Gas-permeable hydrophobic membranes enable transport of CO2 and NH3 to improve performance of bioelectrochemical systems
Sleutels, Tom H.J.A. ; Hoogland, Biense ; Kuntke, P. ; Heijne, A. ter; Buisman, C.J.N. ; Hamelers, Hubertus V.M. - \ 2016
Environmental Science : Water Research & Technology 2 (2016). - ISSN 2053-1400 - p. 743 - 748.
Application of bioelectrochemical systems (BESs), for example for the production of hydrogen from organic waste material, is limited by a high internal resistance, especially when ion exchange membranes are used. This leads to a limited current density and thus to large footprint and capital costs. Ion transport between anode and cathode compartment is one of the factors determining the internal resistance. The aim of this study was to reduce the resistance for ion transport in a microbial electrolysis cell (MEC) through the ion exchange membrane by shuttling of CO2 and NH3 between anode and cathode. The transport of these chemical species was enabled through the use of a hydrophobic TransMembraneChemiSorption module (TMCS) that was placed between anolyte and catholyte circulation outside the cell. The driving force for transport was the pH difference between both solutions. The transport of CO2 and NH3 resulted in an increase in current density from 2.1 to 4.1 A m−2 for a cation exchange membrane (CEM) and from 2.5 to 13.0 A m−2 for an anion exchange membrane (AEM) at 1 V applied voltage. The increase in current density was the result of a lower ion transport resistance through the membrane; this resistance was 60% lower for the CEM, as a result of NH3 recycling from cathode to anode, and 82% for the AEM, as a result of CO2 recycling from anode to cathode with TMCS, compared to experiments without TMCS.
Gas-permeable hydrophobic tubular membranes for ammonia recovery in bio-electrochemical systems
Kuntke, P. ; Zamora, P. ; Saakes, M. ; Buisman, C.J.N. ; Hamelers, H.V.M. - \ 2016
Environmental Science : Water Research & Technology 2 (2016)2. - ISSN 2053-1400 - p. 261 - 265.
The application of a gas-permeable hydrophobic tubular membrane in bio-electrochemical systems enables efficient recovery of ammonia (NH3) from their cathode compartments. Due to a hydrogen evolution reaction at the cathode, no chemical addition was required to increase the pH for continuous NH3 recovery from wastewater.
Revisiting Morrison and Osterle 1965 : The efficiency of membrane-based electrokinetic energy conversion
Catalano, J. ; Hamelers, H.V.M. ; Bentien, A. ; Biesheuvel, Maarten - \ 2016
Journal of Physics-Condensed Matter 28 (2016)32. - ISSN 0953-8984
charged nanopore - desalination - electrokinetic energy conversion
We revisit Morrison and Osterle (1965) who derived a phenomenological expression for the 'figure-of-merit' βEK of the electrokinetic energy conversion (EKEC) of a pressure difference into electric energy (and vice versa) using charged nanotubes, nanopores or ion-exchange membranes. We show the equivalence with Morrison and Osterle of a novel expression of βEK derived by Bentien et al (2013). We analyze two physical models for ionic and solvent flow which directly relate βEK to nanopore characteristics such as pore size and wall charge density. For the uniform potential model, we derive an analytical expression as a function of pore size, viscosity, ion diffusion coefficients and membrane charge density, and compare results with the full space-charge model by Osterle and co-workers as a function of pore size and ion diffusion coefficient. We present a novel expression for βEK for salt solutions with ions with unequal diffusion coefficients (mobilities) and show that to increase βEK the counterion mobility must be low and the coion mobility high.
The concentration gradient flow battery as electricity storage system : Technology potential and energy dissipation
Egmond, W.J. Van; Saakes, M. ; Porada, S. ; Meuwissen, T. ; Buisman, C.J.N. ; Hamelers, H.V.M. - \ 2016
Journal of Power Sources 325 (2016). - ISSN 0378-7753 - p. 129 - 139.
