Search

Transition metal‐nitrogen‐carbon (M‐N‐C) catalysts have emerged as promising candidates for electrocatalytic CO2 reduction reaction (CO2RR) due to their uniform active sites and high atomic utilization rate. However, poor efficiency at low overpotentials and unclear reaction mechanisms limit the application of M‐N‐C catalysts. In this study, Fe‐N‐C catalysts are developed by incorporating S atoms onto ordered hierarchical porous carbon substrates with a molecular iron thiophenoporphyrin. The well‐prepared FeSNC catalyst exhibits superior CO2RR activity and stability, attributes to an optimized electronic environment, and enhances the adsorption of reaction intermediates. It displays the highest CO selectivity of 94.0% at −0.58 V (versus the reversible hydrogen electrode (RHE)) and achieves the highest partial current density of 13.64 mA cm−2 at −0.88 V. Furthermore, when employed as the cathode in a Zn‐CO2 battery, FeSNC achieves a high‐power density of 1.19 mW cm−2 and stable charge–discharge cycles. Density functional theory calculations demonstrate that the incorporation of S atoms into the hierarchical porous carbon substrate led to the iron center becoming more electron‐rich, consequently improving the adsorption of the crucial reaction intermediate *COOH. This study underscores the significance of hierarchical porous structures and heteroatom doping for advancing electrocatalytic CO2RR and energy storage technologies. [ABSTRACT FROM AUTHOR]

Leading-edge (LE) serrations on owls' outermost remiges play a crucial role in the silent flight of owls. While the aeroacoustic characteristics of LE serrations have been widely studied using single feathers/airfoils, how they affect feather–feather (feather slots) interactions during flight remains unclear. Here, we present a numerical analysis of the effects of owl-inspired LE serrations on the aeroacoustics of tandem wing models. Large-eddy simulations and Ffowcs Williams–Hawkings analogy are combined to resolve the flow and acoustic fields around the tandem wings. The results demonstrate that serration-induced aeroacoustics are closely associated with the gap distance (D) between fore and hind wings. At a low AoA of 5°, as D increases, the LE serrations on the fore wing initially reduce the far-field sound pressures (D < 0.22c) by passively altering the laminar–turbulent transition on upper wing surfaces but turn out to increase the sound pressures remarkedly when D > 0.22c due to the flow instability induced at the hind wing LE. However, at a high AoA of 15°, the fore wing serrations enable robust sound reductions for all gap distances by mitigating the flow instabilities in the vicinity of the fore wing trailing edge and hind wing LE. Furthermore, the combination of LE serrations on fore and hind wings is verified to be capable of bringing nonlinear synergetic effects on the suppression of flow fluctuations and noise, which can inspire innovative biomimetic designs for low-noise multirotor drones and wind turbines. [ABSTRACT FROM AUTHOR]