Efficiently capturing sunlight across the entire spectral range of 300-2500 nm is crucial for solar-thermal applications, including concentrating solar power systems, de-icing, therapy, photothermal catalysis, and solar water evaporation.

Spinel oxides, known for their strong solar absorption, ease of fabrication, remarkable thermal stability, and corrosion resistance, have emerged as promising photothermal materials. However, their large band gaps have hindered their full-spectrum solar absorption. Therefore,  a novel strategy to address this limitation is urgently needed.

A recent study published in Matter, conducted by GAO Xianghu’s group from the Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, has made significant strides in this area. The team used a facile sol-gel combustion approach to synthesize high-entropy spinel oxide (CoCrFeMnNi)3O4 powder, which was spray-coated onto a flexible polyvinyl alcohol (PVA) chamois. The coatings exhibited an impressive solar absorptance of 95.5% across the entire solar spectrum.

This full-spectrum absorption arises from bandgap narrowing. The study revealed that energy level splitting, enhanced d-band transition, variable-valence cations, and orbital hybridization collectively narrowed the bandgap of the spinel oxide from 2.65 eV to 0 eV, imparting the high-entropy spinel oxide with a quasi-metallic characteristic.

Figure 1. Electronic structure and absorption band adjustment.

When utilized for solar water evaporation, the high-entropy spinel oxide-based evaporator demonstrated an outstanding evaporation efficiency of 96.53%, along with a competitive evaporation rate of 2.075 kg m-2 h-1 under 1-sun irradiation.

Owing to its exceptional solar harvesting capability and entropy-introduced structural stabilization effect, this material is expected to be applied in various areas, including photothermal sterilization, photocatalysis and so on.

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