Guest Editorial

J. Electrochem. En. Conv. Stor.. 2017;14(2):020301-020301-2. doi:10.1115/1.4036506.

The idea for this special issue was born when two of us (Dirk Henkensmeier and Alexander Dyck) planned the 4th EMEA workshop, which was held on June 27–29, 2016. The Workshop on Ion Exchange Membranes for Energy Applications (EMEA) started as a small workshop with 29 participants in 2013 and grew steadily since that time, reaching over 70 participants in 2016 (Fig. 1). Since the focus of this workshop series is set traditionally on anion exchange membranes (AEMs), we considered it to be the right time to collect contributions for a JEECS “Special Issue on Anion Exchange Membranes and AEM-Based Systems.”

Commentary by Dr. Valentin Fuster

Special Issue Research Papers

J. Electrochem. En. Conv. Stor.. 2017;14(2):020701-020701-8. doi:10.1115/1.4033411.

Fossil fuel power plants are responsible for a significant portion of anthropogenic atmospheric carbon dioxide (CO2) and due to concerns over global climate change, finding solutions that significantly reduce emissions at their source has become a vital concern. When oxygen (O2) is reduced along with CO2 at the cathode of an anion exchange membrane (AEM) electrochemical cell, carbonate and bicarbonate are formed which are transported through electrolyte by migration from the cathode to the anode where they are oxidized back to CO2 and O2. This behavior makes AEM-based devices scientifically interesting CO2 separation devices or “electrochemical CO2 pumps.” Electrochemical CO2 separation is a promising alternative to the state-of-the-art solvent-based methods because the cells operate at low temperatures and scale with surface area, not volume, suggesting that the industrial electrochemical systems could be more compact than amine sorption technologies. In this work, we investigate the impact of the CO2 separator cell potential on the CO2 flux, carbonate transport mechanism, and process costs. The applied electrical current and CO2 flux showed a strong correlation that was both stable and reversible. The dominant anion transport pathway, carbonate versus bicarbonate, undergoes a shift from carbonate to mixed carbonate/bicarbonate with increased potential. A preliminary techno-economic analysis shows that despite the limitations of present cells, there is a clear pathway to meet the U.S. Department of Energy (DOE) 2025 and 2035 targets for power plant retrofit CO2 capture systems through materials and systems-level advances.

Commentary by Dr. Valentin Fuster
J. Electrochem. En. Conv. Stor.. 2017;14(2):020702-020702-6. doi:10.1115/1.4035835.

There is an enormous potential for energy generation from the mixing of sea and river water at global estuaries. Here, we model a novel approach to convert this source of energy directly into hydrogen and electricity using reverse electrodialysis (RED). RED relies on converting ionic current to electric current using multiple membranes and redox-based electrodes. A thermodynamic model for RED is created to evaluate the electricity and hydrogen which can be extracted from natural mixing processes. With equal volume of high and low concentration solutions (1 L), the maximum energy extracted per volume of solution mixed occurred when the number of membranes is reduced, with the lowest number tested here being five membrane pairs. At this operating point, 0.32 kWh/m3 is extracted as electrical energy and 0.95 kWh/m3 as hydrogen energy. This corresponded to an electrical energy conversion efficiency of 15%, a hydrogen energy efficiency of 35%, and therefore, a total mixing energy efficiency of nearly 50%. As the number of membrane pairs increases from 5 to 20, the hydrogen power density decreases from 13.6 W/m2 to 2.4 W/m2 at optimum external load. In contrast, the electrical power density increases from 0.84 W/m2 to 2.2 W/m2. Optimum operation of RED depends significantly on the external load (external device). A small load will increase hydrogen energy while decreasing electrical energy. This trade-off is critical in order to optimally operate an RED cell for both hydrogen and electricity generation.

Commentary by Dr. Valentin Fuster
J. Electrochem. En. Conv. Stor.. 2017;14(2):020703-020703-9. doi:10.1115/1.4036507.

For a gas diffusion cathode for oxygen reduction reaction (ORR) in aqueous alkaline electrolyte, it is important to create networks for O2 gas diffusion, electronic conduction, and liquid-phase OH transport in the cathode at once. In this study, we succeeded to fabricate a promising cathode using hydrophobic vapor grown carbon fibers (VGCF-Xs), instead of hydrophobic carbon blacks (CBs), as additives to its active layer (AL). Mercury porosimetry, as well as electrochemical impedance spectroscopy, showed that porosity of the cathode gradually increased with increasing the amount of the carbon fibers. In other words, addition of larger amount of the carbon fibers creates better O2 gas diffusion channels. Also, the activation polarization resistance for the ORR increased as the carbon fibers' amount from 0 to 0.03–0.04 g and then dropped. In consequence, the cathode with 0.03 g of the carbon fibers exhibited the highest ORR performance among the prepared cathodes.

