Efficiency enhancement of gas evolving electrolysis

Scientific Background:

The efficiency of gas evolving electrolysis depends to a large extend on the hydrodynamics in the electrolytic cell where the gas fraction in the cell leads to increased electrical cell resistance and in turn to an increased cell voltage. Moreover, local flow phenomena like flow instabilities and bubble adhesion at electrodes / membranes may hinder the mass transfer and reduce the lifetime of membranes and electrodes. All those effects come increasingly to bear in case of enhancing the space-time yield by increasing the current density. Despite the local nature of flow effects, the design and optimization of electrolytic cells is mostly done by means of integral parameters. For further enhancement of electrolysis efficiency, the consideration of local phenomena is indispensable. The expertise of HZDR in development and application of multiphase flow measurement techniques as well as in modelling and simulation of multiphase flow using CFD may contribute to overcome technological obstacles.

State of Development:
HZDR has a long tradition in development of multiphase flow sensor and imaging techniques for in-detail flow analyses, with a focus on measurement with high resolution in space and time (see IP-situation). Flow measuring techniques are used successfully to investigate and optimize hydrodynamics in chemical as well as power engineering processes. Examples are investigations on liquid phase dispersion and flow velocity profiles in pilot-scale electrolytic cells using laser induced fluorescence [1]. Furthermore, the institute has experiences in application of MHD methods for active flow control in electrolysis processes [2]. The activities on modeling and simulation focus on the qualification of CFD-codes for multiphase flows. In close cooperation with ANSYS CFX, new modeling and simulation concepts for poly-dispersed bubbly flow including phase transfer have been developed [3].

IP-situation:

HZDR holds 15 patents families for following measuring techniques, which are intended to use within the proposed project: X-ray tomography (4), needle probes (5), field-focusing sensor (5), flow microscope (1)

Proposed Project: Optimization of hydrodynamics and mass transfer in hydrogen evolving electrolyzers
by multiphase flow modeling and active flow control

We offer the following activities to overcome the above-mentioned obstacles:

Experimental investigation of local two-phase flow phenomena in lab-scale and pilot-scale electrolytic cells in order to gain information on integral and local gas fraction, bubble behavior and flow velocity profiles
Investigation on local mass transfer in electrolytic cells by measuring of local species concentration, transmembrane ion transport, local electrical parameters and G/L mass transfer
Development, test and validation of different cell designs, internals and process parameters (e.g. inflow conditions, mixing elements, flow control) based on the above-mentioned measurements
Development and test of active flow control methods (e.g. magnetic fields) for gas bubble detachment and mass transfer intensification
CFD modeling / simulation of two-phase flow in electrolytic cells including local effects (e.g. flow instabilities) as basis for model-based cell design / optimization

References:

[1] Schubert, M.; Kryk, H.; Hessel, G.; Friedrich, H.-J.; Residence Time Measurements in Pilot-Scale Electrolytic Cells: Application of Laser-Induced Fluorescence; Chem. Eng. Comm., 197:1172–1186, 2010
[2] Weier, T.; Landgraf, S.; The two-phase flow at gas-evolving electrodes: bubble-driven and Lorentz-force-driven convection; European Physical Journal - Special Topics 220(2013), 313-322
[3] Ziegenhein, T.; Rzehak, R.; Krepper, E.; Lucas, D.; Numerical simulation of polydispersed flow in bubble columns with the inhomogeneous Multi-Size-Group (iMUSIG) model; Chem.Ing.Tech. 85(2013)7, 1080-1091