Steven J. Visco

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.

Electrochemical properties of organic disulfide thiolate redox couples

The redox behavior, kinetic reversibility, chemical reversibility, and stability, and the specific adsorption or chemisorption at electrode surfaces of a diverse group of organodisulfide cathode materials have been studied by potential-sweep and potential-step methods. The number of electrons involved in the redox reaction and the diffusion coefficients of the organodisulfide species in electrolyte solutions were determined with a rotating disk electrode in conjunction with chronocoulometry/chronoamperometry. Observations indicate that the overall, stoichiometric reaction of those redox couples is RSSR + {r reversible} where R represents an organic moiety. These reactions are chemically reversible, yet kinetically hindered, especially at ambient temperatures. The microscopic reversibility of the redox couples promises the possibility of constructing secondary energy conversion systems based on these materials. The slow electrode kinetics, however, indicates that the introduction of electrocatalysts to assist the electrode reaction may be effective in improving battery performance. The negligible adsorption of these materials at platinum electrodes, in addition, implies that the electrode kinetics can be formulated by simple electrodic equations without consideration of surface coverage.

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.

The Use of Polydisulfides and Copolymeric Disulfides in the Li/PEO/SRPE Battery System

Solid redox polymerization electrodes (SRPEs) have recently been used successfully as cathodes in lithium solid polymer electrolyte batteries. SRPEs contain organopolydisulfides, (SRS) n , as the electroactive material; upon cell discharge these materials are reductively depolymerized via scission of the disulfide linkages to di- or trithiolate salts. The thiolate salts are reoxidized to the polymeric disulfides when the cell is recharged. Organopolydisulfides are easily synthesized via a one-step process, are inexpensive, and exhibit high performance levels in batteries

Deposition and Evaluation of Protective PVD Coatings on Ferritic Stainless Steel SOFC Interconnects

eNASA-Glenn Research Center, Cleveland, Ohio 44135, USA Reduced operating temperatures 600–800°C of solid oxide fuel cells SOFCs may enable the use of inexpensive ferritic steels as interconnects. Due to the demanding SOFC interconnect operating environment, protective coatings are gaining attention to increase long-term stability. In this study, large area filtered arc deposition and hybrid filtered arc deposition-assisted electron beam physical vapor deposition technologies were used to deposit two-segment coatings with Cr-Co-Al-O-N-based bottom segment and Mn-Co-O top segment. The bottom segment serves as a diffusion barrier and bond segment, while the top segment is meant to increase electrical conductivity and inhibit Cr volatility. Coatings were deposited on ferritic steel and subsequently annealed in air for various time intervals. Surface oxidation was investigated using Rutherford backscattering spectrometry, scanning electron microscopy, and energy-dispersive spectrometry analyses. Cr volatilization was evaluated using a transpiration apparatus and inductively coupled plasma-mass spectrometry analysis of the resultant condensate. Electrical conductivity area specific resistance, ASR, was studied as a function of time using the four-point technique. Significant improvement in oxidation resistance, Cr volatility, and ASR were observed in the coated versus uncoated samples. Transport mechanisms for various oxidizing species and coating diffusion barrier properties are discussed.

Ambient temperature high-rate lithium/organosulfur batteries

This paper describes the study of ambient temperature lithium/organosulfer systems. Many organosulfur electrodes are inexpensive, biodegradable, relatively nontoxic, and fairly unreactive to molten sodium, implying safety risks may be minimal for these systems. Early tests showed that lithium metal was passivated by a number of electroactive organosulfur solutions; similar to the behavior of lithium metal in oxychloride catholytes. The results outline the behavior of one of many possible Li/RSSR cells, the lithium/(tetraethyl thiuram disulfide) battery.

Thin film rechargeable room temperature batteries using solid redox polymerization electrodes

Thin-film solid-state batteries consisting of lithium foils, amorphous PEO separators, and solid redox polymerization electrodes (SRPEs) were assembled, discharged, and cycled at room temperature. No solvents were added to any of the components, nor were structural additives used. Performances were studied as a function of cathode thickness and composition of separator and SRPE. At 50 μA/cm 2 , cells could be discharged to a depth of 0.6 to 1.3 C/cm 2 , at 100 μA/cm 2 to a depth of 0.5 C/cm 2 , and at 200 μA/cm 2 to a depth of 0.25 C/cm 2

Thin film solid state sodium batteries for electric vehicles

Research from this laboratory on the sodium/solid polymer electrolyte (SPE) battery is described. Recent results show a performance level that equals or exceeds that of the better-known lithium analogs in terms of rate capability, cycle life and specific power, but at a lower projected cost per kilowatt hour, making sodium/SPE systems attractive for applications such as electric vehicles. Optimization of electrolyte composition and cathodes, using solid redox polymerization electrodes, sodium cobalt oxide or a new manganese oxide, is discussed, and areas for further study are suggested.

Effects of Surface-Deposited Nanocrystalline Chromite Thin Films on the Performance of a Ferritic Interconnect Alloy

LaCrO 3 -based nanocrystalline thin films, substituted with Sr and Zn and coated onto a Fe-26 atom % Cr Ebrite alloy were evaluated at 750-900°C as potential enhancers of oxide properties in ferritic alloy interconnects of a solid oxide fuel cell. It was found that at 750°C the coatings provided (i) lower oxidation rates, (ii) increased electrical conductivity, (iii) protection during 24 h cycling and at least 2375 h of isothermal oxidation, and (iv) a fine-grained and uniform oxide microstructure. Although after oxidation at 850°C the grains grew substantially and the scale seemed to be overgrowing the film, conductivity and oxidation rates still matched that of the uncoated sample. Tensile tests showed that the coating improved scale adhesion after a 100 h oxidation at 850°C. At 900°C, the film was still capable of blocking 70% of the Cr that evaporated from an uncoated Ebrite substrate.

B-Site Doping and Catalytic Activity of Sr ( Y ) TiO3

Doped SrTiO 3 is a potential anode for intermediate and high temperature solid oxide fuel cells, but by itself has limited catalytic activity for the hydrogen oxidation reaction. Its catalytic performance is, however, improved by Ni infiltration. The anode polarization is determined over a range of gas compositions of B-site co-doped Sr 0.88 Y 08 Ti o-95 M o-o5 0 3 _ 8 (SYTMO where M represents the B-site dopants) for sparsely Ni-infiltrated SYTMO. Co and Cr were selected as the B-site dopants and compared with undoped SYTO based on their differing reducibility. All anodes also were subjected to a 12 h reduction/oxidation cycle. While Cr-doped anodes showed the best resistance to oxidation, the Co-doped system exhibited the lowest anode polarization resistance under all conditions. It was found that H transport is the slowest step for all anodes, which could be partly attributed to sparsity of the infiltrated Ni catalyst.