Research Papers

J. Electrochem. En. Conv. Stor.. 2017;14(4):041001-041001-9. doi:10.1115/1.4036956.

The potential of an energy system that comprises hydrogen-fueled polymer electrolyte fuel cells (PEFCs), a steam reformer, and a hydrogen storage tank, using surplus hydrogen produced from an oil refinery, was evaluated using a mathematical model based on linear programming. The aim of this study was to optimize the capacity of the hydrogen-fueled PEFC, the hydrogen production of the steam reformer, and the utilization amount of the hydrogen storage tank in order to minimize the total system cost. Based on the optimization results, the system cost reduction and CO2 emission reduction effects were calculated in relation to the power generation efficiency and the installation cost of the hydrogen-fueled PEFC. As a result, the conditions for the hydrogen-fueled PEFC where a system cost reduction could be achieved in the PEFC power generation system, compared with the conventional system, were shown to be an initial cost lower than 3000 $/kW for a power generation efficiency of 50% or an initial cost lower than 5000 $/kW for a power generation efficiency of 65%.

Commentary by Dr. Valentin Fuster
J. Electrochem. En. Conv. Stor.. 2017;14(4):041002-041002-8. doi:10.1115/1.4037232.

The effects of isothermally long-term and thermal cycling tests on the performance of an ASC type commercial solid oxide fuel cell (SOFC) have been investigated. For the long-term test, the cells were tested over 5000 h in two stages, the first 3000 h and the followed 2000 h, under the different flow rates of hydrogen and air. Regarding the thermal cycling test, 60 cycles in total were also divided into two sections, the temperature ranges of 700 °C to 250 °C and 700 °C to 50 °C were applied for the every single cycle of first 30 cycles and the later 30 cycles, respectively. The results of long-term test show that the average degradation rates for the cell in the first 3000 h and the followed 2000 h under different flow rates of fuel and air are 1.16 and 2.64%/kh, respectively. However, there is only a degradation of 6.6% in voltage for the cell after 60 thermal cycling tests. In addition, it is found that many pores formed in the anode of the cell which caused by the agglomeration of Ni after long-term test. In contrast, the vertical cracks penetrating through the cathode of the cell and the in-plane cracks between the cathode and barrier layer of the cell formed due to the coefficient of thermal expansion (CTE) mismatch after 60 thermal cycling tests.

Commentary by Dr. Valentin Fuster
J. Electrochem. En. Conv. Stor.. 2017;14(4):041003-041003-7. doi:10.1115/1.4037391.

Flow field plays an important role in the performances of the fuel cells, especially in large area fuel cells. In the present work, an innovative, versatile flow field, capable of combining in different conventional modes is reported and evaluated in a polymer electrolyte fuel cell (PEFC) with an active area of 150 cm2. The proposed design is capable of offering serpentine, interdigitated, counterflow, dead-end, and serpentine-interdigitated hybrid mode. Moreover, it is possible to switch over from one flow mode to another mode of flow during operation at any point of time. The flow design consists of the multichannel parallel serpentine flow (SP) field and a pair of an inlet and outlet manifolds instead of conventional single inlet and outlet manifold. Flow distribution was successfully altered without affecting the performances, and it was observed a combination of serpentine and interdigitated on the cathode side offered steady performance for more than 20 min when it was operated at a current density of 700 mA cm−2.

Commentary by Dr. Valentin Fuster
J. Electrochem. En. Conv. Stor.. 2017;14(4):041004-041004-6. doi:10.1115/1.4037532.

In the present paper, a composite electrode material was developed for vanadium redox flow batteries (VRFBs). Activated charcoal particles were evenly immobilized on the graphite felt (GF) via a sucrose pyrolysis process for the first time. The in site formed pyrolytic carbon is used as the binder, because it is essentially carbon material as well as GF and activated charcoal, which has a natural tendency to realize good adhesion and low contact resistance. The activated charcoal decorated GF electrode (abbreviated as the composite electrode) possesses larger surface area (13.8 m2 g−1), more than two times as GF (6.3 m2 g−1). The oxygen content of composite electrode is also higher (7.0%) than that of GF (4.8%). The composite electrode was demonstrated to lower polarization and increase the reversibility toward the VO2+/VO2+ redox couple according to the cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. The charge–discharge cycling test was conducted with a single VRFB cell. The results indicate that the cell with composite electrode presents higher charge–discharge capacity, larger electrolyte utilization efficiency (EU), and higher energy conversion efficiency (79.1%) compared with that using GF electrode. The increasing electrochemical performances of composite electrodes are mainly ascribed to the high electrochemical activity of activated charcoal particles and increasing superficial area.

Commentary by Dr. Valentin Fuster
J. Electrochem. En. Conv. Stor.. 2017;14(4):041005-041005-8. doi:10.1115/1.4037491.