Commentary by Dr. Valentin Fuster

Review Article

J. Electrochem. En. Conv. Stor.. 2017;14(2):020801-020801-17. doi:10.1115/1.4036456.

The performance, safety, and reliability of Li-ion batteries are determined by a complex set of multiphysics, multiscale phenomena that must be holistically studied and optimized. This paper provides a summary of the state of the art in a variety of research fields related to Li-ion battery materials, processes, and systems. The material presented here is based on a series of discussions at a recently concluded bilateral workshop in which researchers and students from India and the U.S. participated. It is expected that this summary will help understand the complex nature of Li-ion batteries and help highlight the critical directions for future research.

Commentary by Dr. Valentin Fuster

Additional Research Papers

J. Electrochem. En. Conv. Stor.. 2017;14(2):021001-021001-8. doi:10.1115/1.4036508.

Hydrogen fuel cells are an important part of a portfolio of strategies for reducing petroleum use and emissions from medium and heavy duty (MD and HD) vehicles; however, their deployment is very limited compared to other powertrains. This paper addresses gaseous hydrogen storage tank design and location on representative MD and HD vehicles. Storage design is based on vehicle size and occupation. The available storage space on representative vehicles is assessed and is used to estimate the weight and capacity of composite material-based compressed gaseous storage at 350 and 700 bar. Results demonstrate the technical feasibility of using hydrogen storage for fuel cell electric trucks (FCETs) across a wide range of the MD and HD vehicle market. This analysis is part of a longer-term project to understand which market segments provide the maximum economic impact and greenhouse gas reduction opportunities for FCETs.

Commentary by Dr. Valentin Fuster
J. Electrochem. En. Conv. Stor.. 2017;14(2):021002-021002-12. doi:10.1115/1.4036278.

In this paper, the electrochemical impedance spectroscopy (EIS) method is applied through a transient in solid oxide fuel cell (SOFC) to obtain the dynamic modeling. Instead of measuring the current response of a fuel cell to a small sinusoidal perturbation in voltage at each frequency, the Hammerstein–Wiener model identification method is applied through a one transient who leads to the significant decrease of computational costs. Dynamic responses are determined as the solutions of coupled partial differential equations derived from conservation laws of charges, mass, momentum, and energy with electrochemical kinetics by using Butler–Volmer model and gas diffusion on the extended Maxwell-Stefan species equations or dusty gas model (DGM). Because the system consisted of electrical and mechanical components, the behavior of the system was nonlinear. The obtained results are in good qualitative agreement with experimental data published in literatures shown the effectiveness of the propose model. Finally, a parametric study based on the obtained model is performed to study the effects of channel length, inlet H2 concentration, inlet velocity, and cell temperature in Nyquist plots and the voltage responses to step changes in the fuel concentration and load current. The model can be useful as a benchmark for illustrating different designs and control schemes.

Commentary by Dr. Valentin Fuster
J. Electrochem. En. Conv. Stor.. 2017;14(2):021003-021003-4. doi:10.1115/1.4036386.

The high voltage cathode material, LiMn1.6Ni0.4O4, was prepared by a polymer-assisted method. The novelty of this work is the substitution of Ni with Mn, which already exists in the crystal structure instead of other isovalent metal ion dopants which would result in capacity loss. The electrochemical performance testing including stability and rate capability was evaluated. The temperature was found to impose a change on the valence and structure of the cathode materials. Specifically, manganese tends to be reduced at a high temperature of 800 °C and leads to structural changes. The manganese substituted LiMn1.5Ni0.5O4 (LMN) has proved to be a good candidate material for Li-ion battery cathodes displaying good rate capability and capacity retention. The cathode materials processed at 550 °C showed a stable performance with negligible capacity loss for 400 cycles.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Electrochem. En. Conv. Stor.. 2017;14(2):024501-024501-5. doi:10.1115/1.4036318.

Li2NixFe1−xSiO4 (x = 0, 0.2, 0.4, 0.6, 0.8, and 1) samples were prepared by sol–gel process. The crystal structure of prepared samples of Li2NixFe1−xSiO4 was characterized by XRD. The different crystallographic parameters such as crystallite size and lattice cell parameters have been calculated. Scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR) investigations were carried out explaining the morphology and function groups of the synthesized samples. Furthermore, electrochemical impedance spectra (EIS) measurements are applied. The obtained results indicated that the highest conductivity is achieved for Li2Ni0.4Fe0.6SiO4 electrode compound. It was observed that Li/Li2Ni0.4Fe0.6SiO4 battery has initial discharge capacity of 164 mAh g−1 at 0.1 C rate. The cycle life performance of all Li2NixFe1−xSiO4 batteries was ranged between 100 and 156 mAh g−1 with coulombic efficiency range between 70.9% and 93.9%.

Commentary by Dr. Valentin Fuster

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