Interfacial Salinity–Transport Matching in 3D Solar Evaporators: A Framework for Brine‐Stable Solar Interfacial Evaporation

Abstract

ABSTRACT Solar‐driven interfacial evaporation is commonly optimized through photothermal absorption and evaporation flux normalized by projected illuminated area. This metric is useful for quasi‐2D evaporators and dilute feeds, but it does not resolve the coupled constraints that emerge in 3D architectures during brine operation. Here, porous polyvinyl alcohol/graphene nanoplatelet evaporators are used to identify the transition from evaporation‐cooled operation to brine transport limitation. GNP incorporation increases dry photothermal temperatures to 150–180°C; however, this dry‐state ranking is not preserved under brine. Under DI water and 3.5 wt.% NaCl, evaporative cooling suppresses dry‐temperature differences and produces stable wet operation. Under 20 wt.% NaCl, several architectures develop delayed sensible heat accumulation after the early operating period despite no visible salt accumulation. Two evaporators with similar dry photothermal temperatures show sharply different brine responses: the low exposed‐boundary structure reaches 131.34°C after 4 h, whereas the high exposed‐boundary structure shows only 5.34°C late‐stage thermal drift and retains the highest brine‐flux stability. Local conductivity, salt mass balance, transport descriptors, and side‐sealed controls show that brine‐stable 3D evaporation requires matched heat generation, capillary replenishment, salt redistribution, and vapor removal, rather than maximum dry temperature, first‐hour flux, or visual salt suppression as sole performance criteria alone.