The large push for more environmental energy storage solutions for the automotive industry by different actors has led to the usage of lithium-ion capacitors (LICs) combining the features of both lithium-ion batteries (LIBs) and electric-double layer capacitors (EDLCs). In this paper, the thermal behavior of two types of advanced LICs has been thoroughly studied and analyzed by developing a three-dimensional (3D) thermal model in COMSOL Multiphysics®. Such an extensive and accurate thermal 3D has not been fully addressed in literature, which is a key building block for designing battery packs with an adequate thermal management. After an extensive measurement campaign, the high accuracy of the developed model in this paper is proven for two types of LICs, the 3300 F and the 2300 F. An error between the simulation and measurements is maximum 2 °C. This 3D model has been developed to gain insight in the thermal behavior of LICs, which is necessary to develop a thermal management system, which can ensure the safe operation of LICs when used in modules or packs.

Commentary by Dr. Valentin Fuster
J. Electrochem. En. Conv. Stor.. 2017;14(4):041006-041006-7. doi:10.1115/1.4037648.

Sealant is used in a solid oxide fuel cell (SOFC) stack to separate fuel and oxygen from burning with each other throughout the stack's lifetime cycle. Various sealing materials have been developed and the glass sealant shows quite a potential for its low leaking rate. However, glass sealants usually suffer from fractures during thermal cycle because of their low-temperature brittleness and mismatched coefficient of thermal expansion. Recently, we have developed a novel glass-based sealant consisting of BaO–CaO–SiO2–CoO and a small amount of Al2O3 powder which is used to adjust the coefficient of thermal expansion (CTE) and reinforce its mechanical performance. The sealant exhibited a good performance with the leaking rates less than 0.04 sccm cm−1 under compressive load of 0.17 MPa at 750 °C and showed stable leak rates over several thermal cycles. The well bonded interfaces and chemical compatibility have been identified by microstructure analysis of the seals. The sealant also demonstrated its applicability in a one-cell stack test.

Commentary by Dr. Valentin Fuster
J. Electrochem. En. Conv. Stor.. 2017;14(4):041007-041007-11. doi:10.1115/1.4038019.

Organic/inorganic materials are investigated as additives to improve the stability of a vanadium electrolyte for a vanadium redox flow battery (VRFB) at operating temperatures of 25 °C and 40 °C. Among these materials, the most effective additive is chosen based on the thermal stability and electrochemical performance with a long inhibition time. Through precipitation time and electrochemical measurements, the results show that the best inhibition effect is achieved by adding sodium pyrophosphate dibasic (SPD, H2Na2O7P2) as an additive at a considerably high H2SO4 concentration (3M) electrolyte, indicating an improved redox reversibility and electrochemical activity. Nonflow cell assembled with the SPD additive exhibits larger discharge capacity retentions of 40% than a blank solution with the retentions of 2% at 600 cycles at 40 °C. In the case of flow cell, the capacity retention on the SPD additive shows 55.4%, which is 5.3% higher than the blank solution at 40 °C and 180 cycles. The morphology of the precipitation is investigated by SEM, which exhibits more severe V2O5 precipitation amount on the carbon felt electrode used in the blank electrolyte at 40 °C, which causes larger capacity losses compared to cells assembled with the SPD additive electrolyte.

Commentary by Dr. Valentin Fuster
J. Electrochem. En. Conv. Stor.. 2017;14(4):041008-041008-8. doi:10.1115/1.4037772.

Membrane electrolyte assembly (MEA) aging is a major concern for deployed proton exchange membrane (PEM) fuel cell stacks. Studies have shown that working conditions, such as the operating temperature, humidity, and open circuit voltage (OCV), have a major effect on degradation rates and also vary significantly from cell to cell. Individual cell health estimations would be very beneficial to maintenance and control schemes. Ideally, estimations would occur in response to the applied load to avoid service interruptions. To this end, this paper presents the use of an extended Kalman filter (EKF) to estimate the effective membrane surface area (EMSA) of each cell using cell voltage measurements taken during operation. The EKF method has a low computational cost and can be applied in real time to estimate the EMSA of each cell in the stack. This yields quantifiable data regarding cell degradation. The EKF algorithm was applied to experimental data taken on a 23-cell stack. The load profiles for the experiments were based on the FTP-75 and highway fuel economy test (HWFET) standard drive cycle tests to test the ability of the algorithm to perform in realistic load scenarios. To confirm the results of the EKF method, low performing cells and an additional “healthy” cell were selected for scanning electron microscope (SEM) analysis. The images taken of the cells confirm that the EKF accurately identified problematic cells in the stack. The results of this study could be used to formulate online sate of health estimators for each cell in the stack that can operate during normal operation.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Electrochem. En. Conv. Stor.. 2017;14(4):044501-044501-4. doi:10.1115/1.4037957.

This work aims at studying protonic transport of mixed proton–electron-conducting Nd5.5WO11.25-δ oxide synthesized by a citrate method as material for hydrogen separation membranes. Structure of samples was characterized by X-ray diffraction (XRD), and protonic mobility was studied using temperature-programmed desorption of H2O and isotope heteroexchange of the bulk protons with D2O as well as mass relaxation after an abrupt change of H2O partial pressure. The temperature range of Nd5.5WO11.25-δ efficient operation is 300–400 °C, where H+ tracer diffusion and chemical diffusion coefficients are ∼1 × 10−11 and ∼2 × 10−5 cm2/s, respectively, being comparable to or even better than those for similar systems. Hence, Nd5.5WO11.25-δ is a promising material for the design of hydrogen separation membranes.

Commentary by Dr. Valentin Fuster

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