General Synthesis of High-Entropy Oxide Nanofibers

The discovery of high-entropy oxides (HEOs) in 2015 has provided a family of potential solid catalysts, due to their tunable components, abundant defects or lattice distorts, excellent thermal stability (Delta G down arrow = Delta H - T Delta S up arrow), and so on. When facing the heterogeneous catalysis by HEOs, the micrometer bulky morphology and low surface areas (e.g., <10 m(2) g(-1)) by traditional synthesis methods obstructed their way. In this work, an electrospinning method to fabricate HEO nanofibers with diameters of 50-100 nm was demonstrated. The key point lay in the formation of one-dimensional filamentous precursors, during which the uniform dispersion of five metal species with disordered configuration would help to crystallize into single-phase HEOs at lower temperatures: inverse spinel (Cr0.2Mn0.2Co0.2Ni0.2Fe0.2)(3)O-4 (400 degrees C), perovskite La(Mn0.2Cu0.2Co0.2Ni0.2Fe0.2)O-3 (500 degrees C), spinel Ni0.2Mg0.2Cu0.2Mn0.2Co0.2)Al2O4 (550 degrees C), and cubic Ni0.2Mg0.2Cu0.2Zn0.2Co0.2O (750 degrees C). As a proof-of-concept, (Ni3MoCoZn)Al12O24 nanofiber exhibited good activity (CH4 Conv. > 96%, CO2 Conv. > 99%, H-2/CO approximate to 0.98), long-time stability (>100 h) for the dry reforming of methane (DRM) at 700 degrees C without coke deposition, better than control samples (Ni3MoCoZn)Al12O24-Coprecipitation-700 (CH4 Conv. < 3%, CO2 Conv. < 7%). The reaction mechanism of DRM was studied by in situ infrared spectroscopy, CO2-TPD, and CO2/CH4-TPSR. This electrospinning method provides a synthetic route for HEO nanofibers for target applications.