Anode Exchange Current Density Research Articles

Multiphysical field simulation of exchange current density effection on solid oxide fuel cell (SOFC) with methane mixture fuel

In order to understand the performance and internal parameter distribution of SOFC fueled by methane mixture in detail, the paper uses numerical simulation method to conduct three-dimensional multiphysics coupling simulation on a single-channel anode-supported planar SOFC. The uniqueness of the three-dimensional model is that it employs the anode exchange current density from the methane gas mixture and considers the electrochemical oxidation of carbon monoxide. The numerical model proposed in this work provides more accurate simulation results. The results show that compared with the model that uses the exchange current density equation from humidified hydrogen for simulation, the model that uses the exchange current density equation from methane mixture to simulate the performance curve is closer to the experimental value. When using methane gas mixture as fuel, the maximum temperature difference along the flow direction is 10 K and the maximum power density can reach 0.482 W/cm2. In the thickness direction of the SOFC, the current density is not much different at the inlet and outlet. Along the direction of flow, the current density decreases near the inlet and outlet. Reducing the rate of fuel flow or increasing gas inflow temperature can improve SOFC performance.

3-Aminopropyltriethoxysilane Complexation with Iron Ion Modified Anode in Marine Sediment Microbial Fuel Cells with Enhanced Electrochemical Performance

Anode modification plays a key role in higher power output in marine sediment microbial fuel cells (MSMFCs). A low-molecular organosilicon compound (3-aminopropyltriethoxysilane) was grafted onto the surface of carbon felt using chemical method and a composite modified anode was prepared through organic ligands coordination Fe3+ for better electro-chemical performance. Results show that the biofilm resistance of the composite modified anode (2707 δ) is 1.3 times greater than that of the unmodified anode (2100 Ω), and its biofilm capacitance also increases by 2.2 times, indicating that the composite modification promotes the growth and attachment of electroactive bacteria on the anode. Its specific capacitance (887.8 F m−2) is 3.7 times higher than that of unmodified anode, generating a maximum current density of 1.5 Am−2. In their Tafel curves, the composite modified anodic exchange current density (5.25×10−6 A cm−2) is 5.8 times bigger than that of unmodified anode, which suggests that the electrochemical activity of redox, anti-polarization ability and electron transfer kinetic activity are significantly enhanced. The marine sediment microbial fuel cell with the composite modified anode generates the higher power densities than the blank (203.8 mWm−2 versus 45.07 mWm−2), and its current also increases by 4.4 times. The free amino groups on the anode surface expands a creative idea that the modified anode ligates the natural Fe(III) ion in sea water in the MSMFCs for its higher power output.

Simulation of SOFC performance using a modified exchange current density for pre-reformed methane-based fuels

Numerical simulations can be used to visualize and better understand various distributions such as gas concentration and temperature in solid oxide fuel cells (SOFCs) under realistic operating conditions. However, pre-existing models generally utilize an anode exchange current density equation which is valid for humidified hydrogen fuels – an unrealistic case for SOFCs, which are generally fueled by hydrocarbons. Here, we focus on developing a new, modified exchange current density equation, leading to an improved numerical analysis model for SOFC anode kinetics. As such, we experimentally determine the exchange current density of SOFC anodes fueled by fully pre-reformed methane. The results are used to derive a new phenomenological anode exchange current density equation. This modified equation is then combined with computational fluid dynamics (CFD) to simulate the performance parameters of a three-dimensional electrolyte-supported SOFC. The new modified exchange current density equation for methane-based fuels reproduces the I–V characteristics and temperature distribution significantly better than the previous models using humidified hydrogen fuel. Better simulations of SOFC performance under realistic operating conditions are crucial for the prediction and prevention of e.g. fuel starvation and thermal stresses.

