Impact of Noncondensable Gases on Solar-Driven Evaporation

Solar-driven interfacial evaporation (SDIE) has emerged as a promising approach for sustainable clean water harvesting, wastewater treatment, and resource recovery by leveraging photothermal transduction to confine heat energy at the water-vapor interface. Although remarkable water production rates above 5.0 L.m^-2.h^-1 have been made possible by substantial advancements in photothermal materials and device architectures, the buildup of non-condensable gases (NCGs) continues to hinder practical deployment. NCGs, originating from dissolved air, organic decomposition, and biological activity, converge at the liquid-vapor interface, forming a mass-transfer barrier that inhibits vapor diffusion and leads to fogging inside the condensation chamber. This phenomenon not only suppresses water yield but also compromises optical transparency and long-term system stability. In this review, we discuss the sources, transport mechanisms, and impacts of NCG accumulation on evaporation efficiency, condensation dynamics, and water quality. We summarize recent strategies to mitigate NCG-induced fogging, including chamber design optimization, gas-purging techniques, membrane-assisted separation, and catalytic decomposition. Furthermore, we highlight knowledge gaps in quantifying NCG concentration under operating conditions and propose standardized testing protocols for evaluating anti-fogging performance. Finally, we outline future research directions for developing fouling-resistant, self-purging, and gas-selective solar evaporators that remain efficient under realistic, fluctuating outdoor conditions. Addressing NCG accumulation is crucial to unlock the full potential of SDIE technologies for decentralized, energy-efficient clean water generation in both low-resource and industrial settings.