Synergy effects of pH and thermal localization on membrane-based salinity gradient energy harvesting

Abstract

Salinity gradient power generation receives increasing attention due to its availability in nature. However, membrane surface charge is not fixed value in isolation but strongly dependent of various conditions. Here, a coupled ion transport model is proposed to study the synergy effects of pH and thermal localization on membrane-based salinity gradient energy conversion. The research illustrates that the surface charge is regulated by solution environment, membrane properties and thermal conditions. Specially, the surface charge sign can be even reversed at certain case that induces distinct ion transports behaviors. Consequently, Al2O3 membrane achieves the better energy conversion performance at low pH with negative temperature difference. While SiO2 membrane obtains the best output performance at high pH with negative temperature difference. Such is ascribed to pH-regulated surface charge and thermal up-diffusion enhancement. The maximum output power of 10 pW with efficiency of 16 % is achieved for individual membrane channel. As a proof of concept, it shows significant deviations between the single and coupling model on power generation. The findings of this study can help for better understanding the coupling mechanisms of solution, membrane and thermal conditions during the energy conversions, thereby providing a reasonable design route for membrane-based energy devices.