General Synthesis of High-Entropy Oxide Nanofibers

Abstract

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.