Aqueous based battery - Flow batteries - Ion-exchange membranes - Large scale electricity energy storage - Reverse electrodialysis - Salinity gradient energy
Unlike traditional fossil fuel plants, the wind and the sun provide power only when the renewable resource is available. To accommodate large scale use of renewable energy sources for efficient power production and utilization, energy storage systems are necessary. Here, we introduce a scalable energy storage system which operates by performing cycles during which energy generated from renewable resource is first used to produce highly concentrated brine and diluate, followed up mixing these two solutions in order to generate power. In this work, we present theoretical results of the attainable energy density as function of salt type and concentration. A linearized Nernst-Planck model is used to describe water, salt and charge transport. We validate our model with experiments over wide range of sodium chloride concentrations (0.025-3 m) and current densities (-49 to +33 A m-2). We find that depending on current density, charge and discharge steps have significantly different thermodynamic efficiency. In addition, we show that at optimal current densities, mechanisms of energy dissipation change with salt concentration. We find the highest thermodynamic efficiency at low concentrate concentrations. When using salt concentrations above 1 m, water and co-ion transport contribute to high energy dissipation due to irreversible mixing.
Selective short-chain carboxylates production : A review of control mechanisms to direct mixed culture fermentations
Arslan, D. ; Steinbusch, K.J.J. ; Diels, L. ; Hamelers, H.V.M. ; Strik, D.P.B.T.B. ; Buisman, C.J.N. ; Wever, H. De - \ 2016
Critical Reviews in Environmental Science and Technology 46 (2016)6. - ISSN 1064-3389 - p. 592 - 634.
Biomass conversion - carboxylates - mixed culture fermentation - operational parameters - organic waste - volatile fatty acids
Anaerobic digestion of organic residual streams can be directed to produce carboxylates such as acetate, propionate, and n-butyrate, which can be either directly used in industry or converted into other valuable compounds. This paper reviews the studies working with mixed culture conversion of organic substrates toward carboxylates. It draws connections between standard fermentation parameters and the carboxylate product concentrations and composition. The use of more concentrated carbohydrate-rich substrates, at longer residence times and at neutral pH ranges, stimulates total acid production. When increasing pH to the neutral range, acetate and propionate fractions are elevated. High propionate concentrations and fractions are infrequently reported and mainly appear on high-protein-containing feedstock. High n-butyrate fraction <70% is usually found when pH > 6, at longer retention times or organic loading rates, under CO2 atmosphere or on substrates with high lactate concentrations. The review concludes with prospects for further developments related to the carboxylate platform.
On-line method to study dynamics of ion adsorption from mixtures of salts in capacitive deionization
Dykstra, J.E. ; Dijkstra, J. ; Wal, A. van der; Hamelers, H.V.M. ; Porada, S. - \ 2016
Desalination 390 (2016). - ISSN 0011-9164 - p. 47 - 52.
Capacitive Deionization - Electrosorption - Ionic mixtures - Salt removal - Selective ion removal
Capacitive Deionization (CDI) is a water desalination technology that adsorbs ions into two oppositely polarized porous carbon electrodes, under the action of an applied voltage. Here, we introduce a novel method to analyze the effluent concentration of multiple ionic species in mixtures of salt solutions by directing the outflow of a CDI cell to an inductively coupled plasma optical emission spectroscopy (ICP-OES) instrument. Compared to previous methods based on manual sampling, the on-line use of ICP-OES allows collecting more accurate time-dependent ion adsorption data, and therefore, ion dynamics can be studied even at very short half-cycle times. We use this method to study ion adsorption from a mixed solution containing two monovalent cations with similar radius, namely potassium and sodium. We find that potassium ions are preferentially adsorbed over sodium ions, due to their higher mobility. Furthermore, we compare our experimental findings with a novel multicomponent electromigration model that calculates dynamic adsorption of ions from solutions of multiple salts. Whereas we find good agreement between data and theory at low half cycle times, we observe a considerable discrepancy at higher values.
Chain Elongation with Reactor Microbiomes: Open-Culture Biotechnology To Produce Biochemicals
Angenent, L.T. ; Richter, H. ; Buckel, W. ; Spirito, C.M. ; Steinbusch, K.J.J. ; Plugge, C.M. ; Strik, D.P.B.T.B. ; Grootscholten, T.I.M. ; Buisman, C.J.N. ; Hamelers, H.V.M. - \ 2016
Environmental Science and Technology 50 (2016)6. - ISSN 0013-936X - p. 2796 - 2810.
