Synthesis of novel mesoporous carbon spheres and their supported Fe-based electrocatalysts for PEM fuel cell oxygen reduction reaction

Carbonized Nickel Complex of Sodium Pectate as Catalyst for Proton-Exchange Membrane Fuel Cells

Sodium pectate derivatives with 25% replacement of sodium ions with nickel ions were obtained by carbonization to temperatures of 280, 550, and 800 °C, under special protocols in an inert atmosphere by carbonization to temperatures of 280, 550, and 800 °C. The 25% substitution is the upper limit of substitution of sodium for nickel ions, above which the complexes are no longer soluble in water. It was established that the sample carburized to 550 °C is the most effective active element in the hydrogen-oxidation reaction, while the sample carbonized up to 800 °C was the most effective in the oxygen-reduction reaction. The poor performance of the catalytic system involving the pectin coordination biopolymer carbonized up to 280 °C was due to loss of proton conductivity caused by water removal and mainly by two-electron transfer in one catalytic cycle of the oxygen-reduction reaction. The improved performance of the system with coordination biopolymer carbonized up to 550 °C was due to the better access of gases to the catalytic sites and four-electron transfer in one catalytic cycle. The (Ni-NaPG)_800C sample contains metallic nickel nanoparticles and loose carbon, which enhances the electrical conductivity and gas capacity of the catalytic system. In addition, almost four-electron transfer is observed in one catalytic cycle of the oxygen-reduction reaction.

Transition Metal–Nitrogen–Carbon (M–N–C) Catalysts for Oxygen Reduction Reaction. Insights on Synthesis and Performance in Polymer Electrolyte Fuel Cells

Platinum group metal (PGM)-free catalysts for oxygen reduction reaction (ORR) have attracted increasing interest as potential candidates to replace Pt, in the view of a future widespread commercialization of polymer electrolyte fuel cell (PEFC) devices, especially for automotive applications. Among different types of PGM-free catalysts, M–N–C materials appear to be the most promising ones in terms of activity. These catalysts can be produced using a wide variety of precursors containing C, N, and one (or more) active transition metal (mostly Fe or Co). The catalysts synthesis methods can be very different, even though they usually involve at least one pyrolysis step. In this review, five different synthesis methods are proposed, and described in detail. Several catalysts, produced approximately in the last decade, were analyzed in terms of performance in rotating disc electrode (RDE), and in H2/O2 or H2/air PEFC. The catalysts are subdivided in five different categories corresponding to the five synthesis methods described, and the RDE and PEFC performance is put in relation with the synthesis method.

Advances in nanostructures fabricated via spray pyrolysis and their applications in energy storage and conversion

This review provides insight into various nanostructures designed by spray pyrolysis and their applications in energy storage and conversion.

Synergistically enhancing Fenton-like degradation of organics by in situ transformation from Fe3O4 microspheres to mesoporous Fe, N-dual doped carbon

Nanocarbon materials are emerging as alternative activators of peroxymonosulfate (PMS) for organics decomposition. However, the relatively low activity and complex syntheses hindered their practical application and innovation with respect to rational design of carbocatalysts is highly desired. Herein, an in situ replication and transformation strategy was employed to facilely convert porous Fe₃O₄ microspheres into novel Fe/N codoped large-pore mesoporous carbon spheres (M‑Fe/NC) as Fenton-like catalysts for PMS activation. Benefiting from the abundance of active sites induced by dual heteroatom doping, the enhanced active site exposure due to the unique mesoporous structure, and the high stability of carbon component, the derived M‑Fe/NC was superior to the pristine Fe₃O₄ for PMS activation to degrade various organics and was efficient over a wide pH range (2-9). Compared with the proposed mechanisms of previous reports, both radical (surface-bound SO₄^- and OH) and nonradical (¹O₂ and direct oxidation) pathways are involved in the M‑Fe/NC/PMS system. Furthermore, experimental observations in combination with DFT calculations reveal that graphitic N and FeN₄ sites serve as dual reaction centers in the catalysis. This research opened an avenue for development of novel multi-doped carbocatalysts used to activate PMS for sustainable remediation.

Sub-50 nm Iron-Nitrogen-Doped Hollow Carbon Sphere-Encapsulated Iron Carbide Nanoparticles as Efficient Oxygen Reduction Catalysts

Sub-50 nm iron-nitrogen-doped hollow carbon sphere-encapsulated iron carbide nanoparticles (Fe3C-Fe,N/C) are synthesized by using a triblock copolymer of poly(styrene-b-2-vinylpyridine-b-ethylene oxide) as a soft template. Their typical features, including a large surface area (879.5 m2 g-1), small hollow size (≈16 nm), and nitrogen-doped mesoporous carbon shell, and encapsulated Fe3C nanoparticles generate a highly active oxygen reduction reaction (ORR) performance. Fe3C-Fe,N/C hollow spheres exhibit an ORR performance comparable to that of commercially available 20 wt% Pt/C in alkaline electrolyte, with a similar half-wave potential, an electron transfer number close to 4, and lower H2O2 yield of less than 5%. It also shows noticeable ORR catalytic activity under acidic conditions, with a high half-wave potential of 0.714 V, which is only 59 mV lower than that of 20 wt% Pt/C. Moreover, Fe3C-Fe,N/C has remarkable long-term durability and tolerance to methanol poisoning, exceeding Pt/C regardless of the electrolyte.

