Development and optimization of flow electrode capacitor technology
Kuupäev
2022-04-08
Autorid
Ajakirja pealkiri
Ajakirja ISSN
Köite pealkiri
Kirjastaja
Abstrakt
Elektrokeemiline voogkondensaator (EFC) on kontseptuaalne lahendus elektrienergia mastaapseks salvestamiseks. Kõnealune seade sarnaneb tööpõhimõttelt superkondensaatorile, aga olulise erinevusena kasutab tahkete elektroodide asemel süsniniku mikro ja nano-osakestest ning elektrolüüdist koosnevat suspensiooni. Elektrolüüdiga suspensioon on eraldatud poorse, ioonjuhtiva membraaniga ja seadmes on tüüpiliselt mõne millimeetrilise diameetriga kanalid, mille sein on voolkollektoriks ning millest pumbatakse läbi eelpool kirjeldatud suspensiooni. Just nimelt süsinikupõhiste vedelate elektroodide kasutamine võimaldab arendatavat seadet olulisel määral skaleerida ning tulevikus integreerida olemasolevatesse elektrivõrkudesse ja/või rakendada seda efektiivselt taastuvate energiaallikate poolt toodetud elektrienergia salvestamiseks.
Doktoritöö keskseks eesmärgiks on EFC-tehnoloogia fundamentaalsete omaduste interpreteerimine. Sellest tulenevalt on töös on läbi viidud EFC elektrokeemilised karakteriseerimised ja arvutisimulatsioonid seadme disainlahenduste optimeerimiseks. Simulatsioonide valdkonnas on sobitatud EFC modelleerimiseks nii olemasolevaid elektrokeemilisi mudeled kui on arendatud ka uudne nn stohhastiline Monte-Carlo põhimõtetel baseeruv mudel. Väljatöötatud mudelid kalibreeriti ja valideeriti põhjalikult võrdluses elektrokeemiliste tulemustega ning neid kasutati voogelektroodide laadimisprotsessi sügavamaks mõistmiseks kolmes fundamentaalses EFC-seadme konstruktsioonis.
Sarnaste elektrokeemiliste seadmete modelleerimiseks kasutatakse tihti Nernst-Planki võrranditel või kontsentreeritud lahuse teooriatel baseeruvaid mudeleid. Luuakse teist järku osatuletsitega diferentsiaalvõrrandite süsteemid, mis kirjeldavad nii ioonide kontsentratsioone kui ka seadmes tekkivaid laenguülekande protsesse. Nende mudelite rakendamine iseloomustas ilmekalt difusiooni tõttu seadmes tekkivaid laengu salvestamise ja osakeste transpordi piiranguid. Efektiivne elektroodimaterjali tsirkulatsioon ning piisavalt kiire laengu transport on teineteisele vastanduvad protsessid – kui esimesel juhul on oluliseks näitajaks piisavalt suur elektroodi voolukanalite diameeter, siis teisel juhul on nõutav just nimelt sama kanali diameetri minimiseerimine. Samas ilmnes eksperimentaalsest tulemustest, et mitte ainult difusioonist tingitud nähtused pole olulised, vaid märkimisväärset mõju omavad ka nn kõrvalreaktsioonid. Töö käigus loodud stohhastiline mudel võimaldas saavutada edukalt elektrokeemiliste mõõtmistulemuste ning Nernst-Planki võrranditel baseeruvate mudelitega leitud tulemuste kokkulangevuse. Enamgi, loodud stohhastiline mudel võimaldab edukalt simuleerida vedelate elektroodide laadumise dünaamikat ja kirjeldada suspensioonis asetleidvaid protsesse ning hinnata kõrvalreaktsioonide mõjusid. Kokkuvõtvalt avab loodud lähenemisviis võimaluse leidmaks lahendust voogkondensaatori disaini kesksele probleemile – kuidas tagada seadmest piisav elektroodimaterjali läbivool ning samas hoiduda laengu transpordi limiteerimisest difusiooni tõttu.
EFC-tehnoloogia edasise arengu puhul võib eeldada taastuvatest allikatest toodetud energia salvestamisvõimsuse märkimisväärset kasvu. Samas tuleb lisada, et EFC võimsustiheduse parandamiseks, ilma et see kahjustaks nende seadmete energiatihedust ning tsükleeritavust, on vaja jälgida arenduste kooskõla ka muude energiasalvestus- ja muundamis-tehnoloogiatega. Olulisteks faktoriteks on nii seadme töötingimuste valik, elektroodide disain, elektrolüüdi materjalid, kuid samuti ka sobilikud katalüsaatorid.
