Electrodeposition and electrodissolution of zinc in mixed methanesulfonate-based electrolytes

The final publication is available at Elsevier via http://dx.doi.org/10.1016/j.electacta.2018.02.087 © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/Zinc electrodeposition and electrodissolution in methanesulfonic acid (MSA) electrolytes mixed with chloride or sulfate are investigated in a 3-electrode cell for eventual use in divided and undivided zinc-cerium redox flow batteries (RFB). Cyclic voltammetry and polarization experiments show that the addition of chloride to methanesulfonate-based electrolytes shifts the nucleation potential in the positive direction, lowers the nucleation overpotential and enhances the kinetics of Zn deposition and subsequent dissolution relative to that achieved when sulfate is added or MSA is the only anion present. In addition, the diffusion coefficient of Zn(II) and the resulting limiting current density for Zn deposition have been found to be moderately higher in mixed methanesulfonate/chloride media than when chloride is absent. The effects of temperature, MSA concentration, Zn(II) concentration and current density on the Zn/Zn(II) system have also been investigated under potentiostatic and galvanostatic conditions. Although an increase in temperature and/or MSA concentration tends to lower the charge efficiency for Zn deposition in both mixed and MSA-only electrolytes due to the higher rate of hydrogen evolution, the amount of zinc deposited, charge and voltage efficiency always remain significantly higher in the mixed methanesulfonate/chloride media than the pure MSA media. Thus, the use of a mixed methanesulfonate/chloride media should enable both divided and undivided zinc-cerium RFBs to operate over a wider range of temperatures and MSA concentrations compared to the case with pure MSA electrolyte. The addition of sulfate to MSA-based electrolytes, however, does not improve the performance of the Zn/Zn(II) system relative to that possible in the MSA-only electrolytes.Natural Sciences and Engineering Research Council of Canada [Discovery Grant 170912

Impact of Liquid Water on Reactant Mass Transfer in PEM Fuel Cell Electrodes

Published by Electrochemical Society. Final version available at: http://dx.doi.org/10.1149/1.3291977The breakthrough conditions (capillary pressure and liquid water saturation) in a fibrous gas diffusion medium (GDM) used in polymer electrolyte membrane (PEM) fuel cell electrodes have been studied experimentally by two independent techniques and numerically by pore network modeling. Experiments show that treatment of the GDMs with a hydrophobic polymer coating reduces the water saturation at a breakthrough by 50%. Invasion percolation modeling is employed to simulate the breakthrough process and to determine mass-transfer rates through the partially saturated network. This model shows that the water saturation at breakthrough is drastically reduced when a microporous layer (MPL) is incorporated into the GDM, agreeing with experiments. However, the simulations yield limiting currents significantly higher than those observed in practice whether or not an MPL is present. Further calculations to include the contribution of condensation to water saturation within the GDM also result in unrealistically high limiting currents and suggest that mass-transfer resistance in the catalyst layer that is not included in the model plays an important role. If condensation is the principal mode for water accumulation within the GDM, simulations show that the MPL has only a small impact on liquid water distribution and does not improve performance, contrary to expectation.Natural Science and Engineering Research Council of Canada (NSERC

Pore network modeling of fibrous gas diffusion layers for polymer electrolyte membrane fuel cells

The final publication is available at Elsevier via http://dx.doi.org/10.1016/j.jpowsour.2007.04.059 © 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/A pore network model of the gas diffusion layer (GDL) in a polymer electrolyte membrane fuel cell is developed and validated. The model idealizes the GDL as a regular cubic network of pore bodies and pore throats following respective size distributions. Geometric parameters of the pore network model are calibrated with respect to porosimetry and gas permeability measurements for two common GDL materials and the model is subsequently used to compute the pore-scale distribution of water and gas under drainage conditions using an invasion percolation algorithm. From this information, the relative permeability of water and gas and the effective gas diffusivity are computed as functions of water saturation using resistor-network theory. Comparison of the model predictions with those obtained from constitutive relationships commonly used in current PEMFC models indicates that the latter may significantly overestimate the gas phase transport properties. Alternative relationships are suggested that better match the pore network model results. The pore network model is also used to calculate the limiting current in a PEMFC under operating conditions for which transport through the GDL dominates mass transfer resistance. The results suggest that a dry GDL does not limit the performance of a PEMFC, but it may become a significant source of concentration polarization as the GDL becomes increasingly saturated with water

Wettability and capillary behavior of fibrous gas diffusion media for polymer electrolyte membrane fuel cells

