[3][4] These materials are based on oxyanion groups such as SO42-, PO43−, SeO42−, or AsO43− linked together by hydrogen bonds and charge-balanced by large cation species such as Cs+, Rb+, NH4+, or K+.
[5][6] Various methods are available for synthesis of the solid acid materials and their composites, including slow isothermal evaporation of mixtures, solvent-induced precipitation, dry mixing, electrospinning, sol-gel, thin-film casting, and impregnation.
[4] The main parameters that must be tuned during synthesis are temperature, pressure, heating duration, and grinding/mixing because these are the factors that affect the resulting structure of the electrolyte.
The consequence of this higher tolerance is that SAFCs can run on hydrogen gas that has been extracted from biodiesels and other impure forms of hydrocarbons, paving the way for a more versatile and deployable fuel cell technology.
[11][12][13] An additional benefit of the higher operating temperatures of SAFCs is that non-platinum alloy and transition metal oxide electrocatalysts can be used, which are typically cheaper than the Pt catalysts found in PEM fuel cells.
[15] This combination of detrimental effects is the reason that recent research efforts have pivoted towards focusing more on developing CsH2PO4 electrolytes.
[16] Another study showed that the humidification of the supplies does not affect fuel cell performance, however, which suggests that further investigation of this behavior is needed.
Anode: H2 → 2H+ + 2e− Cathode: 1/2O2 + 2H+ + 2e− → H2O Overall: H2 + 1/2O2 → H2O In 2005, SAFCs were fabricated with thin CsH2PO4 electrolyte membranes of 25 micrometer thickness, resulting in an eightfold increase in peak power densities compared to earlier models.
[5] These thin electrolyte membranes were fabricated by slurry deposition, wherein toluene was used as the suspension medium for the solid acid.
The ideal solid acid fuel cell anode is a "porous electrolyte nanostructure uniformly covered with a platinum thin film".
Such electrodes can be prepared by spray drying, e.g., depositing CsH2PO4 nanoparticles and creating porous, 3-dimensional interconnected nanostructures of the solid acid fuel cell electrolyte material CsH2PO4.
[29] According to Wagner et al. 2021, local hotspots can form a liquid phase of CsH2PO4 that introduces phosphate groups to the platinum catalyst, degrading fuel cell operation.
The introduction of a microporous current collector was found to improve the morphological stability of CsH2PO4 and, consequently, mitigate catalyst poisoning.
Permanent deformation occurs more readily at elevated temperatures because defects present within the material have sufficient energy to move and disrupt the original structure.
[5] Creep resistance can be obtained by precipitate strengthening using a composite electrolyte whereby ceramic particles are introduced to prevent dislocation motion.
For example, the strain rate of CsH2PO4 was reduced by a factor of 5 by mixing in SiO2 particles with a size of 2 microns, however resulting in a 20% decrease in protonic conductivity.
In particular, SAFC systems for remote oil and gas applications have been deployed to electrify wellheads and eliminate the use of pneumatic components, which vent methane and other potent greenhouse gases straight into the atmosphere.
[10] A smaller, portable SAFC system is in development for military applications that will run on standard logistic fuels, like marine diesel and JP8.