Green Synthesis of Three-Dimensional Hybrid N-Doped ORR Electro-Catalysts Derived from Apricot Sap

Rapid depletion of fossil fuel and increased energy demand has initiated a need for an alternative energy source to cater for the growing energy demand. Fuel cells are an enabling technology for the conversion of sustainable energy carriers (e.g., renewable hydrogen or bio-gas) into electrical power and heat. However, the hazardous raw materials and complicated experimental procedures used to produce electro-catalysts for the oxygen reduction reaction (ORR) in fuel cells has been a concern for the effective implementation of these catalysts. Therefore, environmentally friendly and low-cost oxygen reduction electro-catalysts synthesised from natural products are considered as an attractive alternative to currently used synthetic materials involving hazardous chemicals and waste. Herein, we describe a unique integrated oxygen reduction three-dimensional composite catalyst containing both nitrogen-doped carbon fibers (N-CF) and carbon microspheres (N-CMS) synthesised from apricot sap from an apricot tree. The synthesis was carried out via three-step process, including apricot sap resin preparation, hydrothermal treatment, and pyrolysis with a nitrogen precursor. The nitrogen-doped electro-catalysts synthesised were characterised by SEM, TEM, XRD, Raman, and BET techniques followed by electro-chemical testing for ORR catalysis activity. The obtained catalyst material shows high catalytic activity for ORR in the basic medium by facilitating the reaction via a four-electron transfer mechanism.

Using aminopyrine as a nitrogen-enriched small molecule precursor to synthesize high-performing nitrogen doped mesoporous carbon for catalyzing oxygen reduction reaction

With aminopyrine as a nitrogen-enriched small molecule precursor, a series of nitrogen doped carbon materials have been fabricated and explored as electrocatalysts for oxygen reduction reaction (ORR).

Reactive Multifunctional Template-Induced Preparation of Fe-N-Doped Mesoporous Carbon Microspheres Towards Highly Efficient Electrocatalysts for Oxygen Reduction

A novel in situ replication and polymerization strategy is developed for the synthesis of Fe-N-doped mesoporous carbon microspheres (Fe-NMCSs). This material benefits from the synergy between the high catalytic activity of Fe-N-C and the fast mass transport of the mesoporous microsphere structure. Compared to commercial Pt/C catalysts, the Fe-NMCSs show a much better electrocatalytic performance in terms of higher catalytic activity, selectivity, and durability for the oxygen reduction reaction.

Fe/N/C hollow nanospheres by Fe(iii)-dopamine complexation-assisted one-pot doping as nonprecious-metal electrocatalysts for oxygen reduction

In this work, a series of hollow carbon nanospheres simultaneously doped with N and Fe-containing species are prepared by Fe(3+)-mediated polymerization of dopamine on SiO2 nanospheres, carbonization and subsequent KOH etching of the SiO2 template. The electrochemical properties of the hollow nanospheres as nonprecious-metal electrocatalysts for oxygen reduction reaction (ORR) are characterized. The results show that the hollow nanospheres with mesoporous N-doped carbon shells of ∼10 nm thickness and well-dispersed Fe3O4 nanoparticles prepared by annealing at 750 °C (Fe/N/C HNSs-750) exhibit remarkable ORR catalytic activity comparable to that of a commercial 20 wt% Pt/C catalyst, and high selectivity towards 4-electron reduction of O2 to H2O. Moreover, it displays better electrochemical durability and tolerance to methanol crossover effect in an alkaline medium than the Pt/C. The excellent catalytic performance of Fe/N/C HNSs-750 towards ORR can be ascribed to their high specific surface area, mesoporous morphology, homogeneous distribution of abundant active sites, high pyridinic nitrogen content, graphitic nitrogen and graphitic carbon, as well as the synergistic effect of nitrogen and iron species for catalyzing ORR.

A tungsten carbide/iron sulfide/FePt nanocomposite supported on nitrogen-doped carbon as an efficient electrocatalyst for oxygen reduction reaction

Novel multi-component WC/FeS/FePt/NC electrocatalysts with excellent mass activity and superior durability are developed for the oxygen reduction reaction in fuel cells.