Optimization of operating parameters of a polymer exchange membrane electrolyzer

In this research, the operating parameters of proton exchange membrane (PEM) electrolyzer are optimized in order to decrease the required input voltage using Taguchi method. The considered parameters include the operating temperature, the pressure of cathode and anode, membrane water content, membrane thickness, and cathode and anode exchange current density. First, a thermodynamic model is developed for the PEM electrolyzer, and then the Taguchi method is applied for optimization of the electrolyzer performance. The signal to noise ratio (SNR) and the analysis of variance (ANOVA) method are also performed to determine the contribution ratio of effective parameters. The results reveal that the optimal condition is achieved at maximum working temperature, membrane water content, and cathode and anode exchange current density and at minimum membrane thickness, cathode pressure, and anode pressure. The anode exchange current density has considerable effect on the electrolyzer voltage with contribution of 67.15% while the membrane water content and the anode pressure have a minor influence with contribution of 1.1% and 0.42%, respectively.

Effect of HCO3− on electrochemical kinetics of carbon steel corrosion in CO2-saturated brines

The effect of HCO3−(aq) on CO2 corrosion of carbon steel was investigated in deaerated 3.5 wt% NaCl solutions at 30 °C from pH 3.96 to 7.15. In the CO2-saturated solutions, the pH was adjusted with different HCO3−(aq) concentrations, c[HCO3−(aq)]. The corrosion rate decreased by a factor of 2 as the pH and c[HCO3−(aq)] increased. The cathodic current density during polarization increased at higher pH with higher c[HCO3−(aq)], indicating that HCO3−(aq) acted as an additional hydrogen source for the hydrogen evolution reaction. As the pH increased, the active dissolution regions displayed similar anodic Tafel slopes and suggested a modified Bockris mechanism for the Fe oxidation reaction. The exchange current densities for the half reactions were calculated to study kinetics of the anodic and cathodic half reactions independently. The anodic exchange current density (j0,a) increased by one order of magnitude in the presence of CO2, indicating the involvement of CO2(aq) in the Fe oxidation reaction. As the pH and c[HCO3−(aq)] increased, the cathodic exchange current density (j0,c) decreased by a factor of 50 because the increase in j0,c[HCO3−(aq)] was not high enough to compensate the decline from the other hydrogen sources, especially j0,c[H+(aq)]; and j0,a decreased by a factor of 2.4 because HCO3−(aq) may have competed with CO2(aq) for the surface coverage and the increase in j0,a[HCO3−(aq)] could not compensate the decrease in j0,a[CO2(aq)]. It suggests that the reaction rate constant of HCO3−(aq) was smaller than CO2(aq) for the anodic half reaction and was smaller than H+(aq) for the cathodic half reaction. The XPS results verified that the corrosion products transitioned from iron carbonate to hydroxide as the pH increased while iron carbonate remained the major product. As the pH increased with HCO3−(aq), a second time constant was observed at lower frequencies of the electrochemical impedance spectroscopy (EIS) results.

