Computer simulations for designing green energy solutions

Lassi Hällström

Computer simulations for designing green energy solutions

Julkaisun otsikon käännös: Computer simulations for designing green energy solutions

Lassi Hällström

Elektroniikan ja nanotekniikan laitos

Tutkimustuotos: Doctoral Thesis › Collection of Articles

Abstrakti

Hiilidioksidipäästöjen vähentäminen ja ilmastonmuutoksen hillitseminen on ihmiskunnan suurin haaste seuraavien vuosikymmenten aikana. Vety on noussut taloudellisesti kannattavaksi vaihtoehdoksi fossiilisille hiilipohjaisille polttoaineille eri teollisuudenaloilla, kuten teräksen tuotannossa, liikenteessä ja jopa biokemiallisessa elintarviketuotannossa. Jotta hiilidioksidipäästöjä voitaisiin vähentää tehokkaasti, vetyä on tuotettava elektrolyysillä vedestä, sillä teollisuudessa nykyisin käytetty vakiomenetelmä, höyryreformointi, erottaa vetykaasun fossiilisista hiilivedyistä, jolloin sivutuotteena syntyy samat hiilidioksidipäästöt kuin hiilivedyn polttamisessa suoraan. Hiilidioksidipäästöjen vähentämisessä keskeistä on uusiutuvan energian tuotanto. Tässä väitöskirjassa tutkitaan, miten tietokonesimulaatioita voidaan käyttää ympäristöystävällisten energiaratkaisujen suunnittelussa ja optimoinnissa. Väitöskirjan perusajatus on, että minkä tahansa laitteen optimoimiseksi on ensin ymmärrettävä, miten fysiikan lait vaikuttavat sen toimintaan. Vasta sitten on mahdollista ennustaa eri muutosten vaikutuksia laitteen tehokkuuteen. Tässä väitöskirjassa tutkitaan tietokonesimulaatioita kahdesta erillisestä uusiutuvan energian tuotantomenetelmästä. Ensimmäinen on sähköntuotanto veden haihtumisesta seuraavasta vesivirtauksesta huokoisissa rakenteissa. Huokoisesta rakenteesta seuraa monifaasinen virtausdynamiikan ongelma, jossa sähköä tuottavan veden virtaus riippuu sekä materiaalin ominaisuuksista että toimintaympäristön olosuhteista. Väitöskirjassa osoitetaan, miten huolellisesti suunniteltu simulaatio voi paitsi toistaa kokeelliset tulokset joiden pohjalta malli on rakennettu, myös ennustaa käyttäytymistä, joka voidaan jälkeenpäin todentaa kokeellisesti. Toinen tapaus on valosähkökemiallinen vedyn tuotanto, jossa auringonvalo muunnetaan vedyksi yhdellä monoliittisella puolijohdekomponentilla ilman ulkoista sähköntuotantoa. Tätä tapausta simuloidaan ensin Boltzmannin kuljetusyhtälöön perustuvalla mallilla. Koska uusien materiaalien suunnittelussa ja elektrodien geometriassa hyödynnetään kuitenkin yhä enemmän nanokokoluokan ominaisuuksia, Boltzmannin yhtälön taustalla olevat klassiset oletukset eivät ole enää tarkkoja. Toinen menetelmä puolijohde-elektrodien simuloimiseksi on kvanttimekaaninen formalismi (NEGF, nonequilibrium Green's function), jota on laajalti hyödynnetty aurinkokennojen ja transistorien simuloinnissa. Tässä työssä osoitetaan, että NEGF:ää voidaan soveltaa valosähkökemiallisten laitteiden mallintamiseen, ja se kykenee tuottamaan merkittävästi parempia tuloksia kuin aiemmat menetelmät. Tulokset osoittavat, miten tietokonesimulaatiot voivat sekä auttaa ymmärtämään laitteiden toimintaa syvällisemmin, että tarjota kyvyn optimoida laitesuunnittelua tehokkuuden kasvattamiseksi.

