Accepted Manuscripts

Robert C. McDonald and Monjid Hamdan
J. Electrochem. En. Conv. Stor.   doi: 10.1115/1.4040077
Direct methanol fuel cells (DMFC) are typically supplied under pressure or capillary action with a solution of methanol in water optimized for the best specific power and power density at an operating temperature of about 60 °C. Methanol and water consumption at the anode together with water and methanol losses through membrane due to crossover create an imbalance over time so the fuel concentration at the anode drifts from the optimal ratio. In the present study, we demonstrate a DMFC with a means for continuous adjustment of water and methanol content in the anode fuel mixture of an air-breathing DMFC to maintain the optimal concentration for maximum and continuous power. Two types of piezoelectric micropumps were programmed to deliver the two liquids at the designated rate to maintain optimal concentration at the anode during discharge. The micropumps operate over a wide range of temperature, can be easily reprogrammed and can operate in any orientation. A study of performance at different current densities showed that at 100 mA/cm2, the self-contained, free convection, air-breathing cell delivers 31.6 mW/cm2 of electrode surface with thermal equilibrium reached at 52 °C. The micropumps and controllers consume only 2.6% of this power during 43 hours of continuous unattended operation. Methanol utilization was 1.83 Wh-cm-3.
TOPICS: Design, Direct methanol fuel cells, Micropumps, Methanol, Water, Anodes, Fuels, Thermal equilibrium, Electrodes, Natural convection, Control equipment, Pressure, Capillarity, Temperature, Membranes, Operating temperature, Power density
Jamasb Pirkandi and Mohammad Ommian
J. Electrochem. En. Conv. Stor.   doi: 10.1115/1.4040056
This study investigated the combination of the direct and indirect hybrid systems in order to develop a combined hybrid system. In the proposed system, a direct solid oxide fuel cell and gas turbine hybrid system and an indirect fuel cell cycle were combined and exchanged the heat through a heat exchanger. Several electrochemical, thermal, and thermodynamic calculations were performed in order to achieve more accurate results; then, beside the parametric investigation of the above-mentioned hybrid system, the obtained results were compared to the results of direct and indirect hybrid systems and simple gas turbine cycle. Results indicate that the efficiency of the combined hybrid system was between those of the direct and indirect hybrid systems. The electrical efficiency and overall efficiency of the combined hybrid system were 43% and 59%, respectively. The generation power in the combined hybrid system was higher than that of both other systems, which was the only advantage of using the combined hybrid system. The generation power in the combined hybrid system was higher than that of the direct hybrid system by 16%; accordingly, it is recommended to be used the systems that are supposed to have high generation power.
TOPICS: Energy / power systems, Solid oxide fuel cells, Thermoeconomics, Cycles, Gas turbines, Heat exchangers, Fuel cells, Electrical efficiency, Heat
Maryam Sadeghi Reineh and Faryar Jabbari
J. Electrochem. En. Conv. Stor.   doi: 10.1115/1.4040057
In this paper, we study a Solid Oxide Fuel Cell (SOFC) controlled by a Multi-Input-Multi-Output (MIMO)compensator, which uses the blower/fan power and cathode inlet temperature as actuators. The usable power of the FC is maximized by limiting the air flow rate deliberately, when an increase in power demand is requested. Possible rate bounds on the cathode inlet temperature are also modeled. These bounds could represent the physical limitations (due to slow dynamics of heat exchangers) and/or a control concept for accommodating the power saving objective. Applying proper limits to the amplitude and rate of the actuator signals, and incorporating Anti-Windup (AW) techniques, can raise the net power of the FC by 16% with negligible effects on the spatial temperature profile.
TOPICS: Actuators, Energy generation, Solid oxide fuel cells, Signals, Temperature, Air flow, Heat exchangers, Temperature profiles, Dynamics (Mechanics)
khaled Mammar and Slimane Laribi
J. Electrochem. En. Conv. Stor.   doi: 10.1115/1.4040058
This work defines and implements a technique to predict water activity in PEM fuel cell. This technique is based on the electrochemical impedance spectroscopy EIS as sensor and adaptive neuro-fuzzy inference system (ANFIS) as estimator. For this purpose a PEMFC model has been proposed to study the performances of the fuel cell for different operating conditions where the simulation model for water activity behavior is in the proposed structure. The technique based on ANFIS predicts the PEM fuel cell relative humidity from the electrochemical impedance spectroscopy EIS. For creation ANFIS training and checking database a new method based on Factorial Design of experimental is used. To check the proposed technique, the ANFIS estimator will be compared with the output humidity relative observation.
