Fundamentals of SO2 depolarized water electrolysis and challenges of materials used

Anu Lokkiluoto

Fundamentals of SO2 depolarized water electrolysis and challenges of materials used

Julkaisun otsikon käännös: SO2-depolarisoitu elektrolyysi vedyn valmistamiseksi

Anu Lokkiluoto

Tutkimustuotos: Doctoral Thesis › Monograph

Abstrakti

SO2-depolarisoitu elektrolyysi (SDE) tuottaa vetyä ja rikkihappoa. Käytettävä rikkidioksidi voi olla peräisin erilaisista teollisuusprosesseista, kuten esimerkiksi sulfidisten mineraalien liekkisulatuksesta tai pasutuksesta, jolloin SDE on osa OutotecR open cycle-prosessia. SO2:n kennojännitettä alentavan eli depolarisoivan vaikutuksen vuoksi vedyn valmistus SDE:n avulla kuluttaa merkittävästi vähemmän sähköenergiaa kuin perinteiset elektrolyysitekniikat kuten alkalielektrolyysi. Tässä työssä tutkittiin SO2-depolarisoituun elektrolyysiin sopivia materiaaleja sekä prosessin teoreettisia perusteita ja mahdollisuuksia. Aiemman aihetta koskevan kirjallisuuden perusteella ei ollut selvää kuinka väkevää rikkihappoa prosessilla olisi mahdollista tuottaa. PEM-polttokennoja koskevan kirjallisuuden perusteella oletettiin että sähköosmoottinen vedenimuilmiö johtaisi rikkihapon väkevöitymiseen merkittävissä määrin. Lisäksi oletettiin että anodina voitaisiin käyttää kultapinnoitettua metallielektrodia. Perinteisesti SDE:ssä on käytetty platinaa katalyyttinä sekä anodilla että katodilla. Kultapinnoitteiden kestävyyttä sekä katalyyttistä aktiivisuutta tutkittiin ensin autoklaavi- ja potentiaalipyyhkäisykokeilla, minkä jälkeen elektrodeja tutkittiin laboratoriomittakaavaisessa elektrolyysilaitteistossa (aktiivinen pinta-ala 0,1 m2). Kultapinnoitteiden käyttäytymistä verrattiin puhtaaseen kultaan ja kaupallisiin platinakatalysoituihin titaanielektrodeihin. Elektrolyyttien sekä membraanin käyttäytymistä tutkittiin mallintamalla sekä kokeellisesti. H2SO4-SO2-H2O-systeemin komponenttien aktiivisuudet laskettiin pitoisuuden funktiona koko konsentraatioalueelle, jolla komponentit liukenevat toisiinsa. Ottaen huomioon Nafion-membraanin ominaisuudet koko elektrolyysiprosessille rakennettiin vesitasemalli. Mallinnustuloksia verrattiin kokeellisiin tuloksiin. Mallinnus- sekä koetulokset vahvistivat, että anolyytistä siirtyy katolyyttiin membraanin läpi merkittäviä määriä vettä, mikä mahdollistaa rikkihapon väkevöinnin SO2-depolarisoidun elektrolyysin avulla. Ohuet kultapinnoitteet katalysoivat SO2:n anodista hapettumista, minkä lisäksi samanlaisia elektrodeja voi käyttää myös katodeina.

Julkaisun otsikon käännös	SO2-depolarisoitu elektrolyysi vedyn valmistamiseksi
Alkuperäiskieli	Englanti
Pätevyys	Tohtorintutkinto
Myöntävä instituutio	Aalto-yliopisto
Valvoja/neuvonantaja	Gasik, Michael, Vastuuprofessori Taskinen, Pekka, Ohjaaja
Kustantaja	Aalto University
Painoksen ISBN	978-952-60-5077-5
Sähköinen ISBN	978-952-60-5078-2
Tila	Julkaistu - 2013
OKM-julkaisutyyppi	G4 Monografiaväitöskirja

