Lawrence, KS, United States
Lawrence, KS, United States
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Woo Park J.,Vanderbilt University | Wycisk R.,Vanderbilt University | Lin G.,TVN Systems, Inc. | Ying Chong P.,TVN Systems, Inc. | And 4 more authors.
Journal of Membrane Science | Year: 2017

Nafion® perfluorosulfonic acid (PFSA) and poly(vinylidene fluoride) (PVDF) were electrospun simultaneously as a polymer solution mixture using a single needle spinneret. The nanofiber morphology was highly unusual, with bundled 2–5 nm fibril strands of Nafion and PVDF aligned along the fiber axis. Membranes were made from fiber mats by a simple hot-pressing step, followed by thermal annealing, where the fibril morphology of Nafion and PVDF in the original nanofibers was retained in the membrane. The PVDF component in the final membrane served three roles, as an electrospinning carrier polymer for PFSA, a mechanical reinforcement, and a hydrophobic (uncharged) component to limit PFSA ionomer swelling. A series of single-fiber membranes with Nafion/PVDF contents ranging from 40/60 to 90/10 wt%/wt% were prepared, characterized, and evaluated for use in a regenerative hydrogen/bromine fuel cell. As expected, there was a decrease in proton conductivity, water/electrolyte swelling, and Br2/Br3 - permeability with increasing PVDF content. Membrane conductivity was lower than expected based on the weight fraction of PVDF, due presumably to an unusually large fraction of highly structured water. Nevertheless, a single-fiber Nafion/PVDF membrane with a thickness of 18 µm and an 80/20 wt%/wt% Nafion/PVDF composition performed well in a H2/Br2 regenerative fuel cell due to a combination of low area-specific resistance and low Br2/Br3 - crossover. Thus, with an electrolyte containing 0.9 M Br2 in 1.0 M HBr, the maximum power output was 46% higher than that with a Nafion 212 membrane (1.31 vs. 0.90 W/cm2). © 2017 Elsevier B.V.


Lin G.,TVN Systems, Inc. | Chong P.Y.,TVN Systems, Inc. | Yarlagadda V.,University of Kansas | Nguyen T.V.,University of Kansas | And 6 more authors.
Journal of the Electrochemical Society | Year: 2016

The hydrogen/bromine flow battery is a promising candidate for large-scale energy storage due to fast kinetics, highly reversible reactions and low chemical costs. However, today's conventional hydrogen/bromine flow batteries use membrane materials (such as Nafion), platinum catalysts, and carbon-paper electrode materials that are expensive. In addition, platinum catalysts can be poisoned and corroded when exposed to HBr and Br2, compromising system lifetime. To reduce the cost and increase the durability of H2/Br2 flow batteries, new materials are developed. The new Nafion/polyvinylidene fluoride electrospun composite membranes have high perm-selectivity at a fraction of the cost of Nafion membranes; the new nitrogen-functionalized platinum-iridium catalyst possesses excellent activity and durability in HBr/Br2 environment; and the new carbon-nanotube-based Br2 electrodes can achieve equal or better performance with less materials when compared to baseline electrode materials. Preliminary cost analysis shows that the new materials reduce H2/Br2 flow-battery energy-storage system stack and system costs significantly. The resulting advanced H2/Br2 flow batteries offer high power, high efficiency, substantially increased durability, and expected reduced cost. © The Author(s) 2015.


Tucker M.C.,Lawrence Berkeley National Laboratory | Cho K.T.,Northern Illinois University | Weber A.Z.,Lawrence Berkeley National Laboratory | Lin G.,TVN Systems, Inc. | Van Nguyen T.,University of Kansas
Journal of Applied Electrochemistry | Year: 2015

The Br2/H2 redox flow cell shows promise as a high-power, low-cost energy storage device. The effect of various aspects of material selection, processing, and assembly of electrodes on the operation, performance, and efficiency of the system is determined. In particular, (+) electrode thickness, cell compression, hydrogen pressure, and (−) electrode architecture are investigated. Increasing hydrogen pressure and depositing the (−) catalyst layer on the membrane instead of on the carbon paper backing layers have a large positive impact on performance, enabling a limiting current density above 2 A cm−2 and a peak power density of 1.4 W cm−2. Maximum energy efficiency of 79 % is achieved. In addition, the root cause of limiting-current behavior in this system is elucidated, where it is found that Br− reversibly adsorbs at the Pt (−) electrode for potentials exceeding a critical value, and the extent of Br− coverage is potential-dependent. This phenomenon limits maximum cell current density and must be addressed in system modeling and design. These findings are expected to lower system cost and enable higher efficiency. © 2014, Springer Science+Business Media Dordrecht.


