Lutgard C. De Jonghe

Thin-film solid oxide fuel cell with high performance at low-temperature

Abstract A planar thin-film solid oxide fuel cell (SOFC) was developed at the Lawrence Berkeley National Laboratory – Materials Science Division. The thin-film SOFC is fabricated with an inexpensive and scalable technique involving colloidal deposition of YSZ on porous NiO–YSZ substrates, yielding SOFCs capable of high power density at an operating temperature of 800°C. The thickness of the YSZ film deposited onto the porous substrates is approximately 10 μm after sintering. Ni–YSZ/YSZ/LSM cells built with this technique have exhibited theoretical open circuit voltages (OCVs), high diffusion limited current densities and high power density. The cells have been tested for long periods of time (over 700 h) and have been thermally cycled from 600–800°C while demonstrating excellent stability over time.

Reduced-Temperature Solid Oxide Fuel Cell Based on YSZ Thin-Film Electrolyte

A planar thin-film solid oxide fuel cell has been fabricated with an inexpensive, scalable, technique involving colloidal deposition of yttria-stabilized zirconia (YSZ) films on porous NiO-YSZ substrates, yielding solid oxide fuel cells capable of exceptional power density at operating temperatures of 700 to 800°C. The thickness of the YSZ film deposited onto the porous substrate is approximately 10 Rim after sintering, and is well bonded to the NiO/YSZ substrate. Ni-YSZ/YSZ/LSM cells built with this technique have exhibited theoretical open-circuit potentials (OCPs), high current densities, and exceptionally good power densities of over 1900 mW/cm 2 at 800°C. Electrochemical characterization of the cells indicates negligible losses across the Ni-YSZ/YSZ interface and minor polarization of the fuel electrode. Thinfilm cells have been tested for long periods of time (over 700 h) and have been thermally cycled from 650 to 800°C while demonstrating excellent stability over time.

Novel Solid Redox Polymerization Electrodes All-Solid-State, Thin-Film, Rechargeable Lithium Batteries

This paper reports that lithium batteries using solid redox polymerization electrodes (SRPEs) maintain the inherent advantages of all-solid-state, thin-film systems while overcoming some of the limitations of using intercalation compounds as positive electrode. Laboratory Li/PEO/SRPE cells have demonstrated higher power capability, energy density, and capacity utilization than analogous Li/PEO/TiS{sub 2} cells. One of the Li/PEO/SRPE cells has achieved 350 cycles from 50 to 93{degrees} C with a sustained energy density of 160 Wh/kg (190 Wh/1, power density of 120 W/kg (140 W/1), and 40-75% capacity utilization of the polymerization electrode. At 100{degrees}C, power densities of over 1800 W/kg (2200 W/1) at energy densities of 140 Wh/kg (170 Wh/1) have been achieved with up to 96% utilization of cathode capacity. At ambient temperatures (35{degrees} C), the cells can be discharged at a current density of 250 {mu}a/cm{sup 2}, achieving a film capacity of 0.5 C/cm{sup 2}.

LSM-Infiltrated Solid Oxide Fuel Cell Cathodes

A single-step infiltration method has been developed to incorporate the La 0.85 Sr 0.15 MnO 3-δ (LSM) oxide phase into a pre-sintered, porous yttria-stabilized zirconia (YSZ) network, forming an effective LSM-YSZ composite cathode. The LSM particles, with a size of ∼30 to ∼100 nm, deposit preferentially on the pore walls throughout the porous YSZ, forming a pathway for electron conduction, and creating a high density of active sites for the oxygen reduction reaction. The resulting composite cathode has been evaluated in a solid oxide fuel cell operating at 923 K, and demonstrated the effectiveness of the infiltration process. The single-step infiltration method enables the possibility of producing solid oxide fuel cell cathodes, based on pre-sintered porous YSZ networks, with other catalysts that are not compatible with the high temperature processing that co-firing may require.

Synthesis and Stability of a Nanoparticle-Infiltrated Solid Oxide Fuel Cell Electrode

Nanoparticulate catalysts infiltrated into solid oxide fuel cell (SOFC) electrodes can significantly enhance cell performance, but the stability of these electrodes has been an open issue. An infiltration procedure is reported that leads to stable scandia-stabilized zirconia (SSZ) cathode electrode performance. An SSZ cathode, infiltrated with 50-150 nm lanthanum-strontium manganate electro-catalyst particles, is shown to be voltage-stable for over 500 h of operation at 650°C, at a controlled current density of 150 mA/cm 2 . This demonstrates the potential viability of nanoparticulate-infiltrated electrodes for commercial SOFCs, and illustrates the functional stability of nanoparticulate catalysts in the demanding environment of SOFC electrodes.

