Fast ionic conduction in tetravalent metal pyrophosphate-alkali carbonate composites: New potential electrolytes for intermediate-temperature fuel cells

Water Electrolysis toward Elevated Temperature: Advances, Challenges and Frontiers

“…Materials and performance of proton-conducting ET-ICs (including TMPs, − ,− solid acids ,,,,, and HPAs , ).…”

“…315,321,323,324 When alkali carbonates, including Li 2 CO 3 and Na 2 CO 3 , were incorporated into TMP-based electrolytes, secondary phases were generated by the amorphous phase of carbonates and the crystalline phase of metal pyrophosphates. 314 Although proton conduction dominated at <300 °C, oxygen ion transportation became significant at >300 °C, and the presence of co-ionic conductivity further elevated the applicable temperature of TMP-carbonate composite systems to over 600 °C. 314 The materials and properties of TMP-based electrolytes are presented in Table 16.…”

“…314 Although proton conduction dominated at <300 °C, oxygen ion transportation became significant at >300 °C, and the presence of co-ionic conductivity further elevated the applicable temperature of TMP-carbonate composite systems to over 600 °C. 314 The materials and properties of TMP-based electrolytes are presented in Table 16. Exploiting the transition from a poorly conductive monoclinic phase into a cubic phase at 230 °C, proton transportation in the solid acid CsH 2 PO 4 is drastically promoted by highly disordered hydrogen bonds, phosphate anions and partially occupied oxygen sites, which offers greatly improved proton conductivity (up to 4 orders of magnitude) 18 and potential as an electrolyte material.…”

“…At present, studies concerning this temperature range are still in the infancy stage and published literature majorly focus on the exploration of various ET-ICs as applicable electrolyte materials. Benefiting from the promoted mobility of internal ions, proton conductors, including TMPs, − solid acids ,, and HPAs, , and hydroxide ion conductors, such as Mg–Al LDHs, , have been fabricated as pellets through cold press and sintering, while the insufficient mechanical strength became the universal problem to restrict the reduction of electrolyte thickness and resistance . Since the ionic conductivity of these solid-state ET-ICs are greatly dependent on the moisture content of the surrounding environment, difficulties have been simultaneously offered by precise control of operation conditions and rational design of cell structures .…”

“…Owing to the decomposition of pyrophosphates, the optimal proton conductivity of TMP-based membranes normally occurs at 150–200 °C, and their applications are limited to 250 °C. ,,, When alkali carbonates, including Li 2 CO 3 and Na 2 CO 3 , were incorporated into TMP-based electrolytes, secondary phases were generated by the amorphous phase of carbonates and the crystalline phase of metal pyrophosphates . Although proton conduction dominated at <300 °C, oxygen ion transportation became significant at >300 °C, and the presence of co-ionic conductivity further elevated the applicable temperature of TMP-carbonate composite systems to over 600 °C . The materials and properties of TMP-based electrolytes are presented in Table .…”