New Perspectives in Science Education

Reactions involving proton-coupled electron transfers (PCET) are key processes for the transformation toward a more sustainable industry. These include water electrolysis[1], electrochemical nitrogen fixation[2], and the reduction of carbon dioxide into useful synthetic building blocks[3]. The interdisciplinary collaborative research center (CRC 1633), coordinated by the University of Göttingen, is dedicated to understanding the principles of PCET and its correlation with electronic structure, as well as exploring potential pathways for the rational design of future electrocatalysts. Although this is fundamental research, which can be challenging to communicate briefly, it provides the opportunity to highlight the potential and benefits of electrocatalysis.

In this field, Pourbaix and Pourbaix-type diagrams are frequently used to describe electrochemical systems involving proton and electron transfers without requiring the use of the Nernst equation. Exercises based on these diagrams allow the combination of two major examples of the donor-acceptor principle in school curricula: proton transfer in acid/base reactions and electron transfer in redox chemistry. In this contribution, we present an experiment that correlates the pH-dependent redox behavior of manganese species with an appropriate Pourbaix diagram.

This experiment, including short exercises, was part of an internship for upper secondary level school students at Göttingen University. The station was themed “How to predict a chemical reaction?” to spark student interest and consists of three steps: First, students perform the reduction of Mn(VII) with iodide to Mn(II) at pH 0 and Mn(VI) at pH 14. The distinct colors of the species allow the students to correlate their observations with a Pourbaix diagram, identify the reduced species, and predict the reaction product at pH 7 to be brown manganese dioxide, which was experimentally confirmed afterwards. The contribution concludes with a brief evaluation of how well the students applied their knowledge of pH-dependent redox reactions and adapted Pourbaix diagrams to predict reactions in the Mn/Br system.

References:

[1] Mondal, B. et al. (2023). The Implications of Coupling an Electron Transfer Mediated Oxidation with a Proton Coupled Electron Transfer Reduction in Hybrid Water Electrolysis. ChemSusChem, 16, e202202271

[2] Weinberg, D. R. et al. (2012). Proton-Coupled Electron Transfer. Chem. Rev., 112, 4016−4093

[3] Zhang, S. et al. (2020). CO2 Reduction: From Homogeneous to Heterogeneous Electrocatalysis. Acc. Chem. Res., 53, 255−264