Novel Solid Redox Polymerization Electrodes Electrochemical Properties

In this paper the generic redox reaction of a class of linear sulfur-containing redox polymerization electrodes is described by (SRS){sub n} + n (2e{sup {minus}}) {r reversible} n (SRS), the polymer electrode which can be progressively depolymerized, leading ultimately to monomeric anions, as the sulfur-sulfur bridges between the organic R groups are cleaved during discharge and then the monomer anions can be subsequently reoxidized back to the original polymer during charge. This is the first time the process of electrodepolmerization-electropolymerization has been exploited for energy storage, establishing a broad class of chemically flexible, low equivalent weight, and inexpensive electrodes for advanced batteries. Electrochemical investigation of a diverse group of novel solid redox polymerization electrodes indicates that these materials are excellent candidates for all-solid-state, thin-film, energy-storage systems. some of the advantages offered by the batteries based on these materials include high energy density and rate capability, extensive utilization of positive electrode capacity, ease of fabrication, low cost, and superior reliability, and safety.

Electrode kinetics of organodisulfide cathodes for storage batteries

The electrode kinetics of a diverse group of organodisulfide cathode materials have been systematically investigated. The electrochemical behavior of these redox couples was studied as a function of the organic moiety (R) in the organodisulfide compounds (RSSR). These studies were performed with a variety of working electrodes, including platinum, glassy carbon, graphite, stainless steel, aluminum, and copper. The possible reaction pathways and mechanisms have been hypothetically postulated, theoretically analyzed, and experimentally verified. Observations showed that while electron transfer rate constants varied with organic moiety, the mechanistic details of the redox path were invariant with the R groups of the organodisulfides studies.

Ceria nanocoating for sulfur tolerant Ni-based anodes of solid oxide fuel cells

Conventional nickel yttria-stabilized-zirconia (Ni-YSZ) solid oxide fuel cell anodes infiltrated with ceria nanoparticles showed sustained high sulfur tolerance. Cathode-supported cells with ceria-infiltrated Ni-YSZ anode delivered power density of 220-240 mW cm -2 , at 0.6 V, under an applied current of 0.4 A cm -2 , when operating on humidified H 2 fuel containing 40 ppm H 2 S, at 973 K, for 500 h. In contrast, the power density of a cell with traditional Ni-YSZ anode dropped to near 0 mW cm -2 , in ∼ 13 min, when similarly exposed. The results indicate that ceria nanoparticle infiltration can effectively increase the sulfur tolerance of conventional Ni-YSZ anodes.

LSM-YSZ Cathodes with Reaction-Infiltrated Nanoparticles

To improve the LSM-YSZ cathode performance of intermediate temperature solid oxide fuel cells (SOFCs), Sm0.6Sr0.4CoO3-sigma (SSC) perovskite nanoparticles are incorporated into the cathodes by a reaction-infiltration process. The SSC particles are {approx}20 to 80nm in diameter, and intimately adhere to the pore walls of the preformed LSM-YSZ cathodes. The SSC particles dramatically enhance single-cell performance with a 97 percent H2+3 percent H2O fuel, between 600 C and 800 C. Consideration of a simplified TPB (triple phase boundary) reaction geometry indicates that the enhancement may be attributed to the high electrocatalytic activity of SSC for electrochemical reduction of oxygen in a region that can be located a small distance away from the strict triple phase boundaries. The implication of this work for developing high-performance electrodes is also discussed.

Microencapsulation of silicon nitride particles with yttria and yttria-alumina precursors

Procedures are described to deposit uniform layers of yttria and yttria-alumina prccursors on fine powders and whiskers of silicon nitride. The coatings were produced by aging at elevated temperatures aqueous systems containing the silicon nitride core particles, yttrium and aluminum nitrates, and urea. Optimum concentrations of the core particles, in relation to the reactants, were established to promote surface deposition of the oxide precursors. Polymeric dispersants were used effectively to prevent agglomeration of the solids during the microencapsulation process. The morphology of the powders was characterized using scanning and transmission electron microscopy. The mechanisms for the formation of the coated layers are discussed. A description is provided that allows qualitative assessment of the experimental factors that determine microencapsulation by a slurry method.