[ccooffee]

From reading through the supplementary materials for the paper [0], it seems that the authors are aware of this flaw and they found a way to make it hydrophobic. The approach they tested involved soaking the ceramic in a bath with a commercially available fluorosilane [1] that is used to make things superhydrophobic. Fig. S20 in the supplementary materials has a chart that shows the treated ceramic being very good ("solar reflectivity...remains at ~99.0%") but not quite as stellar as the untreated ceramic.

[0] https://www.science.org/doi/full/10.1126/science.adi4725

[1] https://www.sigmaaldrich.com/US/en/product/aldrich/667420

[scotty79]

Also probably mitigation of leidenfrost effect is gone after turning it hydrophobic.

Maybe it would be better to cover with something deadly to algae. Preferably not toxic. If there are such things. Silver nanoparticles?

[rasz]

PFOETES, sounds as great as PFOA/PFAS.