Design And Preparation Of Micro-nano Graded Porous Metal Ultra-black Materials

Ultra-black materials are materials with light reflectance less than 1%and absorptivity higher than 99%.Since they can capture most of the incident light,ultra-black materials are applied in wide fields such as aerospace,military energy and etc.The reported ultra-black materials include carbon-based materials with low refractive index and materials with structured surfaces,such as highly corroded nickel-phosphorus alloys,black gold and black silicon.However,fabrication of these materials require complex or expensive technology and can be ultra-black in a limited band.Therefore,this work intent to prepare novel broad band ultra-black metallic coatings by a convenient method:dynamic hydrogen bubble template（DHBT）electrodeposition.First,porous Cu coatings with micron holes and micro/nanometer-sized Cu were prepared in one step using DHBT deposition.The structures of the pores and Cu depositions in the porous Cu coatings were tuned by using different additives such as（NH₄）₂SO₄ and benzotriazole（BTA）and deposition parameters.The results showed that when the concentration of BTA in the composite additive was 1 m M and the deposition current density was 4.0 A/cm²,the as-deposited porous Cu with micron holes and nano Cu particles was obtained exhibited the lowest diffused reflectance（lower than 2.5%）in a broad band of200～2500 nm.Then,binary porous NiCu coatings were prepared in one step using DHBT deposition.The coatings also displayed a hierarchical structure composed by micrometer-size pores and micro/nanometer-size NiCu depositions.In order to reduce the reflectance of the coatings,the Ni/Cu atomic ratio in the coatings and the deposition parameters were tuned.The results showed that when the deposition current density was 1 A/cm² and the deposition time was 60s,the porous NiCu coating with an Ni/Cu atomic ratio of 4 had the lowest diffuse reflectance（lower than 1.8%）in the range of 200～2500 nm.Based on the binary porous NiCu coatings with a diffuse reflectance lower than 1.8%,NiCu oxide/NiCu composite coatings were fabricated in two steps using DHBT deposition followed by a heat treatment.The experimental results showed that the reflectance of composite coatings first decreased with the increasing thickness of the oxide layer and then increased rapidly with the further increase in the oxide layer.Such a phenomenon was explained by finite difference time domain（FDTD）simulation.In this section,when the DHBT deposited NiCu coatings were heated 400℃for 15 min in air,the resulted NiCu oxide/NiCu composite coating showed the lowest reflectance,a diffuse reflectance lower than 1%in the rage of 200～2500 nm and a specular reflectance lower than 1%in the mid-infrared range of 2.5～20μm,demonstrating the successful formation of novel wide band ultra-black coatings.Finally,the NiCu oxide/NiCu composite ultra-black coating was applied to solar evaporation.Different substrates such as anodic aluminum oxide（AAO）and sponge were used to grow the ultra-black NiCu oxide/NiCu coatings to construct solar evaporators.The results showed that the ultra-black coatings grown on sponge had the highest water evaporation efficiency of 76%under 1 k Wm^-2 solar radiation intensity.