Using elliptical iron glycolate nanosheets as precursors, elliptical Fe3O4/C core-shell nanorings (NRs) [25 ± 10 nm in wall thickness, 150 ± 40 nm in length, and 1.6 ± 0.3 in long/short axis ratio] are synthesized via a one-pot hydrothermal route. The surface-poly(vinylpyrrolidone) (PVP)-protected-glucose reduction/carbonization/Ostwald ripening mechanism is responsible for Fe3O4/C NR formation. Increasing the glucose/precursor molar ratio can enhance carbon contents, causing a linear decrease in saturation magnetization (Ms) and coercivity (Hc). The Fe3O4/C NRs reveal enhanced low-frequency microwave absorption because of improvements to their permittivity and impedance matching. A maximum RL value of -55.68 dB at 3.44 GHz is achieved by Fe3O4/C NRs with 11.95 wt % C content at a volume fraction of 17 vol %. Reflection loss (RL) values (≤-20 dB) are observed at 2.11-10.99 and 16.5-17.26 GHz. Our research provides insights into the microwave absorption mechanism of elliptical Fe3O4/C core-shell NRs. Findings indicate that ring-like and core-shell nanostructures are promising structures for devising new and effective microwave absorbers.
Investigation of high-efficiency electrocatalysts for acidic overall water splitting is of great significance toward fulfillment of proton exchange membrane (PEM) electrolyzers but still remains challenging. Herein, we report the colloidally synthesis of IrCo alloy nanodendrites with petal-like architecture (NDs). Benefiting from unique hierarchical architecture and strong electronic interaction arising from synergistic alloying effect of IrCo at the atomic level, the resultant IrCo NDs display remarkable hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performances with overpotentials of 17 and 281 mV to achieve 10 mA cm in 0.1 M HClO, respectively. Moreover, when further used as bifunctional electrocatalyst toward acidic overall splitting, a low cell voltage of 1.593 V is achieved at 10 mA cm.
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