Photothermal enhanced salinity-gradient osmotic energy conversion for sustainable power generation with phase change material

Salinity-gradient osmotic energy conversion is one of the key energy-effective strategies to alleviate global power scarcity and is highly dependent on the saline solution temperature. In this study, a solar thermal boosted salinity-gradient osmotic energy conversion with phase change thermal storage is proposed. Phase change materials (PCMs) are integrated into a solar-driven salinity-gradient osmotic energy conversion system to overcome intermittent solar illumination during the entire diurnal cycle. A graphene oxide membrane (GOM)-based experiment is conducted to study the time-dependent solution temperature, current, and power density with three thermal management materials: Cu/PCM composite, pure PCM, and a reference case without PCM in one diurnal cycle, as well as their periodic stability. The solution temperature can be effectively improved by the solar thermal effect. The utilized PCMs, which absorb solar heat during the daytime and release latent heat at nighttime, can effectively maintain the solution temperature to suppress the power decline at night, thereby improving the power generation capacity of the osmotic system during the entire cycle. The combined interaction mechanism of temperature and solution evaporation on the solution concentration, ion diffusivity, ion conductance, ion selectivity, and power density is revealed. The contributions of ion diffusivity, ion conductance, ion selectivity and solution concentration on the power density are obtained. In an illumination cycle, the power density undergoes three processes of growth stage (0 < t < 5 h), high power output stage (5 < t < 13h), and decline stage (13 < t < 23 h). In addition, the present design also demonstrates a consistent solution temperature and short-current stability during successive cycles.