Energy storage and isotope determinations -- an interdisciplinary success story

Go to the profile of Julien Bachmann
Nov 02, 2018

Interdisciplinary work can be frustrating – scientists in related, yet distinct, fields often have distinct educational backgrounds and may consider different aspects of a given research problem as important. Moreover, they often use different languages, which impedes efficient communication. Despite these caveats, I have long enjoyed the exchange of ideas and methods with specialists of sciences related to chemistry and worked with physicists, biologists, materials scientists, and engineers. Discovering novel and unexpected opportunities offered by the combination of various methods is a satisfaction reserved to someone willing to work in interdisciplinary collaborations.

In a conversation with Johannes from the department of Earth Sciences about how isotope compositions serve as environmental tracers, we realized how powerful mass spectrometric methods could become in chemistry. Indeed, isotopes can reveal the mechanisms of important catalytic reactions such as the evolution of O2 or H2 from water. This is rooted in the fact that nuclei of distinct masses can react at specific rates depending on how their bonds are rearranged. Thus, non-identical reaction rates of two isotopes can highlight crucial reaction steps. However, so far the typical procedure has been to determine reaction rates starting with a substrate (water, for example) of different isotopic compositions. This involves isotopically enriched substrates, which are costly, if at all available. A further limitation is that such kinetic isotope effects have mostly been determined for the isotopes of hydrogen 2H and 1H, because their mass ratio and the corresponding isotope effects are large. The level of sensitivity and accuracy reached routinely in the Earth Sciences laboratories, however, allowed us to circumvent both limitations and helped to determine oxygen isotope effects for water oxidation from natural abundance isotope variations in the dissolved oxygen pool directly.

To test this, a group of very talented graduate students from both the chemistry and geosciences laboratories joined forces. Sandra and Stefanie provided our nanostructured iron oxide and iridium electrode samples and performed water electrolyses on these very different surfaces, in contrasting pH conditions and at various applied potentials. Michael and André measured isotope effects that depended on the electrical potential in a systematic manner and that vanished at large overpotentials. The data demonstrated the new approach, but their interpretation left us scratching our heads, since very little has been done with oxygen isotope effects so far. A geologist and a solid-state chemist needed help from a mechanistically inclined molecular chemist with a strong background in kinetic isotope effects. We therefore contacted Alfredo, who agreed to visit us for a couple of weeks, during which we discussed the data and their interpretation. These were fruitful and pleasing discussions, as the photograph documents, and they resulted in our Nature Communications paper!

More importantly, this work simplifies mechanistic investigations significantly, among others for important reactions involved in energy conversion and storage. The method is now available to the community – it has been rendered available by an interdisciplinary collaboration between scientists from three areas of research open to other disciplines.

Go to the profile of Julien Bachmann

Julien Bachmann

Professor, University of Erlangen

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