High‐Entropy‐Alloy Nanoparticles with Enhanced Interband Transitions for Efficient Photothermal Conversion

Abstract

Photothermal materials with broadband optical absorption and high conversion efficiency are intensively pursued to date. Here, proposing by the d‐d interband transitions, we report an unprecedented high‐entropy alloy FeCoNiTiVCrCu nanoparticles that the energy regions below and above the Fermi level (±4 eV) have been fully filled by the 3d transition metals, which realizes an average absorbance greater than 96 % in the entire solar spectrum (wavelength of 250 to 2500 nm). Furthermore, we also calculated the photothermal conversion efficiency and the evaporation rate towards the steam generation. Due to its pronounced full light capture and ultrafast local heating, our high‐entropy‐alloy nanoparticle‐based solar steam generator has over 98 % efficiency under one sun irradiation, meanwhile enabling a high evaporation rate of 2.26 kg m−2 h−1.

Quinary High‐Entropy‐Alloy@Graphite Nanocapsules with Tunable Interfacial Impedance Matching for Optimizing Microwave Absorption

“…The mixing entropies (Δ S mix ) of different HEA@C‐NPs were calculated based on the elemental contents of EDS results. [ 30,33 ] All the Δ S mix values are above 1.5 R ( R = 8.314 J mol −1 K −1 ), indicating that the HEA@C‐NPs are in agreement with the classification of HEAs (Figure S7, Supporting Information). The high‐resolution TEM images of FeCoNiMnCu nanocapsules are shown in Figure 2A.…”

“…(Figure S25 and refs. [19–31], Supporting Information) It can be seen that the HEA@C‐NPs demonstrate a relatively high microwave absorption property among all the HEA‐based absorbers.…”

“…The metallic powders were first mechanically milled to high‐entropy microflakes (HEAMFs) and compressed into cylinder targets. [ 30 ] Then, the nanocapsules were prepared at an atmosphere of methane and argon (CH 4 :Ar = 2:1) via the HEAMF targets, in which the graphitic shells were obtained via the decomposition of methane (CH 4 → C + H 2 ). Here, a typical core@shell structure can be observed in all nanocapsules ( Figure A and Figure S1 (Supporting Information)) using a transmission electron microscope (TEM), in which the core diameters are centered at 24.8 nm and the shell thicknesses are centered at 2.7 nm, respectively (Figure 2D and Figure S2 (Supporting Information), counting by ImageJ software).…”

“…As for the phase structures, face‐centered‐cubic (FCC) crystalline structures were exhibited by X‐ray diffraction (XRD) and can be observed in all the HEA@C‐NPs (Figure 2B), [ 31 ] indicating that different composited elements were uniformly mixed into a solid solution through the arc‐discharged process. Here, assisting the extreme‐high evaporating temperature and ultrafast cooling rate, [ 30,32 ] we expand the arc‐discharged method from high‐entropy‐alloy nanoparticles to HEA@C nanocapsules. It has been found that the decomposition of methane would not induce the phase separation of HEAs but can in situ form the graphitic shells.…”

Magnetic‐Dielectric Complementary Fe‐Co‐Ni Alloy/Carbon Composites for High‐Attenuation C‐Band Microwave Absorption via Carbothermal Reduction of Solid‐Solution Precursor

“…Additionally, due to the high chemical activity of ferromagnetic alloy nanoparticles, the surface of nano‐alloys could be oxidized to form a high valence oxide passivation layer in the ambient environment. [ 48 ] Thus, ionic state peaks of Fe, Co, and Ni species can also be detected in the XPS spectra.…”