Porous and heterogeneous materials are core components in energy conversion and storage devices such as batteries, fuel cells and electrolyzers, or photoelectrochemical fuel generators. The heterogeneity and structural complexity of these components are a result of three main drivers: i) The multi-functional nature of the applications requiring the presence of various functional materials in close vicinity, ii) nano- and micron-scale structuring of the material required to overcome the bulk material transport limitations, and iii) cheap and simple synthesis methods resulting in stochastic and complex morphologies. Consequently, understanding of the multi-physical transport phenomena and optimization of the component for enhanced performance, requires an accurate modelling and prediction of the transport properties, which heavily rely on the complex nano to micron-scale morphology.

In this presentation, I will show how a previously developed combined experimental-numerical approach¹ can be used for the accurate numerical characterization of the heterogeneous components’ transport properties. The methodology consists of (i) the experimental characterization of the material’s exact microstructure via non-intervening, non-destructive imaging techniques, and the subsequent use of this data in (ii) the discrete-scale numerical determination of the medium’s effective transport properties in conjunction with continuum-scale theory. This approach can be extended by using digital image processing on the structure data^2,3 to allow for artificial changes in the morphological characteristics – corresponding to real variations in the fabrication process – and subsequent investigation of the changes in the material’s transport properties.  

I will show results from the application of the combined experimental-computational methodology to three morphologically complex components at very different length-scales and in three different applications: (i) nano-structured multi-component photoelectrodes for the production of solar fuels, (ii) nano-structured porous electrodes in high-temperature electrolysis, and (iii) porous ceramic receivers for the production of concentrated solar power. The approach allowed to quantify for the first time morphological and transport properties of nano-structured photoelectrodes (example i), to characterize novel transport properties such as permeability for porous electrodes in high-temperature electrolysis (example ii), and to propose pore-scale engineering design guidelines for optimized structures of solar receivers (example iii). 

1   J. Petrasch, Ph.D. thesis, ETH Zurich, 2007.

2   S. Haussener, and A. Steinfeld, Materials, 2012, 5, 192–209.

3   S. Suter, A. Steinfeld, and S. Haussener, Int. J. of Heat and Mass Transfer, 2014, 78, 688-698.

4   S. Suter, and S. Haussener, JOM, 2013, 65, 1702-1709.