Evaluation of design options for tubular redox flow batteries

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1 Dept. Mechanical Engineering and Production Heinrich-Blasius-Institute for Physical Technologies Evaluation of design options for tubular redox flow batteries Thorsten Struckmann, Max Nix, Simon Ressel

2 Contents Introduction - Redox flow cells Vanadium Redox Flow Batteries (VRFBs) Planar and tubular cell design Fluid flow design Experiment and Simulation Fluid flow test setup & physics VRFB test setup & physics Results Fluid flow Flow-through (FT) - validation Flow-by (FB) planar and tubular VRFB Validation of FT-VRFB model Parametrization Conclusions & Outlook COMSOL Struckmann 2

3 Intro - Vanadium Redox Flow Battery (VRFB) COMSOL Struckmann 3

4 Intro - Planar and tubular cell design COMSOL Struckmann 4

5 Intro - Fluid flow design options Flow-through cell (FT) - Electrolyte flow through graphite felt electrodes Flow-by cell (FB) - Electrolyte flow in flow channels and graphite felt electrodes COMSOL Struckmann 5

6 Intro Redox UAS (HAW) Hamburg Tubular All Vanadium Cells Tubular Vanadium-Air Cells Stacks State of Charge and Crossover COMSOL Struckmann 6

7 Experimental Fluid flow parameter Measurement setup - Liquid permeability κ H / Kozeny-Carman constant K Tank 1 Scale Temperature Pressure 2 Valve Tank 2 Graphite felt Pump Pressure 1 Zeiss COMSOL Struckmann 7

8 Experimental VRFB test rig Potentials Current Temperatures Pressure drops Electrolyte density. [1] S. Ressel, A. Laube, S. Fischer, A. Chica, T. Flower, T. Struckmann, Performance of a vanadium redox flow battery with tubular cell design, J. Power Sources 355 (2017) COMSOL Struckmann 8

Electrodes: Brinkmann equations Assumptions Incompressible electrolyte (ρ = const, u = 0) Constant dynamic

9 Simulation Electrolyte flow physics Flow through (Porous media flow) Porous Electrodes: Darcy s law with Kozeny-Carman ansatz for κ H Flow-by (Free and porous media flow) Flow channel: Navier-Stokes equations Porous Electrodes: Brinkmann equations Assumptions Incompressible electrolyte (ρ = const, u = 0) Constant dynamic viscosity (μ = const) Laminar flow in the flow channel Homogenous and constant electrode porosity (ε(r) = const) COMSOL Struckmann 9

10 Simulation VRFB phyics Mass transport in felt electrode Charge transport in felt electrode Nernst-Planck N j = c jz j D j F RT Φ D j c j +c j u V x+ V x+ V x+ e e e e migration diffusion convection Mass transport and ionic current Faraday: i l = F j z j N j electrolyte (liquid) electrode (solid) Charge conservation i l + i s = i l + i s = 0 Butler-Volmer reaction with concentration dependent exchange current density j n = i l = ai 0 exp αfη s RT exp (1 α)fη s RT, i 0 = F k 0 c α ox 1 α c red Assumptions Infinitely diluted solutions Isothermal cells (T = const) No side reactions Only proton transport through membrane COMSOL Struckmann 10

11 Results Flow-through fluid dynamics Darcy s law and experimental Kozeny-Carman constant - Validation Accurate pressure drop prediction for Vanadium electrolyte Experiment Analytic/COMSOL SGL group COMSOL Struckmann 11

Results Flow-by fluid dynamics Navier-Stokes and Brinkmann equations in 2D planar cell Electrolyte flow velocity for varying felt fibre diameter tubular geometry V in = 6.4 ml min d f = 9 m = 5.

12 Results Flow-by fluid dynamics Navier-Stokes and Brinkmann equations in 2D planar cell Electrolyte flow velocity for varying felt fibre diameter tubular geometry V in = 6.4 ml min d f = 9 m = m 2 d f = 30 m = m 2 d f = 100 m = m 2 PE FC PE FC Cell width (mm) Plug flow in flow channel Low convective flow in porous electrode Results comparable to data from Ke et al. Cell width [2] X. Ke et al., Flow distribution and maximum current density studies in redox flow batteries with a single passage of the serpentine flow channel, J. Power Sources 270 (2014) COMSOL Struckmann 12

13 Results Flow-by fluid dynamics Tubular cell in 3D Prediction & Validation Outer half cell Inner half cell cm/s Experiment COMSOL Vin = 20 ml/min Fluid: H 2 O; ε = 0,92; κ H = 4, m 2 COMSOL Struckmann 13

