Structural Investigation of Orthoborate-Based Electrolytic Materials for Fuel Cell Applications

• Published in: Energies (Basel) Vol. 17; no. 9; p. 2097
• Main Authors: Milewski, Jarosław, Ryś, Piotr, Krztoń-Maziopa, Anna, Żukowska, Grażyna, Majewska, Karolina, Zybert, Magdalena, Kowalczyk, Jacek, Siekierski, Maciej
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.05.2024
• Subjects: Acids; alkali metal orthoborates; Borates; Carbon; Composite materials; Electrolytes; Fuel cell industry; Fuel cells; Hydrogen; Hydrogen as fuel; molten salt-based electrolytes; Poisoning; Potassium; structural investigations; Temperature; Poland
• ISSN: 1996-1073; 1996-1073
• DOI: 10.3390/en17092097

The paper presented delivers the proof for one of the possible solutions to the so-called medium-temperature gap—the lack of electrolytic systems able to efficiently work in a temperature range spanning from 200 to 450 °C. Regardless of the progress made in this field, the commercially available systems are still operating either at close to ambient temperatures, where hydrogen purity requirements are a significant limit, or above ca. 600 °C, where they suffer from increased corrosion and excessive thermal stresses occurring during startup and shutdown. Alkali metal orthoborates (M3BO3 M = Li, Na, K, or the mixture of these), in contrast to commercially used tetra-(M2B4O7) and meta-(MBO2) borates of these metals, are compounds with relatively poorly understood structure and physicochemical properties. The possibility of their application as an electrolyte in a fuel cell is a relatively new idea and has been preliminary reported. Therefore, an extended phase-focused analysis of the materials applied was needed to re-optimize both the synthetic strategy and the application route. Results of PXRD and FT-IR investigations showed, on the one hand, a complicated multi-phase structure, including the main orthoborate phase, as well as the presence of additional borate-based phases, including boric oxoacid. On the other hand, DTA tests proved not only that their melting temperatures are lower than these characteristics for the tetra- and meta-counterparts, but also that cation mixing leads to a subsequent decrease in this important functional parameter of the materials studied.