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Fuel cell performances at intermediate temperature 600°C were examined for the hydrogen membrane fuel cell (HMFC) designed by rf sputter deposition of a BaCe0.8Y0.2O3-δ thin film electrolyte (1 μm thickness) on a Pd1-xAgx (x = 0, 0.2 and 0.4) solid anode. The maximum power density reached to 1.2 W cm−2 at 600°C with the Pd0.8Ag0.2 anodes, and this value was much higher than the champion data of the recent anode-supported proton-conducting ceramic fuel cells (PCFCs). By electrochemical impedance analysis, it was demonstrated that the hydrogen permeability was crucial to the anode polarization losses of the HMFC because the charge transfer resistances and concentration overpotentials at BaCe0.8Y0.2O3-δ/Pd oxide-metal interfaces are simultaneously improved with the alloys having higher hydrogen permeability.

In this study, aluminosilicate sol-gel coatings were deposited on Type 430 stainless steel by multiple spin casting cycles. Amorphous aluminosilicate coatings, 65 nm thick, were prepared from precursor solutions with 50, 100, and 500 mmol dm(-3) total concentrations of aluminum and silicon species (molar ratio of Al/Si = 1/4) by 10, 5, and 1 spin casting cycles, respectively. Although the obtained coatings had a similar composition with a molar ratio of Al/Si = 25/75, the coatings with increased density were formed by reducing the concentration of precursor solution. The pitting potentials of the coated stainless steels, measured by potentiodynamic polarization in 3.5% NaCl solution, increased remarkably (to 1.1 V vs Ag/AgCl) with a decrease in the concentration of precursor solution. Cyclic corrosion tests, consisting of 30 cycles of spraying of 5% NaCl solution at 35 degrees C for 2 h, drying at 60 degrees C for 4 h, and wetting at 50 degrees C and >95% relative humidity for 2 h, revealed highly improved corrosion resistance. Layer-by-layer sal-gel deposition using diluted precursor solutions is an effective way to obtain highly protective coatings. (C) 2013 The Electrochemical Society.

Novelproton-conductingZrO2-WO3-SiO2 nanofilmsofvariouscompositionsandthicknesses(∼50to ∼300nm)havebeenprepared by anodizing of magnetron-sputtered Zr-W-Si alloys in 0.1 mol dm−3 phosphoric acid electrolyte at 20◦C. All the anodic oxide nanofilms examined reveal efficient proton conductivity after post-annealing at 250 ◦ C. Further increase in the post-annealing temperature results in the conductivity degradation for the anodic oxide nanofilms on the alloy containing only 5 at% silicon, while the high conductivity is maintained even after post-annealing at 300 ◦ C for those containing 15 at% or more silicon. The proton conductivity is dependent upon tungsten content; the conductivity of 5 × 10 −6 Sc m −1 for the ∼100 nm-thick films on the Zr31W55Si14 at 100 ◦ C is approximately 10 times that on the Zr48W37Si15. The anodic oxide nanofilms consist of two layers, comprising a thin outer ZrO2 layer and an inner ZrO2-WO3-SiO2 layer. Both layers show thickness-dependent conductivity and the proton conductivity of the two-layer anodic films is enhanced one order of magnitude by reducing the film thickness from ∼300 nm to ∼100 nm. Different mechanisms are proposed for the thickness dependence of the conductivity of the outer and inner layers.

Novel thin film fuel cell based on the 100 nm-thick electrolyte of amorphous ZrP2.6Ox, working at 400℃, was demonstrated. The hydrogen permeable membrane fuel cell (HMFC) using a Pd foil as a nonporous solid anode was fabricated. Ni interlayer of several hundreds nm thickness was introduced between the Pd anode and the ZrP2.6Ox electrolyte in order to suppress the deterioration of the electrolyte nanofilm by the deformation of the Pd anode during hydrogen absorption. In the ZrP2.6Ox electrolyte the transport number of proton was unity at 400℃ as determined by an EMF measurement. The modification of the Ni anode surface by an ultrathin Pt or Pd layer effectively decreased the anode/electrolyte interfacial polarization. Consequently, the HMFC revealed the OCV of 1.0 V and the maximum power density of 1.8 mW cm^[-2] at 400℃.

Novel proton-conducting amorphous anodic ZrO2-WO3-SiO2 films, 200 nm thick, are prepared by anodizing of sputter-deposited Zr37W47Si16 at 100 V with current decay for 1.8 ks in 0.1 mol dm −3 phosphoric acid electrolyte at 20 ◦ C. The resultant anodic films have been characterized using electrochemical impedance spectroscopy, transmission electron microscopy, glow discharge optical emission spectroscopy and Rutherford backscattering spectroscopy. The addition of silicon species to the anodic ZrO2-WO3 film significantly enhanced the thermal stability. Even after thermal treatment at 300 ◦ C in dry Ar atmosphere, the anodic ZrO2-WO3-SiO2 films revealed stable proton conductivity in the temperature range of 50‐225 ◦ C, while the anodic ZrO2-WO3 on the Zr43W57 loses the proton conductivity by annealing at 250 ◦ C. The anodic film on the Zr37W47Si16 consisted of two layers, comprising an outer thin ZrO2 layer, free from tungsten and silicon species, and an inner main layer containing all zirconium, tungsten and silicon species. The results in this study suggest that the conductivity deterioration at high annealing temperatures is associated with the diffusion-induced formation of a poorly-conducting layer near the alloy/anodic oxide interface.

Uniform, defect-free nanofilms (around 100 nm thick) of hafnium phosphate were prepared via layer-by-layer deposition of precursor solution of metal alkoxides and were shown to give practically useful proton conductivity at 300-400°C as fuel cell electrolyte membrane. Annealing of the deposited precursor film at 500°C gave a lower area specific resistance (R AS ) than that at 400°C, and this effect was coincident with the formation of the pyrophosphate unit. The best (lowest) R AS value of less than 0.1 Ω cm 2 for hafnium phosphate membrane (annealing at 500°C, 291 nm thick, conductivity of 3 × 10 ―4 S cm ―1 at 320°C) was comparable to that of a nanofilm of an yttrium-doped zirconium phosphate. The R AS values of nanofilms of zirconium sulfate and zirconium borate were 2-3 orders higher than that of the corresponding zirconium phosphate. It is clear from these results that nanofilms of various solid acids are promising candidates for the electrolyte membrane of fuel cells operating at the intermediate temperatures of 300-400°C.