Ronald L. Cook

Rational selection of advanced solid electrolytes for intermediate temperature fuel cells

Abstract Discussed here is a strategy for selecting perovskite-based solid electrolytes with the potential for achieving high ionic conductivities at intermediate temperatures (≈600 °C). Activation energies for anionictransport (either O2- or proton) have been shown to be influenced by: (1) the average metal-oxygen bond energy in the perovskite, (2) the lattice free volumes, obtained by subtracting the ionic volumes of cations and O2- in the unit cell volume, (3) the parameter rcritical (rc) which corresponds to the radius of the opening between the two A-site cation and one B-site cation through which the mobile anion must pass, and (4) the lattice polarizability. Low activation energeis for anion migration appear to favor: (1) that the overall lattice possess a moderate metal-oxygen binding energy, (2) perovskite solid electrolytes possess free volumes of 30–35A 3, (3) that the lattice minimally polarizes the mobile anion, and (4) preferred ( r critical r 2- 0 ) 2 ratios for A-A-B saddle points ≅0.5 High ionic conductivities have also been achieved for the perovskite-related brownmillerites A2B2O5 which possess a high intrinsic population of anion vacancies in their lattice. Solid electrolytes evolving from this complimentary rationale, which has included BaTh0.9Gd0.1O3, Sr2Gd2O5 and Sr2Dy2O5, have been incorporated into fuel cells operating at intermediate temperatur es. La0.9Sr0.1CoO3, BaCo0.8Fe0.2O3, Ag and Au have been found candidate cathodes for the intermediate-temperature fuel cell applications.

On the systematic selection of perovskite solid electrolytes for intermediate temperature fuel cells

Abstract The ability to develop a rationale for predicting new perovskite solid electrolytes discussed here relies in part upon empirical relationships found between activation energy for anionic transport and perovskite crystallographic-related parameters including (i) the average metal-oxygen bond energy of the perovskite lattice, (ii) the degree of openness, or “free volume”, of the lattice, and (iii) the critical radius ( r c ) saddle point formed by two A and one site through which anionic mediation proceeds. Resulting relationships are found to hold promise for predicting new perovskite solid electrolytes possessing low activation energies and consequent high ionic conductivity for anionic transport. Upon application of principal component analysis to those major empirical factors appearing to influence high ionic mobility in perovskite lattice along with the Goldschmidt tolerance factor S , new materials were selected, three of which were subjected to preliminary evaluation in small fuel cells operating at 600°C. For less than theoretically dense materials, ionic conductivities for sintered disks of BaTb 0.9 In 0.1 O 3 , CaCe 0.9 Gd 0.1 O 3 and CaCe 0.9 Gd 0.1 O 3 and CaCe 0.9 Er 0.1 O 3 were found to vary between ≊5×10 −2 Ω −1 cm −1 and 5×10 −3 Ω −1 cm −1 with activation energies energies varying between 0.53 and 0.35 eV.

Carbon Dioxide Reduction to Alcohols using Perovskite‐Type Electrocatalysts

Electrochemical reduction of under ambient conditions to methanol, ethanol, and n‐propanol is reported at perovskite‐type electrocatalysts when incorporated into gas diffusion electrodes. In the absence of copper at the perovskite B lattice site, no activity was found. This investigation resulted in the identification of electrochemical conditions whereby perovskite‐type electrocatalysts could achieve cumulative Faradaic efficiencies for reduction to methanol, ethanol, and n‐propanol up to 40% at current densities of 180 mA/cm2.

Evidence for formaldehyde, formic acid, and acetaldehyde as possible intermediates during electrochemical carbon dioxide reduction at copper

Reported here is recent work performed on the electrolysis of aqueous HCOOH, HCHO, MeOH, and CH 3 CHO at copper electrodes to gain insight into the possibility of these species being CO 2 reduction intermediates

Gas‐Phase CO 2 Reduction to Hydrocarbons at Metal/Solid Polymer Electrolyte Interface

La reduction electrochimique du dioxyde de carbone, en phase gazeuse, sur une electrode de platine modifiee par un polyelectrolyte solide contenant differents metaux (Ni, Ru, Rh, Pd, Ag, Re, Os, Ir, Pt, Au) qui servent de catalyseur

Investigations on BaTh0.9Gd0.1 O 3 as an Intermediate Temperature Fuel Cell Solid Electrolyte

The perovskite solid electrolyte BaTh 0.9 Gd 0.1 O 3 incorporated into fuel cells possessing the general configuration H 2 (3% H 2 O) Pd/BaTh 0.9 Gd 0.1 O 3 /La 0.9 Sr 0.1 CoO 3 (3% H 2 O), O 2 has been studied. lonic conductivity was found to progressively increase by ≃30% upon passage of current through cells for over a day, with values up to 8.7×10 -2 S cm -1 being found at 550 o C

