'''Introductory information'''

Title: Data underlying the PhD thesis: Liquid flow characteristics and mass transport in porous carbon electrodes for hydrogen-bromine flow batteries

Author: Author: D.A. Ochoa Fajardo

Corresponding author: R.G.H Lammertink (r.g.h.lammertink@utwente.nl)

Content: This dataset contains data collected during experiments aimed at understanding the liquid flow dynamics and mass transport characteristics of porous carbon electrodes under compression. All data was exported directly from the software associated with the measuring equipment. The dataset contains 6 types of data, pressure drop of water flowing through porous carbon electrodes with controlled thickness, pressure drop of water flowing through porous carbon electrodes under controlled compression, velocity fields of water flowing through porous carbon electrodes, through-plane electrical resistance, electrochemical measurements of electrical double layer capacitance of porous carbon electrodes, and discharge characteristics of H2-Br2 redox flow batteries with porous carbon electrodes at various H2 pressures. The data in this data set was collected at the University of Twente, as part of David Ochoa's Thesis project (DOI: 10.3990/1.9789036564946) in the laboratories of the PhotoCatalytic Synthesis Group & Soft matter, Fluidics and Interfaces Group. 

Naming conventions: 
Pressure drop of water flowing through porous carbon electrodes under controlled compression: YYYY-MM-DD_sampleName_gasketThickness_compressionPressure.txt
Pressure drop of water flowing through porous carbon electrodes with controlled thickness: YYYY-MM-DD_sampleName_gasketThickness.txt
Through-plane electrical resistance of porous carbon electrodes: YYYY-MM-DD_sampleName_sampleThickness_measurementGoal_technique_potentialRange_scanRate_potentiostatChannel.txt
Velocity fields of water flowing through porous carbon electrodes: YYYYMMDD_sampleName_flowChannelType_location_compressivePressure_waterInletPressure_magnification_delayBetweenImagePairs_ID.txt
Electrochemical measurements of electrical double layer capacitance of porous carbon electrodes: YYYY-MM-DD_sampleName_sampleThickness_measurementGoal_cellConfiguration_technique_potentiostatChannel.txt
Discharge characteristics of H2-Br2 redox flow batteries with porous carbon electrodes at various H2 pressures: YYYY-MM-DD_sampleName_flowField_sampleThickness_measurement_h2pressure_pumpRPM_technique_potentiostatChannel.txt

File format: tabulated data in .txt format.


'''Methodological information'''

Pressure drop of water flowing through porous carbon electrodes under controlled compression:
Carbon paper, Sigracet 39 AA, and carbon cloth, AvCarb 1071 HCB, were investigated as electrode materials. The electrodes were used as received or treated by an oxidative heat treatment in static air at 400 C for 24 hours. Measurements of the pressure drop of room temperature water for different flow rates through a cell with 3 cm path length. The electrode are compressed using pressurized water pushing against a Nafion 212 membrane in contact with the electrode. The flow rate was varied using a microfluidic flow controller (Elveflow OB1-BSF) in the range 0.5 mL min−1 to 3 mL min−1, in 0.5 mL min−1 steps. Pressure and flow rate measured with Elveflow sensors. Data exported directly from the flow controller.

Pressure drop of water flowing through porous carbon electrodes with controlled thickness:
Carbon paper, Sigracet 39 AA, and carbon cloth, AvCarb 1071 HCB, were investigated as electrode materials. The electrodes were used as received or treated by an oxidative heat treatment in static air at 400 C for 24 hours. Measurements of the pressure drop of room temperature water for different flow rates through a cell with 3 cm path length. The electrode thickness is controlled using rigid PTFE gaskets. The flow rate was varied using a microfluidic flow controller (Elveflow OB1-BSF) in the range 0.5 mL min−1 to 3 mL min−1, in 0.5 mL min−1 steps. Pressure and flow rate measured with Elveflow sensors. Data exported directly from the flow controller.

Through-plane electrical resistance of porous carbon electrodes:
Carbon paper, Sigracet 39 AA, and carbon cloth, AvCarb 1071 HCB, were investigated as electrode materials, the electrodes were used as received. The current-voltage relation was obtained using linear sweep voltametry in the absolute range 0 V to 2 V with a 10 mV s−1 scan rate. In the measurement setup, a 9 cm2 electrode was placed between 2 graphite composite current collectors, and its thickness was controlled using rigid PTFE gaskets.