Julkaisun otsikon käännös	Computer simulations for designing green energy solutions
Alkuperäiskieli	Englanti
Pätevyys	Tohtorintutkinto
Myöntävä instituutio	Aalto-yliopisto
Valvoja/neuvonantaja	Tittonen, Ilkka, Vastuuprofessori
Kustantaja	Aalto University
Painoksen ISBN	978-952-64-1390-7
Sähköinen ISBN	978-952-64-1391-4
Tila	Julkaistu - 2023
OKM-julkaisutyyppi	G5 Artikkeliväitöskirja

Tutkimusalat

simulaatio
energia
sähkökemia
puolijohde
kvanttimekaniikka

YK:n kestävän kehityksen tavoitteet

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http://urn.fi/URN:ISBN:978-952-64-1391-4

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Rissanen, A. (Manager)
Aalto-yliopisto
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Repo, P. (Manager) & Rissanen, A. (Other)
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Seitsonen, J. (Manager) & Rissanen, A. (Other)
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@phdthesis{1a3ce9f65ac74eb18495f711b92df0c4,

title = "Computer simulations for designing green energy solutions",

abstract = "Reducing the CO2 emissions and mitigating climate change is the grand challenge facing humanity in the next couple of decades. Hydrogen has emerged as an economically viable alternative to fossil carbon based fuels in various industries, such as steel production, transportation and even biochemical food production. In order to effectively reduce the carbon emissions the hydrogen must be produced via electrolysis from water, as the prevailing standard method of steam reforming extracts hydrogen from fossil hydrocarbons, producing carbon emissions as byproduct. The fundamental theme in reducing carbon emissions is renewable energy production. This thesis studies how computer simulations can be used in designing and improving different solutions tapping into the vast amount of energy available in everyday environment. The paradigm behind this thesis work is that in order to optimize any design, we must first understand how the laws of physics influence the operation of the device to be optimized, while ultimately pursuing the ability to predict the effects of design changes. This thesis covers two separate cases of developing computer models explaining the operation of renewable energy devices. The first case is electricity production from streaming current in nanoscale porous structures, driven by constant evaporation of water. The porous structure presents a multiphase fluid dynamics problem, where the flow of water generating the electricity depends on various material properties and ambient conditions. The work in this thesis demonstrates how a carefully designed multiphysics simulation can not only reproduce experimental results known when building the model, but also produce emergent behaviour that can be experimentally verified. The second case is photoelectrochemical water splitting, converting sunlight to hydrogen with a single, monolithic semiconductor device without the need for electrical grid connections. This case is first simulated using a semi-classical theory based on the Boltzmann transport equation. However, as the design of new materials and electrode geometry increasingly utilizes nanoscale features, the classical approximations behind the Boltzmann equation are no longer accurate. Another method to simulate the semiconductor electrodes is the quantum mechanical formalism of nonequilibrium Green's functions (NEGF), which has been widely utilized in simulating solar cells and transistors. This work demonstrates that NEGF can be applied to modeling photoelectrochemical devices, offering significant improvement.The results cover how computational models can help not only understanding the behaviour of nanoscale solutions for renewable energy, but also provide critical ability to optimize device design to maximize the efficiency.",

keywords = "simulation, energy, electrochemistry, semiconductor, quantum mechanics, simulaatio, energia, s{\"a}hk{\"o}kemia, puolijohde, kvanttimekaniikka, simulation, energy, electrochemistry, semiconductor, quantum mechanics",