TOPICS: Proton exchange membrane fuel cells, Water, Electrochemical impedance spectroscopy, Design, Fuel cells, Databases, Sensors, Simulation models
Shivom Sharma and Francois Marechal
J. Electrochem. En. Conv. Stor.   doi: 10.1115/1.4039944
Chemical process optimization problems often have multiple and conflicting objectives, such as capital cost, operating cost, production cost, profit, energy consumptions and environmental impacts. In such cases, Multi-Objective Optimization (MOO) is suitable in finding many Pareto optimal solutions, to understand the quantitative trade-offs among the objectives, and also to obtain the optimal values of decision variables. Gaseous fuel can be converted into heat, power and electricity, using combustion engine, gas turbine (GT) or Solid Oxide Fuel Cell (SOFC). Of these, SOFC with GT has shown higher thermodynamic performance. This hybrid conversion system leads to a better utilization of natural resource, reduced environmental impacts, and more profit. This study optimizes performance of SOFC-GT system for maximization of annual profit and minimization of annualized capital cost, simultaneously. For optimal SOFC-GT designs, the composite curves for maximum amount of possible heat recovery indicate good performance of the hybrid system. Further, first law energy and exergy efficiencies of optimal SOFC-GT designs are significantly better compared to traditional conversion systems. In order to obtain flexible design in the presence of uncertain parameters, robust MOO of SOFC-GT system was also performed. Finally, Pareto solutions obtained via normal and robust MOO approaches are considered for parametric uncertainty analysis with respect to market and operating conditions, and solution obtained via robust MOO found to be less sensitive.
TOPICS: Solid oxide fuel cells, Cycles, Pareto optimization, Uncertainty analysis, Gas turbines, Natural resources, Optimization, Tradeoffs, Chemical processes, Heat, Combustion, Composite materials, Fuels, Engines, Heat recovery, Exergy, Design
Kuber Mishra, Wu Xu, Mark H. Engelhard, RG Cao, Jie Xiao, Ji-Guang Zhang and Xiao-Dong Zhou
J. Electrochem. En. Conv. Stor.   doi: 10.1115/1.4039860
A thin and mechanically stable solid electrolyte interphase (SEI) is desirable for a stable cyclic performance in a lithium ion battery. For the electrodes that undergo a large volume expansion such as Si, Ge and Sn, the presence of a robust SEI layer can improve the capacity retention. In this work, the role of solvent choice on the electrochemical performance of Ge electrode is presented by a systematic comparison of the SEI layers in EC-based and FEC-based electrolytes. The results show that the presence of FEC as a co-solvent in a binary or ternary solvent electrolyte results in an excellent capacity retention of ~ 85% after 200 cycles at the current density of 500 mA·g-1; while EC-based electrode suffers a rapid capacity degradation with a capacity retention of just 17% at the end of 200 cycles. Post analysis by an extensive use of x-ray photoelectron spectroscopy was carried out, which showed that the presence of Li2O in FEC-based SEIs was the origin for the improved electrochemical performance.
TOPICS: Anodes, Germanium, Lithium-ion batteries, Electrodes, Cycles, Electrolytes, Solid electrolytes, Tin, Current density, Photoelectron spectroscopy, X-rays
Steven Beale, Uwe Reimer, Dieter Froning, Hrvoje Jasak, Martin Andersson, Jon G. Pharoah and Werner Lehnert
J. Electrochem. En. Conv. Stor.   doi: 10.1115/1.4039858
Code stability is a matter of concern for three-dimensional fuel cell models operating both at high current density and at high cell voltage. An idealized mathematical model of a fuel cell should converge for all potentiostatic or galvanostatic boundary conditions ranging from open-circuit to closed-circuit. Many fail to do so, due to: (i) Fuel or oxygen starvation causing divergence as local partial pressures and mass fractions of fuel or oxidant fall to near zero. (ii) Non-linearities in the Nernst and Butler-Volmer equations near open-circuit conditionss. This paper describes in detail, specific numerical methods used to improve the stability of a previously-existing fuel cell performance calculation procedure, at both low and high current density. Four specific techniques are identified. The example of a straight channel operating as a (i) solid-oxide, (ii) low and high temperature polymer electrolyte membrane fuel cell is used to illustrate the efficacy of the modifications.
TOPICS: Fuel cells, Stability, Circuits, Current density, Fuels, Matter, Oxygen, Proton exchange membrane fuel cells, High temperature, Numerical analysis, Solid oxide fuel cells, Boundary-value problems

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