Yuelan Zhang

Ultrathin LiCoO2 Nanosheets: An Efficient Water-Oxidation Catalyst

Ultrathin cation-exchanged layered metal oxides are promising for many applications, while such substances are barely successfully synthesized to show several atomic layer thickness, owing to the strong electrostatic force between the adjacent layers. Herein, we took LiCoO2, a prototype cation-exchanged layered metal oxide, as an example to study. By developing a simple synthetic route, we synthesized LiCoO2 nanosheets with 5-6 cobalt oxide layers, which are the thinnest ever reported. Ultrathin nanosheets thus prepared showed a surprising coexistence of increased oxidation state of cobalt ions and oxygen vacancy, as demonstrated by magnetic susceptibility, X-ray photoelectron, electron paramagnetic resonance, and X-ray absorption fine spectra. This unique feature enables a higher electronic conduction and electrophilicity to the adsorbed oxygen than the bulk. Consequently ultrathin LiCoO2 nanosheets provided a current density of 10 mA cm-2 at a small overpotential of a mere 0.41 V and a small Tafel slope of ∼88 mV/decade, which is strikingly followed by an excellent cycle life. The findings reported in this work suggest that ultrathin cation-exchanged layered metal oxides could be a next generation of advanced catalysts for oxygen evolution reaction.

Smart Solution Chemistry to Sn‐Containing Intermetallic Compounds through a Self‐Disproportionation Process

Developing new methods to synthesize intermetallics is one of the most critical issues for the discovery and application of multifunctional metal materials; however, the synthesis of Sn-containing intermetallics is challenging. In this work, we demonstrated for the first time that a self-disproportionation-induced in situ process produces cavernous Sn-Cu intermetallics (Cu3 Sn and Cu6 Sn5 ). The successful synthesis is realized by introducing inorganic metal salts (SnCl2 ⋅2 H2 O) to NaOH aqueous solution to form an intermediate product of reductant (Na2 SnO2 ) and by employing steam pressures that enhance the reduction ability. Distinct from the traditional in situ reduction, the current reduction process avoided the uncontrolled phase composition and excessive use of organic regents. An insight into the mechanism was revealed for the Sn-Cu case. Moreover, this method could be extended to other Sn-containing materials (Sn-Co, Sn-Ni). All these intermetallics were attempted in the catalytic effect on thermal decompositions of ammonium perchlorate. It is demonstrated that Cu3 Sn showed an outstanding catalytic performance. The superior property might be primarily originated from the intrinsic chemical compositions and cavernous morphology as well. We supposed that this smart solution reduction methodology reported here would provide a new recognition for the reduction reaction, and its modified strategy may be applied to the synthesis of other metals, intermetallics as well as some unknown materials.

Interfacial Doping of Heteroatom in Porous SnO2 for Highly Sensitive Surface Properties

The design and synthesis of heteroatom-doping porous materials with unique surface/interfaces are of great significance for enhancing the sensitive surface performance in the fields of catalytic energy, especially gas sensor, CO oxidation, and ammonium perchlorate decomposition. Usually, the template method followed by a high-temperature calcination process is considered as the routes of choice in preparing ion-doped porous materials, but it requires extra templates and will undergo complicated steps. Here, we present a simple fusion/diffusion-controlled intermetallics-transformation method to synthesize various heteroatom-doping porous SnO2 only by changing the species of intermetallics. By this new method, Ni-doped popcornlike SnO2 with plenty of ∼30 nm pores and two kinds of Cu-doped SnO2 nanocages was successfully constructed. Phase-evolution investigations demonstrated that growth kinetics, diffusion, and solubility of the intermediates are highly related to the architecture of final products. Moreover, low-solid-solution limit of MOx (M: Ni, Cu) in SnO2 made the ion dope close to the surface to form a special surface/interfaces structure, and selective removal of MOx produce abundant pores to increase the surface area. As a consequence, Ni-doped composite exhibits higher sensitivity in formaldehyde detection with a relative low-operating temperature in a short response time (i.e., 23.7–50 ppm formaldehyde, 170 °C, and 5 s) and Cu-doped composites show excellent activity in decreasing the catalytic temperature of CO oxidation and ammonium perchlorate decomposition. The fusion/diffusion-controlled intermetallics-transformation method reported in this work could be readily adopted for the synthesis of other active heteroatom-doping porous materials for multipurpose uses.