A photothermal and conductive composite hydrogel membrane for solar-driven synchronous desalination and salinity power generation

Solar-driven interfacial evaporation is increasingly used in desalination due to its excellent evaporation performance. The continuous evaporation of water would lead to an increase in the salinity of the evaporator, which has been often neglected and rarely exploited. In this work, a calcium alginate hydrogel and nickel foam composited membrane (CHN) was proposed as a new platform for constructing solar-powered hybrid systems with the function of synchronous desalination and salinity power generation. The calcium alginate hydrogels can reduce the enthalpy of water evaporation and convert the salinity gradient between the evaporator and seawater into electrical energy. The evaporation rate of the mixed system (CHN-CB) with carbon black (CB) as the solar absorber is greater than 2.1 kg m-2 h-1. Additionally, under 1 sun, the system achieved a maximum short-circuit current of 20.3 mA m-2 and generated an extra electrical power of 5.3 mW m-2. As a universal multi-energy conversion platform, the CHN membranes can combine different photothermal materials for synchronous evaporation and salinity gradient power generation. These results open new paths for the combination of desalination and power generation, demonstrating the potential for diversified use of blue energy. A calcium alginate hydrogel and nickel foam composite membrane (CHN) can achieve desalination and salinity gradient power generation by solar energy. The CHN membrane can be used as a universal solar conversion platform to obtain blue energy.