Thermoelectric Properties and Applications of Aqueous Sodium Sulfate Electrolyte Infiltrated in Nanochannels for Energy Harvesting

Abstract: The global shift towards decarbonisation has sparked significant interest in more sustainable energy sources that can reduce reliance on fossil fuels. One of the key methods to meet the growing energy demand and cut down carbon dioxide emissions is the direct conversion of heat into electricity. Thermal energy that is released into the environment as waste heat, which usually exists at temperatures below 100 °C, comes from a wide range of sources, including both industrial and natural processes, transport, household electronics, and even the human body. Utilizing ion transfer in nanofluidic channels in order to develop a new nanofluidic platform, could revolutionize flexible and sustainable energy harvesting and storage. Achieving this requires the precise design of nanofluidic platforms that can generate a substantial thermovoltage – i.e., a high ionic Seebeck coefficient – by confining ion transport in charged nanochannels when exposed to a temperature gradient. In this study, a nanofluidic platform with average pore diameter of 25 nm was developed and infiltrated with Na2SO4 aqueous electrolyte of different concentrations, to facilitate ion transport and energy generation by converting electrokinetic and thermal energy into electricity. To test the thermoelectric properties of aqueous electrolyte-infiltrated nanofluidic platforms, a sandwich-type cell design was employed. When a temperature gradient was applied across the cell, the output voltage increased due to thermally driven ion transport in the nanochannels, with a tendency to decrease in aqueous electrolytes of higher concentration. The relationship between the output voltage per Kelvin, derived from the thermal diffusion of ions within the nanofluidic channels, and the electrolyte concentration can be used to explore the role of electrokinetic effects occurring in the nanochannels. Keywords: Energy harvesting, confined electrolytes, ionic thermoelectrics