Enhanced Thermopower In Thermogalvanic Cells Using D₂O As a Solvent

Thermogalvanic cells have emerged as promising devices for direct heat-to-electricity conversion. In this study, we investigate the utilization of heavy water $\left(\text{D}_{2} \text{O}\right)$ as a solvent in thermogalvanic cells, with a focus on two systems: $\text{K}_{3}\left[\text{Fe}(\text{CN})_{6}\right] / \text{K}_{4}\left[\text{Fe}(\text{CN})_{6}\right] \quad$ and guanidinium chloride (GdmCl) added $\text{K}_{3}\left[\text{Fe}(\text{CN})_{6}\right] / \text{K}_{4}\left[\text{Fe}(\text{CN})_{6}\right]$. For the $\text{K}_{3}\left[\text{Fe}(\text{CN})_{6}\right] / \text{K}_{4}\left[\text{Fe}(\text{CN})_{6}\right]$ system, D<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O consistently exhibits a higher Seebeck coefficient compared to regular water $\left(\text{H}_{2} \text{O}\right)$ across a wide range of concentration levels, which could be attributed to the dielectric constant difference of D<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O. However, the higher internal resistance resulting from D<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O 's higher viscosity offsets the improved Seebeck coefficient, leading to a diminished power output. For the GdmCl added $\text{K}_{3}\left[\text{Fe}(\text{CN})_{6}\right] / \text{K}_{4}\left[\text{Fe}(\text{CN})_{6}\right]$ system, the cell utilizing D<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O not only shows a higher Seebeck coefficient but also demonstrates a higher power output, unlike the system without GdmCl addition. UV-Vis measurements and quantification of precipitated crystals provide evidence of a stronger interaction between $\text{Gdm}^{+}$ and $\text{Fe}(\text{CN})_{6}{ }^{4-}$ in D<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O. The higher reaction equilibrium constant between $\text{Gdm}^{+}$and $\text{Fe}(\text{CN})_{6}{ }^{4}$ in D<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O supports the observed enhancement in $S_{\text{e}}$, consistent with our previous studies. This investigation highlights the promising potential of D<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>O as a solvent in thermogalvanic cells, offering valuable insights into the intricate interplay between solvent properties, ion interactions, and thermoelectric performance.