Simulation and Visualization of Cell Performance Distribution of SOFCs

Introduction It has been reported for SOFC systems that high electrical efficiency beyond 70% could be achieved theoretically in a recent study[1]. It is important to understand the internal characteristics to design highly efficient SOFC. However, it is difficult to visualize internal reactions experimentally. From these reasons, it is desired to develop a simulation technique for visualizing various phenomena within fuel cell stacks. Here, we focus on numerical analysis on electrode kinetics. Exchange current density is an important phenomenological parameter in considering electrochemical reaction kinetics at SOFC electrodes and in simulating cell performance. Here, the exchange current density of fully pre-reformed methane-fueled SOFC anodes is measured and phenomenological equations of anode exchange current density are derived. Furthermore, we combine numerical analysis with the phenomenological relations to simulate the spatial distribution of anode overvoltages. Experimental conditions In this study, electrolyte-supported cells were used to measure the anode exchange current density. The electrolyte material was ScSZ (ScSZ:10mol% Sc2O3–1mol% CeO2–89mol% ZrO2) and the electrode prepared using NiO-ScSZ was applied to the anode. The electrode prepared using LSM（LSM: (La0.8Sr0.2)0.98MnO3）and LSM-ScSZ was applied to the cathode. By changing operation temperature, fuel utilization (Uf), and steam-to-carbon ratio (S/C), anode overvoltage was measured at each current density (0.25, 0.3, 0.35, and 0.4 cm2) for methane-fueled pre-reformed SOFCs by the current interrupt method. The anode exchange current density was then derived from the current density and anode overvoltage values. In simulation, three-dimensional cell model was created using a numerical analysis software. A parallel co-flow model was considered. The inlet gas temperature was 800°C and the anode gas composition was fixed with the S/C of 2.5. Results and discussion The equation of anode exchange current density based on hydrogen-fueled model[2] was revised to consider the equilibrium reforming reaction, the water gas shift reaction, and the conservation law of anode gas partial pressure. It has been reported that the electrochemical reaction, where the adsorbed hydrogen atom (Had) in hydrogen-based fuels is rate-limiting[2], an Arrhenius-type equation shown in Eq. 1 has been proposed based on the assumption that the electrochemical reaction of Had is rate- limiting: i 0,a = a·exp(b/RT)·PH2(A) 0.5·PH2O(A) 0.5 (1) The partial pressure terms were modified considering the equilibrium reforming reaction and the water gas shift reaction. Pre-exponential factor a and activation energy b were fixed using the experimental results. Fig. 1 shows the experimental results of anode exchange current density. The phenomenological values derived from Eq. 1 are shown in Fig. 1. As the fuel utilization varied, the exchange current density increased and reached the maximum at around 40% of Uf. The experimental results could be well fitted by Eq.1. The SOFC cell performance simulation was performed using the three-dimensional SOFC model. Fig. 2 shows the anode overvoltage distribution along the fuel flow direction from the left side to the right side. The overvoltage decreased from the inlet towards the outlet. This is partly because oxygen partial pressure on the anode increased to the outlet and the electromotive force and the exchange current decreased.

Effect of Amino Acid Addition in Marine Sediment on Electrochemical Performance in Microbial Fuel Cells

AbstractAs exogenous substances, L‐methionine, L‐threonine and L‐lysine were added into the marine sediment to construct marine sediments microbial fuel cells (MSMFCs) and the effects on the anodic electrochemical activity were following investigated. The results show that the addition of the amino acid increases anodic electrochemical activity, and the anode in L‐methionine modified sediment presents better performance than others. The specific capacitance of anode in L‐methionine modified sediment (192.00 F cm−2) is 4.0 times bigger than that of anode in unmodified sediment, generating a maximum current density of 2.560 × 10−4 A cm−2. In their Tafel curves, the anodic exchange current density in the L‐methionine modified sediment (2.14 × 10−6 A cm−2) is 93.04 times higher than that of unmodified anode, which suggests that the electrochemical activity of redox, anti‐polarization ability and electron transfer kinetic activity are improved significantly. The MSMFC with L‐methionine modified sediment generates the higher power densities than the blank (143.2 mW m−2 versus 59.2 mW m−2), and its current also increases by 2.8 times. This demonstrates that L‐methionine provides a practical advantage on the anodic electrochemical and battery performance. Therefore, amino acids are good tools to evaluate its power generation of the MSMFCs.

Effect of Exchange Current Density on Current Distribution at Planar-Type SOFC Anodes

