Periodic Reporting for period 1 - ORION (Operando Interfacial Ionics)
Reporting period: 2023-01-01 to 2025-06-30
Interfacial ion solvation is omnipresent across electro- and biochemistry. For example, for every single electrocatalytic reaction, ions either need to shed their solvation shell before adsorbing onto the catalyst surface or they need to gain a solvation shell when they are generated at the catalyst surface. This complex process occurs inside the electrochemical double layer that can change its molecular arrangement as a function of applied electrochemical bias. As result, so far, our understanding of interfacial solvation kinetics is very limited, despite its relevance in battery ion intercalation, the production of green H2 or the electrodeposition of metals and development of anti-corrosion coatings. In biochemistry, ions often need to transverse ion channels, motors and pumps across membrane interfaces or desolvate inside structurally complex and highly dynamic enzyme environments. Therefore, understanding this activated process in the inner-sphere of the electrochemical double layer is of broad importance for technology and fundamental science.
At the interface between solvent and surface, properties of one phase can influence the other. For example, a metal electrode might possess excess charge that has a heterogenous distribution on the surface and, thus, the entailing electric fields will lead to a heterogenous double layer structure. Understanding the energetic landscape of these valleys and mountains, and how they impact the interfacial solvation kinetics is the main goal of ORION. To that end, we develop local probes that are sensitive to the local solvation kinetics.
At the interface between solvent and surface, properties of one phase can influence the other. For example, a metal electrode might possess excess charge that has a heterogenous distribution on the surface and, thus, the entailing electric fields will lead to a heterogenous double layer structure. Understanding the energetic landscape of these valleys and mountains, and how they impact the interfacial solvation kinetics is the main goal of ORION. To that end, we develop local probes that are sensitive to the local solvation kinetics.
The first phase of the project was mostly dedicated to the challenging technical development of the setup and probes and first preliminary results.
To speed up progress, we further started to study interfacial solvation kinetics on macroscopic substrates. This allowed us to form a fundamental understanding that is needed to identify ideal conditions for the spatially resolved measurements. In fact, our fundamental results have already motivated the development of a new type of probe that is currently in development.
In the first phase, the main achievement has been the work of interfacial solvation kinetics on macroscopic bipolar membrane junctions and on polycrystalline and nanoparticle metal surfaces. Our results across reactions, surfaces an electrolyte conditions show that the interfacial solvation kinetics can be strongly impacted by bias dependent entropic effects inside the electrochemical double layer. More specifically, we observed that catalytic rates can increase due to a bias dependent activation entropy that is overcompensated an increasing activation energy. Our results, that have been published in Nature Energy and Nature Communications, are a major step forward in our understanding, not only of bipolar membranes, but also interfacial solvation in electrocatalysis. This fundamental understanding is critical to develop electrochemical probes that are able to sense and drive interfacial solvation kinetics and other interfacial ionics.
To speed up progress, we further started to study interfacial solvation kinetics on macroscopic substrates. This allowed us to form a fundamental understanding that is needed to identify ideal conditions for the spatially resolved measurements. In fact, our fundamental results have already motivated the development of a new type of probe that is currently in development.
In the first phase, the main achievement has been the work of interfacial solvation kinetics on macroscopic bipolar membrane junctions and on polycrystalline and nanoparticle metal surfaces. Our results across reactions, surfaces an electrolyte conditions show that the interfacial solvation kinetics can be strongly impacted by bias dependent entropic effects inside the electrochemical double layer. More specifically, we observed that catalytic rates can increase due to a bias dependent activation entropy that is overcompensated an increasing activation energy. Our results, that have been published in Nature Energy and Nature Communications, are a major step forward in our understanding, not only of bipolar membranes, but also interfacial solvation in electrocatalysis. This fundamental understanding is critical to develop electrochemical probes that are able to sense and drive interfacial solvation kinetics and other interfacial ionics.
The results that we obtained on interfacial ion solvation are critically important across electrochemistry and, in particular, electrocatalysis. In fact, our results even indicate that certain kinetic fingerprints of the solvation kinetics in the bias dependent activation enthalpy and entropy of electrocatalytic reactions, such as the hydrogen evolution reaction, can directly inform on the amount of excess charge that is present at the surface. In general, excess charge is associated with sluggish kinetics and irreversible reactions. However, so far, it was not clear how this (bias dependent) excess charge impacts the bias dependent activation parameters. Our results show that activation entropy-activation enthalpy compensation effects arise for the interfacial solvation kinetics whenever the bias increases the excess charge at the surface. This effect appears to be broadly relevant across many different electrocatalytic reactions, but has almost completely been neglected in contemporary electrocatalyst research. In fact, popular theoretical and experimental approaches in electrocatalysis treat the reaction with kinetic models that arose from outer-sphere adiabatic electron transfer. For the latter, all activity differences of different catalysts or as function of bias are related to activation energy differences, while the activation entropy in the Arrhenius pre-exponential factor stays constant. Our published and forthcoming results show that this assumption is not valid in general. Therefore, we expect that our results will have a large impact across the fundamental (electro)catalyst research community. Furthermore, they raise the question how these findings can be linked to operando microscopy and spectroscopy to inform on bias dependent changes in the heterogeneous double layer and the surface, which we will address in the next funding period.