Tucker M.C.,Lawrence Berkeley National Laboratory | Cho K.T.,Northern Illinois University | Weber A.Z.,Lawrence Berkeley National Laboratory | Lin G.,TVN Systems, Inc. | Van Nguyen T.,University of Kansas
Journal of Applied Electrochemistry | Year: 2014

The Br2/H2 redox flow cell shows promise as a high-power, low-cost energy storage device. The effect of various aspects of material selection, processing, and assembly of electrodes on the operation, performance, and efficiency of the system is determined. In particular, (+) electrode thickness, cell compression, hydrogen pressure, and (−) electrode architecture are investigated. Increasing hydrogen pressure and depositing the (−) catalyst layer on the membrane instead of on the carbon paper backing layers have a large positive impact on performance, enabling a limiting current density above 2 A cm−2 and a peak power density of 1.4 W cm−2. Maximum energy efficiency of 79 % is achieved. In addition, the root cause of limiting-current behavior in this system is elucidated, where it is found that Br− reversibly adsorbs at the Pt (−) electrode for potentials exceeding a critical value, and the extent of Br− coverage is potential-dependent. This phenomenon limits maximum cell current density and must be addressed in system modeling and design. These findings are expected to lower system cost and enable higher efficiency. © 2014, Springer Science+Business Media Dordrecht.


Tucker M.C.,Lawrence Berkeley National Laboratory | Cho K.T.,Lawrence Berkeley National Laboratory | Cho K.T.,Northern Illinois University | Spingler F.B.,Lawrence Berkeley National Laboratory | And 2 more authors.
Journal of Power Sources | Year: 2015

Abstract The Br2/H2 redox flow cell shows promise as a high-power, low-cost energy storage device. In this paper, the effect of various aspects of material selection and processing of proton exchange membranes on the operation of the Br2/H2 redox flow cell is determined. Membrane properties have a significant impact on the performance and efficiency of the system. In particular, there is a tradeoff between conductivity and crossover, where conductivity limits system efficiency at high current density and crossover limits efficiency at low current density. The impact of thickness, pretreatment procedure, swelling state during cell assembly, equivalent weight, membrane reinforcement, and addition of a microporous separator layer on this tradeoff is assessed. NR212 (50 μm) pretreated by soaking in 70 C water is found to be optimal for the studied operating conditions. For this case, an energy efficiency of greater than 75% is achieved for current density up to 400 mA cm-2, with a maximum obtainable energy efficiency of 88%. A cell with this membrane was cycled continuously for 3164 h. Membrane transport properties, including conductivity and bromine and water crossover, were found to decrease moderately upon cycling but remained higher than those for the as-received membrane. © 2015 Elsevier B.V. All rights reserved.


Grant
Agency: Department of Energy | Branch: ARPA-E | Program: STTR | Phase: Phase I | Award Amount: 225.00K | Year: 2012

"It is our objective to develop a cost effective, durable and reliable hydrogen-bromine flow battery system for small-scale electrical energy storage applications. H2/Br2 flow battery technology has been around for decades, however, the lack of low-cost and durable electrode and membrane materials in addition to non-optimal cell/stack configurations have prevented this technology from widespread deployment. TVN Systems Inc. teams up with research groups at Vanderbilt University and The University of Kansas to develop innovative electrodes, membranes and optimal cell/stack design to reduce cost and to increase cycle life and overall efficiency of an H2/Br2 flow battery system. In Phase I we will (1) identify and fabricate inexpensive and durable electrocatalysts and nanofiber composite membranes to replace platinum-based electrode materials and Nafion membranes, and (2) develop optimal electrode and cell design. In Phase II, a 250W stack module will be developed employing the new materials and optimal cell design to demonstrate the cost reduction and performance gain as opposed to stacks using state-of-the-art materials. A number of modules can be combined in parallel to support large power demands. An analysis on a 2.5kW-4hour energy storage system consisting of ten proposed modules shows that it meets the ARPA-E’s primary targets: 1.2m3 footprint, at least 80% round trip efficiency, lifetime more than 1250 cycles and under $1000 per unit. It can be charged by solar power systems or electric grids to store off-peak electricity at customer’s location. The success of this project will be truly transformational for large-scale H2/Br2 electrochemical energy storage systems to have a greater impact on economic and energy security of the United States."