Velocity fields of water flowing through porous carbon electrodes:
Carbon paper, Sigracet 39 AA, and carbon cloth, AvCarb 1071 HCB, were investigated as electrode materials. The electrodes were used as received or treated by an oxidative heat treatment in static air at 400 C for 24 hours. The velocity of liquid flow through the electrodes was measured using µPIV in an optically accessible cell that resembled the liquid side of a H2 -Br2 redox flow battery cell. The compression ratio (CR) of the electrodes was fixed using rigid PTFE gaskets to the values expected at 0 bar, 1 bar, and 3 or 8 bar inside a H2 -Br2 redox flow battery cell. Inlet pressure was set using a pressure controller (OB1, Elveflow). Room temperature ultrapure water seeded with 0.1 % w/v fluorescent polystyrene particles of 1 µm diameter (PS-FluoRed, microParticles GmbH) was used in the cell. The suspension was placed in an ultrasonic bath for 20 minutes before use. The cell was placed on an inverted microscope (Zeiss) and illuminated with a 527 nm dual cavity Nd:YLF laser (Litron lasers). The scale calibration was obtained from images of microscope rulers placed in the flow cell at the measurement depth. At each location selected for measurement, a set of 50 image pairs was taken at a depth of 20 µm from the optical window. DaVis 10.1 was used to manage the recording of image pairs and to calculate the velocity fields. The algorithm to calculate the velocity fields consists of image pre-processing, vector calculation, and vector validation. The image pairs were pre-processed by applying a sliding background removal filter where the intensity of each pixel was decreased by the minimum intensity of the 4 surrounding pixels. The vectors were calculated from an interrogation window of 32×32 pixels and the maximum particle displacement in each image pair using a multi-pass calculation with decreasing window size. The vector field was validated by applying a median filter which compares the components of each vector to the median of surrounding vector components in a 5×5 vector window and removes them if they are outside the deviation of the median. The velocity field was calculated for each of the 50 image pairs, and the velocity fields were averaged to produce the final result. For single location measurements image pairs taken at 30 adjacent locations were composed to generate a measurement window of 4.04×3.64×0.016 mm3 at 20x magnification. For grid measurements 9 spots on the electrode area, located in a 3×3 grid with 1 mm uniform spacing, were selected for measurement, at a magnification of 20x for uncompressed electrodes and 10x. The electrodes were used in their uncompressed state, as well as at the compression expected in a battery cell operated at 1 bar gauge H2 and 8 bar gauge H2. The image pairs were taken at 4 flow rates, set by a linearly increasing range of inlet pressures.

Electrochemical measurements of electrical double layer capacitance of porous carbon electrodes:
Carbon paper, Sigracet 39 AA, and carbon cloth, AvCarb 1071 HCB, were investigated as electrode materials. The electrodes were used as received or treated by an oxidative heat treatment in static air at 400 C for 24 hours. The electrochemical active surface area (ECSA) was approximated by the electrical double layer capacitance (EDLC) of the electrodes, calculated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in a square 9 cm2 symmetric cell using 1.5 M HCl under flow conditions. The cell had a symmetric flow-through configuration, and the compression ratio of the electrodes was fixed using rigid PTFE gaskets. The flow rate through the cell was controlled using a peristaltic pump (Masterflex L/S). The electrodes were initially saturated by running the pump at 60 RPM and then the flow rate was decreased to the minimum of 3 RPM for all measurements. A potentiostat (VMP-3, BioLogic) was used for all measurements. After the open circuit voltage (OCV) stabilized, a potentiostatic EIS measurement was taken at OCV from 100 m Hz to 100 k Hz with 5 m V peak amplitude, 25 points per decade, and 2 points averaged per frequency. Immediately after the EIS measurement the cell was left at rest until the OCV stabilized, and CVs were taken in the range −55 m V to 55 m V from OCV at the scan rates 1 m V s−1 , 3 m V s−1 , 5 m V s−1 , 7 m V s−1 , 11 m V s−1 , 13 m V s−1 , 17 m V s−1 , 23 m V s−1 , 29 m V s−1 , 50 m V s−1 , 100 m V s−1 and 200 m V s−1 with 3 cycles at each scan rate.

