Keqiang Xu

Cyanide-metal framework derived CoMoO4/Co3O4 hollow porous octahedrons as advanced anodes for high performance lithium ion batteries

In this work, CoMoO4/Co3O4 hollow porous octahedrons are synthesized by thermal conversion of a cyanide-metal framework (CMF) compound of Co2[Mo(CN)8]·xH2O. As anode materials for lithium ion batteries (LIBs), the CoMoO4/Co3O4 electrodes exhibit a remarkably improved electrochemical performance in terms of large lithium storage capacity (1175.1 mA h g−1 at 200 mA g−1), high initial coulombic efficiency (86.9%), outstanding cycling stability (96.9% capacity retention after 100 cycles) and remarkable rate capability (924.2 mA h g−1 at 2000 mA g−1). The excellent electrochemical performance of the CoMoO4/Co3O4 composite can be ascribed to the hollow porous structure and the possible synergistic effect of different components, which could provide more efficient charge storage sites, shorten ion diffusion and electron transport paths, and accommodate the volume change during cycling. The facile synthesis strategy and excellent lithium storage performance make the CoMoO4/Co3O4 hollow porous octahedrons a promising candidate for high-performance LIB anode materials.

Metal-organic framework derived Fe/Fe 3 C@N-doped-carbon porous hierarchical polyhedrons as bifunctional electrocatalysts for hydrogen evolution and oxygen-reduction reactions

The development of simple and cost-effective synthesis methods for electrocatalysts of hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) is critical to renewable energy technologies. Herein, we report an interesting bifunctional HER and ORR electrocatalyst of Fe/Fe3C@N-doped-carbon porous hierarchical polyhedrons (Fe/Fe3C@N-C) by a simple metal-organic framework precursor route. The Fe/Fe3C@N-C polyhedrons consisting of Fe and Fe3C nanocrystals enveloped by N-doped carbon shells and accompanying with some carbon nanotubes on the surface were prepared by thermal annealing of Zn3[Fe(CN)6]2·xH2O polyhedral particles in nitrogen atmosphere. This material exhibits a large specific surface area of 182.5 m2 g-1 and excellent ferromagnetic property. Electrochemical tests indicate that the Fe/Fe3C@N-C hybrid has apparent HER activity with a relatively low overpotential of 236 mV at the current density of 10 mA cm-2 and a small Tafel slope of 59.6 mV decade-1. Meanwhile, this material exhibits excellent catalytic activity toward ORR with an onset potential (0.936 V vs. RHE) and half-wave potential (0.804 V vs. RHE) in 0.1 M KOH, which is comparable to commercial 20 wt% Pt/C (0.975 V and 0.820 V), and shows even better stability than the Pt/C. This work provides a new insight to developing multi-functional materials for renewable energy application.

Nanocomposites Based on CoSe2-Decorated FeSe2 Nanoparticles Supported on Reduced Graphene Oxide as High-Performance Electrocatalysts toward Oxygen Evolution Reaction

FeCo-based materials are promising candidates as efficient, affordable, and sustainable electrocatalysts for oxygen evolution reaction (OER). Herein, a composite based on FeSe2@CoSe2 particles supported on reduced graphene oxide (rGO) was successfully prepared as an OER catalyst. In the catalyst, the CoSe2 phase was located on the FeSe2 surface, forming a large number of exposed heterointerfaces with acidic iron sites because of strong charge interaction between CoSe2 and FeSe2. It is believed that the exposed heterointerfaces act as catalytic active sites for OER via a two-site mechanism, manifesting an overpotential as low as 260 mV to reach the current density of 10 mA cm-2 in 1 M KOH and excellent stability for at least 6 h, which is superior to those of CoSe2/rGO, FeSe2/rGO, as well as most of the FeNi- and FeCo-based electrocatalysts reported in recent literatures. It was demonstrated that the most optimal composite electrocatalysts release more Fe species into the electrolyte during the OER process, whereas the releasing of Co species is negligible. When the FeSe2@CoSe2/rGO catalysts were loaded on a α-Fe2O3 photoanode, the photocurrent density was increased by three times. These results may open up a promising avenue into the design and engineering of highly active and durable catalysts for water oxidation.

Synthesis of GO-AgIO4 nanocomposites with enhanced photocatalytic efficiency in the degradation of organic pollutants

Graphene oxide (GO)–AgIO4 nanocomposites with excellent photocatalytic performance have been prepared through a facile ion-exchange method. The as-prepared samples are characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. The GO–AgIO4 nanocomposites exhibit an enhanced photocatalytic activity in the degradation of organic pollutants as compared to bare AgIO4. It is revealed that the introduction of GO can relieve the agglomeration of AgIO4 particles, enhance the light absorption of the materials, and promote the separation of photoexcited electron–hole pairs. In addition, the possible transfer and separation behaviors of the charge carriers and the photocatalytic mechanism are discussed in detail. The excellent photocatalytic performance makes the GO–AgIO4 nanocomposites a promising photocatalyst for organic pollutant treatment.