Thermoelectric-Mediated Selective Ion Transport in Liquid-Exfoliated Molybdenum Sulfide Thin Films for Applications in Novel Filtration and Energy Devices

Molybdenum sulfide (MoS₂), a member of the widely studied transition metal chalcogenide family of compounds, may play a role in novel applications for water desalination, biomedicine and energy storage thanks to its propensity for ionic transport. By exploiting its thermoelectric capability, and the respective properties of its 1T/2H crystalline phases, liquid-exfoliated MoS₂ can serve as a medium for selective capture and movement of ions from solution. Here, we introduce our work undertaken to synthesize and characterize thin films of this material alongside utilizing it for Seebeck-driven water purification and rechargeable battery technologies. Prototype chambered desalination devices incorporating MoS₂ films were constructed and tested to determine changes in electric potential and solution osmolarity following exposure to temperature gradients. In these systems, two salts (NaCl and KBr) were studied at various concentrations to assess MoS₂’s potential for ion transport under different conditions. Furthermore, some analysis of film deterioration and attempts to mitigate this problem using polymers or other chalcogenides were explored. Results from these studies indicate that thermoelectric MoS₂ films can effectively filter ions, thereby generating significant voltages across their surfaces via combined carrier/ionic transport. However, ion contact with the film surface and subsequent movement through the film bulk may lead to destabilization, erratic fluctuations in electric potential and impaired transport. Deposition of PVDF on the film surface provides some protection from this breakdown, and studies of hybrid chalcogenides like molybdenum disulfide/antimony telluride that aid in maintaining film integrity are ongoing. Battery architectures that make use of MoS₂ films as both intercalating storage matrices and separation membranes, and recharge through application of thermal gradients, are under investigation as well. We will discuss some of our recent efforts in this area, specifically, design, construction and testing of thermoelectric batteries. While some hurdles remain, MoS₂-based filtration and energy devices can make a significant contribution to solving problems like freshwater scarcity and increasing energy costs facing the world today.