Zheng Kun Yang

2D Nanoporous Fe-N/C Nanosheets as Highly Efficient Non-Platinum Electrocatalysts for Oxygen Reduction Reaction in Zn-Air Battery.

It is an ongoing challenge to fabricate nonprecious oxygen reduction reaction (ORR) catalysts that can be comparable to or exceed the efficiency of platinum. A highly active non-platinum self-supporting Fe-N/C catalyst has been developed through the pyrolysis of a new type of precursor of iron coordination complex, in which 1,4-bis(1H-1,3,7,8-tetraazacyclopenta(1)phenanthren-2-yl)benzene (btcpb) functions as a ligand complexing Fe(II) ions. The optimal catalyst pyrolyzed at 700 °C (Fe-N/C-700) shows the best ORR activity with a half-wave potential (E1/2 ) of 840 mV versus reversible hydrogen electrode (RHE) in 0.1 m KOH, which is more positive than that of commercial Pt/C (E1/2 : 835 mV vs RHE). Additionally, the Fe-N/C-700 catalyst also exhibits high ORR activity in 0.1 m HClO4 with the onset potential and E1/2 comparable to those of the Pt/C catalyst. Notably, the Fe-N/C-700 catalyst displays superior durability (9.8 mV loss in 0.1 m KOH and 23.6 mV loss in 0.1 m HClO4 for E1/2 after 8000 cycles) and better tolerance to methanol than Pt/C. Furthermore, the Fe-N/C-700 catalyst can be used for fabricating the air electrode in Zn-air battery with a specific capacity of 727 mA hg-1 at 5 mA cm-2 and a negligible voltage loss after continuous operation for 110 h.

Ethylenediamine-modulated synthesis of highly monodisperse copper sulfide microflowers with excellent photocatalytic performance

Highly monodisperse CuS microflowers with uniform size and shape were successfully constructed by a simple one-pot solvothermal approach assisted by EDA and PVP. When used as photocatalysts, the as-obtained CuS materials exhibited excellent photocatalytic activity and good selectivity for the degradation of organic contamination in waters.

Nickel oxide nanoflowers: formation, structure, magnetic property and adsorptive performance towards organic dyes and heavy metal ions

Well-ordered NiO nanoflowers were successfully constructed by sintering flower-like nickel ethylene glycol nanocrystals derived from the thermal decomposition of rod-like nickel tartrate. We found that the NiO nanoflowers have a high adsorption selectivity to organic dyes and a strong adsorption capacity to toxic heavy metal ions in water owing to their porous structure.

Self‐Assembled Metastable γ‐Ga2O3 Nanoflowers with Hexagonal Nanopetals for Solar‐Blind Photodetection

Metastable γ-Ga2O3 nanoflowers assembled from hexagonal nanopetals are successfully constructed by the oxidation of metallic Ga in acetone solution. The nanoflowers with a hollow interior structure exhibit a short response time and a large light-current-dark-current ratio under a relatively low bias voltage, suggesting an especially important potential application in solar-blind photodetection.

Direct growth of cobalt-rich cobalt phosphide catalysts on cobalt foil: an efficient and self-supported bifunctional electrode for overall water splitting in alkaline media

The design of high-efficiency, economical and self-supported bifunctional electrodes for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is extremely crucial to renewable energy conversion processes, yet remains a long and arduous task. Here, we report the first example of cobalt-rich cobalt phosphide catalysts directly grown on cobalt foil (denoted as Co2P/Co-foil) as a novel non-noble metal and integrated electrode by one-step phosphorization of a pre-oxidized Co foil. Owing to the intrinsic catalytic properties of cobalt-rich cobalt phosphide and the intimate contact between Co2P and highly conductive Co foil, the resulting Co2P/Co-foil electrode exhibits excellent catalytic performances for both the HER and OER in basic solution, affording a current density of 10 mA cm−2 at low overpotentials of 157 mV for the HER and 319 mV for the OER, respectively. More importantly, these electrodes can be directly employed as both the anode and cathode in an alkaline electrolyzer, showing noble metal-like water splitting performances and long-term stability. Density functional theory (DFT) calculations suggest that the sites on the top of the P atoms in Co2P are the most active sites for the HER. This work would open an exciting new avenue to synthesize other metal-rich metal phosphide catalysts on conductive metal foil as self-supported electrodes using this facile, cost-effective and easy scale-up fabrication method for overall water splitting.

Supramolecular polymers-derived nonmetal N, S-codoped carbon nanosheets for efficient oxygen reduction reaction

The rational design and fine synthesis of highly efficient and cost-effective electrocatalysts for oxygen reduction reaction (ORR) is crucial for the wide application of fuel cells (FCs). In this work, we select a novel nitrogen and sulfur-rich supramolecular polymer as a precursor for in situ, large scale and controlled synthesis of nitrogen and sulfur dual doped carbon (N, S–C) nanosheets as a catalyst for ORR. The supramolecular polymer MTCA particles are quickly self-assembled via triple-hydrogen-bonding between melamine (M) and trithiocyanuric acid (TCA). The uniform distribution and high content of nitrogen and sulfur in the polymer is beneficial to the high and homogeneous doping in the produced self-supporting catalyst after pyrolysis. When evaluated as an electrocatalyst, the catalyst pyrolyzed at 800 °C (N, S–C/800) shows a superior ORR activity in alkaline solution. Furthermore, the N, S–C/800 catalyst exhibits superb durability and immunity towards methanol crossover. This metal-free, cost-effective and highly efficient ORR catalyst will find wide potential applications in fuel cells.

