Membrane-less hydrogen bromine flow battery

In order for the widely discussed benefits of flow batteries for electrochemical energy storage to be applied at large scale, the cost of the electrochemical stack must come down substantially. One promising avenue for reducing stack cost is to increase the system power density while maintaining efficiency, enabling smaller stacks. Here we report on a membrane-less hydrogen bromine laminar flow battery as a potential high-power density solution. The membrane-less design enables power densities of 0.795 W cm[superscript −2] at room temperature and atmospheric pressure, with a round-trip voltage efficiency of 92% at 25% of peak power. Theoretical solutions are also presented to guide the design of future laminar flow batteries. The high-power density achieved by the hydrogen bromine laminar flow battery, along with the potential for rechargeable operation, will translate into smaller, inexpensive systems that could revolutionize the fields of large-scale energy storage and portable power systems.American Society for Engineering Education. National Defense Science and Engineering Graduate FellowshipMIT Energy Initiative (Seed Fund

Microfluidic Screening of Electric Fields for Electroporation

Electroporation is commonly used to deliver molecules such as drugs, proteins, and/or DNA into cells, but the mechanism remains poorly understood. In this work a rapid microfluidic assay was developed to determine the critical electric field threshold required for inducing bacterial electroporation. The microfluidic device was designed to have a bilaterally converging channel to amplify the electric field to magnitudes sufficient to induce electroporation. The bacterial cells are introduced into the channel in the presence of SYTOX[superscript ®], which fluorescently labels cells with compromised membranes. Upon delivery of an electric pulse, the cells fluoresce due to transmembrane influx of SYTOX[superscript ®] after disruption of the cell membranes. We calculate the critical electric field by capturing the location within the channel of the increase in fluorescence intensity after electroporation. Bacterial strains with industrial and therapeutic relevance such as Escherichia coli BL21 (3.65 ± 0.09 kV/cm), Corynebacterium glutamicum (5.20 ± 0.20 kV/cm), and Mycobacterium smegmatis (5.56 ± 0.08 kV/cm) have been successfully characterized. Determining the critical electric field for electroporation facilitates the development of electroporation protocols that minimize Joule heating and maximize cell viability. This assay will ultimately enable the genetic transformation of bacteria and archaea considered intractable and difficult-to-transfect, while facilitating fundamental genetic studies on numerous diverse microbes.United States. Defense Advanced Research Projects Agency (Grant D13AP00025

Nonlinear electrophoresis in the presence of dielectric decrement

The nonlinear phenomena that occur in the electric double layer (EDL) that forms at charged surfaces strongly influence electrokinetic effects, including electro-osmosis and electrophoresis. In particular, saturation effects due to either dielectric decrement or ion crowding effects are of paramount importance. Dielectric decrement significantly influences the ionic concentration in the EDL at high ζ potential, leading to the formation of a condensed layer near the particle's surface. In this article, we present a model incorporating both steric effects due to the finite size of ions and dielectric decrement to describe the physics in the electric double layer. The model remains valid in both weakly and strongly nonlinear regimes, as long as the electric double layer remains in quasiequilibrium. We apply this model to the study of two archetypal problems in electrokinetics, namely the electrophoresis of particles with fixed surface charges and the electrophoresis of ideally polarizable particles

Toward establishing model organisms for marine protists : Successful transfection protocols for Parabodo caudatus (Kinetoplastida: Excavata)

Author Posting. © The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Environmental Microbiology 19 (2017): 3487-3499, doi:10.1111/1462-2920.13830.We developed protocols for, and demonstrated successful transfection of, the free-living kinetoplastid flagellate Parabodo caudatus with three plasmids carrying a fluorescence reporter gene (pEF-GFP with the EF1 alpha promoter, pUB-GFP with Ubiquitin C promoter, and pEYFP37 Mitotrap with CMV promoter). We evaluated three electroporation approaches: 1) a square-wave electroporator designed for eukaryotes, 2) a novel microfluidic transfection system employing hydrodynamically-controlled electric field waveforms, and 3) a traditional exponential decay electroporator. We found the microfluidic device provides a simple and efficient platform to quickly test a wide range of electric field parameters to find the optimal set of conditions for electroporation of target species. It also allows for processing large sample volumes (> 10 ml) within minutes, increasing throughput 100 times over cuvettes. Fluorescence signal from the reporter gene was detected a few hours after transfection and persisted for 3 days in cells transformed by pEF-GFP and pUB-GFP plasmids and for at least 5 days post-transfection for cells transformed with pEYFP-Mitotrap. Expression of the reporter genes (GFP and YFP) was also confirmed using reverse transcription-PCR (RT-PCR). This work opens the door for further efforts with this taxon and close relatives toward establishing model systems for genome editing.This project was funded by the Gordon and Betty Moore Foundation through Grant GBMF4963 to V. Edgcomb, P. Girguis, and C. Buie

