Proton-Conducting Fuel Cells Research Articles

Adjusting the conduction properties of La 0.995Ca 0.005NbO 4 − δ by doping for proton conducting fuel cells electrode operation

Structural characterization and transport properties of A- (Ce and Pr) and B-site (Mn) doped La 0.995Ca 0.005NbO 4 − δ (LCN) have been investigated. Conductivity data have been analyzed in the temperature range from 400 to 800 °C as a function of the oxygen partial pressure under dry atmospheres and under different wet atmospheres. All compounds present changes in the activation energy due to a phase transformation at ca. 550 °C. Under wet conditions the conductivity is predominantly protonic in all compounds except for the Ce doped sample under oxidizing atmospheres. The conductivity of Ce doped sample is principally electronic at high pO 2 and high temperatures while it becomes more ionic at low pO 2 and temperatures. The combination of n-type electronic and protonic conductivity for Ce doped LCN under reducing atmospheres suggests its potential application as an anode component for LCN-based proton conducting fuel cells (PCFC). Moreover, Pr doped LCN shows remarkable p-type electronic conductivity at high pO 2 in combination with protonic conductivity, which are interesting properties for LCN-based PCFC cathode components. Furthermore, Ce and Pr addition have allowed increasing the sintering activity with respect to LCN powders. The activation energies and the preexponential factors under wet atmospheres have been studied and correlated. It was found that they obey the Meyer–Neldel law and an estimation of the activation energy of protons in both crystal structures has been derived.

FeCr2O4 Nanoparticles as Anode Catalyst for Ethane Proton Conducting Fuel Cell Reactors to Coproduce Ethylene and Electricity

Ethylene and electrical power are cogenerated in fuel cell reactors with FeCr2O4 nanoparticles as anode catalyst, La0.7Sr0.3FeO3-δ (LSF) as cathode material, and BaCe0.7Zr0.1Y0.2O3-δ (BCZY) perovskite oxide as proton‐conducting ceramic electrolyte. FeCr2O4, BCZY and LSF are synthesized by a sol‐gel combustion method. The power density increases from 70 to 240 mW cm−2, and the ethylene yield increases from about 14.1% to 39.7% when the operating temperature of the proton‐conducting fuel cell reactor increases from 650 ∘C to 750 ∘C. The FeCr2O4 anode catalyst exhibits better catalytic performance than nanosized Cr2O3 anode catalyst.

Electron Microscopy Study of interfaces of Proton Conducting Fuel Cell Anodes

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

Ca 3−xLa xCo 4O 9+δ ( x=0, 0.3): New cobaltite materials as cathodes for proton conducting solid oxide fuel cell

Misfit-type Ca 3− x La x Co 4O 9+ δ ( x=0, 0.3) oxides were synthesised to be evaluated as possible cathode materials for proton conducting fuel cells (PCFCs) based on BaCe 0.9Y 0.1O 3− δ (BCY10) dense ceramic electrolyte. The electrical conductivity value of Ca 2.7La 0.3Co 4O 9+ δ ( σ≈53 S cm –1 at 600 °C) is in the range of usually required value for a cathode application (about 50–100 S cm –1). In order to test the performance of each compound as cathode material, impedance measurements were carried out on Ca 3− x La x Co 4O 9+ δ /BaCe 0.9Y 0.1O 3− δ /Ca 3− x La x Co 4O 9+ δ symmetrical half cells over the temperature range 400–800 °C under wet air. A promising electrocatalytic activity has been observed with both compounds Ca 3Co 4O 9+ δ and Ca 2.7La 0.3Co 4O 9+ δ . Factually, the area specific resistance obtained was about 2.2 Ω cm 2 at 600 °C.