Introduction It has been reported for SOFC systems that high electrical efficiency of more than 70-80% could be achieved theoretically in a recent study [1]. However, their electrochemical performance would become lower due to an increase in ohmic and nonohmic resistances and possible fuel starvation. From these reasons, it is desired to develop a simulation technique for visualizing various phenomena in fuel cells. Here, we focus on numerical analysis on electrode kinetics. Since exchange current density is an important phenomenological parameter in considering electrochemical reaction kinetics at an SOFC electrode and in simulating the performance, the exchange current density of methane-fueled pre-reformed SOFC anodes was measured and compared with that of hydrogen-based fuel. Furthermore, the spatial distribution of current density was simulated for given average current density in case anode exchange current density i0 is either constant or variable. Experiment In this study, electrolyte-supported cells Ni-ScSZ/ScSZ/LSM-ScSZ (ScSZ:10mol%Sc2O3- 1mol%CeO2-89mol% ZrO2) were used. The electrode area was 8×8mm2 for i0 measurements. Pt mesh was used as a current collector. In this study, by changing operation temperature, fuel utilization (Uf), and steam-to-carbon ratio (S/C), anode overvoltage was measured at each (average) current density (0.25, 0.3, 0.35, and 0.4 cm2) for methane-fueled pre-reformed SOFCs by the current interrupt method. The anode exchange current density was then derived from the current density and anode overvoltage values. Results and discussion Anode exchange current density for hydrogen-fueled SOFCs may be described by Eq. (I) after Hosoi et al. [2]. Anode exchange current density could also be described by Eq. (II) in case vacant surface adsorption sites are predominant [2,3]. Figure 1(a) shows experimental values derived for the pre-reformed fuel in this study. The values derived from Eq. (i) are also shown with solid lines in Fig. 1(a) and (b), while the values derived from Eq. (II) are shown with dashed lines in Fig. 1(b). All these figures indicate gradual decrease in anode exchange current density in the high fuel utilization (Uf) region. i0,a = 3.5・exp(-6.2×104[Jmol-1] / RT)・(PH2 / PH2,ref)0.41・(PH2O/PH2O,ref)0.4 Eq. (I) i0,a = a’・exp(b’ [Jmol-1] /RT)・PH2 0.5 ・PH2O 0.5 Eq. (II) 3D-numerical simulation has been made using the software COMSOL to derive 2D current density of the cell shown in Fig. 1(c). Current density distribution for various average current densities is derived as a function of Uf and shown in Figs. 1(d) and 1(e) for constant i0 and variable i0 , respectively. While Fig. 1(d) suggests continuous decrease in current density from inlet to outlet, Fig. 1(e) suggests almost constant current density near the inlet and its gradual decrease near the outlet. The tendency of the latter is rather consistent with the dependence of anode exchange current density as a function of Uf in Figs. 1(a) and 1(b) for hydrogen-based fuels. Figure 1

Effect of Exchange Current Density on Current Distribution at Planar-Type SOFC Anodes

Cell stack structure of solid oxide fuel cells (SOFCs) affects to their performance. Its optimization is important to realize highly efficient SOFCs. In this study, we focus on the numerical simulation method combined with experimentally obtained exchange current density. Deriving the anode exchange current density for fully pre-reformed methane-fueled SOFCs, the effect on the current distribution is evaluated. Current distribution was calculated using variable anode exchange current density after taking into account the pressure of CO and CO2.

Polymer electrolyte membrane water electrolysis: Restraining degradation in the presence of fluctuating power

Abstract Polymer electrolyte membrane (PEM) water electrolysis generates ‘green’ hydrogen when conducted with electricity from renewable - but fluctuating - sources like wind or solar photovoltaic. Unfortunately, the long-term stability of the electrolyzer performance is still not fully understood under these input power profiles. In this study, we contrast the degradation behavior of our PEM water electrolysis single cells that occurs under operation with constant and intermittent power and derive preferable operating states. For this purpose, five different current density profiles are used, of which two were constant and three dynamic. Cells operated at 1 A cm −2 show no degradation. However, degradation was observed for the remaining four profiles, all of which underwent periods of high current density (2 A cm −2 ). Hereby, constant operation at 2 A cm −2 led to the highest degradation rate (194 μV h −1 ). Degradation can be greatly reduced when the cells are operated with an intermittent profile. Current density switching has a positive effect on durability, as it causes reversible parts of degradation to recover and results in a substantially reduced degradation per mole of hydrogen produced. Two general degradation phenomena were identified, a decreased anode exchange current density and an increased contact resistance at the titanium porous transport layer (Ti-PTL).

