Passive solar photothermal generation of high localized temperatures for water desalination and hydrogen production

The generation of high localized temperatures (T ≥ 100 °C) using passive solar interfacial steam generation (SSG) technology typically requires expensive optical concentrators to amplify the incident solar flux. Herein, we demonstrate the generation of a high localized temperature under a low ambient solar irradiance in a passive, non-pressurized system, eliminating the need for optical concentration. Inspired by the greenhouse effect, a novel SSG device was designed to maximize thermal concentration and significantly enhance localized heating. The operating mechanism involves two sequential processes. First, efficient interfacial photothermal conversion is achieved using a kaolin clay-modified activated carbon/CuO photothermal layer, which minimizes heat loss owing to its high thermal inertia. Second, the generated heat is confined within a hollow porous cellulosic tube, where vapour condensation and internal heat recirculation promote extreme heat localization, enabling the localized temperature to reach as high as 160.9 °C under an ambient solar irradiance of 500 W.m − 2 . The system demonstrated outstanding solar seawater desalination performance, achieving an evaporation rate of 3.7 kg.m −2 .h −1 under 0.5-sun illumination. Furthermore, photothermal-photocatalytic H 2 production over commercial TiO 2 P25 modified with AC-K@CuO reached 28.734 mmol.g −1 .h −1 under half-sun illumination without the use of noble-metal co-catalysts or external energy input. This device introduces a new concept for generating superheated steam under realistic operating conditions, paving the way for diverse applications in remote areas.