Chain elongation into medium-chain carboxylates, such as n-caproate and n-caprylate, with ethanol as an electron donor and with open cultures of microbial consortia (i.e., reactor microbiomes) under anaerobic conditions is being developed as a biotechnological production platform. The goal is to use the high thermodynamic efficiency of anaerobic fermentation to convert organic biomass or organic wastes into valuable biochemicals that can be extracted. Several liter-scale studies have been completed and a first pilot-plant study is underway. However, the underlying microbial pathways are not always well understood. In addition, an interdisciplinary approach with knowledge from fields ranging from microbiology and chemical separations to biochemistry and environmental engineering is required. To bring together research from different fields, we reviewed the literature starting with the microbiology and ending with the bioprocess engineering studies that already have been performed. Because understanding the microbial pathways is so important to predict and steer performance, we delved into a stoichiometric and thermodynamic model that sheds light on the effect of substrate ratios and environmental conditions on product formation. Finally, we ended with an outlook
Parallel up-scaling of Capacitive Mixing (CapMix) system enhances the specific performance
Liu, Fei ; Donkers, Tim F.W. ; Wagterveld, R.M. ; Schaetzle, Olivier ; Saakes, Michel ; Buisman, Cees J.N. ; Hamelers, Hubertus V.M. - \ 2016
Electrochimica Acta 187 (2016). - ISSN 0013-4686 - p. 104 - 112.
Capacitive Donnan Potential - Capacitive Mixing - Ion exchange membrane - Salinity gradient energy - Wire-shaped electrode
Given the considerable amount of energy dissipated in the salinity gradient at the point where a river flows into the sea, we investigate the technology of capacitive mixing (CapMix), an attractive technology for generating electrical power from this gradient. We determine the performances of multiple wire-shaped electrode pairs connected either in series or in parallel in a CapMix system. The bundles of pairs were immersed in synthetic river and seawater. Pairs connected in parallel and placed next to each other allowed for 18% more energy extraction than the total energy extracted by the same number of pairs individually. An even higher additional energy gain is possible if contact resistances are further minimized. The improvement is due to the additional flow paths for ions between electrode pairs in parallel connection, reducing the total internal resistance. The highest power density achieved (in terms of the mass of activated carbon material used) was 2.7 mW/g, which was higher than the power densities that have been achieved previously using a flat plate CapMix cell (1.26 mW/g) and a wire electrode cell (0.34 mW/g). The lower ohmic resistance in the parallel system was identified using a current distribution model and experimental measurements.
Theory of Water Desalination by Porous Electrodes with Immobile Chemical Charge
Biesheuvel, P.M. ; Hamelers, H.V.M. ; Suss, M.E. - \ 2015
Colloids and Interface Science Communications 9 (2015). - ISSN 2215-0382 - p. 1 - 5.
In capacitive deionization (CDI), water is desalinated by storing ions in electrical double layers (EDLs) within the micropores of charged porous carbon electrodes. Recent experiments using chemically modified electrodes have shown differing, novel phenomena such as "inverted CDI," "enhanced CDI," and "inversion peaks." We here present an EDL and dynamic model which includes immobile chemical charge in the micropores and show that the models predict these disparate experimental observations. Our model also makes predictions for a previously undiscovered operational regime with higher salt adsorption, which we term extended voltage CDI.
Analysis of bio-anode performance through electrochemical
Heijne, A. ter; Schaetzle, O.C. ; Gimenez, S. ; Navarro, L. ; Hamelers, B. ; Fabregat-Santiago, F. - \ 2015
Bioelectrochemistry 106 (2015)part A. - ISSN 1567-5394 - p. 64 - 72.
In this paper we studied the performance of bioanodes under different experimental conditions using polarization curves and impedance spectroscopy. We have identified that the large capacitances of up to 1 mF·cm- 2 for graphite anodes have their origin in the nature of the carbonaceous electrode, rather than the microbial culture. In some cases, the separate contributions of charge transfer and diffusion resistance were clearly visible, while in other cases their contribution was masked by the high capacitance of 1 mF·cm- 2. The impedance data were analyzed using the basic Randles model to analyze ohmic, charge transfer and diffusion resistances. Increasing buffer concentration from 0 to 50 mM and increasing pH from 6 to 8 resulted in decreased charge transfer and diffusion resistances; lowest values being 144 O·cm2 and 34 O·cm2, respectively. At acetate concentrations below 1 mM, current generation was limited by acetate. We show a linear relationship between inverse charge transfer resistance at potentials close to open circuit and saturation (maximum) current, associated to the Butler–Volmer relationship that needs further exploration.
Energy from CO2 using capacitive electrodes – A model for energy extraction cycles
Paz-García, J.M. ; Dykstra, J.E. ; Biesheuvel, P.M. ; Hamelers, H.V.M. - \ 2015
Journal of Colloid and Interface Science 442 (2015). - ISSN 0021-9797 - p. 103 - 109.
