# Multi Material Electrocatalysis

Project heads : Manuel Landstorfer, Jürgen Fuhrmann Project staff : Rüdiger Müller

## Goals

Electrocatalysis is a central ingredient for a variety of modern technologies to store, convert and generate electric power.

Important applications are fuel cells and electrolysers, redox flow- and metal-air batteries as well as material synthesis and conversion.

In order to apply these technologies on a scale sufficient for the Energiewende, new catalysts need to be developed which are cheap, non-toxic, durable, processable, and efficient for a specific process.

This requires fundamental insights and new ideas in electrochemistry and electrochemical engineering.

Electrochemistry research depends on a variety of experimental methods to characterize electro-catalytic reactions occurring on the interface between an electrolyte and the conductive material of the catalyst.

The project goal are continuum models for electrocatalysis at the $$nm$$$$\mu{}m$$ scale coupling reactions on catalytic interfaces, reactant transport in electrolytes and charge transport in catalyst substrates. Implementation into numerical simulation tools will support the interpretation of electrochemical measurements.

## Results

First results on modeling, simulation and validation of electrochemical interfaces on polycrystalline materials cover the case of ideally polarizable electrodes. A methodology to predict important characteristics like double layer capacity of an electrode described as an ensemble of grain surfaces from the corresponding information of the individual grain types has been developed.

Left: profile of the electrostatic potential for a bi-crystalline interface with different grain sizes. Right: double layer capacity curves for different electrolyte concentrations. Solid lines (—) refer to the weighted sum of the grain contributions., (+) and dashed (- -) lines mark data obtained from numerical simulations for small and large grain sizes, respectively [1]

## Literature

[1] J. Fuhrmann, M. Landstorfer, and R. Müller, “Modeling polycrystalline electrode-electrolyte interfaces: The differential capacitance.” Journal of the Electrochemical Society, 2020.

[2] W. Dreyer, C. Guhlke, and R. Müller, “Overcoming the shortcomings of the Nernst–Planck model,” PCCP, vol. 15, no. 19, pp. 7075–7086, 2013.

[3] W. Dreyer, C. Guhlke, and M. Landstorfer, “A mixture theory of electrolytes containing solvation effects,” Electrochemistry Communications, vol. 43, pp. 75–78, 2014.

[4] M. Landstorfer, C. Guhlke, and W. Dreyer, “Theory and structure of the metal-electrolyte interface incorporating adsorption and solvation effects,” Electroch. Acta, vol. 201, pp. 187–219, 2016.

[5] M. Landstorfer, “Boundary conditions for electrochemical interfaces,” Journal of The Electrochemical Society, vol. 164, no. 11, pp. E3671–E3685, 2017.

[6] J. Fuhrmann, “A numerical strategy for Nernst-Planck systems with solvation effect,” Fuel cells, vol. 16, no. 6, pp. 704–714, 2016. DOI: 10.1002/fuce.201500215.

[7] C. Cancès, C. Chainais-Hillairet, J. Fuhrmann, and B. Gaudeul, “A numerical analysis focused comparison of several Finite Volume schemes for an Unipolar Degenerated Drift-Diffusion Model,” IMA J. Numer. Anal., 2020.