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Selectivity and gas composition in electrochemical systems by mass spectrometry
KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemiteknik, Tillämpad elektrokemi.ORCID-id: 0000-0003-2344-327x
2024 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

This doctoral thesis presents experimental studies of gaseous products of two electrochemical systems: the chlorate process and the nickel-metal hydride (NiMH) battery, employing mass spectrometry.

The cathodic efficiency for the hydrogen evolution reaction (HER) of the chlorate process was investigated by employing ex-situ synthesized MnOx electrodes. Without the addition of toxic chromium (VI), used today in industry, high cathodic efficiency was achieved. The effect of different annealing temperatures in the electrode preparation on HER efficiency was examined. The addition of 1000 times lower concentrations of chromium (VI) than used in the industry today, together with in-situ added molybdate,showed promising results in keeping high cathodic efficiency and selectivity towards HER. The evolution of oxygen decreases anodic efficiency and also presents a safety risk due to simultaneously proceeding of HER in the undivided cell. The amount of produced oxygen by two types of electrodes TiRu and TiRuSnSb, was followed. Oxygen is produced by homogenous hypochlorite decomposition, heterogeneously by different electrode surface present in the electrolyte solution and anodically during the electrolysis i.e. electrochemically.

Investigating gas composition in batteries presents a challenge due to the complexity of reactions leading to the gas evolution.Additionally, the gas consumption has a significant impact on the amount and constituents of the collected gases. The methodology for investigating gas composition of the NiMH battery without influencing the battery performance was established. Two technologies, sampler and microcapillary, gave reasonable and complementing results.

Abstract [sv]

Denna doktorsavhandling presenterar experimentella studier av gasformiga produkter från två olika elektrokemiska system: kloratprocessen och Nickel Metallhydrid batteriet (NiMH), med användning av masspektrometri.

Den katodiska effektiviteten för vätgasutvecklingsreaktionen (HER) i kloratprocessen undersöktes genom att använda ex-situ syntetiserade MnOx-elektroder. Utan tillsats av giftig krom (VI), som används idag inom industrin, uppnåddes hög katodisk effektivitet. Effekten av olika ugnstemperaturer vid syntesen av elektrodbeläggningen på HER-effektiviteten undersöktes. Tillsatsen av krom (VI) i koncentrationer som är 1000 gånger lägre än de som används inom industrin idag, tillsammans med in-situ tillsattsmolybdat, visade lovande resultat för att bibehålla hög katodisk effektivitet och selektivitet gentemot HER. Bildningen av syrgas minskar den anodiska effektiviteten samt utgör en säkerhetsrisk på grund av samtidig förekomst av HER i den odelade cellen. Mängden producerat syre från två typer av elektroder, TiRu och TiRuSnSb,följdes. Syrgas produceras genom homogen hypokloritnedbrytning,heterogent på olika katalytiska ytor i kontakt med elektrolytlösningen och anodiskt under elektrolys, det vill säga elektrokemiskt.

Att undersöka gas-sammansättningen i batterier är en utmaning på grund av komplexiteten hos de reaktioner som leder till gas-utvecklingen.Dessutom har gasförbrukningen en betydande inverkan på mängden och sammansättningen av de insamlade gaserna. En metod för att undersöka gas-sammansättningen hos NiMH-batteriet, utan att påverka batteriprestanda, utvecklades. Två teknologier, provtagare och mikrokapillär, gav rimliga och kompletterande resultat.

Abstract [sr]

У оквиру ове докторске тезе представљене су експерименталне студије гасовитих продуката два електрохемијска система: електролизе хлората и никл метал хидридне (NiMH) батерије,користећи масену спектрометрију.

