Tomography based screening of flow field / current collector combinations for PEM water electrolysis

L Zielke,N Paust,R Zengerle,A Fallisch,S Thiele

doi:10.1039/c4ra12402b

Abstract

Current collectors in PEM water electrolysis perform several functions that influence overall performance. These include conducting heat and electrons, as well as transporting water and gas. X-ray tomography, standardized reconstruction, and calculation methods are used to compare the morphological and transport parameters of eight different current collectors functioning as flow fields for PEM water electrolysis. We find simple exponential relations between through-plane thermal conductivity λ and porosity p (λ20°C(p) = 1749p−1.306 − 4.420), as well as between through-plane electrical conductivity σ and water permeability K (σ(K) = 10−6 × K−0.6376). In addition, we use both local and global concepts to investigate the pore space of current collectors. We hereby investigate homogeneity and characteristic sizes, like mean pore diameter or mean distance between solid parts at the catalytic interface. Moreover, we find that the local concept of mean chord lengths can be used to explain electrical and thermal conductivity anisotropies. These chords can be used to predict the direction of the largest conductivity for fibrous current collectors.

Highlights

As the share of renewable energy sources is steadily growing worldwide, the storage of uctuating renewables becomes an important issue
In order to conclude how these morphological parameters affect transport parameters, thermal conductivity, electrical conductivity, and water permeability are calculated in all microstructures
The rst thing to notice is that the highly porous gradient mat and the least porous sinter sample are the two extremes in this diagram. This visualizes the dilemma of porosity for water electrolysis performance: high porosity usually leads to weak electrical conductivity and less efficiency, whereas low porosity leads to high ow resistances and weak mass transport.[1]

Summary

Introduction

As the share of renewable energy sources is steadily growing worldwide, the storage of uctuating renewables becomes an important issue. Another exponential relation between electrical conductivity from the CL to the solar cell, and in-plane water permeability of the FF/CC itself. These two relations hold true even for morphologically different materials, such as brous and sintered titanium FF/CCs. They can be used to predict thermal conductivity from porosity, water permeability from electrical conductivity, or the other way around.

Results

Conclusion