14 Results Validation of FT-VRFB model Validation with literature model y 3 Neg. HC Pos. HC y 2 2D planar flow-through VRFB model Vanadium concentrations y 1 Potentials at mid cell Results comparable with Gandomi et al. [3] Y.A. Gandomi et al., In Situ Pot. Distribution Measurement and Validated Model for All-Vanadium Redox Flow Battery, J. of The Electrochem. Soc. 163 (1) (2016) COMSOL Struckmann 14

15 Results Experimental data for FT-VRFB Tubular flow-through Polarization Curve Discharge High overpotential = U OCV Ohmic contribution dominant Ohm = - i * ASR High ASR (18.33±0.03) cm 2 due to contact resistance? Residual overpotential limited by electrode surface? Charge Overpotential (i) COMSOL Struckmann 15

16 Results Validation of FT-VRFB parameters Flow-through cell polarization curves Experiment and simulation Overpotential (i) = U(i) OCV - deviations simulation vs. experiment Small deviations after adding Ohmic contact resistance contribution Ohm = - i * ASR COMSOL Struckmann 16

17 Results Simulation of FT-VRFB model Planar flow-through cell ( tubular geometry ) Surface current densities Electric potentials (mid cell) i = 20 ma/cm 2 SOC ~ 50% neg HC pos HC neg HC pos HC COMSOL Struckmann 17

18 Electrolyte flow Conclusions & Outlook Flow velocity distribution and pressure drop for flow-through and flow-by cells Tubular model (3D) vs. planar approximation (2D) Model parameter from experimental data Model validation with experimental data and literature Vanadium redox flow cell VRFB model implemented and validated with literature data Experimental data for tubular flow-through cell Validation of flow-through cell parameters Simulation data for flow-through cell Outlook Validation/calibration with additional experimental data Simulation and parametrization of flow-by cells Effective models Cell optimization COMSOL Struckmann 18

19 Thanks for your attention! Thorsten Struckmann University of Applied Sciences Hamburg Faculty for Engineering and Computer Science Dept. of Mechanical Engineering and Production Management Heinrich Blasius Institute for Physical Technologies Berliner Tor 21, D Hamburg Fon: COMSOL Struckmann 19

Abstract Evaluation of design options for tubular redox flow batteries Thorsten Struckmann, Max-William Nix, Simon Ressel Hamburg University of Applied Sciences, Department of Mechanical Engineering

20 Abstract Evaluation of design options for tubular redox flow batteries Thorsten Struckmann, Max-William Nix, Simon Ressel Hamburg University of Applied Sciences, Department of Mechanical Engineering and Production Management, Hamburg, Germany Redox flow batteries are promising candidates for future stationary electrical energy storage systems. All vanadium redox flow batteries (VRFBs) are already used in demonstration projects (e.g. [1]). While the common VRFB cell design is planar, a tubular cell design might display advantages as reduced sealing lengths and reduced manufacturing costs due to an extrusion production process. In this work, as a first step in a cell optimization process, selected design options for tubular VRFB cells starting from a base design [2] are studied. Electrolyte flow is considered in flow-through (fluid flow through porous electrodes) and flow-by design (fluid flow through separate electrolyte channels and porous electrodes). Furthermore the electrode parameters are varied. The analysis comprises quantities like flow velocities, potential und species concentrations. The modelling steps are carried out in COMSOL multiphysics software. Models are parametrized and validated with standard VRFB parameters and model results [3] and with first experimental data for tubular cells [2]. [1] P. Alotto, M. Guarnieri, F. Moro, Redox flow batteries for the storage of renewable energy: A review, Renewable and Sustainable Energy Reviews 29 (2014) [2] S. Ressel, A. Laube, S. Fischer, A. Chica, T. Flower, T. Struckmann, Performance of a vanadium redox flow battery with tubular cell design, J. Power Sources 355 (2017) [3] Y.A. Gandomi et al., In Situ Potential Distribution Measure-ment and Validated Model for All-Vanadium Redox Flow Battery, Journal of The Electrochemical Society 163 (1) (2016) A5188-A5201. COMSOL Struckmann 20

Modeling as a tool for understanding the MEA. Henrik Ekström Utö Summer School, June 22 nd 2010

Modeling as a tool for understanding the MEA Henrik Ekström Utö Summer School, June 22 nd 2010 COMSOL Multiphysics and Electrochemistry Modeling The software is based on the finite element method A number