Висока ефикасност катодне реакције, издвајања водоника, у електролизи хлората се данас постиже додавањем токсичног хрома (VI) процесу. Овде је испитана катодна ефикасност за реакцију издвајања водоника у електролизи хлората користећи екс-ситу синтетисане MnOx електроде и без додатка токсичног хрома (VI), који се данас користи у индустрији,постигнута је висока ефикасност. Испитан је ефекат различитих температура жарења у току припреме електрода на ефикасност реакције издвајања водоника. Такође је испитана могућност додатка 1000 пута мање концентрације хрома у поређењу с данашњим стандардом у индустрији, заједно с ин-ситу додатком молибдата и забележени су обећавајући резултати у одржавању високе ефикасности и селективности на реакцију издвајања водоника. Eволуција кисеоника снижава анодну ефикасност процеса и представља безбедоносни ризик услед истовремене еволуције водоника у електролитичкој ћелији. У овој тези је такође истражена и количина произведеног кисеоника користећи два типа електрода TiRu и TiRuSnSb. Први састав одговара стандардном саставу димензионо стабилних анода (ДСА), а други састав је њихова допингована варјанта. Закључено је да се кисениок производи хомогенo -разлагањем хипохлорита, хетерогено - помоћу различитих електродних површина присутних у електролиту и анодно - током електролизе, односно електрохемијски.

Услед сложености реакција које доводе до еволуције гасова,истражити састав гаса у батеријама представља изазов. Такође, потрошња гаса утиче на количину и састав узоркованих гасова. Развијена је методологија за испитивање састава гаса NiMH батерије,без утицаја на перформансе батерије. Две различите технологије,узоркивач и микрокапилара су дале разумне и комплементарнерезултате.

Ort, förlag, år, upplaga, sidor
Stockholm: KTH Royal Institute of Technology, 2024. , s. 69
Serie
TRITA-CBH-FOU ; 2024:11
Nyckelord [en]
electrolysis, chlorate, selectivity, chromate, DSA, HER, OER, hypochlorite, ClER, catalysis, gases, NiMH battery
Nyckelord [sr]
електролиза, хлорат, селективност, хромат, ДСА, реакција издвајања водоника, еволуција кисеоника, хипохлорат, еволуција хлора, катализа, гасови, NiMH батерије
Nyckelord [sv]
elektrolys, klorat, selektivitet, kromat, DSA, vätgasutvecklingsreaktion, syrgasutvecklingsreaktion, hypoklorit, klorgasutvecklingsreaktion, katalys, gaser, NiMH batteri
Nationell ämneskategori
Annan kemiteknik
Forskningsämne
Kemiteknik
Identifikatorer
URN: urn:nbn:se:kth:diva-345628ISBN: 978-91-8040-893-6 (tryckt)OAI: oai:DiVA.org:kth-345628DiVA, id: diva2:1852214
Disputation
2024-05-24, E3, Osquars backe 2, floor 2. Via Zoom: https://kth-se.zoom.us/webinar/register/WN_TYnpeqQpQFCcA2UYIo-LyA, Stockholm, 13:00 (Engelska)
Opponent
Handledare
Anmärkning

QC 20240418

Tillgänglig från: 2024-04-18 Skapad: 2024-04-17 Senast uppdaterad: 2024-04-24Bibliografiskt granskad
Delarbeten
1. Selective Hydrogen Evolution on Manganese Oxide Coated Electrodes: New Cathodes for Sodium Chlorate Production
Öppna denna publikation i ny flik eller fönster >>Selective Hydrogen Evolution on Manganese Oxide Coated Electrodes: New Cathodes for Sodium Chlorate Production
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2019 (Engelska)Ingår i: ACS Sustainable Chemistry and Engineering, E-ISSN 2168-0485, Vol. 7, nr 14, s. 12170-12178Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The safety and feasibility of industrial electrochemical production of sodium chlorate, an important chemical in the pulp and paper industry, depend on the selectivity of the electrode processes. The cathodic reduction of anodic products is sufficiently suppressed in the current technology by the addition of chromium(VI) to the electrolyte, but due to the high toxicity of these compounds, alternative pathways are required to maintain high process efficiency. In this paper, we evaluate the electrochemical hydrogen evolution reaction kinetics and selectivity on thermally formed manganese oxide-coated titanium electrodes in hypochlorite and chlorate solutions. The morphology and phase composition of manganese oxide layers were varied via alteration of the annealing temperature during synthesis, as confirmed by scanning electron microscopy, X-ray diffraction, synchrotron radiation X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure spectroscopy measurements. As shown in mass spectroscopy coupled electrochemical measurements, the hydrogen evolution selectivity in hypochlorite and chlorate solutions is dictated by the phase composition of the coating. Importantly, a hydrogen evolution efficiency of above 95% was achieved with electrodes of optimized composition (annealing temperature, thickness) in hypochlorite solutions. Further, these electrode coatings are nontoxic and Earth-abundant, offering the possibility of a more sustainable chlorate production.

