Subnano Amorphous Fe-Based Clusters with High Mass Activity for Efficient Electrocatalytic Oxygen Reduction Reaction

Intermetallic Pd-Y nanoparticles/N-doped carbon nanotubes as multi-active catalysts for oxygen reduction reaction, ethanol oxidation reaction, and zinc-air batteries

Intermetallic nanomaterials are unique in terms of their band gap, atomic-level arrangement, and well-defined stoichiometry, which allows them to exhibit significantly enhanced catalytic performance in electrochemical applications. However, the preparation of durable intermetallic catalysts with a lower content of platinum group metals is challenging, while the lack of control over the loss of active components limits their long-term application due to weak interaction between the support and the nanostructure. Here, we have designed the intermetallic alloyed nanoparticles (NPs) of PdY on N-doped carbon nanotubes (PdY/NCNTs) as a multifunctional catalyst for the oxygen reduction reaction (ORR), the ethanol oxidation reaction (EOR), and zinc-air batteries (ZABs). The strong adhesion through nitrogen ensures the anchoring of alloyed PdY NPs on the NCNTs, which restrains atomic migration and sintering during their conversion to intermetallic phases. This study confirms that there is negligible active site leaching owing to the strong and multiple dative bonds between the NCNTs and PdY NPs. Therefore, this catalyst exhibits remarkable catalytic activity, resulting in a mass activity of 1317 and 2902 mA mgPd-1 at jk and jf for the ORR and the EOR, respectively, and remains stable for a longer period. In addition, the PdY/NCNT-containing air cathode-fabricated ZAB achieved a higher power density (0.236 W cm-2) compared to the benchmark Pt/C.

Nanoreactor of Fe, N Co-Doped Hollow Carbon Spheres for Oxygen Reduction Catalysis

A simple template strategy was applied to prepare a Fe, N co-doped hollow carbon (Fe-NHC) nanoreactor for the oxygen reduction reaction (ORR) by coating Fe nanoparticles (Fe-NPs) with polydopamine (PDA), followed by high temperature pyrolysis and acid-leaching. With this method, Fe-NPs were used as both the template and the metal precursor, so that the nanoreactors can preserve the original spherical morphology and embed Fe single atoms on the inner walls. The carbonized PDA contained abundant N content, offering an ideal coordination environment for Fe atoms. By regulating the mass ratio of Fe-NPs and PDA, an optimal sample with a carbon layer thickness of 12 nm (Fe-NHC-3) was obtained. The hollow spherical structure of the nanoreactors and the atomically dispersed Fe were verified by various physical characterizations. As a result, Fe-NHC-3 performed well in ORR tests under alkaline conditions, with high catalytic activity, durability, and methanol resistance, demonstrating that the as-fabricated materials have the potential to be applied in the cathodic catalysis of fuel cells.

Synergies of Fe Single Atoms and Clusters on N-Doped Carbon Electrocatalyst for pH-Universal Oxygen Reduction

Single atomic metal-N-C materials have attracted immense interest as promising candidates to replace noble metal-based electrocatalysts for the oxygen reduction reaction (ORR). The coordination environment of metal-N-C active centers plays a critical role in determining their catalytic activity and durability, however, attention is focused only on the coordination of metal atoms. Herein, Fe single atoms and clusters co-embedded in N-doped carbon (Fe/NC) that deliver the synergistic enhancement in pH-universal ORR catalysis via the four-electron pathway are reported. Combining a series of experimental and computational analyses, the geometric and electronic structures of catalytic sites in Fe/NC are revealed and the neighboring Fe clusters are shown to weaken the binding energies of the ORR intermediates on Fe-N sites, hence enhancing both catalytic kinetics and thermodynamics. This strategy provides new insights into the understanding of the mechanism of single atom catalysis.

Iron-Based Catalytically Active Complexes in Preparation of Functional Materials

Iron complexes are particularly interesting as catalyst systems over the other transition metals (including noble metals) due to iron’s high natural abundance and mediation in important biological processes, therefore making them non-toxic, cost-effective, and biocompatible. Both homogeneous and heterogeneous catalysis mediated by iron as a transition metal have found applications in many industries, including oxidation, C-C bond formation, hydrocarboxylation and dehydration, hydrogenation and reduction reactions of low molecular weight molecules. These processes provided substrates for industrial-scale use, e.g., switchable materials, sustainable and scalable energy storage technologies, drugs for the treatment of cancer, and high molecular weight polymer materials with a predetermined structure through controlled radical polymerization techniques. This review provides a detailed statement of the utilization of homogeneous and heterogeneous iron-based catalysts for the synthesis of both low and high molecular weight molecules with versatile use, focusing on receiving functional materials with high potential for industrial application.