Enhanced power production of microbial fuel cells by reducing the oxygen and nitrogen functional groups of carbon cloth anode

The physicochemical properties of anode material are important for the electron transfer of anode bacteria and electricity generation of microbial fuel cells (MFCs). In this work, carbon cloth anode was pretreated with isopropanol, hydrogen peroxide (H2O2) and sodium hypochlorite (NaOCl) in order to reduce the anode functional groups. The influence of functional groups on the electrochemical properties of carbon cloth anode and power generation of MFCs was investigated. The anode pretreatments removed the surface sizing layer of carbon cloth and substantially reduced the contents of C‐O and pyridinic/pyrrolic N groups on the anode. Electrochemical impedance spectroscopy and cyclic voltammetry analyses of the biofilm‐matured anodes revealed an enhanced electrochemical electron transfer property because of the anode pretreatments. As compared with the untreated control (612 ± 6 mW m−2), the maximum power density of an acetate‐fed single‐chamber MFC was increased by 26% (773 ± 5 mW m−2) with the isopropanol treated anode. Additional treatment with H2O2 and NaOCl further increased the maximum power output to 844 ± 5 mW m−2 and 831 ± 4 mWm−2. A nearly inverse liner relationship was observed between the contents of C‐O and pyridinic/pyrrolic N groups on anodes and the anodic exchange current density and the power output of MFCs, indicating an adverse effect of these functional groups on the electricity production of anodes. Results from this study will further our understanding on the microbial interaction with carbon‐based electrodes and provide an important guidance for the modification of anode materials for MFCs in future studies. Copyright © 2016 John Wiley & Sons, Ltd.

An analysis of degradation phenomena in polymer electrolyte membrane water electrolysis

Abstract The durability of a polymer electrolyte membrane (PEM) water electrolysis single cell, assembled with regular porous transport layers (PTLs) is investigated for just over 1000 h. We observe a significant degradation rate of 194 μV h−1 and conclude that 78% of the detectable degradation can be explained by an increase in ohmic resistance, arising from the anodic Ti-PTL. Analysis of the polarization curves also indicates a decrease in the anodic exchange current density, j0, that results from the over-time contamination of the anode with Ti species. Furthermore, the average Pt-cathode particle size increases during the test, but we do not believe this phenomenon makes a significant contribution to increased cell voltages. To validate the anode Ti-PTL as a crucial source of increasing resistance, a second cell is assembled using Pt-coated Ti-PTLs. This yields a substantially reduced degradation rate of only 12 μV h−1, indicating that a non-corroding anode PTL is vital for PEM electrolyzers. It is our hope that forthcoming tailored PTLs will not only contribute to fast progress on cost-efficient stacks, but also to its long-term application of PEM electrolyzers involved in industrial processes.

Relating Anode Gaps to the Positioning of the Reference Electrode in PEM Fuel Cells

We present analytical solutions for the potential and current density distributions in the vicinity of inactive (“dead”) regions inside a PEM fuel cell anode. For simplicity, the dead region is modeled as a step function for the anode exchange current density, representing membrane gaps or delamination. The solutions exhibit a large peak of the anode current density just outside the dead region. This overshoot can substantially exceed the average current density, thereby accelerating membrane degradation. In the limit of large gap sizes, we demonstrate how these findings relate to the positioning of a reference electrode which can independently measure the anode and cathode overpotential, respectively. [1] A. A. Kulikovsky and P. Berg, Analytical description of a dead spot in a PEM fuel cell anode, ECS Electrochem. Lett., 2, pp. F64-F67 (2013) [2] P. Berg and A. A. Kulikovsky, A model for a crack or a delaminated region in a PEM fuel cell anode: Analytical solutions, Electrochim. Acta, submitted.

