Highly Enhanced Thermal Robustness and Photothermal Conversion Efficiency of Solar-Selective Absorbers Enabled by High-Entropy Alloy Nitride MoTaTiCrN Nanofilms

Abstract

Recent advances in high-entropy alloys have spurred many breakthroughs in the fields of high-temperature materials and optical materials and they provide incredible application potentialities for photothermal conversion systems. Solar-selective absorbers (SSAs), as key components, play a vital role in photothermal conversion efficiency and service life. The most pressing problem with SSAs is their inconsistent optical performance, an instability constraint induced by thermal stress. A feasible method of improving performance stability is the introduction of high-entropy materials, such as high-entropy alloy nitrides. In this study, enabled by an intrinsic MoTaTiCrN absorption layer, the solar configuration achieves greatly enhanced, exceptional thermotolerance and optical properties, leading to the formation of a scalable, highly efficient, and costeffective structure. Computational and experimental approaches are employed to achieve optimum preparation parameters for thicknesses and constituents. The crystal structure of high-entropy ceramic MoTaTiCrN is fully investigated, including thicknessdependent crystal nucleation. High-temperature and long-term thermal stability tests demonstrate that our proposed SSA is mechanically robust and chemically stable. Moreover, a low thermal emittance (15.86%) at 500 °C promotes the photothermal conversion efficiency. In addition, due to the exceptional spectral selectivity (α/ε = 92.3/6.5%), thermal robustness (550 °C for 168 h), and photothermal conversion efficiency (86.9% at 550 °C under 100 sun), it is possible for our proposed SSA to enhance the practical realization of large-area photothermal conversion applications, especially for concentrated solar power systems.

A Focused Review on Engineering Application of Multi-Principal Element Alloy

“…The phase constitutions changed by alloying or phase transformation play an important role on the magnetic properties of MPEAs (Marshal et al, 2019;Zhao C. et al, 2021). With the addition of Al in the FeMnCoCr MPEA, the formation of the BCC structure shows a ferromagnetic behavior (Marshal et al, 2019).…”

“…The high-entropy alloy nitrides (HEANs) synthesized with refractory elements have become an ideal material for manufacturing SSAC, due to their excellent high-temperature resistance and optical properties. The optical properties of NbMoTaWN, MoNbHfZrTiN, and MoTaTiCrN HEANs are investigated, showing the exceptional spectral selectivity (α/ε 0.944/0.12, 0.934/0.09, and 0.923/0.065 for NbMoTaWN, MoNbHfZrTiN, and MoTaTiCrN) (Guo et al, 2020;He et al, 2020;Yu D. M. et al, 2021;Yu D.-M. et al, 2021;He et al, 2021). These HEANs show excellent thermal stability and corrosion resistance.…”

“…These HEANs show excellent thermal stability and corrosion resistance. After annealing at 600 °C for 100 h, NbMoTaWN still maintains good optical properties (α/ε 0.902/0.106) (Yu D.-M. et al, 2021). For MoNbHfZrTiN, the solar absorptance and thermal emittance are only slightly raised and lowered, respectively, (α/ε ranges from 0.935/0.09 to 0.912/0.11) in a 3.5% NaCl solution for 24 h at room temperature (He et al, 2020).…”

“…Therefore, MPEAs containing Al, Si and Cr have excellent high temperature thermal stability. AlCrTaTiZrN MPEA has excellent spectral selectivity (α/ε 0.928/0.051), high temperature thermal stability (little change in the spectral selectivity after annealing at 800 °C for 2 h), and long-time thermal stability (little change in the spectral selectivity after annealing at 650 °C for 300 h) (He et al, 2021). In addition, AlCrTaTiZrN MPEA achieves the optimal photothermal conversion efficiency at high sunlight exposure (He et al, 2021).…”

“…AlCrTaTiZrN MPEA has excellent spectral selectivity (α/ε 0.928/0.051), high temperature thermal stability (little change in the spectral selectivity after annealing at 800 °C for 2 h), and long-time thermal stability (little change in the spectral selectivity after annealing at 650 °C for 300 h) (He et al, 2021). In addition, AlCrTaTiZrN MPEA achieves the optimal photothermal conversion efficiency at high sunlight exposure (He et al, 2021). Thus, MPEAs with excellent optical and thermal stability properties have the great application potential for the solar-thermal technology.…”