A model is presented for the process of harvesting electrical energy from CO2 emissions using capacitive cells. The principle consists of controlling the mixing process of a concentrated CO2 gas stream with a dilute CO2 gas stream (as, for example, exhaust gas and air), thereby converting part of the released mixing energy into electrical energy. The model describes the transient reactive transport of CO2 gas absorbed in water or in monoethanolamine (MEA) solutions, under the assumption of local chemical equilibrium. The model combines the selective transport of ions through ion-exchange membranes, the accumulation of charge in the porous carbon electrodes and the coupling between the ionic current and the produced electrical current and power. We demonstrate that the model can be used to calculate the energy that can be extracted by mixing concentrated and dilute CO2 containing gas streams. Our calculation results for the process using MEA solutions have various counterintuitive features, including: 1. When dynamic equilibrium is reached in the cyclical process, the electrical charge in the anode is negative both during charging and discharging; 2. Placing an anion-exchange membrane (AEM) in the system is not required, the energy per cycle is just as large with or without an AEM.
Carbon nanotube yarns as strong flexible conductive capacitive electrodes
Liu, F. ; Wagterveld, R.M. ; Gebben, B. ; Otto, M.J. ; Biesheuvel, P.M. ; Hamelers, H.V.M. - \ 2015
Colloids and Interface Science Communications 3 (2015). - ISSN 2215-0382 - p. 9 - 12.
Carbon nanotube (CNT) yarn, consisting of 23 µm diameter CNT filaments, can be used as capacitive electrodes that are long, flexible, conductive and strong, for applications in energy and electrochemical water treatment. We measure the charge storage capacity as function of salt concentration, and use Gouy–Chapman–Stern theory to describe the data. CNT yarn can also be used as conductive scaffold for the application of a porous activated carbon (AC) layer. We show the potential of CNT yarn for the generation of electrical energy from environmental entropy differences, by coating yarn (both with and without AC coating) with ion-exchange membranes (IEMs) and generating power from the salt concentration difference between river water and seawater. The use of flexible and conductive CNT yarns as capacitive electrodes and electrode scaffolds breaks with the paradigm of planar static electrodes, and opens up a range of alternative designs for electrochemical cells with enhanced performance.
Advancing CapMix for electricity generation : system operation, cell design and material selection
Liu, F. - \ 2015
Wageningen University. Promotor(en): Cees Buisman, co-promotor(en): Bert Hamelers. - Wageningen : Wageningen University - ISBN 9789462573079 - 164
hernieuwbare energie - bio-energie - energiebronnen - capacitantie - vermenging - zout water - zoet water - elektrodialyse - biobased economy - renewable energy - bioenergy - energy sources - capacitance - mixing - saline water - fresh water - electrodialysis - biobased economy
Capacitive energy extraction of the mixing process, also referred as Capacitive Mixing (CapMix), is a novel and promising technology that can convert salinity gradient power into electricity directly. This technology uses two porous activated carbon electrodes. The energy extraction is directly linked to the mixing process, while no emission of greenhouse gases and no thermal pollution occur. This emerging CapMix technology is still immature. In order to transform the proof-of-principle into a viable technology, many questions remain to be answered, not only in science (i.e. understanding what is happening), but also in technology (i.e. how to design and manufacture the system). In this thesis, the author investigated the optimized way to operate the system. Moreover, models were developed to understand the physical-chemical process; material including ion exchange membranes and activated carbon electrodes were evaluated; and the innovative cell design was made.
Fluidized Capacitive Bioanode As a Novel Reactor Concept for the Microbial Fuel Cell
Deeke, A. ; Sleutels, T.H.J.A. ; Donkers, T.F.W. ; Hamelers, B. ; Buisman, C.J.N. ; Heijne, A. ter - \ 2015
Environmental Science and Technology 49 (2015)3. - ISSN 0013-936X - p. 1929 - 1935.
waste-water treatment - electricity-generation - power-generation - iron reduction - scaled-up - performance - carbon - resistance - membranes - biofilms
The use of granular electrodes in Microbial Fuel Cells (MFCs) is attractive because granules provide a cost-effective way to create a high electrode surface area, which is essential to achieve high current and power densities. Here, we show a novel reactor design based on capacitive granules: the fluidized capacitive bioanode. Activated carbon (AC) granules are colonized by electrochemically active microorganisms, which extract electrons from acetate and store the electrons in the granule. Electricity is harvested from the AC granules in an external discharge cell. We show a proof-of-principle of the fluidized capacitive system with a total anode volume of 2 L. After a start-up period of 100 days, the current increased from 0.56 A/m2 with 100 g AC granules, to 0.99 A/m2 with 150 g AC granules, to 1.3 A/m2 with 200 g AC granules. Contact between moving AC granules and current collector was confirmed in a control experiment without biofilm. Contribution of an electro-active biofilm to the current density with recirculation of AC granules was limited. SEM images confirmed that a biofilm was present on the AC granules after operation in the fluidized capacitive system. Although current densities reported here need further improvement, the high surface area of the AC granules in combination with external discharge offers new and promising opportunities for scaling up MFCs.