Tutkimusalat

SO2-depolarisoitu elektrolyysi
rikkihappo
vety
Nafion-membraani
vesitase
kulta

Pääsy asiakirjaan

http://urn.fi/URN:ISBN:978-952-60-5078-2

Siteeraa tätä

@phdthesis{300756cb52f547d38bce3a7708e8599d,

title = "Fundamentals of SO2 depolarized water electrolysis and challenges of materials used",

abstract = "Sulfur dioxide depolarized water electrolysis (SDE) produces sulfuric acid and hydrogen. Due to its lower cell voltage, the process requires far less electricity than traditional water electrolysis. When SO2 is obtained from flash smelting, sulfides roasting, sulfur combustion, or any other similar operation, SDE is a part of the OutotecR open cycle process. In the present work, materials to be used in SDE were studied together with the fundamentals of the process. Data on the co-production of concentrated acid and hydrogen are scarce in the earlier literature. Theoretical modeling work covering the entire concentration range was deemed necessary in addition to experimental testing to settle this issue. Based on the literature concerning PEM Fuel Cells, it was assumed that the water transport properties of the membrane used as a separator in the electrolysis have a significant effect on the water balance. The activities of the electrolyte components were calculated for the whole concentration range of the ternary H2O-H2SO4-SO2 system relevant for the SDE process using a mathematical model elaborated during the present work. The calculated activities were combined with the model for water transport through a Nafion membrane, and an overall model for SDE was built. The reversible cell potential was calculated for the entire concentration range. The model was used to predict the overall water balance of the electrolysis process with changing electrolyte concentrations. The stability of thin gold coatings and their activity towards electrochemical oxidation of SO2 were studied first in autoclave tests and with linear sweep voltammetry, and the performance of the coatings was compared to that of gold. Next, the performance of the gold-coated electrodes was tested in bench-scale SDE. Even though the oxidation of SO2 has previously been studied on gold, such experiments have seldom been carried out in as high concentrations of sulfuric acid as in this work, and the results obtained with gold coatings are believed to be original. The modeling results were compared with the actual performance of the electrolyzer. Based on the combined results of the experimental and theoretical work, it was possible to explain and predict the remarkable changes in the SDE process that take place with changing electrolyte concentrations. A significant amount of water is transported from the anolyte to the catholyte through the membrane due to the electro-osmotic water drag effect. This phenomenon is beneficial for the production or concentration of sulfuric acid by SO2 depolarized electrolysis. Thin gold coatings on stainless steel surface can be used to catalyze the anodic oxidation of SO2, and similar electrodes can be used as cathodes.",

keywords = "SO2 depolarized electrolysis, sulfuric acid, hydrogen, Nafion membrane, water transport, gold, SO2-depolarisoitu elektrolyysi, rikkihappo, vety, Nafion-membraani, vesitase, kulta, SO2 depolarized electrolysis, sulfuric acid, hydrogen, Nafion membrane, water transport, gold",

author = "Anu Lokkiluoto",

year = "2013",

language = "English",

isbn = "978-952-60-5077-5",

series = "Aalto University publication series DOCTORAL DISSERTATIONS",

publisher = "Aalto University",

number = "49",

address = "Finland",

school = "Aalto University",

}

TY - BOOK

T1 - Fundamentals of SO2 depolarized water electrolysis and challenges of materials used

