DARWIN Digitale Dissertationen German Version Strich

FU Berlin
Digitale Dissertation

Peter Friebe :
Adsorption and reduction of carbon dioxide on transition metals
Adsorption und Reduktion von Kohlendioxid an Übergangsmetallen

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Abstract

The electrochemical adsorption and reduction of carbon dioxide on platinum, rhenium and copper was examined.

Special emphasis was laid on the reversibility of the adsorption and on the reduction catalysis.

The applied techniques DEMS (Differential Electrochemical Mass Spectroscopy), EQMB (Electrochemical Quartz Microbalance), FTIR spectroscopy and cyclovoltammetry showed in general agreement a potential-dependent distinction of the CO2/metal interaction into physisorption and chemisorption.

Using double potential steps on DEMS, a reversibility coefficient was introduced showing a very high reversibility of the CO2 adsorption on rhenium, which was remarkably lower on platinum. The CO2 adsorption on copper w as almost irreversible.

In comparative measurements active carbon proved to be an interesting substrate for a highly reversible electrochemical adsorption of carbon dioxide.

FTIR spectroscopy revealed absorption peaks at 1350 1400 cm-1 on all investigated metals during cathodic polarization. These bonds were assigned to CO2 which adsorbs on the metal losing its linear configuration.

EQMB measurements produced a maximum CO2 coverage of 6.8 (platinum), 5.4 (rhenium) and 7.0 (copper) nmol/cm2. With respect to the space required for each molecule, these values were converted to 8.5, 6.8 and 7.0 monolayers of carbon dioxide. Using this technique, the flown charge on copper could be compared with the amount of adsorbed CO2. This comparison gave an approximate maximum value of one transferred electron per CO2 molecule.

In order to achieve a more reliable quantification, a new method, the Electrochemical Pressure-Monitoring Cell (EDMZ) was developed, constructed and tested. With this technique , CO2-coverage/potential diagrams of platinum, rhenium and copper could be recorded and compared which each other. They showed a maximum CO2 coverage of 8.0, 8.8 and 11 monolayers, respectively.

In addition, EDMZ proved that pressure gradien ts can be generated and controlled by the ad- and desorption of CO2.

With a simultaneous electrochemical deposition of copper and carbon dioxide, the reduction catalysis of CO2 to ethene could be improved drastically. The onset potent ial for the ethene production was shifted in anodic direction by 500 mV. This selective potential shift from 1.6 to 1.1 V NHE corresponds to an improvement of almost 40 % with respect to the thermodynamic redox potential.

EDX investigations showed that the in situ-deposited CO2 is partially reduced to carbon and is dispersed inhomogeniously on the electrode. Apparently, carbon domains in the copper matrix are responsible for an improved CO2 reduction catalysis.

Table of Contents

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0 Titelblatt und Inhaltsverzeichnis

1 Einführung

2 Zielsetzung

2.1 Reaktionsweg

2.2 Adsorption

2.3 Quantifizierung der CO2-Adsorption

3 Planung der Arbeit

3.1 Auswahl der Metalle

3.2 Auswahl der Techniken

4 Grundlagen

4.1 Chemie des CO2

4.2 Elektrochemische Grundlagen

4.3 Eingesetzte Techniken

5 Experimentelles

5.1 Techniken und deren Grundlagen

5.2 Elektrochemie

6 Resultate und Diskussion

6.1 I/U-Kennlinien

6.2 Differentielle elektrochemische Massenspektroskopie (DEMS)

6.3 Die Elektrochemische Quarz-Mikrowaage (EQMB)

6.4 FTIR-Spektroskopie

6.5 Die elektrochemische Druckmeßzelle (EDMZ)

6.6 Vergleich der Ergebnisse der angewendeten Techniken

6.7 Beeinflussung des Onset-Potentials der CO2-Reduktionsprodukte

7 Zusammenfassung

8 Aussichten

9 Literaturverzeichnis

More Information:

Online available: http://www.diss.fu-berlin.de/1999/20/indexe.html
Language of PhDThesis: german
Keywords: adsorption, carbon dioxide, copper, rhenium, platinum
DNB-Sachgruppe: 30 Chemie
Date of disputation: 10-Dec-1998
PhDThesis from: Fachbereich Biologie, Chemie, Pharmazie, Freie Universität Berlin
First Referee: Prof. Dr. Helmut Tributsch
Second Referee: Prof. Dr. Jürgen K. Dohrmann
Contact (Author): friebe@hmi.de
Contact (Advisor): tributsch@hmi.de
Date created:25-Mar-1999
Date available:31-Mar-1999

 

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