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This work investigates the electrochemical dynamics and performance of additively manufactured composite electrolytes for resistive switching. Devices are comprised of a Ag/AgI–Al2O3/Pt stack, where the solid state electrolyte is additively manufactured using extrusion techniques. AgI–Al2O3 composite electrolytes are characterized by x-ray diffraction and electrochemical impedance spectroscopy. The ionic conductivities of the electrolytes were measured for different concentrations of Al2O3, observing a maximum conductivity of 4.5 times the conductivity of pure AgI for composites with 20 mol. % Al2O3. There was little change in activation energy with the addition of Al2O3. Setting the Ag layer as the positive electrode and the Pt layer as the negative electrode, a high conductivity state was achieved by applying a voltage to electrochemically establish an electrically conducting Ag filament within the solid state AgI–Al2O3 electrolyte. The low conductivity state was restored by reversing this applied voltage to electrochemically etch the newly grown Ag filament. Pure AgI devices switch between specific electrical resistivity states that are separated by five orders of magnitude in electrical conductivity. Endurance tests find that the AgI resistive switches can transition between a low and high electrical conductivity state over 8500 times. Composite AgI–Al2O3 resistive switches formed initial Ag filaments significantly faster and also demonstrated two orders of magnitude separation in resistivity when cycling for 1600 cycles. [ABSTRACT FROM AUTHOR]

The performance degradation and recovery of a polymer electrolyte fuel cell exposed to ammonia is described. The effect of ammonia contamination on each component of the MEA was studied using Neutron Imaging, lifetime tests, cell polarization measurements, potentiostatic measurements, and AC impedance spectroscopy. It is found that among the detrimental effects of the contaminant, mass transport and ORR kinectic are mostly affected. Reductions in electrolyte conductivity are not playing a major role in cell performance losses for the low levels of contamination studied here. Shifts in electrolyte proton activity reduce oxygen reduction reaction mixed equilibrium potential and so cell potential. In addition, cell potential might also be affected by overpotentials on the oxygen reduction reaction caused by oxidation of ammonia at cell potential above 0.7 V. It is demonstrated that cell initial performance can be recovered after contamination and ammonia-contaminated PEFC recovering mechanisms are discussed. [ABSTRACT FROM AUTHOR]

A sulfide antioxidant buffer solution was used to trap and concentrate trace quantities of H2S that permeated through 50 cm2 samples of fuel cell Nafion 117, 212, and 112 membranes using a H2S partial pressure difference up to 1000 ppm at room temperature. Experiments were conducted between 24 and 48 h to achieve sulfide ion concentrations high enough to be determined accurately by subsequent titration with Pb(NO3)2. In contrast to previous work, a special H2S mixing system was employed to achieve reproducible delivery of H2S concentrations throughout each experiment. The calculated rates of H2S crossover, normalized for membrane area, thickness, and differential PH2S varied from as low as 7.58 X 10-10 to 4.65 X 109 g/s atm cm depending on the type of Nafion sample and humidity conditions. Even low levels of humidification of the membrane and gases (saturated at 25°C) increased the crossover rate of H2S in the Nafion materials. H2S permeation through the electrolyte membrane negatively impacts the oxygen reduction rate occurring on the cathode and possibly causes an irreversible decrease in the overall fuel cell performance. [ABSTRACT FROM AUTHOR]

Abstract: The article details the application of commercial manufacturing methods towards the development of NO x /NH3 sensors for vehicle on-board emissions control. These sensors possess a unique mixed potential sensor design. This unique LANL (Los Alamos National Laboratory) design results in improved sensitivity, selectivity and response time over conventional mixed potential sensors incorporating a stable three-phase interface using a porous electrolyte coated over a dense electrode. A prototype gas sensing platform conducive to large-scale manufacturing and commercialization is also been presented. The observed results indicate the possibility of evolution towards a combined NO x /NH3 sensor on the same platform. Finally, critical challenges towards developing field deployable mixed potential NO x /NH3 sensors are identified and discussed. [Copyright &y& Elsevier]

This article presents a study regarding the scientific aspects of polymer electrolyte fuel cell durability and degradation. Durability is one of the major remaining barriers to commercialization of fuel cells. It mentions that the correlation of durability with cost cannot be overlooked in creating fuel cell systems because the two are interrelated in materials.