Using the C-Flow LAB cell for laboratory electrochemistry

CASE STUDYThis study investigates a well-defined electrochemical system with the C-Flow LAB cell to show the versatility and ease ofuse of this device for making electrochemical measurements.
Author: Clare Downs, Research Scientist at C-Tech Innovation (clare.downs@ctechinnovation.com)
The one electron reduction of ferricyanide to ferrocyanide
was chosen as this redox couple exhibits a nearly reversible

Apparatus

electrode reaction with no complications of proceedingA 6 x 4 cm C-Flow cell was used for the purposes of thisor post chemical reactions and has therefore become acase study and is shown in Figure 1 (“C-Flow LAB 6x4”).

popular choice as a standard for the demonstration ofThis experiment was run with an undivided cell so part

cyclic voltammetry (CV).

no. 8 (the membrane/separator) was omitted.

1

In this case study two types of experiments werecarried out. One was a typical cyclic voltammetry(CV) experiment to show the effect of scan rate and asecond featured linear sweep voltammetry to determine
the limiting current density at different flow rates whichthen allowed calculation of mass transfer coefficients for
ferricyanide reduction. Linear sweep voltammetry wascarried out with a flat two dimensional nickel electrode,with the addition of HDPE mesh to show the effect ofadded turbulence,2 and with the addition of a nickel
foam to increasing the electrode surface area.3
The cathode reaction for the reduction of ferricyanide is:[Fe(CN)6]3- + e- → [Fe(CN)6]4The CV portion of this experiment could also be carriedout in a beaker but using the cell gives a well definedelectrode surface area with electrodes at a controlled
distance from each other, with no issues of interface
potentials or the need to de-gas with nitrogen and allows

Figure 1 – Expanded view of the C-flow cell

Figure 2 shows the polypropylene cell frames and flow
distribution inserts that direct the electrolyte flow into thecell space close to the electrode surfaces. Figure 3 shows
the dimensions.

easy connection to current collectors. The ability to carryout hydrodynamic experiments also makes it possible
to calculate mass transfer coefficients, understandturbulence effects and the behaviour of three three
dimensional electrodes.

1 J. Bard, L. R. Faulkner, Electrochemical Methods: Fundamentals andApplications, 2nd Ed., John Wiley and Sons, Inc., 2001
2 Pletcher et al, Journal of Applied Electrochemistry 24 (1994) 95-106
3 Ponce De Leon C et al 2014, Chemical Engineering Transactions, 41(2014) 1-6. DOI 10.3303/CET1441001

C-Flow is a registered trademark of C-Tech Innovation LtdFigure 2 – Cell frames and flow distribution inserts

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Technology Park CH1 6EH
United Kingdom+44 (0) 151 347 2900
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m2). In this configuration the effect of additional electrodesurface area on the mass transfer coefficients could bedetermined.
Electrolyte: A 10mM potassium ferricyanide (AnalR Lot#3512110L) in 1M potassium carbonate solution (SigmaAldrich batch #0281MH) with a 5x molar excess ofpotassium ferrocyanide (Sigma Lot MKBR6235V) was
made with de-ionised water from a Millipore purification
system. An excess of ferrocyanide was used to ensure thatthe anode reaction did not become rate determining. For
the CV experiments the solution contained only 10mM
Figure 3: Dimension of flow channels in C-Flow LAB 6x4 cell

The apparatus was set up as shown in Figure 4.

ferrocyanide.
Electrochemical measurements: All electrochemical
experiments were carried out with a Biologic potentiostat
model SP150 with all potentials in this study measured
against a DirectIon Hg/HgSO4 reference electrode. CV
was carried out at stationary flow, i.e. the electrolyte
was pumped into the cell and then the pump switched
off and were initially at 1V to -1V where it was foundthat the reduction peak was measured at 0.175V and theoxidation peak at 0.245V versus Hg/HgSO4 at ambient
temperature. The values measured depend on the natureof the electrolyte, pH, temperature etc.4 CV traces
were then measured at 0V-0.5V versus Hg/HgSO4 forfuture experiments, at varying scan rates. Linear sweep
voltammetry was carried out from OCV (near 0V) to -1.4V

Figure 4: C-flow test set up

The C-Flow LAB cell was assembled using flat nickel
plate electrodes for both anode and cathode. These
were 7.2 cm x 5.2 cm rectangles cut from commerciallyavailable nickel sheet (Ni200, 1.2 mm thick), giving anactive electrode area of 6 cm x 5 cm. The cell was leaktested with water at 0.5 bar. Subsequent experiments

versus Hg/HgSO4 at a scan rate of 3mV/s and at different
electrolyte flow rates from 40-2000ml/min. The limiting
current was obtained at approximately -0.8V versus thereference.

