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

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.