Grant
Agency: Department of Energy | Branch: ARPA-E | Program: STTR | Phase: Phase II | Award Amount: 1.50M | Year: 2012

"It is our objective to develop a cost effective, durable and reliable hydrogen-bromine flow battery system for small-scale electrical energy storage applications. H2/Br2 flow battery technology has been around for decades, however, the lack of low-cost and durable electrode and membrane materials in addition to non-optimal cell/stack configurations have prevented this technology from widespread deployment. TVN Systems Inc. teams up with research groups at Vanderbilt University and The University of Kansas to develop innovative electrodes, membranes and optimal cell/stack design to reduce cost and to increase cycle life and overall efficiency of an H2/Br2 flow battery system. In Phase I we will (1) identify and fabricate inexpensive and durable electrocatalysts and nanofiber composite membranes to replace platinum-based electrode materials and Nafion membranes, and (2) develop optimal electrode and cell design. In Phase II, a 250W stack module will be developed employing the new materials and optimal cell design to demonstrate the cost reduction and performance gain as opposed to stacks using state-of-the-art materials. A number of modules can be combined in parallel to support large power demands. An analysis on a 2.5kW-4hour energy storage system consisting of ten proposed modules shows that it meets the ARPA-E’s primary targets: 1.2m3 footprint, at least 80% round trip efficiency, lifetime more than 1250 cycles and under $1000 per unit. It can be charged by solar power systems or electric grids to store off-peak electricity at customer’s location. The success of this project will be truly transformational for large-scale H2/Br2 electrochemical energy storage systems to have a greater impact on economic and energy security of the United States."


Yarlagadda V.,University of Kansas | Lin G.,TVN Systems, Inc. | Chong P.Y.,TVN Systems, Inc. | Nguyen T.V.,University of Kansas
Journal of the Electrochemical Society | Year: 2016

In a hydrogen-bromine (H2-Br2) fuel cell, the Br2 reactions don't require precious metal catalysts, hence porous carbon gas diffusion media (GDM) are widely used as electrodes. However, the specific surface areas of the commercial carbon gas diffusion electrodes (GDEs) are quite low and need to be enhanced. In order to improve the active surface area of carbon GDEs, a study was conducted to grow multi-walled carbon nanotubes (MWCNTs) directly on the carbon electrode fiber surface. Both constant and pulse current electrodeposition techniques were used to deposit Co nanoparticles to catalyze the MWCNT growth. The MWCNTs were grown in the presence of a mixture of acetylene, argon, and hydrogen gases using the chemical vapor deposition process. Based on the results obtained from SEM, TEM, and EDX analysis, MWCNT growth following the tip model was confirmed. The results from the multi-step chronoamperometry study have shown that the synthesized carbon GDEs with MWCNTs have 7 to 50 times higher active surface area than that of a plain GDE. The performance of a single layer of the best MWCNT GDE measured in a H2-Br2 fuel cell was found to be equal or slightly higher compared to that obtained using a three-layer plain carbon electrode. © The Author(s) 2015.


Yarlagadda V.,University of Kansas | Lin G.,TVN Systems, Inc. | Chong P.Y.,TVN Systems, Inc. | Nguyen T.V.,University of Kansas
Journal of the Electrochemical Society | Year: 2016

The commercially available carbon gas diffusion electrodes (GDEs) with low specific active area but high permeability are often used as Br2 electrodes in the H2-Br2 fuel cell. In order to increase the specific active surface area of the existing carbon GDEs, a study was conducted to grow multi-wall carbon nanotubes (MWCNTs) directly on the surface of carbon fibers of a commercial carbon electrode. Experimental fixtures were developed to promote the electrodeposition of cobalt and the growth of MWCNTs on the carbon GDE. The MWCNT growth across the carbon electrode was confirmed by SEM. The carbon GDE with a dense distribution of shortMWCNTs evaluated in a H2-Br2 fuel cell has 29 times higher active surface area than a plain carbon electrode and was found to be highly durable at an electrolyte flow rate of 10 cc/min/cm2. The performance of the best single layer MWCNT GDE measured at 80% discharge voltage efficiency in a H2-Br2 fuel cell was found to be 16% higher compared to that obtained using three layers of plain carbon electrodes. Finally, the preliminary material cost analysis has shown that the MWCNT-based carbon electrodes offer significant cost advantages over the plain carbon electrodes. © The Author(s) 2015.


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TVN Systems, Inc. is a developer and manufacturer of fuel cell systems for energy storga and power generation

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