Results
1. Investigation of Different Scan Rates

used other cell configurations. To investigate the effects

Cyclic voltammetry with increasing scan rates is shown inof turbulence in the cell three pieces of HDPE mesh

Figure 5. Note from the figure the position of the maximum(NetLon, 6mm diamond 2.4 mm thick) were inserted intocurrent, with the peak occurring at approximately the samethe cell. In a third configuration a 6 cm x 4 cm piece ofvoltage regardless of scan rate. This is a characteristic ofnickel foam in electrical contact with the nickel cathode

this redox couple which is known to have rapid electron

was included (nickle foam from Linyi Gelon LIB Co Ltd,transfer kinetics at the electrode. The maximum currents

90ppi, dimensions 300 x 400 x 1.6 mm, density 320 g/
4 Rock, P.A et al, J. Phys. Chem., 70 (1996), 576-580

C-Flow is a registered trademark of C-Tech Innovation Ltd

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Technology Park CH1 6EH
United Kingdom+44 (0) 151 347 2900
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for oxidation and reduction are of similar magnitudes but
not equal, showing that the system is not fully reversible.

to increase electrode surface area.
Reduction sweeps with a limiting plateau extending overapproximately 1V were obtained for all cell configurations
as shown in Figure 7. The limiting currents, IL, were
measured at 0.8V versus Hg/HgSO4 reference electrode.
Figure 8 shows the limiting current as a function offlow velocity. This shows that at high flow rates there islittle difference between the current measured with andwithout the addition of mesh whereas at lower flow rates
the addition of mesh does improve the limiting current
somewhat. The use of the nickel foam in contact with theplanar nickel electrode has the effect of increasing theFigure 5 Ferri/Ferrocyanide CV’s in C-Flow cell at different
scan rates

limiting current measured by an order of magnitude dueto the greatly increased surface area at the electrode.

Figure 6 shows that the peak currents are proportional to
the square root of the scan rate, which is as predicted by
the Randles-Sevcik equation. This is due to the change
in the thickness of the diffusion layer with changing scanrate. At slower scan rates, the diffusion layer grows muchfurther from the electrode than with faster scan rates andas a consequence the flux toward the electrode surface isgreater at faster scan rates, resulting in greater currents.

Figure 7: Linear Sweep Voltammetry - HDPE mesh added to Nielectrode example

Figure 6: Correlation between scan rate and peak current

2. Determination of Mass Transfer Coefficient
Current-potential curves were recorded for ferricyanide

Figure 8: Limiting currents as a function of flow velocity for (i)in 1M potassium hydroxide solution at increasing

a flat Ni plate electrode (ii) with HDPE mesh for turbulence

electrolyte flow rates with a planar Ni electrode andpromotion and (iii) a Ni foam electrodethen with addition of non electro-active HDPE mesh topromote turbulence in the cell and finally with a Ni foam

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Reduction of the ferricyanide at the nickel electrode is

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mass transport controlled and the mass transfer coefficientfor electrode of specified area can be calculated from thefollowing equation:5
IL = nkLFCb (1)Where IL is the limiting current, n is the number ofelectrons in the reaction, kL is the mass transfer coefficient,
F is the Faraday constant and Cb is the bulk concentration.
At the lowest flow measured in this experiment the masstransfer coefficients were calculated as:

Electrode set-up

Planar nickel
Planar nickel with HDPEmesh
Planar nickel with nickel
foam at the cathode

Mass transfer coefficientkL (cm/s)
5 x 10-8

1.5 x 10-7

6.4 x 10-6

Conclusions
Two types of electrochemical measurements have been
made with the ferri/ferrocyanide redox couple in a
C-Flow LAB cell. Experimental data showed the expected
relationship between scan rate and peak current in cyclic
voltammetry. Mass transfer coefficients for different cellconfigurations were obtained from the measured valuesof limiting currents.

5 Pletcher et al, Journal of Applied Electrochemistry 24 (1994) 95-106

C-Flow is a registered trademark of C-Tech Innovation Ltd

C-Tech Innovation Ltd Capenhurst
Technology Park CH1 6EH
United Kingdom+44 (0) 151 347 2900
info@ctechinnovation.com
www.ctechinnovation.com