Research of the Leiden Institute of Chemistry into the development of a sustainable fuel cell has accidentally resulted in an exceptionally efficient catalyst for the production of hydrogen peroxide. The catalyst, discovered by Dennis Hetterscheid and PhD candidate Michiel Langerman, may lead to a more sustainable production of hydrogen peroxide. Publication in Angewandte Chemie.
Langerman is a PhD candidate under the ERC Starting Grant that Hetterscheid received in 2014. With this grant, Hetterscheid is investigating ways to reduce oxygen to water in an electrochemical way. This reaction is essential in a fuel cell that converts sunlight into hydrogen – a sustainable fuel. The current catalysts that can reduce oxygen to water are either not efficient enough or made of rare, expensive metals. Hetterscheid is trying to develop better catalysts in his lab in order to convert water and sunlight into hydrogen on a large scale.
Looking at nature
To create new catalysts, Hetterscheid lets nature inspire him. He examines the laccase enzyme, which is found in many plants, fungi and microorganisms. This enzyme is capable of converting oxygen into water very efficiently, without forming hydrogen peroxide – an unstable oxygen compound that would be fatal for a fuel cell. The core of laccase contains four copper ions that work in a cooperative fashion. Hetterscheid and his group make similar copper complexes, but vary the number of copper ions at the core and the molecules around them.
One of those complexes, Cu-tmpa, has a core with one copper ion. During a control experiment, the two researchers discovered that this complex does not produce water, but hydrogen peroxide at certain voltages. And all that extremely efficiently. ‘This catalyst has a turnover frequency of 1.8 million,’ says Hetterscheid. ‘This means that a molecule of the catalyst can form 1.8 million hydrogen peroxide molecules per second. As far as we know from the literature, this is the most efficient molecular copper catalyst.’
Making hydrogen peroxide cleaner
Apart from the fact that the catalyst is extremely efficient, it is also very practical. Langerman: ‘Hydrogen peroxide is currently not produced in a sustainable way. The method is cumbersome, polluting and relatively expensive’. Hetterscheid therefore sees added value in their new catalyst: ‘Instead of hydrogen peroxide being produced on a large scale, concentrated, shipped, and then diluted again, you could now produce it locally on a small scale.’ However, both researchers argue that follow-up research is needed before it is clear whether this catalyst can be used on a larger scale than in the lab.
Michiel Langerman & Dennis G. H. Hetterscheid (2019) – Fast Oxygen Reduction Catalyzed by a Copper(II) Tris(2‐pyridylmethyl)amine Complex through a Stepwise Mechanism
Hydrogen peroxide is used to disinfect drinking water and inflammations in the oral cavity. In addition, hydrogen peroxide is often found in bleaching agents, for example for bleaching hair, teeth, fabrics and paper. About 60 percent of the world’s hydrogen peroxide production is used for bleaching wood pulp and paper. In 2006, the estimated production of hydrogen peroxide was 2.2 million tonnes.
Text: Bryce Benda