Electrochemical Natural Gas Conversion to More Valuable Species

This paper reports on the electrochemical oxidative dimerization of methane to give C{sub 2} hydrocarbon species investigated in solid oxide fuel cells possessing the general configuration: CH{sub 4}, anode electrocatalyst/ZrO{sub 2}(8 m/o Y{sub 2}O{sub 3})/La{sub 0.9}Sr{sub 0.1}MnO{sub 3}O{sub 2}(air). Perovskite anode electrocatalysts shown to possess activity toward promoting the subject reaction include Sm{sub 0.5}Ce{sub 0.5}CuO{sub 3}, Tb{sub 0.8}Sm{sub 0.2}CuO{sub 3}, Gd{sub 0.9}Th{sub 0.1}CuO{sub 3}, Gd{sub 0.9}Na{sub 0.1}MnO{sub 3}, and Th{sub 0.8}Yb{sub 0.2}NiO{sub 3}. Maximum partial faradaic current densities at active perovskite anode electrocatalysts for promoting the subject reaction were found to be directly correlatable to their calculated oxygen binding energies on the perovskite surface, where increasing binding energies were found to favor higher rates for electrochemical partial methane oxidation. Increasing surface oxygen binding energies at perovskite anode electrocatalysts were found to correlate with increasing perovskite lattice-free volumes with electrochemical measurements, supporting increasing surface oxygen binding energies and perovskite lattice-free volumes as leading to enhanced rates for the subject reaction. As a consequence, synergism was found between experimentally determined perovskite anode electrocatalyst activities, their calculated surface oxygen binding energies, and lattice ionic-free volumes.

Reversible detection of sulfur dioxide by using a multiple reflecting optical waveguide sensor

Abstract The reversible detection of sulfur dioxide at levels down to 100 μl l−1 has been demonstrated by using a Cu (PBz3)2SPh-coated optical waveguide. The optical waveguide consisted of a Pyrex tube initially coated with the subject complex with an unfiltered tungsten-halogen light source at one end. Interaction of sulfur dioxide with the initially white complex resulted in reversible formation of an orange adduct, Cu (PBz3)2SPh·SO2, which was detected by a change in transmitted light intensity via a photodiode located opposite the light source.

Organophosphine transition metal complexes as selective surfaces for the reversible detection of sulfur dioxide with piezoelectric crystal sensors

Abstract Some organotransition metal complexes, bis (sulfur dioxide)tetrakis (triphenylphosphine oxide) manganese(II)dioxide [Mn(OPPh 3 ) 4 I 2 (SO 2 ) 2 ] and bis(tribenzylphosphine)copper(II) thiophenolate [Cu(PBz 3 ) 2 SPh], were identified as candidate coatings for the detection of sulfur dioxide on piezoelectric crystal sensors. After treatment to form the mono (sulfur dioxide) adduct, the first complex binds sulfur dioxide to reform the bis adduct, and can be used as a coating for an integrating piezoelectric sensor. The initial complex can be regenerated by placing the coated piezoelectric sensor under vacuum for 4 h. The specified copper complex was found to act as a reversible coating for the detection sulfur dioxide in the range 10–1000 mg l −1 .

The electrochemical oxidative dimerization of methane

Abstract The electrochemical oxidative dimerization of methane to give C 2 hydrocarbon species was investigated in solid oxide fuel cells (SOFCs) possessing the general configuration: CH 4 , (anode) electrocatalyst/ZrO 2 (8m/oY 2 O 3 )/La 0.9 Sr 0.1 MnO 3 , O 2 (air). Perovskite anode electrocatalysts shown to possess activity towards promoting the subject reaction included Sm 0.5 Ce 0.5 CuO 3 , Tb 0.8 Sm 0.2 CuO 3 , Gd 0.9 Th 0.1 CuO 3 , Gd 0.9 Na 0.1 MnO 3 and Th 0.8 Yb 0.2 NiO 3 . An inverse linear dependence was found for methane conversion to C 2 species on both perovskite electrocatalyst molecular volumes and their lattice-ionic free volumes. These observations suggested that anode electrocatalyst activity towards promoting C 2 synthesis may be either dependent upon lattice spacings or on their intrinsic ionic transport properties, both of which might be expected to be related to the lattice metal-oxygen bonding energy. The maximum partial Faradaic current densities at copper based perovskite were found to exhibit a linear dependence to the experimentally determined magnetic moments, consistent with an increasing population of Cu 3+ sites, favoring stabilization of reactive surface O - species.