A Microfluidic Platform for Evaluating Anode Substrates for Microbial Fuel Cells

Microbial fuel cell technology is a new technology for producing green energy from wastewater. While lab scale and commercial microbial fuel cells typically utilize graphite as the film substrate, it is difficult to rapidly prototype micro-patterned graphite and it has not been used to date. Our design sandwiches graphite sheets under a channel layer creating a microfluidic microbial fuel cell with graphite electrodes. The microfluidic microbial fuel cell uses Geobacter sulfurreducens fed with acetate in a phosphate buffer media. Ferricyanide is used as the catholyte so that the system is anodically limited. Current versus time and open circuit voltage are reported showing biofilm growth microbial fuel cell operation.Massachusetts Institute of Technology. A. Neil Pappalardo FellowshipMassachusetts Institute of Technology. Lemelson Presidential Fellowshi

Non-Invasive Sorting of Lipid Producing Microalgae With Dielectrophoresis Using Microelectrodes

In order to advance the algae biofuel industry, we are constructing a dielectrophoretic, single-cell sorter that selects algae based on lipid content. This tool can lower production costs by aiding in strain selection, online culture monitoring, or directed evolution studies. Dielectrophoresis (DEP) is the polarization of particles or cells in a non-uniform electric field, which leads to a Coulomb force on the cell. Lipids and cell cytoplasm have vastly different dielectric properties. Therefore, as a cell accumulates lipid, we predict a change in the overall DEP response. Our models show that in algae culture medium, we should be able to distinguish between high and low lipid content cells at frequencies above 100 MHz. This was confirmed by experiments, in which high and low lipid cultures of Neochloris oleoabundans have DEP crossover frequencies of 190 MHz and 125 MHz, respectively. We have also fabricated a proof-of-concept device validating that cells can be manipulated under DEP. However, in order to achieve sorting, we will require higher frequencies as well as a modified design to eliminate non-uniformities in the electric field through the channel height

Scaling laws for drop impingement on porous films and papers

This study investigates drop impingement on highly wetting porous films and papers. Experiments reveal previously unexplored impingement modes on porous surfaces designated as necking, spreading, and jetting. Dimensional analysis yields a nondimensional parameter, denoted the Washburn-Reynolds number, relating droplet kinetic energy and surface energy. The impingement modes correlate with Washburn-Reynolds number variations spanning four orders of magnitude and a corresponding energy conservation analysis for droplet spreading shows good agreement with the experimental results. The simple scaling laws presented will inform the investigation of dynamic interactions between porous surfaces and liquid drops.National Science Foundation (U.S.) (Award DMR-08-19762)Battelle Memorial Institut

Boundary Layer Analysis of Membraneless Electrochemical Cells

A mathematical theory is presented for the charging and discharging behavior of membraneless electrochemical cells that rely on slow diffusion in laminar flow to separate the half reactions. Ion transport is described by the Nernst-Planck equations for a flowing quasi-neutral electrolyte with heterogeneous Butler-Volmer kinetics. Analytical approximations for the current-voltage relation and the concentration and potential profiles are derived by boundary layer analysis (in the relevant limit of large Peclet numbers) and validated against finite-element numerical solutions. Both Poiseuille and plug flows are considered to describe channels of various geometries, with and without porous flow channels. The tradeoff between power density and reactant crossover and utilization is predicted analytically. The theory is applied to the membrane-less Hydrogen Bromine Laminar Flow Battery and found to accurately predict the experimental and simulated current-voltage data for different flow rates and reactant concentrations, during both charging and discharging. This establishes the utility of the theory to understand and optimize the performance of membrane-less electrochemical flow cells, which could also be extended to other fluidic architectures

Antiwetting Fabric Produced by a Combination of Layer-by-Layer Assembly and Electrophoretic Deposition of Hydrophobic Nanoparticles

This work describes a nanoparticle coating method to produce durable antiwetting polyester fabric. Electrophoretic deposition is used for fast modification of polyester fabric with silica nanoparticles embedded in polymeric networks for high durability coatings. Typically, electrophoretic deposition (EPD) is utilized on electrically conductive substrates due to its dependence on an applied electrical field. EPD on nonconductive materials has been attempted but are limited by weak adhesion, cracks, and other irregularities. To resolve these issues, we coat polyester fabric with thin polymer layers using electrostatic self-assembly (layer-by-layer self-assembly). Next, silica nanoparticles are uniformly dispersed on the polymer layers. Finally, polymerically stabilized silica nanoparticles are deposited by EPD on the fabric, followed by heat treatment. The modified fabric shows high static contact angle and low contact angle hysteresis, while keeping its original color, flexibility, and air permeability. During a skin fiction resistance test, the hydrophobicity of the coating layer was maintained over 500 h. Furthermore, we also show that this approach facilitates patterned regions of wettability by modifying the electric field in EPD