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Water splitting catalysis studied by real time Faradaic efficiency obtained by coupled electrolysis and mass spectrometry
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
2017 (English)In: ChemElectroChem, ISSN 2196-0216Article in journal (Refereed) Epub ahead of print
Abstract [en]

An experimental setup and routine is presented for evaluating potential catalysts for water splitting by means of measuring Faradaic efficiency in real time by coupled potentiometry and mass spectrometry. The aim was to simulate a potential industrial scale setup and generate results such as H2 production versus power input at a certain potential or current density in addition to electrochemical parameters. Three types of electrodes were tested: A) planar metal electrodes; B) metal foam based electrodes; C) porous electrodes with carbon additive. The results verify that the experimental routine yield desired accuracy, sensitivity and a negligible accumulation of gaseous products in the cell; thus the Faradaic efficiency is measured in real time. The metal based electrodes of category A and B proved to be durable with low overpotentials and high gas output to power input, whereas three tested metal oxide electrodes in C revealed (i) potential-dependent deviation in Faradaic efficiency, (ii) phase decomposition and (iii) an optimum operational power range.

Place, publisher, year, edition, pages
2017.
National Category
Chemical Sciences
Research subject
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:su:diva-148175DOI: 10.1002/celc.201701086OAI: oai:DiVA.org:su-148175DiVA: diva2:1149964
Available from: 2017-10-17 Created: 2017-10-17 Last updated: 2017-10-18
In thesis
1. Water splitting by heterogeneous catalysis
Open this publication in new window or tab >>Water splitting by heterogeneous catalysis
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A sustainable solution for meeting the energy demands at our planet is by utilizing wind-, solar-, wave-, thermal-, biomass- and hydroelectric power. These renewable and CO2 emission-free energy sources are highly variable in terms of spatial and temporal availability over the Earth, introducing the need for an appropriate method of storing and carrying energy. Hydrogen has gained significant attention as an energy storage- and carrier media because of the high energy density that is exploited within the ‘power-to-gas’ process chain. A robust way of producing sustainable hydrogen is via electrochemical water splitting.

In this work the search for new heterogeneous catalyst materials with the aim of increasing energy efficiency in water splitting has involved methods of both electrochemical water splitting and chemical water oxidation. Some 21 compounds including metal- oxides, oxofluorides, oxochlorides, hydroxide and metals have been evaluated as catalysts. Two of these were synthesized directly onto conductive backbones by hydrothermal methods. Dedicated electrochemical cells were constructed for appropriate analysis of reactions, with one cell simulating an upscale unit accounting for realistic large scale applications; in this cell gaseous products are quantified by use of mass spectrometry. Parameters such as real time faradaic efficiency, production of H2 and O2 in relation to power input or overpotentials, Tafel slopes, exchange current density and electrochemical active surface area as well as turnover numbers and turnover frequencies have been evaluated.

Solubility, possible side reactions, the role of the oxidation state of catalytically active elements and the nature of the outermost active surface layer of the catalyst are discussed. It was concluded that metal oxides are less efficient than metal based catalysts, both in terms of energy efficiency and in terms of electrode preparation methods intended for long time operation. The most efficient material was Ni-Fe hydroxide electrodeposited onto Ni metal foam as conductive backbone. Among the other catalysts, Co3Sb4O6F6 was of particular interest because the compound incorporate a metalloid (Sb) and redox inert F and yet show pronounced catalytic performance.

In addition, performance of materials in water splitting catalysis has been discussed on the basis of results from electron microscopy, solubility experiments and X-ray diffraction data.

Place, publisher, year, edition, pages
Stockholm: Department of Materials and Environmental Chemistry, Stockholm University, 2017. 93 p.
Keyword
Faradaic efficiency, electrocatalysis, electrolysis, water oxidation, hydrogen reduction, H2, O2, mass spectrometry
National Category
Inorganic Chemistry
Research subject
Inorganic Chemistry
Identifiers
urn:nbn:se:su:diva-148181 (URN)978-91-7797-039-2 (ISBN)978-91-7797-040-8 (ISBN)
Public defence
2017-12-06, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2017-11-13 Created: 2017-10-17 Last updated: 2017-11-03Bibliographically approved

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Svengren, HenrikChamoun, MyladGrins, JekabsJohnsson, Mats
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