Synthesis of nanoporous structured iron carbide/Fe–N–carbon composites for efficient oxygen reduction reaction in Zn–air batteries

Large-scale industrial level applications of fuel cells and metal–air batteries have called for the development of highly efficient and low-cost oxygen reduction electrodes. Here we report the effective and simple preparation of iron carbide-embedded Fe–N-doped carbon (Fe3C/Fe–N/C) composites using an iron–phenanthroline (Fe–Phen) complex and dicyandiamide (DCA) as the precursors that are subsequently heat treated. The optimal catalyst pyrolyzed at 800 °C (Fe–Phen–N-800) exhibits superior oxygen reduction activity with onset and half-wave potentials of 0.99 and 0.86 V in 0.1 M KOH, respectively, which are higher than those of Pt/C (onset and half-wave potentials of 0.98 and 0.84 V) at the same catalyst loading. Moreover, the obtained Fe–Phen–N-800 displays comparable activity to Pt/C in 0.1 M HClO4 solution. Notably, the well-developed Fe–Phen–N-800 catalyst shows much higher long-term stability and better methanol tolerance than Pt/C. The results suggest that our catalyst is one of the most promising candidates to replace Pt catalysts toward oxygen reduction. Strikingly, a primary Zn–air battery using Fe–Phen–N-800 as the air cathode catalyst delivers higher voltages and gravimetric energy densities than those of a Pt/C-based system at the discharge current densities of 10 and 25 mA cm−2, thus demonstrating the potential applications of our catalyst for energy conversion devices.

Construction and application of α-Fe2O3 nanocubes dominated by the composite interaction between polyvinyl chloride and potassium ferrocyanide

The present work provides a novel route for the preparation of hematite (α-Fe2O3) nanocubes by a facile, one-step procedure through a noncovalent composite interaction between polyvinyl chloride (PVC, a polymer) and potassium ferrocyanide (PF, a coordination compound) with an initial molar ratio of 20 : 1. Field-emission scanning electron microscopy analysis reveals the formation of well-ordered α-Fe2O3 nanocube granules featuring a uniform and smooth outer surface. Control experiments show that the composite ratios of PVC to PF played a crucial role in generating the nanocubic structure. Temperature-dependent sintering experiments proved that the α-Fe2O3 nanocubes were derived from a structural transformation from nanoplates emerging at lower temperatures, suggesting a condition optimization process of the 2D plate structure to the 3D cubic structure. The one-step synthesis of the nanoplates at lower temperatures is considered to be related to the composite interaction between PVC and PF. A series of independent experiments including Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and conductivity were performed to explain the presence of the composite interaction. Interestingly, we found that the composite interaction has improved considerably the physical properties of the polymer (e.g., crystallization degree and glass transition temperature) and the coordination compound (e.g., conductivity and microwave absorption ability). Finally, our data indicate that the as-prepared α-Fe2O3 nanocubes exhibited a higher lithium storage capacity and better cycling performance than the α-Fe2O3 nanoparticles with irregular shapes. We believe that the present results open up many opportunities in nanostructural materials of metal oxides associated with the composite interaction between a polymer and a coordination compound.

Synthesis and lithium storage performance of nickel oxide octahedra

The present work was devoted to the construction of nickel oxide (NiO) polyhedral structures through a simple, efficient and environmentally friendly one-step process. Initially, a series of intimate mixtures of nickel chloride (NiCl2) and β-cyclodextrin (β-CD) with different initial molar ratios were used as precursors. By simply sintering the precursors, we successfully obtained NiO octahedra with smooth surfaces and uniform size distribution. Control experiments showed that the formation, morphologies and grain sizes of NiO octahedra can be finely modulated by changing two parameters: the initial molar ratio of NiCl2 to β-CD and the sintering time. The former is a decisive factor for creating the NiO octahedra, while the latter is a key factor for regulating their size and shape evolution. Moreover, we found that the role of β-CD can be played by other carbon sources such as active carbon and glucose, but not as well as β-CD. Several independent experiments (FTIR spectroscopy, conductivity and thermogravimetric analyses) were performed to understand the mechanism of this role. Our data suggested that β-CD has a stronger interaction with NiCl2 than the other two carbon sources, leading to an earlier transformation from NiCl2 to NiO. Further, this octahedral material exhibited a very small hysteresis loop below 1000 Oe at 300 K, indicating ferromagnetic behaviour, which is different from the antiferromagnetic behaviour of bulk NiO materials. Electrochemical tests demonstrated that the octahedral structure as well as the agglomerate structure has high lithium storage capacity. Also, the agglomerate structure presented very low irreversible capacity loss and good cyclability. Therefore, the results give the impression that they are promising anode materials for rechargeable lithium-ion batteries and for high-power applications, in particular. We believe that these results will increase our understanding of the relationship between structures, properties and functions of transition metal oxide materials.

Temperature-dependent formation of Ru-based nanocomposites: structures and properties

A new route to produce Ru-based nanocomposites with mixed valence states of ruthenium is reported in this paper via a solid-phase sintering process. Precursor particles were prepared by an intimate mixing of RuCl3 and native β-cyclodextrin (β-CD) with a molar ratio of 1 : 1, followed by a sintering process at various temperatures ranging from 573 to 1173 K in ambient atmosphere. The so-obtained composite nanomaterials have been characterized by X-ray diffraction and notably the results show that an adjustment of the temperature enabled us to obtain Ru-based nanoparticles with controllable compositions. The surface-enhanced Raman scattering performances of the obtained nanomaterials have been analyzed using Rhodamine 6G (R6G) as the Raman probe. Their magnetic behaviors have been investigated as a function of the field strengths. The present work provides a significant advance in the development of both transformation in valence states of transition metals and in situ nanocomposites of metal/metal oxide combinations.