Multi-Physics Modeling of Solid Oxide Fuel Cell Fueled by Methane and Analysis of Carbon Deposition

Internal reformation of low steam methane fuel is important for the high efficiency and low cost operation of solid oxide fuel cell. Understanding and overcoming carbon deposition is crucial for the technology development. Here a multi-physics model is established for the relevant experimental cells. Balance of electrochemical potentials for the electrochemical reactions, generic rate expression for the methane steam reforming, dusty gas model in a form of Fick＇s model for anode gas transport are used in the model. Excellent agreement between the theoretical and experimental current-voltage relations is obtained, demonstrating the validity of the proposed theoretical model. The steam reaction order in low steam methane reforming reaction is found to be 1. Detailed information about the distributions of physical quantities is obtained by the numerical simulation. Carbon deposition is analyzed in detail and the mechanism for the coking inhibition by operating current is illustrated clearly. Two expressions of carbon activity are analyzed and found to be correct qualitatively, but not quantitatively. The role of anode diffusion layer on reducing the current threshold for carbon removal is also explained. It is noted that the current threshold reduction may be explained quantitatively with the carbon activity models that are only qualitatively correct.

Contribution of Iron and Aluminum Oxides to Electrokinetic Characteristics of Variable Charge Soils in Relation to Surface Charge

The contribution of iron and aluminum oxides to electrokinetic characteristics of variable charge soils was studied through determination of electrophoretic mobilities of the red soils treated with either removal of iron oxides or coating of aluminum oxides, and of those deferrated under natural conditions. After removal of the iron oxides, zeta potentials of the latosol and the red earth decreased obviously with a shift of IEP to a lower pH, from 6.4 to 5.3 and 4.1 to 2.4 for the former and the latter, respectively, and the electrokinetic change for the latosol was greater than for the red earth. Zeta potentials of the kaolinite sample increased markedly after coated with iron oxides. The striking effect of iron oxides on electrokinetic properties of the soils was also demonstrated by the electrokinetic differences between the samples from the red and white zones of a plinthitic horizon formed naturally, and between the samples from the gley and bottom horizons of a paddy soil derived from a red earth. The coatings of aluminum oxides on the latosol and the yellow earth made their zeta potentials rise pronouncedly and their IEPs move toward higher pHs, from 6.2 to 6.8 and 4.3 to 5.3 for the former and the latter, respectively. The samples with different particle sizes also exhibited some electrokinetic variation. The experiment showed that the effects of iron and aluminum oxides were closely related to the pH and type of the soils.

Restructuring of well-defined Pt-based electrode surfaces under mild electrochemical conditions

Since the 1980s,single-crystal Pt electrodes with well-defined surface structures have been deemed stable under mild electrochemical conditions(e.g.,in the potential region of electric double layers,underpotential deposition of hydrogen,or mild hydrogen evolution/OH adsorption)and have served as model electrodes for unraveling the structure-performance relation in electrocatalysis.With the advancement of in situ electrochemical microscopy/spectroscopy techniques,subtle surface restructuring under mild electrochemical conditions has been achieved in the last decade.Surface restructuring can considerably modify electrocatalytic properties by generating/destroying highly active sites,thereby interfering with the deduction of the structure-performance relation.In this review,we summarize recent progress in the restructuring of well-defined Pt(-based)electrode surfaces under mild electrochemical conditions.The importance of the meticulous structural characterization of Pt electrodes before,during,and after electrochemical measurements is demonstrated using CO adsorption/oxidation,hydrogen adsorption/evolution,and oxygen reduction as examples.The implications of present findings for correctly identifying the reaction mechanisms and kinetics of other electrocatalytic systems are also briefly discussed.

Predictive Spectrum Sensing Strategy Based on Reinforcement Learning

In this paper,we consider a cognitive radio(CR) system with a single secondary user(SU) and multiple licensed channels.The SU requests a fixed number of licensed channels and must sense the licensed channels one by one before transmission.By leveraging prediction based on correlation between the licensed channels,we propose a novel spectrum sensing strategy,to decide which channel is the best choice to sense in order to reduce the sensing time overhead and further improve the SU's achievable throughput.Since the correlation coefficients between the licensed channels cannot be exactly known in advance,the spectrum sensing strategy is designed based on the model-free reinforcement learning(RL).The experimental results show that the proposed spectrum sensing strategy based on reinforcement learning converges and outperforms random sensing strategy in terms of long-term statistics.

Radiation-Induced Graft Polymerization of Sodium 4-Styrene Sulfonate onto Multiwalled Carbon Nanotubes and Their Application as Electrogenerated Chemiluminescence Biosensors

Sulfonate groups were introduced to the surfaces of multiwalled carbon nanotubes by the radiation-induced graft polymerization of sodium 4-styrene sulfonate for the use as biosensor supports. Alcohol dehydrogenase was immobilized onto a sulfonated nanotube-supporting electrode with tris（2,2＇-bipyridyl） ruthenium（II） complex to form an electrogenerated chemilluminesce sensor of alcohol. When it was used to detect alcohol in cyclic voltammetric measurements, the sensor showed the linearity over the range of 1.0 × 10^-4 M-5.0 ×10^-2 M, with a correlation coefficient of 0.992 and a detection limit of 1.9 ×10^-6 M. In electrogenerated chemilluminesce detection, it showed linearity over 5.0 × 10^-4 M-1.0 × 10^-2 M, with a correlation coefficient of 0.986 and a detection limit of 1.0 × 10^-6 M. The sensor was demonstrated to be able to detect ethanol in commercial drinks.

Quantum heat engine cycle working with a strongly correlated electron system

A new model of a quantum heat engine （QHE） cycle is established, in which the working substance consists of an interacting electrons system. One of our purposes is to test the validity of the second law of thermodynamics by this model, which is more general than the spin-1/2 antiferromagnetic Heisenberg model since it would recover the spin model when the on-site Coulomb interaction U is strong enough. On the basis of quantum mechanics and the first law of thermodynamics, we show no violation of the second law of thermodynamics during the cycle. We further study the performance characteristics of the cycle by investigating in detail the optimal relations of efficiency and dimensionless power output. We find that the efficiency of our engine can be expressed as η = t22/t21 in the large-U limit, which is valid even for a four sites QHE.

Asymptotic Structure in the Classically Forbidden Region of the Hooke’s Atoms

The two-electron Hooke's atom - a quantum mechanical system with two electrons bound in a harmonic potential - is well known for its exact analytical properties at certain oscillator strengths. The Hooke's atoms with more than two electrons offer more scope for valuable practical applications. In this work, we study the asymptotic structure of these Hooke's atoms in the classically forbidden region. The leading-order term of the long-range expression for the KS exchange-correlation potential v xc (r) is shown to be-1/r. The second and third higher order terms are also exactly obtained. Various components of v xc (r) are also studied. It is shown that the leading term of O(1/r) in vxc (r) is due to the pure Pauli correlation, while the leading contribution of the Coulomb correlation is of O(1/r3 ). Neither of them makes contribution to the term of O(1/r2 ), which is shown to be solely due to the kinetic correlation effect. Results for the two-electron Hooke's atom were obtained before in the literature. Our results reduce to those of the two-electron Hooke's atom as a special case.