Single entity electrochemistry and the electron transfer kinetics of hydrazine oxidation

Ruiyang Miao,Richard G Compton,Lidong Shao

doi:10.1007/s12274-021-3353-8

Ruiyang Miao, Richard G Compton + Show 1 more

Open Access

https://doi.org/10.1007/s12274-021-3353-8

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Abstract

The mechanism and kinetics of the electro-catalytic oxidation of hydrazine by graphene oxide platelets randomly decorated with palladium nanoparticles are deduced using single particle impact electrochemical measurements in buffered aqueous solutions across the pH range 2–11. Both hydrazine, N2H4, and protonated hydrazine N2H5+ are shown to be electroactive following Butler-Volmer kinetics, of which the relative contribution is strongly pH-dependent. The negligible interconversion between N2H4 and N2H5+ due to the sufficiently short timescale of the impact voltammetry, allows the analysis of the two electron transfer rates from impact signals thus reflecting the composition of the bulk solution at the pH in question. In this way the rate determining step in the oxidation of each specie is deduced to be a one electron step in which no protons are released and so likely corresponds to the initial formation of a very short-lived radical cation either in solution or adsorbed on the platelet. Overall the work establishes a generic method for the elucidation of the rate determining electron transfer in a multistep process free from any complexity imposed by preceding or following chemical reactions which occur on the timescale of conventional voltammetry.

Highlights

This paper seeks to develop and illustrate a generic methodology for the study of complex multi-electron electrode processes mediated via nano-particulate materials and to illustrate this with reference to the electro-catalytic oxidation of hydrazine
A carbon fibre microwire electrode [29] of 7 μm in diameter and 1 mm in length functioned as the working electrode whilst the reference and counter electrodes were as mentioned above. 5 mL of the appropriate buffer solution containing 1.5 mM hydrazine was degassed with N2 for 15 min to remove the dissolved oxygen, followed by the addition of the suspension to form a final solution with 1.1 × 10−14 M Pd/graphene oxide (GO) while N2 kept bubbling for 10 s to make it well-dispersed
The catalytic ability of the sample Pd nanoparticles decorated graphene oxide (Pd/GO) was first discussed by comparing the electrochemical responses of CV from between the bare glassy carbon (GC) electrode and the Pd/GO modified via dropcast

Summary

Introduction

This paper seeks to develop and illustrate a generic methodology for the study of complex multi-electron electrode processes mediated via nano-particulate materials and to illustrate this with reference to the electro-catalytic oxidation of hydrazine. N2H4(l) + O2(g) = 2H2O(l) + N2(g) has ΔG° = −623 kJ/mol with ΔH° = −622 kJ/mol and ΔS° = 3.3 J/(mol·K) [5] These favourable energetics give the basis for fuel cells in which hydrazine is oxidised to nitrogen at the anode whilst the cathodic reaction involves the reduction of oxygen from air to water. The impacting particles can make transient electrical contact with the electrode for the duration of the impact which can last from a few milliseconds to tens or even hundreds of seconds in the case of carbon nanotubes [27] In this situation for the time of the impact, the collided particle acts as a tiny electrode of a size corresponding to that of the particle itself and, if the solution contains species such as N2H4 in the present case to which the particle is electro-catalytic currents can flow if suitable potentials are applied to the immersed electrode. In this way a generic methodology is established and illustrated for deducing the rate determining electron transfer step in a complex multi-electron process with coupled chemical reactions mediated via nanomaterials

Chemicals

Cyclic voltammetry of hydrazine oxidation at a

Results and discussion

Demonstration of the electro-catalytic ability of

Conclusions