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 (ΔG↓ = ΔH - TΔS↑), and so on. When facing the heterogeneous catalysis by HEOs, the micrometer bulky morphology and low surface areas (e.g., <10 m² 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_0.2Mn_0.2Co_0.2Ni_0.2Fe_0.2)₃O₄ (400 °C), perovskite La(Mn_0.2Cu_0.2Co_0.2Ni_0.2Fe_0.2)O₃ (500 °C), spinel Ni_0.2Mg_0.2Cu_0.2Mn_0.2Co_0.2)Al₂O₄ (550 °C), and cubic Ni_0.2Mg_0.2Cu_0.2Zn_0.2Co_0.2O (750 °C). As a proof-of-concept, (Ni₃MoCoZn)Al₁₂O₂₄ nanofiber exhibited good activity (CH₄ Conv. > 96%, CO₂ Conv. > 99%, H₂/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 (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.