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Solar driven water electrolysis based on silicon solar cells and earth-abundant catalysts

Welter, Katharina (2020):
Solar driven water electrolysis based on silicon solar cells and earth-abundant catalysts.
Darmstadt, Technische Universität,
DOI: 10.25534/tuprints-00011547,
[Ph.D. Thesis]

Abstract

In the present work “proof of concept” upscaling steps were taken for a PV-EC device of 100 cm² substrate size. The active thin film silicon solar cell area was increased to 64 cm², while earth-abundant nickel based catalysts were scaled up by a factor of 100 to electrode areas of 50.3 cm². Implementing the thin film silicon solar cell into the PV-EC device in combination with the earth-abundant catalysts yielded a solar-to-hydrogen efficiency of 5.1 %, which is significantly improved compared to a PV-EC device based on nickel electrodes. It is shown that noble metal catalysts can be replaced by earth-abundant materials without performance losses. The long-term stable operation of the scaled up PV-EC devices is ensured by the use of metal sheet electrodes serving as substrate for the catalyst deposition. Regarding the catalyst stability, an excellent performance over 4 days under day-night-cycling was found for the earth-abundant nickel based system. Furthermore, the characterization of integrated PV-EC devices was expanded to illumination conditions similar to those obtained outdoors. All components used in water splitting devices are usually optimized under standard test conditions in the laboratory, which only represent one set of a wide range of possible outdoor operating conditions. For a combined PV-EC system the generation of hydrogen will only occur for output voltages above a certain value (thermodynamic potential + overpotential losses). This means, any illumination conditions shifting the illuminated current-voltage curve of the coupled system such that the voltage at the operating point is too low, will switch the system off. The influence of the operating temperature has been investigated prior to the present work, but studies concerning other possible illumination conditions were missing and therefore investigated in the present work. Additionally, a first estimation of the annual hydrogen output is given to compare devices based on different multi-junction cells and employing different catalyst systems for spectral data reported in literature.

Item Type: Ph.D. Thesis
Erschienen: 2020
Creators: Welter, Katharina
Title: Solar driven water electrolysis based on silicon solar cells and earth-abundant catalysts
Language: English
Abstract:

In the present work “proof of concept” upscaling steps were taken for a PV-EC device of 100 cm² substrate size. The active thin film silicon solar cell area was increased to 64 cm², while earth-abundant nickel based catalysts were scaled up by a factor of 100 to electrode areas of 50.3 cm². Implementing the thin film silicon solar cell into the PV-EC device in combination with the earth-abundant catalysts yielded a solar-to-hydrogen efficiency of 5.1 %, which is significantly improved compared to a PV-EC device based on nickel electrodes. It is shown that noble metal catalysts can be replaced by earth-abundant materials without performance losses. The long-term stable operation of the scaled up PV-EC devices is ensured by the use of metal sheet electrodes serving as substrate for the catalyst deposition. Regarding the catalyst stability, an excellent performance over 4 days under day-night-cycling was found for the earth-abundant nickel based system. Furthermore, the characterization of integrated PV-EC devices was expanded to illumination conditions similar to those obtained outdoors. All components used in water splitting devices are usually optimized under standard test conditions in the laboratory, which only represent one set of a wide range of possible outdoor operating conditions. For a combined PV-EC system the generation of hydrogen will only occur for output voltages above a certain value (thermodynamic potential + overpotential losses). This means, any illumination conditions shifting the illuminated current-voltage curve of the coupled system such that the voltage at the operating point is too low, will switch the system off. The influence of the operating temperature has been investigated prior to the present work, but studies concerning other possible illumination conditions were missing and therefore investigated in the present work. Additionally, a first estimation of the annual hydrogen output is given to compare devices based on different multi-junction cells and employing different catalyst systems for spectral data reported in literature.

Place of Publication: Darmstadt
Divisions: 11 Department of Materials and Earth Sciences
11 Department of Materials and Earth Sciences > Material Science
Date Deposited: 05 Apr 2020 19:57
DOI: 10.25534/tuprints-00011547
Official URL: https://tuprints.ulb.tu-darmstadt.de/11547
URN: urn:nbn:de:tuda-tuprints-115472
Referees: Jaegermann, Prof. Dr. Wolfram and Rau, Prof. Dr. Uwe
Refereed / Verteidigung / mdl. Prüfung: 23 January 2020
Alternative Abstract:
Alternative abstract Language
In der vorliegenden Arbeit wurden Aufskalierungsschritte als "Proof of Concept" für ein PV-EC Bauteil der Substratgröße von 100 cm² durchgeführt. Die Fläche der aktiven Dünnschichtsilizium-Solarzellen wurde auf 64 cm² erhöht, während nickel-basierte Katalysatoren um den Faktor 100 vergrößert wurden (Elektrodenflächen = 50,3 cm²). Die Implementierung der Dünnschichtsilizium-Solarzelle in das PV-EC Bauteil kombiniert mit nickel-basierten Katalysatoren ergab einen Gesamtwirkungsgrad von Solar zu Wasserstoff von 5,1 %, welcher im Vergleich zu einem auf Nickelelektroden basierenden PV-EC Bauteil deutlich verbessert ist. In der vorliegenden Arbeit wird gezeigt, dass Edelmetallkatalysatoren ohne Leistungsverluste durch erdreichere Materialien ersetzt werden können. Der langzeitstabile Betrieb der aufskalierten PV-EC Elemente wird durch die Verwendung von Metallblechen als Elektroden gewährleistet, die zudem als Substrat für die Katalysatorabscheidung dienen. In Bezug auf die Katalysatorstabilität, welche in einem Tag-Nacht-Zyklus evaluiert wurde, wurde eine hervorragende Leistung über vier Tage für das nickelbasierte Katalysatorsystem gefunden. Darüber hinaus wurde die Charakterisierung integrierter PV-EC Bauteile auf Beleuchtungsbedingungen erweitert, welche ähnlich sind zu den Bedingungen, die im Freien erwartet werden. Alle Komponenten, die in Wasserspaltungsbauteilen verwendet werden, werden normalerweise unter Standardtestbedingungen im Labor optimiert. Diese stellen allerdings nur einen Satz einer Vielzahl möglicher Betriebsbedingungen im Freien dar. Für kombinierte PV-EC Systeme tritt die Wasserstofferzeugung nur für Ausgangsspannungen oberhalb eines bestimmten Werts (thermodynamisches Potential + Überspannungsverluste) auf. Das bedeutet, dass alle Beleuchtungsbedingungen das PV-EC System ausschalten, die die Strom-Spannungs-Kurve des gekoppelten Systems unter Beleuchtung so verschieben, dass die Spannung am Arbeitspunkt zu niedrig ist. Der Einfluss der Betriebstemperatur wurde in einer vorherigen Arbeit untersucht. Studien zu weiteren möglichen Beleuchtungsbedingungen wurden in der vorliegenden Arbeit ergänzt. Zusätzlich wird eine Schätzung der jährlichen Wasserstoffausbeute für in der Literatur beschriebene Spektraldaten angegeben, aufgrund welcher Bauelemente basierend auf verschiedenen Mehrfachzellen und unterschiedlichen Katalysatorsystemen verglichen werden.German
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