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Studies have shown that brain lipid metabolism is associated with biological aging and influenced by dietary and genetic manipulations; however, the underlying mechanisms are elusive. High-resolution imaging techniques propose a novel and potent approach to understanding lipid metabolic dynamics in situ. Applying deuterium water (D2O) probing with stimulated Raman scattering (DO-SRS) microscopy, we revealed that lipid metabolic activity in Drosophila brain decreased with aging in a sex-dependent manner. Female flies showed an earlier occurrence of lipid turnover decrease than males. Dietary restriction (DR) and downregulation of insulin/IGF-1 signaling (IIS) pathway, two scenarios for lifespan extension, led to significant enhancements of brain lipid turnover in old flies. Combining SRS imaging with deuterated bioorthogonal probes (deuterated glucose and deuterated acetate), we discovered that, under DR treatment and downregulation of IIS pathway, brain metabolism shifted to use acetate as a major carbon source for lipid synthesis. For the first time, our study directly visualizes and quantifies spatiotemporal alterations of lipid turnover in Drosophila brain at the single organelle (lipid droplet) level. Our study not only demonstrates a new approach for studying brain lipid metabolic activity in situ but also illuminates the interconnection of aging, dietary, and genetic manipulations on brain lipid metabolic regulation.

Hydrogen production by electrochemical water splitting suffers from high kinetic barriers in the anodic oxygen evolution reaction (OER), which limits the overall efficiency. Herein, we report a structural and electronic engineering strategy by integrating self-standing Fe-doped Ni3S2 (denoted by Fe-Ni3S2) nanosheet arrays with Ni(OH)2 subunits to form heterostructured Fe-Ni3S2/Ni(OH)2 on a Ni Foam substrate. The strong electronic interaction between the Fe-Ni3S2 and Ni(OH)2 constituents contributes abundant catalytic sites and ensures high electron transfer. Moreover, the combined experimental and theoretical study revealed that the coupling of Ni(OH)2 onto the Fe-Ni3S2 is favorable for lowering the activation energy of water oxidation for favorable OER kinetics and upshifting the Ni d-band center to facilitate the adsorption of O-containing intermediates. Consequently, the optimized Fe-Ni3S2/Ni(OH)2 hybrid catalyst exhibits excellent OER performance in alkaline electrolytes with an ultralow overpotential of 202 mV at 10 mA cm−2, a small Tafel slope of 50.6 mV dec−1, and long-term durability under high current density (0.25 A cm−2) for up to 60 h without significant deactivation. Moreover, a two-electrode Fe-Ni3S2/Ni(OH)2‖‖Pt/C electrolyzer requires only a low voltage of 1.54 V at 10 mA cm−2 for overall water splitting. This study emphasizes the importance of interface and surface engineering in achieving highly efficient electrocatalysts. [ABSTRACT FROM AUTHOR]

Hydrogen production by electrochemical water splitting suffers from high kinetic barriers in the anodic oxygen evolution reaction (OER), which limits the overall efficiency. Herein, we report a structural and electronic engineering strategy by integrating self-standing Fe-doped Ni 3 S 2 (denoted by Fe-Ni 3 S 2 ) nanosheet arrays with Ni(OH) 2 subunits to form heterostructured Fe-Ni 3 S 2 /Ni(OH) 2 on a Ni Foam substrate. The strong electronic interaction between the Fe-Ni 3 S 2 and Ni(OH) 2 constituents contributes abundant catalytic sites and ensures high electron transfer. Moreover, the combined experimental and theoretical study revealed that the coupling of Ni(OH) 2 onto the Fe-Ni 3 S 2 is favorable for lowering the activation energy of water oxidation for favorable OER kinetics and upshifting the Ni d-band center to facilitate the adsorption of O-containing intermediates. Consequently, the optimized Fe-Ni 3 S 2 /Ni(OH) 2 hybrid catalyst exhibits excellent OER performance in alkaline electrolytes with an ultralow overpotential of 202 mV at 10 mA cm -2 , a small Tafel slope of 50.6 mV dec -1 , and long-term durability under high current density (0.25 A cm -2 ) for up to 60 h without significant deactivation. Moreover, a two-electrode Fe-Ni 3 S 2 /Ni(OH) 2 ||Pt/C electrolyzer requires only a low voltage of 1.54 V at 10 mA cm -2 for overall water splitting. This study emphasizes the importance of interface and surface engineering in achieving highly efficient electrocatalysts.