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 (Δ G ↓ = Δ H - T Δ S ↑), 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 (Cr 0.2 Mn 0.2 Co 0.2 Ni 0.2 Fe 0.2 ) 3 O 4 (400 °C), perovskite La(Mn 0.2 Cu 0.2 Co 0.2 Ni 0.2 Fe 0.2 )O 3 (500 °C), spinel Ni 0.2 Mg 0.2 Cu 0.2 Mn 0.2 Co 0.2 )Al 2 O 4 (550 °C), and cubic Ni 0.2 Mg 0.2 Cu 0.2 Zn 0.2 Co 0.2 O (750 °C). As a proof-of-concept, (Ni 3 MoCoZn)Al 12 O 24 nanofiber exhibited good activity (CH 4 Conv. > 96%, CO 2 Conv. > 99%, H 2 /CO ≈ 0.98), long-time stability (>100 h) for the dry reforming of methane (DRM) at 700 °C without coke deposition, better than control samples (Ni 3 MoCoZn)Al 12 O 24 -Coprecipitation-700 (CH 4 Conv. < 3%, CO 2 Conv. < 7%). The reaction mechanism of DRM was studied by in situ infrared spectroscopy, CO 2 -TPD, and CO 2 /CH 4 -TPSR. This electrospinning method provides a synthetic route for HEO nanofibers for target applications.