeneously on the carbon frameworks. As a result, HQDC-X catalysts exhibit excellent electrocatalytic activity for ORR via a dominant four-electron oxygen reduction pathway in alkaline medium, which is comparable with that of commercial Pt/C. More importantly, HQDC-X catalysts show better tolerance for methanol crossover and CO poisoning effects, long-term durability than commercial Pt/C, which could be promising alternatives to costly Pt-based electrocatalysts for ORR. The method may provide a promising avenue to develop cheap ORR catalysts from inexpensive, scalable and biological recursors.

IL-derived N, S co-doped ordered mesoporous carbon for high-performance oxygen reduction

A highly efficient N, S co-doped porous carbon ORR catalyst was simply designed in our report from ordered mesoporous carbon (OMC) and trace ionic liquids (ILs). The microstructure OMC was chosen as the template for improving the specific area, confining the ILs in the mesopores, and promoting the formation of the planar N and S doping. The resulting IL/OMC (IOMC) nanostructure exhibits comparable ORR activity and better stability than the commercial Pt/C catalyst in 0.10 M KOH solution, which makes it one of the best-performing metal-free carbon ORR catalysts. We deduced that the excellent ORR activity is attributed to the synergistic effect of N, S, and the ordered mesoporous structure. Interestingly, the ORR activity can be further boosted in both basic and acidic solutions after Fe doping into the IOMC nanostructures which clearly emphasizes that transition metal Fe is important for the construction of ORR active functional sites especially in acidic solution.

Carbon-Coated Core-Shell Fe-Cu Nanoparticles as Highly Active and Durable Electrocatalysts for a Zn-Air Battery

Understanding the interaction between a catalyst and oxygen has been a key step in designing better electrocatalysts for the oxygen reduction reaction (ORR) as well as applying them in metal-air batteries and fuel cells. Alloying has been studied to finely tune the catalysts' electronic structures to afford proper binding affinities for oxygen. Herein, we synthesized a noble-metal-free and nanosized transition metal CuFe alloy encapsulated with a graphitic carbon shell as a highly efficient and durable electrocatalyst for the ORR in alkaline solution. Theoretical models and experimental results demonstrated that the CuFe alloy has a more moderate binding strength for oxygen molecules as well as the final product, OH(-), thus facilitating the oxygen reduction process. Furthermore, the nitrogen-doped graphitic carbon-coated layer, formed catalytically under the influence of iron, affords enhanced charge transfer during the oxygen reduction process and superior durability. These benefits were successfully confirmed by realizing the catalyst application in a mechanically rechargeable Zn-air battery.

A low-cost cementite (Fe3C) nanocrystal@N-doped graphitic carbon electrocatalyst for efficient oxygen reduction

A core–shell structure Fe₃C nanocrystal@N-doped graphitic carbon (Fe₃C@NGC) nanocomposite was successfully fabricated, and used as an electrocatalyst with large surface area, exhibiting great potential for oxygen reduction reaction (ORR).