Preparation and Characterization of Nanocrystalline Mixed Proton−Electronic Conducting Materials Based on the System Ln6WO12

The tungstates Ln6WO12 are proton-conducting materials exhibiting sufficient electronic conductivity to consider them as potential candidates for the separation of hydrogen at high temperature. Hydrogen-permeable membranes will find application in power plants applying precombustion strategies, process intensification using high-temperature catalytic membrane reactors, and in components for electrochemical systems as proton conducting fuel cells (PCFCs) and electrolyzers. This work presents the preparation and characterization of nanocrystalline mixed conducting materials with three different nominal compositions (Nd6WO12−Eu6WO12−Er6WO12) using a sol−gel complexation synthesis method. The evolution of the crystalline structure and crystallite size is studied as a function of the sintering temperature. Generally, the nanosized oxides show a (pseudo)-cubic crystalline fluorite structure which evolves into the most stable fluorite symmetry (tetragonal for Nd and rhombohedral for Er) with increasing sintering...

Proton-Conducting Fuel Cell Operating on Hydrocarbon Fuels

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Propane Dehydrogenation in a Proton-conducting Fuel Cell

The process and reaction mechanism of propane dehydrogenation in a proton-conducting fuel cell were studied at 600−700 °C using Y-doped BeCeO3 as protonic electrolyte and Pt as electrode catalysts. The electrochemical dehydrogenation of propane was in competition with side reactions caused by the gas species (H2, C2H6, C2H4 etc.), which were the products of nonelectrochemical reactions (e.g., thermal cracking) in the anode chamber. Among those side electrochemical reactions, hydrogen disassociation into hydrogen ions was predominant. At 650 °C electrochemical dehydrogenation of propane has a higher activation energy than hydrogen disassociation over the anode platinum catalyst; however, the former reaction was more readily achieved at 700 °C.

Polysulfones Grafted with Poly(vinylphosphonic acid) for Highly Proton Conducting Fuel Cell Membranes in the Hydrated and Nominally Dry State

Mechanically strong and flexible membranes with very high local concentrations of immobilized proton-conducting phosphonic acid have been achieved by grafting poly(vinylphosphonic acid) side chains onto polysulfones. The graft copolymers were prepared by anionic polymerization of diethyl vinylphosphonate initiated from lithiated polysulfones, followed by quantitative cleavage of the ester functions. The resulting phosphonic acid units acted like monoprotic acids to indicate a high level of intramolecular interactions, and the phase-separated nature of the copolymers was shown by dual glass transitions. Fully polymeric membranes were conveniently cast from solution and showed high proton conductivities, e.g., 5 mS/cm under nominally dry conditions at 120 °C and up to 93 mS/cm under 100% relative humidity at the same temperature. The corresponding conductivities measured for Nafion 115 under the same conditions were 0.04 and 105 mS/cm, respectively. The former membranes furthermore showed high thermal stability with decomposition temperatures exceeding 300 °C under air. Additions of 2−5 wt % of a perfluorosulfonic acid polymer to the phosphonated membranes were found to reduce the water uptake significantly, thus improving the mechanical properties. The conductivity of these fully polymeric doped membranes was generally observed to be enhanced, or at least to remain at the same level, under both humidified and nominally dry conditions. The findings of this study demonstrate that phosphonated membranes with a proper macromolecular design may potentially show some important advantages in relation to the more commonly studied sulfonated membranes in fuel cell applications.

Chemically Modified Poly(vinyl alcohol)−Poly(2-acrylamido-2-methyl-1-propanesulfonic acid) as a Novel Proton-Conducting Fuel Cell Membrane

Polymer blends of poly(vinyl alcohol)−poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PVA−PAMPS) family membranes have been prepared and evaluated as novel proton-conducting materials on the ba...

Thermal Studies of the State of Water in Proton Conducting Fuel Cell Membranes

Thermal Studies of the State of Water in Proton Conducting Fuel Cell Membranes

Sulfophenylation of Polysulfones for Proton-Conducting Fuel Cell Membranes

Polysulfone has been sulfophenylated by lithiation and anionic reaction with 2-sulfobenzoic acid cyclic anhydride. This provides a new convenient method to modify polysulfones by attaching pendant sulfonated phenyl groups via ketone links. Membranes of the sulfophenylated polysulfones show promise for use in proton-exchange-membrane fuel cells. For example, a membrane with 0.9 sulfophenyl units per repeating polysulfone unit and 30 wt.-% water was found to have a proton conductivity of 32 mS/cm at 60°C.