The final publication is available at Elsevier via http://dx.doi.org/10.1016/j.jpowsour.2009.04.052 © 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/The relationship of capillary pressure to liquid saturation for the water-air fluid pair in two different types of gas diffusion media (GDM) used in polymer electrolyte membrane fuel cell (PEMFC) electrodes is elucidated. It is experimentally demonstrated that GDM samples with and without treatment with poly(tetrafluoroethylene) (PTFE) ubiquitously display permanent capillary pressure hysteresis. Water does not imbibe spontaneously into a dry GDM, neither is it ejected spontaneously from a water-saturated GDM. Rather, positive displacement pressure is required to force both water and air into GDMs, whereas the main effect of adding PTFE is to increase the amount of work required for forcing water into the GDM. and to decrease the work required for water removal. Irrespective of PTFE content, the GDM samples tested are generally shown to behave as materials of intermediate (neutral) wettability. The US Bureau of Mines (USBM) wettability index nevertheless shows that water is the preferentially non-wetting phase in PTFE-treated GDMs and the preferentially wetting phase in untreated GDMs. Water-air capillary pressure curves are found to depend on sample thickness, clearly demonstrating that finite size effects are important. Finally, compression of the GDM is found to increase the capillary pressures for water injection and decrease the capillary pressures required for water withdrawal. These results should aid the design of GDMs with improved water management properties and the modeling of PEMFC electrodes in general. (C) 2009 Elsevier B.V. All rights reserved.Natural Science and Engineering Research Council of Canada (NSERC

On the role of the microporous layer in PEMFC operation

The final publication is available at Elsevier via http://dx.doi.org/10.1016/j.elecom.2008.12.053 © 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/The condition of liquid water breakthrough at the cathode of polymer electrolyte fuel cells (PEMFC) is studied experimentally and data on corresponding water saturation and capillary pressure are provided for gas diffusion layers (GDL) with and without a microporous layer (MPL). The data demonstrate that the GDL saturation at water breakthrough is drastically reduced from ca. 25% to ca. 5% in the presence of MPL This observation is consistent with considerations of invasion percolation in finite-size lattices and suggests an explanation for the role of MPL in improving PEMFC performance at high current densities

Direct measurement of the capillary pressure characteristics of water-air-gas diffusion layer systems for PEM fuel cells

The final publication is available at Elsevier via http://dx.doi.org/10.1016/j.elecom.2008.08.008 © 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/A method and apparatus for measuring the relationship between air-water capillary pressure and water saturation in PEMFC gas diffusion layers is described. Capillary pressure data for water injection and withdrawal from typical GDL materials are obtained, which demonstrate permanent hysteresis between water intrusion and water withdrawal. Capillary pressure, defined as the difference between the water and gas pressures at equilibrium, is positive during water injection and negative during water withdrawal. The results contribute to the understanding of liquid water behavior in GDL materials which is necessary for the development of effective PEMFC water management Strategies

Peptide and peptide-carbon nanotube hydrogels as scaffolds for tissue & 3D tumor engineering

The final publication is available at Elsevier via http://dx.doi.org/10.1016/j.actbio.2017.12.012 © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/The use of hybrid self-assembling peptide (EFK8)-carbon nanotube (SWNT) hydrogels for tissue engineering and in vitro 3D cancer spheroid formation is reported. These hybrid hydrogels are shown to enhance the attachment, spreading, proliferation and movement of NIH-3T3 cells relative to that observed using EFK8-only hydrogels. After five days, ∼30% more cells are counted when the hydrogel contains SWNTs. Also, 3D encapsulation of these cells when injected in hydrogels does not adversely affect their behavior. Compressive modulus measurements and microscopic examination suggest that SWNTs have this beneficial effect by providing sites for cell anchorage, spreading and movement rather than by increasing hydrogel stiffness. This shows that the cells have a particular interaction with SWNTs not shared with EFK8 nanofibers despite a similar morphology. The effect of EFK8 and EFK8-SWNT hydrogels on A549 lung cancer cell behavior is also investigated. Increasing stiffness of EFK8-only hydrogels from about 44 Pa to 104 Pa promotes a change in A549 morphology from spheroidal to a stretched one similar to migratory phenotype. EFK8-SWNT hydrogels also promote a stretched morphology, but at lower stiffness. These results are discussed in terms of the roles of both microenvironment stiffness and cell-scaffold adhesion in cancer cell invasion. Overall, this study demonstrates that applications of peptide hydrogels in vitro can be expanded by incorporating SWNTs into their structure which further provides insight into cell-biomaterial interactions. Statement of significance For the first time we used hybrid self-assembling peptide-carbon nanotube hybrid hydrogels (that we have recently introduced briefly in the “Carbon” journal in 2014) for tissue engineering and 3D tumor engineering. We showed the potential of these hybrid hydrogels to enhance the efficiency of the peptide hydrogels for tissue engineering application in terms of cell behavior (cell attachment, spreading and migration). This opens up new rooms for the peptide hydrogels and can expand their applications. Also our system (peptide and peptide-CNT hydrogels) was used for cancer cell spheroid formation showing the effect of both tumor microenvironment stiffness and cell-scaffold adhesion on cancer cell invasion. This was only possible based on the presence of CNTs in the hydrogel while the stiffness kept constant. Finally it should be noted that these hybrid hydrogels expand applications of peptide hydrogels through enhancing their capabilities and/or adding new properties to them.Natural Sciences and Engineering Research Council of Canada (NSERC)Canada Foundation for Innovation (CFI)Canada Research Chairs (CRC) progra