Complementary optical absorption and enhanced solar thermal conversion of CuO-ATO nanofluids

Broad-band solar thermal conversion materials are highly desired for solar energy harvesting. The purpose of this work is to demonstrate a simple and straightforward strategy to engineer broad-band solar thermal conversion nanofluids. Stable two-component nanofluids containing copper (II) oxide (CuO) and antimony doped tin oxide (ATO) nanoparticles were prepared after surface modification of the CuO nanoparticles. As a reference, the CuO nanofluids have strong absorption in the visible region but not the near-infrared region. On the contrary, the ATO nanofluids have strong absorption in the near-infrared region, but the absorption in the visible region is comparatively weak. The combination of CuO and ATO nanoparticles endows the two component nanofluids with broad-band absorption across the visible and near-infrared region. The two component nanofluids of 0.1 vol% show an absorption spectrum match well with the solar spectrum and give a solar weighted absorption fraction of 99.6% compared to 89.5% and 89.8% for the CuO and ATO nanofluids, respectively. The solar thermal utilization efficiency of the two-component nanofluids was determined to be 92.5% compared to 81.3% and 80.7% for the CuO and ATO nanofluids, respectively. The enhanced solar thermal conversion properties of the two-component nanofluids are attributed to the complementary optical absorption of the CuO and ATO nanoparticles. This work provides a promising strategy to engineer nanofluids for solar energy harvesting.