Ort, förlag, år, upplaga, sidor
American Chemical Society (ACS), 2019
Nyckelord
Cathode selectivity, HER, Industrial electrochemistry, Chemical technology, Dichromate
Nationell ämneskategori
Energiteknik
Identifikatorer
urn:nbn:se:kth:diva-255559 (URN)10.1021/acssuschemeng.9b01279 (DOI)000475838100027 ()2-s2.0-85073662618 (Scopus ID)
Anmärkning

QC 20190805

Tillgänglig från: 2019-08-05 Skapad: 2019-08-05 Senast uppdaterad: 2024-04-17Bibliografiskt granskad
2. Catalytic effects of molybdate and chromate–molybdate films deposited on platinum for efficient hydrogen evolution
Öppna denna publikation i ny flik eller fönster >>Catalytic effects of molybdate and chromate–molybdate films deposited on platinum for efficient hydrogen evolution
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2023 (Engelska)Ingår i: Journal of chemical technology and biotechnology (1986), ISSN 0268-2575, E-ISSN 1097-4660, Vol. 98, nr 5, s. 1269-1278Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

BACKGROUND: Sodium chlorate (NaClO3) is extensively used in the paper industry, but its production uses strictly regulated highly toxic Na2Cr2O7 to reach high hydrogen evolution reaction (HER) Faradaic efficiencies. It is therefore important to find alternatives either to replace Na2Cr2O7 or reduce its concentration.

RESULTS: The Na2Cr2O7 concentration can be significantly reduced by using Na2MoO4 as an electrolyte co-additive. Na2MoO4 in the millimolar range shifts the platinum cathode potential to less negative values due to an activating effect of cathodically deposited Mo species. It also acts as a stabilizer of the electrodeposited chromium hydroxide but has a minor effect on the HER Faradaic efficiency. X-ray photoelectron spectroscopy (XPS) results show cathodic deposition of molybdenum of different oxidation states, depending on deposition conditions. Once Na2Cr2O7 was present, molybdenum was not detected by XPS, as it is likely that only trace levels were deposited. Using electrochemical measurements and mass spectrometry we quantitatively monitored H2 and O2 production rates. The results indicate that 3 μmol L−1 Na2Cr2O7 (contrary to current industrial 10–30 mmol L−1) is sufficient to enhance the HER Faradaic efficiency on platinum by 15%, and by co-adding 10 mmol L−1 Na2MoO4 the cathode is activated while avoiding detrimental O2 generation from chemical and electrochemical reactions. Higher concentrations of Na2MoO4 led to increased oxygen production.

CONCLUSION: Careful tuning of the molybdate concentration can enhance performance of the chlorate process using chromate in the micromolar range. These insights could be also exploited in the efficient hydrogen generation by photocatalytic water splitting and in the remediation of industrial wastewater. 

