A Simple Liquid–Liquid Biphasic System for Hydrogen Peroxide Generation

What is it about?

This is a study investigating the generation of hydrogen peroxide at liquid|liquid interfaces. This is the latest in a series of papers about various reactions at the interface between immiscible liquids. Here we show that the studied system provides conditions for spontaneous transfer of protons from the aqueous to the organic phase, even if no potential determining ions or phase transfer catalysts are used.

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Why is it important?

Reactions at liquid|liquid interfaces are interesting from a fundamental science perspective, as such interfaces exist in many technological and biological systems, but also because such reactions can be useful in industrial processes. One example could be that reactions can take place at the interface, with the reactants in one phase and the product going into the other phase, potentially saving on purification of the end product. In this manuscript the reaction is hydrogen peroxide generation. It’s a deceptively simple reaction, but as usually the difficulties are in the details. With some 2 million tons of H2O2 produced every year, generation of hydrogen peroxide is an important industrial process and ways of lowering the cost of production could be very valuable. Prof Hubert Girault has been investigating H2O2 generation at liquid|liquid interfaces for a long time now, experimenting with different solvents, catalysts, redox probes, etc. In this paper, in collaboration with Prof Girault, we have looked at what is likely the simplest possible biphasic system for H2O2 generation, since it contains only the solvents, the reactants (in this case dissolved oxygen and protons from an acidic solution), and an electron donor (DMFc). DMFc gives off an electron to compensate for the positive charge of the protons to create the neutral H2O2 molecule. Without this donor the system doesn’t work. So, removing any of the components would stop the H2O2 generation, which is why we consider this as the simplest system for this process. However, it’s slow and not very efficient, so from an industry perspective finding a good, cheap and reusable catalyst is still necessary. Here we used a scanning electrochemical microscope tip to detect the generated hydrogen peroxide and measure how much is created. The results from the SECM measurements were compared with some simple computer models to see if we could say something about the reaction process. We also measured the partitioning of H2O2, and found that about 3% of the peroxide escapes into the organic solution.