Extraction of Energy from Small Thermal Differences near Room Temperature Using Capacitive Membrane Technology
Sales, B.B. ; Burheim, O.S. ; Porada, S. ; Presser, V. ; Buisman, C.J.N. ; Hamelers, H.V.M. - \ 2014
Environmental Science & Technology Letters 1 (2014)9. - ISSN 2328-8930 - p. 356 - 360.
charged membranes - performance - electrodes - systems
Extracting electric energy from small temperature differences is an emerging field in response to the transition toward sustainable energy generation. We introduce a novel concept for producing electricity from small temperature differences by the use of an assembly combining ion exchange membranes and porous carbon electrodes immersed in aqueous electrolytes. Via the temperature differences, we generate a thermal membrane potential that acts as a driving force for ion adsorption/desorption cycles within an electrostatic double layer, thus converting heat into electric work. We report for a temperature difference of 30 degrees C a maximal energy harvest of similar to 2 mJ/m(2), normalized to the surface area of all the membranes.
Capacitive bioanodes for electricity storage in Microbial Fuel Cells
Deeke, A. - \ 2014
Wageningen University. Promotor(en): Cees Buisman, co-promotor(en): Bert Hamelers; Annemiek ter Heijne. - Wageningen : Wageningen University - ISBN 9789462571105 - 151
afvalwaterbehandeling - organische stof - brandstofcellen - energiebronnen - elektriciteit - opslag - energiegebruik - elektrodes - elektrolyten - bio-energie - onderzoek - biobased economy - waste water treatment - organic matter - fuel cells - energy sources - electricity - storage - energy consumption - electrodes - electrolytes - bioenergy - research - biobased economy
Denkend aan het opraken van de fossiele brandstoffen, wordt de noodzaak om naar hernieuwbare alternatieven te kijken alleen maar groter. Zon, wind, water en biomassa zijn al hernieuwbare bronnen die actueel gebruikt worden. Maar voor zonne-, wind- en waterenergie beperkt die discontinue aanwezigheid de verdere ontwikkeling en wordt de noodzaak voor elektriciteitsopslag benadrukt. Een andere technologie voor hernieuwbare elektriciteitsopwekking is de microbiële brandstofcel (MFC). In een MFC worden de organische bestanddelen van het afvalwater rechtstreeks in elektrische energie omgezet. MFCs zijn een opkomende technologie van de afgelopen 10 jaar en vele onderzoekers hebben onderzoek gedaan naar de verbetering van de stroomdichtheid en het vermogen. De continue verwerking van het afvalwater vraagt om opslag van het afvalwater of om opslag van de geproduceerde elektriciteit. Opslag van de elektriciteit kan bewerkstelligd worden door het combineren van een MFC met een condensator.
Carbon flow electrodes for continuous operation of capacitive deionization and capacitive mixing energy generation
Porada, S. ; Hamelers, H.V.M. ; Bryjak, M. ; Presser, V. ; Biesheuvel, P.M. ; Weingarth, D. - \ 2014
Journal of Materials Chemistry. A, Materials for energy and sustainability 2 (2014)24. - ISSN 2050-7488 - p. 9313 - 9321.
graphite powder suspensions - activated carbon - electrochemical polarization - salinity differences - porous-electrodes - constant-current - co2 capture - desalination - ions - performance
Capacitive technologies, such as capacitive deionization and energy harvesting based on mixing energy (“capmix” and “CO2 energy”), are characterized by intermittent operation: phases of ion electrosorption from the water are followed by system regeneration. From a system application point of view, continuous operation has many advantages, to optimize performance, to simplify system operation, and ultimately to lower costs. In our study, we investigate as a step towards second generation capacitive technologies the potential of continuous operation of capacitive deionization and energy harvesting devices, enabled by carbon flow electrodes using a suspension based on conventional activated carbon powders. We show how the water residence time and mass loading of carbon in the suspension influence system performance. The efficiency and kinetics of the continuous salt removal process can be improved by optimizing device operation, without using less common or highly elaborate novel materials. We demonstrate, for the first time, continuous energy generation via capacitive mixing technology using differences in water salinity, and differences in gas phase CO2 concentration. Using a novel design of cylindrical ion exchange membranes serving as flow channels, we continuously extract energy from available concentration differences that otherwise would remain unused. These results may contribute to establishing a sustainable energy strategy when implementing energy extraction for sources such as CO2-emissions from power plants based on fossil fuels.
