Posted by Optimizing electrochemical reactions is essential for the transition to renewable energies. In electrochemical reactions, electric currents and potential differences are used to binding and induce reactions. Electrochemistry is a pre-requisite for hydrogen production, and for batterie technology, and thus for sustainable chemistry. Although there has been a lot of technological development in this area in recent years, there is still room for improvement and a long way towards large scale industrial applications. Scientists from the Cluster of Excellence RESOLV at the Ruhr University Bochum and École normale supérieure in Paris discovered two new aspects to control and thus optimize electrochemical reactions at electrified interfaces. They describe their results in the Journal of the American Chemical Society published online on April, 10, 2024.
Surface sensitive spectroscopy
In order to understand the complex behavior at electrified interfaces, the team examined a critical parameter, called the acid dissociation constant (pKa) of molecules at electrified metal/water interfaces. Whereas in bulk solutions, this value is well known, it has been speculated that this parameter, which is essential for acid/base chemistry can be quite different in the vicinity of electrodes. However, measuring pKa values under electrochemical conditions is experimentally challenging. To address this, the group of Havenith have combined advanced surface specific spectroscopic techniques, notably Surface-Enhanced Raman Spectroscopy (SERS), with theoretical modelling. The results vary with the applied voltage: Acid-base chemistry at electrified interfaces, is clearly different from chemistry in the bulk solution.
Hydrophobic layer and strong electric fields
Their findings highlight two key mechanisms governing acid-base reactions at electrified interfaces: The influence of local hydrophobicity and the impact of strong local electric fields. By analyzing the protonation/deprotonation of glycine molecules, the researchers observed a hydrophobic water/water interface close to the metal surface, leading to a destabilization of zwitterionic forms of glycine. When increasing the applied potential the effect is amplified.
Their results showcase the changes of local solvation properties at metal/water interfaces, presenting new avenues for fine-tuning reactivity in electrochemistry. These insights offer new opportunities for optimizing electrochemical processes and designing novel strategies for catalysis as both factors can be tuned in a controlled way.