AU - Lokkiluoto, Anu

PY - 2013

Y1 - 2013

N2 - Sulfur dioxide depolarized water electrolysis (SDE) produces sulfuric acid and hydrogen. Due to its lower cell voltage, the process requires far less electricity than traditional water electrolysis. When SO2 is obtained from flash smelting, sulfides roasting, sulfur combustion, or any other similar operation, SDE is a part of the OutotecR open cycle process. In the present work, materials to be used in SDE were studied together with the fundamentals of the process. Data on the co-production of concentrated acid and hydrogen are scarce in the earlier literature. Theoretical modeling work covering the entire concentration range was deemed necessary in addition to experimental testing to settle this issue. Based on the literature concerning PEM Fuel Cells, it was assumed that the water transport properties of the membrane used as a separator in the electrolysis have a significant effect on the water balance. The activities of the electrolyte components were calculated for the whole concentration range of the ternary H2O-H2SO4-SO2 system relevant for the SDE process using a mathematical model elaborated during the present work. The calculated activities were combined with the model for water transport through a Nafion membrane, and an overall model for SDE was built. The reversible cell potential was calculated for the entire concentration range. The model was used to predict the overall water balance of the electrolysis process with changing electrolyte concentrations. The stability of thin gold coatings and their activity towards electrochemical oxidation of SO2 were studied first in autoclave tests and with linear sweep voltammetry, and the performance of the coatings was compared to that of gold. Next, the performance of the gold-coated electrodes was tested in bench-scale SDE. Even though the oxidation of SO2 has previously been studied on gold, such experiments have seldom been carried out in as high concentrations of sulfuric acid as in this work, and the results obtained with gold coatings are believed to be original. The modeling results were compared with the actual performance of the electrolyzer. Based on the combined results of the experimental and theoretical work, it was possible to explain and predict the remarkable changes in the SDE process that take place with changing electrolyte concentrations. A significant amount of water is transported from the anolyte to the catholyte through the membrane due to the electro-osmotic water drag effect. This phenomenon is beneficial for the production or concentration of sulfuric acid by SO2 depolarized electrolysis. Thin gold coatings on stainless steel surface can be used to catalyze the anodic oxidation of SO2, and similar electrodes can be used as cathodes.

AB - Sulfur dioxide depolarized water electrolysis (SDE) produces sulfuric acid and hydrogen. Due to its lower cell voltage, the process requires far less electricity than traditional water electrolysis. When SO2 is obtained from flash smelting, sulfides roasting, sulfur combustion, or any other similar operation, SDE is a part of the OutotecR open cycle process. In the present work, materials to be used in SDE were studied together with the fundamentals of the process. Data on the co-production of concentrated acid and hydrogen are scarce in the earlier literature. Theoretical modeling work covering the entire concentration range was deemed necessary in addition to experimental testing to settle this issue. Based on the literature concerning PEM Fuel Cells, it was assumed that the water transport properties of the membrane used as a separator in the electrolysis have a significant effect on the water balance. The activities of the electrolyte components were calculated for the whole concentration range of the ternary H2O-H2SO4-SO2 system relevant for the SDE process using a mathematical model elaborated during the present work. The calculated activities were combined with the model for water transport through a Nafion membrane, and an overall model for SDE was built. The reversible cell potential was calculated for the entire concentration range. The model was used to predict the overall water balance of the electrolysis process with changing electrolyte concentrations. The stability of thin gold coatings and their activity towards electrochemical oxidation of SO2 were studied first in autoclave tests and with linear sweep voltammetry, and the performance of the coatings was compared to that of gold. Next, the performance of the gold-coated electrodes was tested in bench-scale SDE. Even though the oxidation of SO2 has previously been studied on gold, such experiments have seldom been carried out in as high concentrations of sulfuric acid as in this work, and the results obtained with gold coatings are believed to be original. The modeling results were compared with the actual performance of the electrolyzer. Based on the combined results of the experimental and theoretical work, it was possible to explain and predict the remarkable changes in the SDE process that take place with changing electrolyte concentrations. A significant amount of water is transported from the anolyte to the catholyte through the membrane due to the electro-osmotic water drag effect. This phenomenon is beneficial for the production or concentration of sulfuric acid by SO2 depolarized electrolysis. Thin gold coatings on stainless steel surface can be used to catalyze the anodic oxidation of SO2, and similar electrodes can be used as cathodes.

KW - SO2 depolarized electrolysis

KW - sulfuric acid

KW - hydrogen

KW - Nafion membrane

KW - water transport

KW - gold

KW - SO2-depolarisoitu elektrolyysi

KW - rikkihappo

KW - vety

KW - Nafion-membraani

KW - vesitase

KW - kulta

KW - SO2 depolarized electrolysis

KW - sulfuric acid

KW - hydrogen

KW - Nafion membrane

KW - water transport

KW - gold

M3 - Doctoral Thesis

SN - 978-952-60-5077-5

T3 - Aalto University publication series DOCTORAL DISSERTATIONS

PB - Aalto University

ER -

Fundamentals of SO2 depolarized water electrolysis and challenges of materials used

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