Two-stage medium chain fatty acid (MCFA) production from municipal solid waste and ethanol
Grootscholten, T.I.M. ; Strik, D.P.B.T.B. ; Steinbusch, K.J.J. ; Buisman, C.J.N. ; Hamelers, B. - \ 2014
Applied Energy 116 (2014)1. - ISSN 0306-2619 - p. 223 - 229.
clostridium-kluyveri - carboxylic-acids - carbon-dioxide - elongation - biomass - inhibition - caprylate - caproate - bacteria - acetate
Chain elongation is an anaerobic fermentation that produces medium chain fatty acids (MCFAs) from volatile fatty acids and ethanol. These MCFAs can be used as biochemical building blocks for fuel production and other chemical processes. Producing MCFAs from the organic fraction of municipal solid waste (OFMSW) is attractive because it combines waste treatment with biochemical production. We investigated whether higher MCFA production rates can be achieved from OFMSW by applying a two-stage conversion, consisting of the OFMSW acidification step followed by chain elongation, compared to a single-stage system. We obtained higher MCFA production rates with a two-stage system than with a single-stage system. The obtained caproate concentrations were above the solubility of caproic acid in water. Furthermore, this work discussed competitive processes for MCFA production and shows how these processes can be controlled in a two-stage system. Finally an outlook was given on research required to prevent too much production of the intermediate co-product butyrate instead of MCFAs, which occurred several times during the experiment.
Energy from CO2 using capacitive electrodes – Theoretical outline and calculation of open circuit voltage
Par-Garcia, J.M. ; Schaetzle, O. ; Biesheuvel, P.M. ; Hamelers, H.V.M. - \ 2014
Journal of Colloid and Interface Science 418 (2014). - ISSN 0021-9797 - p. 200 - 207.
anion-exchange membranes - porous-electrodes - carbamate formation - aqueous-solution - acid anions - monoethanolamine - equilibrium - absorption - simulation - capture
Recently, a new technology has been proposed for the utilization of energy from CO2 emissions (Hamelers et al., 2014). The principle consists of controlling the dilution process of CO2–concentrated gas (e.g., exhaust gas) into CO2–dilute gas (e.g., air) thereby extracting a fraction of the released mixing energy. In this paper, we describe the theoretical fundamentals of this technology when using a pair of charge–selective capacitive electrodes. We focus on the behavior of the chemical system consisting of CO2 gas dissolved in water or monoethanolamine solution. The maximum voltage given for the capacitive cell is theoretically calculated, based on the membrane potential. The different aspects that affect this theoretical maximum value are discussed.
Harvesting Energy from CO2 Emissions
Hamelers, H.V.M. ; Schaetzle, O. ; Paz-García, J.M. ; Biesheuvel, P.M. ; Buisman, C.J.N. - \ 2014
Environmental Science & Technology Letters 1 (2014)1. - ISSN 2328-8930 - p. 31 - 35.
water salinity difference - capacitive deionization - carbon electrodes - extraction - power - capture
When two fluids with different compositions are mixed, mixing energy is released. This holds true for both liquids and gases, though in the case of gases, no technology is yet available to harvest this energy source. Mixing the CO2 in combustion gases with air represents a source of energy with a total annual worldwide capacity of 1570 TWh. To harvest the mixing energy from CO2-containing gas emissions, we use pairs of porous electrodes, one selective for anions and the other selective for cations. We demonstrate that when an aqueous electrolyte, flushed with either CO2 or air, alternately flows between these selective porous electrodes, electrical energy is gained. The efficiency of this process reached 24% with deionized water as the aqueous electrolyte and 32% with a 0.25 M monoethanolamine (MEA) solution as the electrolyte. The highest average power density obtained with a MEA solution as the electrolyte was 4.5 mW/m2, significantly higher than that with water as the electrolyte (0.28 mW/m2).