A model for a crack or a delaminated region in a PEM fuel cell anode: analytical solutions

We develop a model for the potential and current density distributions in and around a long, straight and inactive (“dead”) gap inside a PEM fuel cell anode. Physically speaking, such gaps represent cracked or delaminated domains in an anode catalyst layer. The dead region is modeled as a step function for the anode exchange current density. An analytical solution to the model equations is derived; the solution exhibits a large peak of the anode current density japeak just outside the gap. For a typical cell current density of 1Acm−2, a gap with a width of 400μm induces japeak of about 4Acm−2. For smaller gap widths on the order of 10μm, which is typical for cracks, the effect is marginal. Variations in membrane thickness have a minor effect on japeak.

Concepts for Ultra-High Power Density Solid Oxide Fuel Cells (SOFC)

Over the past two decades, considerable work has been reported on solid oxide fuel cells (SOFC) [1-3]. While progress has been made, there has not been significant further gain in performance (at 800oC), beyond that achieved about fifteen years ago (~2 Wcm-2), despite using many different cathodes. Thus in many cases, the cathode may not be limiting the performance. To achieve further improvements in cell performance beyond what has been discussed in previous studies [4,5], it will require accurate identification of various polarization losses, their sources, and dependence on material and microstructural parameters, atmosphere and temperature. The majority of the modeling studies do not provide the required guidance as they rely on a number of often not so easily measurable parameters thus necessitating a somewhat arbitrary selection of such parameters. The objective of this work is to estimate various polarization losses based on out-of-cell measurements made using micro-fabricated electrodes, microstructural measurements on cells, and cell electrochemical performance measurements using a parametric model. Such an approach may identify where the dominant losses are and how to further improve cell performance. The minimum number of independent parameters necessary to model cell performance for an anode-supported SOFC with five distinct layers are 9 and they are: Deff1 O2-N2 and Deff2 O2-N2 , the effective binary diffusivities through the cathode current collector and the cathode functional layer, respectively; Deff1 H2-H2Oand Deff2 H2-H2O , the effective binary diffusivities through the anode support and the anode functional layer, respectively; cathode exchange current density (i0c ); anode exchange current density ((i0a ), cathode transfer coefficient (αc), anode transfer coefficient (αa), and ohmic resistance Ri. The parametric model is given by equation (1). V(i)=E0-iRi-(RT/2F)arcsinh(i/2i0 c)-(RT/2F)arcsinh(i/2i0 a)+( RT/2F)ln(pH2'(i)pH2Oo /( pH2o pH2O')+ ( RT/4F)ln(pO2'(i)/ pO2o ) (1) where pO2o and pO2'(i) are the oxygen partial pressures just outside the cathode current collector and close to the cathode functional layer/electrolyte interface, respectively; pH2o and pH2'(i) are the hydrogen partial pressures in the fuel just outside the anode support and close to the anode functional layer/electrolyte interface, respectively; pH2Oo and pH2O' are the water vapor partial pressures in the fuel just outside the anode and close to the anode functional layer/electrolyte interface, respectively. In equation (1), both transfer coefficients are assumed to be 0.5. As seen in Fig. 1, at low current density, the most dominant contribution is cathodic activation polarization for a cathode grain size of 2 mm. However, beyond about 1.3 A/cm2, the ohmic contribution is the dominant one, and underscores its importance. In Figs. 2a to 2b, the cathode functional layer grain size is varied from 2 μm to 0.2 μm. This increases the maximum power density by 0.3 W/cm2. However, if the ohmic resistance can be somehow reduced from 0.1 to 0.05 Ωcm2, the maximum power density increases by 1.2 W/cm2 (Figs. 2b and 2c) even in a thin electrolyte, anode-supported cell. This shows the profound role of ohmic contribution on cell performance. By contrast, a change from LSM/YSZ to Pt/YSZ only leads to a modest increase in maximum power density of about 0.4 W/cm2 (Figs. 2c and 2d). This is consistent with the observation that cells with several very different cathodes exhibit similar performance. Further work is thus required in lowering the ohmic contribution. Many cathodes that have been developed over the years appear quite satisfactory and not limiting cell performance for operation at 800oC. Funded by DOE EFRC Grant Number DE-SC0001061 as a flow-through from the University of South Carolina.

