Electrochemistry of hydrazine

Thesis

The electrochemical oxidation of hydrazine is of widespread importance particularly in the area of fuel cells and also provides the basis for chemical sensors for this toxic chemical. In this thesis, electrochemical methods including cyclic voltammetry, chronoamperometry and nano-impacts are employed to develop a comprehensive understanding of the reaction mechanistically and kinetically.

Chapter 1 introduces the basic principles of electrochemistry and electrochemical techniques while the generic chemicals, reagents and instrumentation used in this thesis are summarised in Chapter 2.

Chapter 3 reports the electrochemical characterisation of Palladium nanoparticles decorated graphene oxides nanoplatelets (Pd/GO) via nano-impacts in terms of the hydrogen evolution (HER) and oxidation reactions (HOR). The key conclusion is that only the zone of the individual platelets physically close to the electrode surface is effectively catalytic, and this insight provides the basis of the study of the Pd/GO catalytic ability towards hydrazine oxidation in Chapter 6.

The investigation into hydrazine oxidation starts in Chapter 4 where the focus is placed on the interpretation of the mechanism and kinetics of hydrazine oxidation at generic carbon surfaces, necessarily prior to any catalysis study. It was found that the Marcus-Hush theory is more appropriate for describing the voltammetry of hydrazine oxidation in comparison with the well-recognized Butler-Volmer theory.

In Chapter 5, the mechanism of hydrazine oxidation is probed further at carbon surfaces meanwhile with focus on the variation of the pH and buffer capacity of the electrolytes. It is revealed that the oxidation reaction is self-inhibited as the protons released from the oxidation easily combines with the electro-active N2H4 molecules (local to the working electrode surface) to form inactive N2H5+.

Chapter 6 targets the catalysis of the above-mentioned Pd/GO nanoplatelets towards hydrazine oxidation via studies using both macroelectrodes modified by drop-casting and by single entity electrochemistry using nano-impacts, demonstrating that the first electron transfer of the four electron, four proton oxidation of hydrazine is rate-determining and involves no proton loss in the initial step. The electro-catalysis towards hydrazine oxidation is then extended to bulk Palladium (Chapter 7) and Palladium nanoparticles (Chapter 8). Chapter 7 evidences the existence of a long-lived radical di-cation N2H5•2+ on the voltammetric timescale. Finally in Chapter 8, the markedly reduced over-potential for the oxidation at the surface of Palladium nanoparticles is identified quantitatively to arise from partly the increased surface area of the interface and partly an increased catalytic ability of the nanoparticles relative to the bulk Palladium.

Authors: Miao, R

• DOI: 10.5287/ora-xqdk7poge
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: hydrazine oxidation; Palladium; electrochemistry; catalysis
• Subjects: Heterogeneous catalysis; Nanoparticles; Electrochemical analysis; Hydrazine