Coupling photothermal and Joule-heating conversion for self-heating membrane distillation enhancement

• Coupling photothermal and Joule-heating MD was achieved by a composite membrane. • Water flux of coupling process was greater than combined values of independent MD. • Higher efficiency was achieved by larger power density due to nonlinear process. • The coupling process achieved stable freshwater output and improved the efficiency. The self-heating-membrane distillation (SHMD) process proposed by many researchers has clear advantages in enhancing the membrane distillation (MD). However, the unstable freshwater production associated with photothermal MD and the high electrical-energy consumption of Joule heating has impeded development. In this study, highly efficient coupling photothermal and Joule-heating MD was achieved using a composite membrane that provided good photothermal and Joule heating simultaneously. The highest productivity was achieved at lower feed flux; under these conditions, the temperature was relatively high and salinity had little effect on vapor concentration. Through the analysis of the energy conversion process and the heat energy consumption of each part, the results revealed that the freshwater production of the coupling process was greater than the combined values of the two independent processes. And higher freshwater productivity and higher thermal efficiency were achieved with a larger power density because the vapor concentration had a nonlinear relationship with the input power density in SHMD. The realization of this coupling photothermal and Joule-heating MD process using one composite membrane combines the advantages of the two processes. This could help to achieve stable freshwater output and further improve the SHMD process, promoting actual applications to relieve freshwater shortages.