Sulfur Poisoning of SOFCs: A Model Based Explanation of Polarization Dependent Extent of Poisoning

Several experimental studies have shown that, 1) the extent of the poisoning effect due to trace amounts of sulfur compounds in the fuel is lower if a SOFC is operated at a higher current density, and 2) the performance drop due to sulfur poisoning is much lower for Ni-GDC or Ni-ScSZ anodes when compared to Ni-YSZ anodes. This work presents a first principles numerical model that simulates experimental studies of sulfur poisoning on SOFC button cells. The exchange current densities for the electrodes are determined using sulfur-free polarization data for cells fueled by humidified mixtures of H2 and N2. A detailed surface reaction model that predicts the fractional coverage of all adsorbed species at the three phase interface is coupled to the SOFC model and the sulfur coverage is used to alter the anode exchange current density. The resulting model predictions match experimental observations during both galvanostatic and potentiostatic operation. Our analysis shows that the observed lower performance drop at higher current density is due to the non-linear nature of the electrochemical rate equations, and that the lower impact of sulfur poisoning on Ni-GDC and Ni-ScSZ anodes (compared to Ni-YSZ anodes) is due to their higher electrochemical activity.

Exchange Current Density of SOFC Anodes

While Solid Oxide Fuel Cells (SOFCs) have attracted increasing attention, there are only a limited number of papers on exchange current density, representing electrode activity to describe and simulate SOFC performance. In this study, theoretical relationships on anode exchange current density has been derived as a function of various operational parameters by taking into account elementary reaction processes. Analytical relations under various boundary conditions are also derived with respect to gas partial pressures.

Computational Study of Performance Drop Phenomena Based on Sulfur Adsorption and Desorption Model in Planar-Type SOFCs

For solid oxide fuel cell (SOFC) systems operating with practical fuels, it is important to simulate the distribution of sulfur poisoning and its dependence on the operating conditions in planar-type SOFCs. In this paper, by taking into account the sulfur poisoning effect and its distribution in planar-type SOFC simulation, numerical analysis is performed using anode exchange current density data and Temkin-like sulfur adsorption isotherm on Ni surface. From this numerical analysis, it is found that the distribution of current density after sulfur poisoning is changed, depending on operating temperature and fuel utilization.

Carbon Oxidation in Fuel Cells and H2 Production

High temperature direct carbon fuel cells (DCFCs) offer potentially high efficiencies for conversion of the chemical energy of solid carbonaceous fuel(s) into electrical energy. DCFCs with molten metal anodes consume carbonaceous fuels by oxygen dissolved within the melt, which functions as an anode in an otherwise conventional solid oxide fuel cell (SOFC). Such reactors can also be used in electrolytic mode for reducing steam to hydrogen at the cathode, which enables the specific electrical energy consumption for H2 production to be decreased compared with conventional steam electrolysis. 2-D models have been developed to predict the behavior of a micro-tubular hollow fiber SOFC (ca. 1 mm ID) with a molten metal (Sn) anode, using assumed values for the anode exchange current density. Results are reported for the temperature dependence of open circuit potentials for the reactor: Sn | SnO2 | YSZ | Air measured using a pellet cell and compared with thermodynamic predictions.

Exchange Current Density of Solid Oxide Fuel Cell Electrodes

It is desired to develop computational procedures to simulate an internal current density, anode/cathode gas concentrations and a temperature distribution in solid oxide fuel cell (SOFC) systems. In this study, the influences of various operational conditions on the exchange current density which is the essential parameter to simulate SOFC performance were discussed. The anodic exchange current density depended strongly on the humidity of H2, and it exhibited the highest value at around 40% H2O. The cathodic exchange current density was strongly affected by the operational temperature. Parameters necessary to describe dependences of exchange current density on the operational conditions were determined by fitting measured exchange current density with the empirical equations.