Xia Zuo

The self-template synthesis of highly efficient hollow structure Fe/N/C electrocatalysts with Fe–N coordination for the oxygen reduction reaction

The exploration of highly efficient catalysts to replace noble metal platinum for the oxygen reduction reaction, on which M/N/C catalysts have shed brilliant light, is greatly significant but challenging. This paper presents a strategy for synthesizing highly efficient and stabilized hollow structure Fe/N/C catalysts with iron and nitrogen doped into the carbon layer by the self-template method. The prepared Fe/N/C catalysts with NaCl protection during pyrolysis are characterized by a unique hollow structure, porous morphology and Fe–N coordination as the active sites, all of which significantly endow the materials with excellent properties towards the ORR, including high electrical conductivity, long-term durability and outstanding capacity for methanol tolerance. We employed X-ray absorption fine structure spectrometry to investigate the chemical state and coordination environment of the central iron atoms of the Fe/N/C catalysts, which also clarified the promoting effect of the NaCl protection for Fe–N coordination during pyrolysis. In particular, the Fe/N/C catalysts exhibit positive half-wave potentials (0.84 V vs. RHE) and Tafel slope comparable to 20% commercial Pt/C, possessing four-electron transfer pathway as well as excellent long-term stability and methanol tolerance in alkaline medium.

Anisotropic tough poly(vinyl alcohol)/graphene oxide nanocomposite hydrogels for potential biomedical applications

Hydrogels, one of the most important bioinspired materials, are receiving increasing attention because of their potential applications as scaffolds for artificial tissue engineering and vehicles for drug delivery, etc. However, these applications are always severely limited by their microstructure and mechanical behavior. Here we report the fabrication of a tough polyvinyl alcohol/graphene oxide (PVA/GO) nanocomposite hydrogel through a simple and effective directional freezing–thawing (DFT) technique. The resulting hydrogels show well-developed anisotropic microstructure and excellent mechanical properties with the assistance of DFT method and lamellar graphene. The hydrogels with anisotropic porous structures that consisted of micro-sized fibers and lamellas exhibit high tensile strengths, up to 1.85 MPa with a water content of 90%. More interestingly, the PVA/GO composite hydrogels exhibit the better thermostability, which can maintain the original shape when swollen in hot water (65 °C). In addition, the hydrogels with biocompatibility show good drug release efficiency due to the unique hierarchical structure. The successful synthesis of such hydrogel materials might pave the way to explore applications in biomedical and soft robotics fields.