Protic organic ionic plastic crystals (POIPCs) are shown to be novel anhydrous solid-state proton conductors for fuel cells.

Composite proton conducting materials based on cesium dihydrogen phosphate and neodymium phosphate hydrate were prepared and investigated in terms of X-ray diffraction, thermogravimetry, conductivity, stability and fuel cell performance. At 150 • C the conductivity was 1.8 × 10 −6 S cm −1 for the pristine cesium dihydrogen phosphate and 0.8 × 10 −4 S cm −1 for neodymium phosphate hydrate, while that of the composite containing 29 mol% neodymium phosphate and 71 mol% cesium dihydrogen phosphate was 0.4 × 10 −2 S cm −1 . It was proposed that the interaction between the two components establishes a dynamic hydrogen bonding network enabling efficient proton conduction long before the development of the extensive phase disordering of the superprotonic transition. The presence of thermally stable hydrate water present in neodymium phosphate may also play a role in improving both conductivity and stability of the solid acid. The electromotive force, open circuit voltage and fuel cell performance were measured as demonstration of the material application.

Thin film silica coatings have proven to be efficient barrier coatings to protect stainless steels from corrosion in aggressive environments. The deposition of sub-μm silica films from liquid hydrogen silsesquioxane precursor has previously been demonstrated on metallic substrates, whereby the films were thermally cured in inert atmosphere, which required complicated processing equipment, such as gas or vacuum furnaces. In contrast, curing in air is a promising routine to simplify the curing process, reduce curing cost and increase the curing efficiency. In the present work, silica-like thin films were deposited on 316L grade austenitic stainless steel and oxidatively cured at 450 • C in ambient air. Oxidative curing yielded well adherent films which solely showed microscopic delamination after standardized adherence testing. Further, the oxidative curing led to the formation of a pronounced interfacial duplex-oxide with an outer zone composed of Fe 2 O 3 in a SiO 2-x matrix and an inner zone composed of complex (Cr 3+ ,Fe 2+ ,Mn 2+ )-oxides. Moreover, a Cr depletion of the substrate in the immediate vicinity of the surface was observed. It was concluded that the interfacial formation is controlled by the kinetic limitation of Cr transport to the interface, which consequently led to the Cr-depletion of the sub-surface region.

The application of stainless steels in hostile environments, such as concentrated acid or hot sea water, requires additional surface treatments, considering that the native surface oxide does not guarantee sufficient corrosion protection under these conditions. In the present work, silica-like thin-film barrier coatings were deposited on AISI 316 L grade austenitic stainless steel with 2B surface finish from Hydrogen Silsesquioxane (HSQ) spin-on-glass precursor and thermally cured to tailor the film properties. Results showed that curing at 500 ˚C resulted in a filmstructure with a polymerized siloxane backbone and a reduced amount of Si-H moieties. The coatings showed good substrate coverage and the average thickness was between 200 and 400 nm on the rough substrate surface, however, film thicknesses of more than 1400 nm were observed at substrate defects. Deposition of these films significantly improved the barrier properties by showing a 1000 times higher modulus while an ionic transport over the coating was also observed.

A new proton conductor based on niobium phosphates was synthesized using niobium pentoxide and phosphoric acid as precursors. The existence of hydroxyl groups in the phosphates was confirmed and found to be preserved after heat treatment at 500 C or higher, contributing to an anhydrous proton conductivity of 1.6 Â 10 À2 S cm À1 at 250 C. The conductivity increased with water content in the atmosphere and reached 5.8 Â 10 À2 S cm À1 under pure water vapour at the same temperature. The conductivity showed good stability in the low water partial pressure range of up to 0.05 atm. The metal phosphates are of high interest as potential proton conducting electrolytes for fuel cells operational in an intermediate temperature range.