author = "Lassi H{\"a}llstr{\"o}m",

year = "2023",

language = "English",

isbn = "978-952-64-1390-7",

series = "Aalto University publication series DOCTORAL THESES",

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N2 - Reducing the CO2 emissions and mitigating climate change is the grand challenge facing humanity in the next couple of decades. Hydrogen has emerged as an economically viable alternative to fossil carbon based fuels in various industries, such as steel production, transportation and even biochemical food production. In order to effectively reduce the carbon emissions the hydrogen must be produced via electrolysis from water, as the prevailing standard method of steam reforming extracts hydrogen from fossil hydrocarbons, producing carbon emissions as byproduct. The fundamental theme in reducing carbon emissions is renewable energy production. This thesis studies how computer simulations can be used in designing and improving different solutions tapping into the vast amount of energy available in everyday environment. The paradigm behind this thesis work is that in order to optimize any design, we must first understand how the laws of physics influence the operation of the device to be optimized, while ultimately pursuing the ability to predict the effects of design changes. This thesis covers two separate cases of developing computer models explaining the operation of renewable energy devices. The first case is electricity production from streaming current in nanoscale porous structures, driven by constant evaporation of water. The porous structure presents a multiphase fluid dynamics problem, where the flow of water generating the electricity depends on various material properties and ambient conditions. The work in this thesis demonstrates how a carefully designed multiphysics simulation can not only reproduce experimental results known when building the model, but also produce emergent behaviour that can be experimentally verified. The second case is photoelectrochemical water splitting, converting sunlight to hydrogen with a single, monolithic semiconductor device without the need for electrical grid connections. This case is first simulated using a semi-classical theory based on the Boltzmann transport equation. However, as the design of new materials and electrode geometry increasingly utilizes nanoscale features, the classical approximations behind the Boltzmann equation are no longer accurate. Another method to simulate the semiconductor electrodes is the quantum mechanical formalism of nonequilibrium Green's functions (NEGF), which has been widely utilized in simulating solar cells and transistors. This work demonstrates that NEGF can be applied to modeling photoelectrochemical devices, offering significant improvement.The results cover how computational models can help not only understanding the behaviour of nanoscale solutions for renewable energy, but also provide critical ability to optimize device design to maximize the efficiency.

AB - Reducing the CO2 emissions and mitigating climate change is the grand challenge facing humanity in the next couple of decades. Hydrogen has emerged as an economically viable alternative to fossil carbon based fuels in various industries, such as steel production, transportation and even biochemical food production. In order to effectively reduce the carbon emissions the hydrogen must be produced via electrolysis from water, as the prevailing standard method of steam reforming extracts hydrogen from fossil hydrocarbons, producing carbon emissions as byproduct. The fundamental theme in reducing carbon emissions is renewable energy production. This thesis studies how computer simulations can be used in designing and improving different solutions tapping into the vast amount of energy available in everyday environment. The paradigm behind this thesis work is that in order to optimize any design, we must first understand how the laws of physics influence the operation of the device to be optimized, while ultimately pursuing the ability to predict the effects of design changes. This thesis covers two separate cases of developing computer models explaining the operation of renewable energy devices. The first case is electricity production from streaming current in nanoscale porous structures, driven by constant evaporation of water. The porous structure presents a multiphase fluid dynamics problem, where the flow of water generating the electricity depends on various material properties and ambient conditions. The work in this thesis demonstrates how a carefully designed multiphysics simulation can not only reproduce experimental results known when building the model, but also produce emergent behaviour that can be experimentally verified. The second case is photoelectrochemical water splitting, converting sunlight to hydrogen with a single, monolithic semiconductor device without the need for electrical grid connections. This case is first simulated using a semi-classical theory based on the Boltzmann transport equation. However, as the design of new materials and electrode geometry increasingly utilizes nanoscale features, the classical approximations behind the Boltzmann equation are no longer accurate. Another method to simulate the semiconductor electrodes is the quantum mechanical formalism of nonequilibrium Green's functions (NEGF), which has been widely utilized in simulating solar cells and transistors. This work demonstrates that NEGF can be applied to modeling photoelectrochemical devices, offering significant improvement.The results cover how computational models can help not only understanding the behaviour of nanoscale solutions for renewable energy, but also provide critical ability to optimize device design to maximize the efficiency.

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KW - energy

KW - electrochemistry

KW - semiconductor

KW - quantum mechanics

KW - simulaatio

KW - energia

KW - sähkökemia

KW - puolijohde

KW - kvanttimekaniikka

KW - simulation

KW - energy

KW - electrochemistry

KW - semiconductor

KW - quantum mechanics

M3 - Doctoral Thesis

SN - 978-952-64-1390-7

T3 - Aalto University publication series DOCTORAL THESES

PB - Aalto University

ER -

Computer simulations for designing green energy solutions

Abstrakti

Tutkimusalat

YK:n kestävän kehityksen tavoitteet

Pääsy asiakirjaan

Sormenjälki

Laitteet

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OtaNano Nanofab

OtaNano Nanomikroskopiakeskus

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