Discharge characteristics of H2-Br2 redox flow batteries with porous carbon electrodes at various H2 pressures:
Carbon paper, Sigracet 39 AA, and carbon cloth, AvCarb 1071 HCB, were investigated as electrode materials. The electrodes were used as received or treated by an oxidative heat treatment in static air at 400 C for 24 hours. The discharge characteristics of the battery were measured in a 9 cm2 H2 -Br2 RFB cell. The battery cell used graphite-PVDF composite flow plates, which were directly connected to the electrical leads, and had a PTFE body. The thickness of both electrodes was matched to their uncompressed thickness using rigid PTFE gaskets, and the cell was closed with stainless steel compression plates. The liquid flow rate through the cell was controlled using a peristaltic pump with PTFE head and tubing (Masterflex L/S). The liquid side electrodes were initially saturated by running the pump at 60 RPM for 30 seconds. The gas side of the cell was flushed with H2 at low pressure for 5 minutes after cell assembly. The pressure of H2 gas was set with a pressure regulator, and the outlet valve closed during experiments to maintain constant pressure. The liquid electrolyte was prepared by charging a solution of 1.5 M HBr at 400 mA until a Br2 concentration of 0.0055 M had been reached. The liquid electrolyte concentration resembled total discharge of the battery. The low concentration of Br2 and high platinum loading of the gas side electrode were chosen to ensure mass transfer limitations on the liquid side during discharge. The liquid electrolyte was not recirculated to the feed reservoir, to guarantee an unchanging feed concentration during measurements. A potentiostat (VMP-3, BioLogic) was used for all measurements. The experiments were performed at multiple operating pressures and 4 flow rates, 4.19, 8.40, 16.8, and 33.6 mL/min. During each experiment, the OCV was held until stable, and then the current was measured while the cell voltage was increased sequentially in steps. The potentiostatic discharge used 18 potentiostatic steps, each held for 90 seconds to exclude capacitive currents, in the range of 0-600 mV from OCV. After potentiostatic discharge, the ohmic resistance in the cell was obtained at each flow rate from the high frequency intercept of potentiostatic EIS measurements taken at -25 mV from OCV from 100 mHz to 100, 200, 300 or 400 kHz depending on the pressure, with 5 mV peak amplitude, 25 points per decade, and 2 points averaged per frequency.


'''Data specific information'''

Pressure drop of water flowing through porous carbon electrodes under controlled compression:
Column headings: 
Coriolis1(Read) is the flow rate recorded
30psi(Read) is the inlet pressure recorded
15psi(Read) is the outlet pressure recorded if applicable
Units: Included in the file, µl/min for flow rate, mbar for pressure.

Pressure drop of water flowing through porous carbon electrodes with controlled thickness:
Column headings: 
Coriolis1(Read) is the flow rate recorded
30psi(Read) is the inlet pressure recorded
15psi(Read) is the outlet pressure recorded if applicable
Units: Included in the file, µl/min for flow rate, mbar for pressure.

Through-plane electrical resistance of porous carbon electrodes:
Column headings: 
Time | Working electrode potential | Counter electrode potential | Current
Units: Included in the file, s for time, mA for current, V for voltage.

Velocity fields of water flowing through porous carbon electrodes:
Column headings: 
X coordinate of the vector
Y coordinate of the vector
X component of the velocity
Y component of the velocity
Units: Included in the file, mm for position coordinate, m/s for velocity.

Electrochemical measurements of electrical double layer capacitance of porous carbon electrodes:
Column headings: 
Cyclic voltammetry: Time | Current | Working electrode potential | Cell voltage | Cycle number
Potentiostatic impedance: Frequency | Real component of the impedance | Negative of the imaginary component of the impedance | Impedance magnitude | Phase angle
Units: Included in the file, s for time, mA for current, V for voltage, Hz for frequency, Ohm for impedance, degrees for phase.

Discharge characteristics of H2-Br2 redox flow batteries with porous carbon electrodes at various H2 pressures:
Column headings: 
Potentiostatic discharge: Time | Current | Working electrode potential | Cell voltage | Power
Potentiostatic impedance: Frequency | Real component of the impedance | Negative of the imaginary component of the impedance | Impedance magnitude | Phase angle
Units: Included in the file, s for time, mA for current, V for voltage, W for power, Hz for frequency, Ohm for impedance, degrees for phase.
