This paper presents a new computational framework for modeling chemically reacting flow in anode-supported solid-oxide fuel cells ͑SOFC͒. Depending on materials and operating conditions, SOFC anodes afford a possibility for internal reforming or catalytic partial oxidation of hydrocarbon fuels. An important new element of the model is the capability to represent elementary heterogeneous chemical kinetics in the form of multistep reaction mechanisms. Porous-media transport in the electrodes is represented with a dusty-gas model. Charge-transfer chemistry is represented in a modified Butler-Volmer setting that is derived from elementary reactions, but assuming a single rate-limiting step. The model is discussed in terms of systems with defined flow channels and planar membrane-electrode assemblies. However, the underlying theory is independent of the particular geometry. Solid oxide fuel cells ͑SOFC͒ can be operated with a variety of fuels, including hydrogen, CO, hydrocarbons, or mixtures of these. This is possible because of the relatively high operating temperatures, and, at least in conventional SOFC anodes, the use of transition metal catalysts that promote the water-gas-shift reactionand steam reforming, which for methane may be written globally asIf sufficient steam is produced electrochemically at the anode/ electrolyte interface by the reactionthen reforming and shifting can, in principle, lead to full ͑if indirect͒ electrochemical oxidation of a hydrocarbon fuel. However, competing reaction pathways catalyzed by transition metals may also lead to solid carbon deposition, which can quickly destroy the anode. For this reason, some degree of upstream fuel processing, eiher by catalytic partial oxidation or by steam reforming, is usually used to produce a fuel stream that is rich in H 2 and CO and dilute in residual hydrocarbons before reaching the SOFC. Because upstream processing adds to the complexity, size, and cost of the overall plant, it is of considerable interest to minimize or even eliminate the need for it. There is evidence that mixing some oxygen with a hydrocarbon fuel can deliver good performance.1 In this case there must be partial oxidation within the anode structrue. Another promising alternative to utilize hydrocarbon fuels "directly" in SOFCs is to use a ceria oxidation catalyst instead of a transition metal. 2Whether an SOFC uses a "reforming anode" with a transition metal catalyst, or a "direct oxidation" anode with a ceria-based catalyst, or perhaps uses a different, novel anode design, optimizing the system to run efficiently on hydrocarbon or hydrocarbon-derived fuels is a very challenging problem, due to the complex, coupled physico-chemical processes involved. When significant CO and/or hydrocarbons are present in the fuel, models must also account for the in situ production of hydrogen through reforming and shifting reactions within the anode, as well as solid-carbon formation.Many questions of interest for optimization studies cannot currently be answered easily. For example, for...

We introduce a new method for performing and miniaturizing many types of heterogeneous catalysis involving nanoparticles. The method makes use of the plasmon resonance present in nanoscale metal catalysts to provide the necessary heat of reaction when illuminated with a low-power laser. We demonstrate our approach by reforming a flowing, liquid mixture of ethanol and water over gold nanoparticle catalysts in a microfluidic channel. Plasmon heating of the nanoparticles provides not only the heat of reaction but the means to generate both water and ethanol vapor locally over the catalysts, which in turn allows the chip and the fluid lines to remain at room temperature. The measured products of the reaction, CO 2 , CO, and H 2 , are consistent with catalytic steam reforming of ethanol. The approach, which we refer to as plasmon-assisted catalysis, is general and can be used with a variety of endothermic catalytic processes involving nanoparticles.

A computational model is developed to represent the coupled behavior of elementary chemistry, electrochemistry, and transport in the vicinity of solid-oxide fuel cell three-phase boundaries. The model is applied to assist the development and evaluation of H 2 charge-transfer reaction mechanisms for Ni-yttria-stabilized zirconia ͑YSZ͒ anodes. Elementary chemistry and surface transport for the Ni and YSZ surfaces are derived from prior literature. Previously published patterned-anode experiments ͓J. Mizusaki et al., Solid State Ionics, 70/71, 52 ͑1994͔͒ are used to evaluate alternative electrochemical charge-transfer mechanisms. The results show that a hydrogen-spillover mechanism can explain the Mizusaki polarization measurements over wide ranges of gas-phase composition with both anodic and cathodic biases. Establishing elementary charge-transfer reaction pathways is one of the most difficult aspects of understanding the fundamental behavior of solid oxide fuel cells ͑SOFCs͒. Most modeling efforts represent charge transfer in terms of activation overpotentials and the Butler-Volmer equation. The objective of the present paper is to develop an elementary representation of the transport, chemistry, and electrochemistry in the vicinity of an anode three-phase boundary ͑TPB͒ between gas-phase H 2 , a Ni anode, and a yttria-stabilized zirconia ͑YSZ͒ electrolyte. The approach is based upon quantitative models and previously reported patterned-anode experiments by Mizusaki et al. Mizusaki et al.2 developed model anode structures using thin nickel films on single-crystal YSZ. The nickel films were patterned lithographically into an array of lines. By varying the linewidth and spacing, it was possible to control the TPB length per unit area. Others have followed Mizusaki's lead, and several experimental studies have been reported. [3][4][5][6][7] Nevertheless, Mizusaki's 1994 paper stands as the most complete data set available. The experiments were carefully designed to impose both cathodic and anodic potentials and to systematically vary the H 2 partial pressure while holding H 2 O partial pressure constant and vice versa.In addition to electrochemical charge transfer, the model simultaneously represents the competing processes of surface-diffusive transport and nonfaradaic chemistry on the Ni and YSZ surfaces. The reaction pathways and rates for thermal surface reactions are drawn from independent experimental and theoretical literature. The reaction mechanisms are constructed hierarchically, beginning with the nonfaradaic processes, and then adding charge-transfer reactions at the TPB, without modifying the rates or equilibrium constants for the nonfaradaic reactions. In this way, it is possible to develop robust reaction mechanisms that are applicable over wide ranges of operating conditions.The model is used to evaluate the validity of two alternative charge-transfer pathways. One is an oxygen-spillover mechanism in which the rate-limiting reaction involves atomic oxygen from the YSZ surface crossing over to the Ni...

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