Ort, förlag, år, upplaga, sidor
Wiley, 2023
Nyckelord
chlorate process, chromate, hydrogen evolution reaction, molybdenum
Nationell ämneskategori
Kemiteknik
Identifikatorer
urn:nbn:se:kth:diva-331087 (URN)10.1002/jctb.7345 (DOI)000947824200001 ()2-s2.0-85150630457 (Scopus ID)
Anmärkning

QC 20230705

Tillgänglig från: 2023-07-05 Skapad: 2023-07-05 Senast uppdaterad: 2024-04-17Bibliografiskt granskad
3. Sources of Oxygen Produced in the Chlorate Process Utilizing Dimensionally Stable Anode (DSA) Electrodes Doped by Sn and Sb
Öppna denna publikation i ny flik eller fönster >>Sources of Oxygen Produced in the Chlorate Process Utilizing Dimensionally Stable Anode (DSA) Electrodes Doped by Sn and Sb
2021 (Engelska)Ingår i: Industrial & Engineering Chemistry Research, ISSN 0888-5885, E-ISSN 1520-5045, Vol. 60, nr 37, s. 13505-13514Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Identifying the sources of oxygen in the chlorate process is challenging due to the complex set of chemical and electrochemical reactions involved. Here, two types of electrodes have been investigated-Ti0.7Ru0.3Ox, and electrodes with aimed composition Ti0.34Ru0.3Sn0.3Sb0.06Ox, both compared with platinum anodes. The cell oxygen off-gas was analyzed employing mass spectrometry together with ex situ UV-vis spectroscopy to quantify the kinetic rate constants. Noteworthy is that the respective rates of oxygen formation from anodic and chemical reactions in the presence of hypochlorite are of the same magnitude. The addition of Sn and Sb doubled the surface area of the electrodes and decreased oxygen production when electrodes were used for the first time. However, rate constants for total oxygen production with reused electrodes follow the trend: homogeneous hypochlorite decomposition < TiRu < TiRuSnSb to the highest value obtained by Pt. The same trend is noticed for rate constants concerning the hypochlorite decomposition.

Ort, förlag, år, upplaga, sidor
American Chemical Society (ACS), 2021
Nationell ämneskategori
Annan kemiteknik Oorganisk kemi
Identifikatorer
urn:nbn:se:kth:diva-303185 (URN)10.1021/acs.iecr.1c02004 (DOI)000700883000008 ()2-s2.0-85115656808 (Scopus ID)
Anmärkning

QC 20211011

Tillgänglig från: 2021-10-11 Skapad: 2021-10-11 Senast uppdaterad: 2024-04-17Bibliografiskt granskad
4. Gas phase composition of a NiMH battery during a work cycle
Öppna denna publikation i ny flik eller fönster >>Gas phase composition of a NiMH battery during a work cycle
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(Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
Abstract [en]

NiMH batteries are popular in the electromotive industry due to good rate capability, reliability, and environmental friendliness. Although the battery type is thoroughly investigated, studies of battery gas composition formed during a work cycle are few. The gas composition would be useful to understand the reactions occurring in the battery during cycling and could be used to optimize battery operation. 

In this study, two methods for investigating the internal NiMH battery gas phase composition during different charge/discharge cycles using mass spectrometer (MS) were developed. In the first method, the battery module was connected by a sampler system. In the second method, the battery was connected directly using a microcapillary, and the gas composition was continuously measured. In addition to the gas composition the voltage, pressure, and temperature of the battery were recorded. 

The biggest contributor in the measured gas phase was N2, followed by H2. A clear rising trend of H2 pressure as SOC increased was recorded, while O2 levels were low except around end of charge. Thus, the methods were found to be a reliable way of investigating NiMH gas composition without negatively affecting the battery.

Nyckelord
NiMH batteries, gas phase composition, mass spectrometry
Nationell ämneskategori
Annan kemiteknik
Forskningsämne
Kemiteknik
Identifikatorer
urn:nbn:se:kth:diva-338252 (URN)
Forskningsfinansiär
Stiftelsen för strategisk forskning (SSF), ID16-0111Energimyndigheten, 42791-1
Anmärkning

QC 20231030

Tillgänglig från: 2023-10-18 Skapad: 2023-10-18 Senast uppdaterad: 2024-04-17Bibliografiskt granskad

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