Scalable Successive-Cancellation Hardware Decoder for Polar Codes

Polar codes, discovered by Ar{\i}kan, are the first error-correcting codes with an explicit construction to provably achieve channel capacity, asymptotically. However, their error-correction performance at finite lengths tends to be lower than existing capacity-approaching schemes. Using the successive-cancellation algorithm, polar decoders can be designed for very long codes, with low hardware complexity, leveraging the regular structure of such codes. We present an architecture and an implementation of a scalable hardware decoder based on this algorithm. This design is shown to scale to code lengths of up to N = 2^20 on an Altera Stratix IV FPGA, limited almost exclusively by the amount of available SRAM

A Study of Thermal Stability and Methane Tolerance of Cu-Based SOFC Anodes with Electrodeposited Co

Cu-based, solid oxide fuel cell (SOFC) electrodes were modified by electrodeposition of Co. The addition of only 5-vol% Co by electrodeposition significantly improved the thermal stability compared to either Cu-ceria-YSZ, Cu-Co-ceria-YSZ, or Co-ceria-YSZ electrodes prepared only by impregnation with much higher metal loadings, demonstrating that electrodeposited metal layers form metal films with better connectivity. In the absence of Co, SEM showed structural changes in the impregnated Cu after heating to 1173 K in humidified H2 and these changes caused large increases in the ohmic resistance of fuel cells, as measured by impedance spectroscopy. In contrast, the ohmic resistance of a cell with 13-vol% Cu, 9-vol% ceria, and 5-vol% Co increased only slightly after 48 h at 1173 K in humidified H2. While a Co-ceria-YSZ composite was found to form large amounts of carbon upon exposure to dry CH4 at 1073 K for 3 h, the Co-Cu-ceria-YSZ composites did not form measurable amounts of carbon for the same conditions. XPS results for a Cu foil with a 250-nm Co film demonstrated that Cu migrates to the surface of the Co upon heating above 873 K, forming a stable Cu layer that appears to be approximately one monolayer thick. The implication of these results for the development of practical SOFC electrodes for the direct utilization of hydrocarbons is discussed

An Examination of SOFC Anode Functional Layers Based on Ceria in YSZ

The properties of solid oxide fuel cell (SOFC) anode functional layers prepared by impregnation of ceria and catalytic metals into porous yttria-stabilized zirconia (YSZ) have been examined for operation at 973 K. By varying the thickness of the functional layer, the conductivity of the ceria-YSZ composite was determined to be only 0.015–0.02 S/cm. The initial performance of anodes made with ceria loadings of 40 or 60 wt % were similar but the anodes with lower loadings lost conductivity above 1073 K due to sintering of the ceria. The addition of dopant levels of catalytic metals was found to be critical. The addition of 1 wt % Pd or Ni decreased the anode impedances in humidified H2 dramatically, while the improvement with 5 wt % Cu was significant but more modest. Pd doping also decreased the anode impedance in dry CH4 much more than did Cu doping; however, addition of either Pd or Cu led to similar improvements for operation in n-butane. Based on these results, suggestions are made for ways to improve SOFC anode functional layers

Multilayer High-Performance Ceramic Anodes

A new approach to the design of ceramic anodes that uses a thin catalytically active functional layer that has only modest electronic conductivity sandwiched between the electrolyte and a non-catalytic elecronically conducting ceramic layer that is used as the current collector is described. The anode design is flexible and allows various materials to be used in the functional and current collector layers. Results are presented for anodes with thin functional layers (12 µm) consisting of a porous CeO2/YSZ composite impregnated with 1 wt% Pd to optimize catalytic activity and a 100 µm thick layer of porous La0.3Sr0.7TiO3 (LST) as the current collector. Low anode impedances and excellent overall performance were obtained with cells with these anodes while operating on both humidified hydrogen and hydrocarbon fuels

Recent Progress in SOFC Anodes for Direct Utilization of Hydrocarbons

There would be significant advantages to having anodes for solid oxide fuel cells (SOFC) that were capable of directly utilizing hydrocarbon fuels. Because conventional Ni-based anodes catalyze the formation of carbon fibers, new anode compositions are required for this application, but most of the materials that have been proposed exhibit either limited thermal stability or poor electrochemical activity. In this paper, we will describe two strategies for the development of new anodes with improved performance. The first strategy involves the use of bimetallic compositions with layered microstructures. In the bimetallic anodes, one metal is used for thermal stability while the other provides the required carbon tolerance. The second strategy involves separating the anode into two layers: a thin functional layer for electrocatalysis and a thicker conduction layer for current collection. With this approach, the functional layer can be optimized for catalytic activity and, if it is thin enough, requires minimal conductivity. Examples are shown for each of these approaches and possible future directions are outlined

A Strategy for Achieving High-performance with SOFC Ceramic Anodes

A proposal that high solid oxide fuel cell (SOFC) anode performance can be achieved by using a very thin, catalytically active functional layer, with a noncatalytic conduction layer, has been tested. An anode impedance of 0.26 Ω cm2 was obtained at 973 K in humidified H2 using a Ag-paste conduction layer and a 12 µm thick functional layer made from 1 wt % Pd and 40 wt % ceria in yttria-stabilized zirconia. Replacing the Ag paste with a 100 µm layer of porous La0.3Sr0.7TiO3 (LST) had minimal effect on cell performance. The anode concept is flexible and should allow various materials to be used in the functional and the current-collector layers

Electrodeposition of Cu into a Highly Porous Ni/YSZ Cermet

The electrochemical deposition of Cu into 0.12 cm and 60 µm thick, highly porous 65 vol % Ni/yttria-stabilized zirconia (YSZ) cermets was investigated. An electrochemical cell in which the electrolyte solution was allowed to flow through a porous Ni/YSZ substrate was used to eliminate mass-transfer limitations and to determine the conditions for which the potential drop in the electrolyte solution was minimized and a uniform Cu layer was produced throughout the porous substrate. The conditions determined from these experiments were then used to electrodeposit Cu throughout a thin, porous Ni–YSZ cermet anode layer on a solid oxide fuel cell (SOFC) using a standard nonflow-through setup. This SOFC was found to exhibit stable operation while using methane as the fuel