An electrochemical flow capacitor (EFC) is a conceptual approach to meet large-scale electricity storage. This device is similar in operation to a supercapacitor but uses a concentrated solution of carbon micro and nanoparticles and an electrolyte instead of solid electrodes. It typically flows in channels with a diameter of a few millimeters, the wall of which is a flow collector and through which the liquid electrode material is pumped. A porous ion-conducting membrane separates the electrodes. Using carbon-based liquid electrodes in the device under development will allow the technology to be significantly scaled up and integrated into existing electricity grids and used effectively to support renewable energy production. The central goal of the work presented is to understand the fundamental properties of EFC technology. As a result, EFC laboratory tests and computer simulations have been performed to design and optimize the device architecture. In the field of simulations, both existing electrochemical models have been adapted for EFC modeling, and a new stochastic model based on Monte-Carlo principles has been developed. Both implemented and developed models were thoroughly calibrated and validated against laboratory experiments and used to understand the flow electrode charging process in three fundamental EFC device designs. Models based on Nernst-Planck equations or concentrated solution theories are often used to model similar electrochemical devices. Second-order differential equations systems with partial derivatives describe both the ion concentrations and the charge exchange processes occurring in the device. The application of these models was characterized by the limitations of charge storage and transport processes in the device due to diffusion. If the electrode material circulation and sufficiently fast charge transport are critical processes, then a sufficiently large diameter of the electrode flow channels is important. Otherwise, it is necessary to minimize the diameter of the same channel. At the same time, the experimental work showed that the phenomena caused by diffusion are critical side effects and have a significant effect on electrode charging processes. The models based on the Nernst-Planck equations and the stochastic model developed successfully matched the experimental results. Moreover, the developed stochastic model allows to simulate the convection and mixing processes of liquid electrodes successfully and to apply the effects of side reactions. Thus, the developed approach opens the possibility to find a solution to the central problem of the flow capacitor design - how to ensure sufficient flow of electrode material from the device and at the same time avoid limiting the transport of charge due to diffusion. Due to the development of EFC technology, a significant increase in the storage capacity of energy from renewable sources can be expected. At the same time, to improve the power density of EFCs without compromising their high energy density and cyclicality, it is necessary to monitor the coherence of developments with other energy storage and conversion technologies. Important factors are the choice of operating conditions of the device, the design of the electrodes, the materials of the electrolyte, as well as suitable catalysts.
An electrochemical flow capacitor (EFC) is a conceptual approach to meet large-scale electricity storage. This device is similar in operation to a supercapacitor but uses a concentrated solution of carbon micro and nanoparticles and an electrolyte instead of solid electrodes. It typically flows in channels with a diameter of a few millimeters, the wall of which is a flow collector and through which the liquid electrode material is pumped. A porous ion-conducting membrane separates the electrodes. Using carbon-based liquid electrodes in the device under development will allow the technology to be significantly scaled up and integrated into existing electricity grids and used effectively to support renewable energy production. The central goal of the work presented is to understand the fundamental properties of EFC technology. As a result, EFC laboratory tests and computer simulations have been performed to design and optimize the device architecture. In the field of simulations, both existing electrochemical models have been adapted for EFC modeling, and a new stochastic model based on Monte-Carlo principles has been developed. Both implemented and developed models were thoroughly calibrated and validated against laboratory experiments and used to understand the flow electrode charging process in three fundamental EFC device designs. Models based on Nernst-Planck equations or concentrated solution theories are often used to model similar electrochemical devices. Second-order differential equations systems with partial derivatives describe both the ion concentrations and the charge exchange processes occurring in the device. The application of these models was characterized by the limitations of charge storage and transport processes in the device due to diffusion. If the electrode material circulation and sufficiently fast charge transport are critical processes, then a sufficiently large diameter of the electrode flow channels is important. Otherwise, it is necessary to minimize the diameter of the same channel. At the same time, the experimental work showed that the phenomena caused by diffusion are critical side effects and have a significant effect on electrode charging processes. The models based on the Nernst-Planck equations and the stochastic model developed successfully matched the experimental results. Moreover, the developed stochastic model allows to simulate the convection and mixing processes of liquid electrodes successfully and to apply the effects of side reactions. Thus, the developed approach opens the possibility to find a solution to the central problem of the flow capacitor design - how to ensure sufficient flow of electrode material from the device and at the same time avoid limiting the transport of charge due to diffusion. Due to the development of EFC technology, a significant increase in the storage capacity of energy from renewable sources can be expected. At the same time, to improve the power density of EFCs without compromising their high energy density and cyclicality, it is necessary to monitor the coherence of developments with other energy storage and conversion technologies. Important factors are the choice of operating conditions of the device, the design of the electrodes, the materials of the electrolyte, as well as suitable catalysts.
Kirjeldus
Väitekirja elektrooniline versioon ei sisalda publikatsioone
Märksõnad
condensers (electricity)