Electrospun Fe2C-loaded carbon nanofibers as efficient electrocatalysts for oxygen reduction reaction.

Carbon-based non-precious metal catalysts have been regarded as the most promising alternatives to the state-of-art Pt/C catalyst for the oxygen reduction reaction (ORR). However, there are still some unresolved challenges such as agglomeration of nanoparticles, complex preparation process and low production efficiency, which severely hamper the large-scale production of non-precious metal catalysts. Herein, a novel carbon-based non-precious metal catalyst, i.e. iron carbide nanoparticles embedded on carbon nanofibers (Fe2C/CNFs), prepared via the direct pyrolysis of carbon- and iron-containing Janus fibrous precursors obtained by electrospinning. The Fe2C/CNF catalyst shows uniform dispersion and narrow size distribution of Fe2C nanoparticles embedded on the CNFs. The obtained catalyst exhibits positive onset potential (0.87 V versus RHE), large kinetic current density (1.9 mA cm-2), and nearly follows the effective four-electron route, suggesting an outstanding electrocatalytic activity for the ORR in 0.1 M of KOH solution. Besides, its stability is better than that of the commercial Pt/C catalyst, due to the strong binding force between Fe2C particles and CNFs. This strategy opens new avenues for the design and efficient production of promising electrocatalysts for the ORR.

Post-formation Copper-Nitrogen Species on Carbon Black: Their Chemical Structures and Active Sites for Oxygen Reduction Reaction.

The 3d transition metal and nitrogen co-doped carbon materials (TM-N-C) are considered as the most promising next-generation electrocatalysts, as alternatives to precious Pt, for the oxygen reduction reaction (ORR). Herein, we have fabricated a Cu-N-C catalyst through directly grafting copper-nitrogen complexes, composed by cuprous chloride and ammonia water, onto the surface of carbon black at 500 °C. In an alkaline environment, the synthesized catalyst exhibits excellent ORR catalytic activity, which is comparable to the state-of-the-art Pt/C catalyst, but far exceeding that obtained by the original carbon. Moreover, the catalyst displays much better stability than Pt/C. The enhanced ORR performance is proven to originate from the post-formation CuI -N2 and CuII -N4 sites at the carbon surface, as evidenced by X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The possible ORR process catalyzed by these Cu-Nx species is discussed at the atomic level. This work provides a simple and fast synthesis strategy for efficient TM-N-C catalysts on a large scale for energy storage and conversion systems.

Atomic Pt Promoted N-Doped Carbon as Novel Negative Electrode for Li-Ion Batteries.

In this work, platinum single-atom enhanced mushroom-based carbon (Pt1/MC) materials have been facilely synthesized and served as novel electrode materials in lithium-ion batteries (LIBs). The as-synthesized Pt1/MC active material shows a uniform dispersion of isolated Pt atoms on an MC support with high specific surface area and large total pore volume. As a negative electrode material for LIBs, the Pt1/MC exhibits excellent electrochemical properties, which retains a capacity of 846 mA h g-1 after 800 cycles at 2 A g-1 and 349 mA h g-1 (near to the theoretical capacity of graphite) after 6000 cycles at a high current density of 5 A g-1. The remarkable high capacity and excellent cycling stability can be attributed to their porous nanostructures and atomic-Pt-enhanced lithium-ion storage. Atomic Pt can compound with Li+ ions to form a platinum-lithium alloy during the discharge and charge process. Density functional theory (DFT) calculations are performed to verify that the PtLi5 alloy is the most stable intermedium on the MC substrate, which further enhances the lithiation and delithiation kinetics. This novel perspective is helpful to explore next-generation negative electrode materials with high capacities and good stabilities for LIBs.