Calibrating the Oxidative Capacity of Microdroplets

Area of Science:

• Electrochemistry
• Physical Chemistry
• Chemical Physics

Background:

• Spontaneous redox chemical transformations in microdroplets are a recent discovery.
• The origins and thermodynamic correlations of this novel reactivity remain debated.

Purpose of the Study:

• To investigate the correlation between oxidation potential and ion yield in microdroplet redox reactions.
• To explore the thermodynamic and kinetic factors governing reactivity in microdroplets.

Main Methods:

• Outer-sphere, one-electron oxidation of ferrocene derivatives in acetonitrile microdroplets.
• Generation of microdroplets via nebulization.
• Analysis of ferrocenium ions using mass spectrometry.

Main Results:

• Ion yields decreased monotonically with increasing oxidation potential of ferrocene derivatives.
• Redox processes in microdroplets did not follow Nernstian ratios, indicating deviation from bulk electrochemistry.
• Evidence of finite oxidative capacity or oxidant concentration was observed through competitive oxidation studies.

Conclusions:

• Microdroplet redox reactions, while potentially out-of-equilibrium and kinetically limited, show a correlation between oxidative yield and thermodynamics.
• A possible free energy relationship exists between the kinetics and thermodynamics of redox processes in microdroplets.