Interfacial Ionics

And their manifestation in the overpotential and pressure-dependent Arrhenius activation parameters of single- and multi-step reactions.

In our laboratory, we study interfacial ionic processes at technologically-relevant, operational bipolar membrane and (electro)catalyst interfaces and during electrodeposition. We want to understand how molecules are dissociated and formed and ions are (de)solvated. How can we separate such processes from other overpotential-dependent processes at the interface, such as overpotential-dependent intermediate coverages, structural and chemical rearrangements and mass-transport? How can we temporally resolve the apparent activation parameters?

To address these questions, our team employs extensive temperature- and pressure-dependent electrochemistry and (electro)catalyst characterization across different experimental platforms, while also employing microkinetic modelling to better understand overpotential-dependent rate-limiting steps in multi-step sequences. Additionally, we are developing new electrochemical methods to track the overpotential-dependent kinetics in time and space at a plethora of heterogeneous interfaces.

Discoveries about the Arrhenius activation parameters

Our team made true discoveries about the overpotential-dependent kinetics in electrocatalysis, but also in bipolar membranes and other areas. We uncovered an ubiquitous compensation effect at low overpotentials across reactions and catalysts, where an increasing Arrhenius pre-exponential factor  is overcompensating an increasing apparent activation energy. Such an effect was previously relegated to much narrower conditions or even questioned altogether based on uncertain mass transport conditions in conventional experimental setups. Instead, our team expanded Arrhenius analysis heavily on various experimental platforms, including membrane electrode assemblies that provide much higher mass transport than many liquid electrochemical cells.

We hypothesized that such an ubiquitous compensation across many reactions and interfaces might arise for a dominating ion solvation step that is impacted by excess charge and the electric-field-dependent hydrogen bond network, a picture that has recently found important support by new theory. However, in our work on the multi-step oxygen evolution and reduction reactions we also clearly observed complex changes in the kinetic regimes that show overpotential-dependent rate-limiting steps and transition states. Thus, both electric-field effects and overpotential-dependent rate limiting steps and transition states can give rise to compesation effects. Naturally, this requires care to isolate one effect from the other.

In summary, by expanding overpotential-dependent Arrhenius analysis to many reactions and conditions, our team made true discoveries that naturally challenge decade-old assumptions and approaches that arose from outer-sphere electrochemistry, surface science and computationally-limited theory. In parallel, we are also driving genuinely new technical developments, such as introducing µs-s time resolution to Arrhenius analysis to track the kinetics over dynamically changing interfaces.

Applying

Dr. Sebastian Oener strongly encourages applications from women and people of all backgrounds.

1. Check the FHI career homepage for specific open position: https://www.fhi.mpg.de/open-positions.
2. We always consider outstanding candidates. Please send a CV and cover letter describing succinctly how your skill set and interests specifically address our research program to oener@fhi-berlin.mpg.de. Due to the volume of applications received, we cannot respond to each one. 

Recent Publications

Articles, peer-reviewed

Articles, non peer-reviewed