Investigations of electron-coupled-proton-buffers: from fundamentals to application

Rausch, Benjamin (2014) Investigations of electron-coupled-proton-buffers: from fundamentals to application. PhD thesis, University of Glasgow.

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The work detailed in this thesis is presented and discussed in six chapters, which constitute a general and progressive study into both inorganic and organic electron-coupled-proton buffers (ECPBs). ECPBs allow the decoupling of the oxygen evolving reaction and the hydrogen evolving reaction during electrolytic water splitting into two separated steps.

A range of commercial and literature based inorganic polyoxometallates (POMs) were investigated to determine their redox potentials and solubility in aqueous media. Of these, the Keggin-structured POM silicotungstic acid (H4[SiW12O40], STA) was investigated in detail. The cyclic voltammogram (CV) of STA shows two reversible 1-electron redox waves on carbon electrodes at E1/2 = +0.01 V vs. NHE and E1/2 = –0.22 V vs. NHE, where the latter is cathodic of the reduction potential of hydrogen on platinum electrodes (E1/2 = ±0.00 V vs. NHE). Electrochemical studies, in combination with gas chromatography show that H4[SiW12O40] can be reduced by two electrons to form H6[SiW12O40] on carbon electrodes, while effectively suppressing hydrogen evolution during electrolysis.

The reduced H6[SiW12O40] species can then be utilised for rapid and spontaneous hydrogen evolution, either on demand or via a continuous flow setup, if in contact with suitable catalysts. Platinum was found to be the best catalyst for spontaneous hydrogen evolution and was tested at a range of loadings, supported on carbon and ultimately indicated that an STA-based electrolytic system can utilise platinum up to 30 times more efficiently than a conventional proton-exchange-membrane electrolyser (PEME). A modified PEME was built for H4[SiW12O40] reduction and various methods for catalyst immobilisation were tested.

In an attempt to mimic photosynthetic water splitting, a range of quinone derivatives were also investigated as organic, low molecular weight ECPBs. 1,4-hydroquinone-sulfonic acid was found to efficiently decouple hydrogen and oxygen evolution, with a redox potential of E1/2 = 0.65 V vs. NHE and showed an 80% – 90% energy efficiency compared to conventional electrolysis, whilst using 50% less catalytic platinum in the 2-step electrolysis.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Subjects: Q Science > QD Chemistry
Colleges/Schools: College of Science and Engineering > School of Chemistry
Supervisor's Name: Cronin, Prof. Leroy
Date of Award: 2014
Embargo Date: 22 February 2019
Depositing User: Benjamin Rausch
Unique ID: glathesis:2014-5654
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 22 Oct 2014 08:57
Last Modified: 03 Jan 2019 15:26

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