Publication Details
Abstract
This study systematically investigates the physicochemical and conductive properties of aqueous and immobilized potassium hydroxide (KOH) electrolytes, providing critical data for the optimization of high-performance alkaline electrochemical devices, the ionic conductivity of KOH solutions at varying concentrations (35, 45, and 55 wt.%) was meticulously characterized across a broad operational temperature range (25–220°C), to maintain the liquid phase at temperatures exceeding the normal boiling point, all measurements were conducted under high pressure (up to 30 bar), a necessity dictated by the material's phase diagram, the experimental setup utilized custom-designed cells for both bulk aqueous solutions and electrolytes immobilized within porous pellets, with impedance spectroscopy employed as the primary analytical technique.
The results reveal a complex, non-linear relationship between conductivity, temperature, and concentration. For aqueous solutions, conductivity initially increases with temperature, driven by enhanced ionic mobility and reduced solvent viscosity, before reaching a distinct peak, the 35% KOH solution exhibited a peak conductivity of 2.8 S·cm⁻¹ at 206°C. Notably, a critical performance crossover was identified: while the 35% solution displayed superior conductivity at ambient temperature (25°C), the 45% solution demonstrated significantly higher conductivity at elevated temperatures (≥ 200°C), in contrast, the effective conductivity of immobilized electrolytes was, as expected, attenuated by the tortuous pathways and inherent porosity of the pellet matrix, the highest immobilized conductivity of 0.84 S·cm⁻¹ was achieved with the 45% solution at 200°C. Crucially, porosimetry analysis revealed that the pellet pores were only partially saturated (74–83% filled), indicating that these measured values represent a conservative baseline with substantial potential for enhancement through improved wetting protocols, the temperature-dependent behavior for all systems was accurately modeled using cubic regression equations, which showed excellent fidelity with both experimental data and established literature values, within a total estimated measurement uncertainty of ±10%, ultimately, this work provides a fundamental framework and predictive models for selecting the optimal electrolyte concentration based on specific operating temperatures, it quantifies the performance trade-offs between aqueous and immobilized systems and identifies key material engineering strategies such as reducing pellet thickness and ensuring complete pore saturation for minimizing ohmic losses and advancing the next generation of alkaline electrolyzers and fuel cells.