Three-Electrode Cell Calorimeter for Electrical Double Layer Capacitors Three-Electrode Cell Calorimeter for Electrical Double Layer Capacitors Joren E. Vos1Hendrik P. Rodenburg1Danny Inder Maur1Ties J. W. Bakker1Henkjan Siekman2and Ben H.

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Three-Electrode Cell Calorimeter for Electrical Double Layer Capacitors

Joren E. Vos,1Hendrik P. Rodenburg,1Danny Inder Maur,1Ties J. W. Bakker,1Henkjan Siekman,2and Ben H.

Erné1

1)Van ’t Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute for Nanomaterials Science, Utrecht University,

Padualaan 8, 3584 CH Utrecht, The Netherlands

2)Instrumentation Department, Utrecht University, Sorbonnelaan 4, 3584 CA Utrecht, The Netherlands

(Dated: 4 October 2022)

A calorimeter was built to measure the heat from a porous capacitive working electrode connected in a three-electrode

conﬁguration. This makes it possible to detect differences between cathodic and anodic heat production. The elec-

trochemical cell contains a large electrolyte solution reservoir, ensuring a constant concentration of the salt solution

probed by the reference electrode via a Luggin tube. A heat ﬂux sensor is used to detect the heat, and its calibration as a

gauge of the total amount of heat produced by the electrode is done on the basis of the net electrical work performed on

the working electrode during a full charging-discharging cycle. In principle, from the measured heat and the electrical

work, the change in internal energy of the working electrode can be determined as a function of applied potential. Such

measurements inform about the potential energy and average electric potential of ions inside the pores, giving insight

into the electrical double layer inside electrode micropores. Example measurements of the heat are shown for porous

carbon electrodes in aqueous salt solution.

I. INTRODUCTION

Capacitive porous electrodes are of interest for instance as

supercapacitors in power delivery systems1and as reversible

salt absorbants in water desalination.2During charging of a

porous electrode, electrical energy and ions are stored in the

electrical double layer (EDL). Experimental characterization

of the EDL helps to elucidate the energetic or ionic uptake ca-

pacity of the electrode. Changes in the amount of charge can

be measured in the external electrical circuit.3,4 Additional

information on the charging mechanism and the amounts of

ions inside the pores can for instance be obtained from in situ

NMR spectroscopy,5–8 infrared spectroscopy,9,10 and small-

angle neutron scattering.11,12 Here, we will focus on a thermo-

dynamic characterization approach that consists of measuring

the heat exchanged while the electrode is being charged or

discharged.

Electrodes in any electrochemical cell produce heat, al-

though this is generally not the intended outcome. One

example is heat generation during electrolysis reactions.13

Another is Joule heat produced by supercapacitors,14 which

can cause a strong temperature rise that can be damaging

for their performance.15–17 When it is possible to determine

the reversible heat, this provides valuable information on

the change in thermodynamic state of the system. The re-

versible heat can for example correspond to the change in

enthalpy of electrochemical reactions18,19 or to the entropic

heat from batteries, in agreement with the temperature de-

pendence of their open circuit voltage.20 For supercapacitors,

the reversible heat has been interpreted in different ways, as

the entropic heat from the conﬁnement of ions into the pores

of the electrodes,21 or as changes in the entropic part of the

grand potential energy,22,23 or as due to several entropic and

enthalpic contributions because of mixing as well as electrical

and steric interactions of the ions,24–26 or as due to nonzero

potential energy of the ions in the pores.27

Measuring heat from porous electrodes requires a different

measurement approach than measuring heat from submono-

layer changes at a ﬂat electrode,28 which result in very little

heat, produced very brieﬂy.29 This requires highly sensitive

and rapid detection, which can for instance be achieved using

lithium tantalate-based sensors.30 Porous electrodes have a

much higher surface area and slow ionic transport in an ex-

tensive porous network,31,32 resulting in much more heat pro-

duction but spread out over a much longer time. Due to the

long duration of heat production, the measurement requires a

very stable background temperature to differentiate from heat

exchange due to temperature changes in the environment.

Here, a setup is presented that measures the heat of charg-

ing and discharging from a capacitive porous carbon33 elec-

trode, connected in a 3-electrode conﬁguration. The setup

was ﬁrst used in Ref. 27, where it was described much more

brieﬂy. Earlier experiments on capacitive porous electrodes

were done on 2-electrode cells, by measuring the temper-

ature of the complete cell using a resistance temperature

detector,21,34 or by measuring the separate heats of both elec-

trodes, using heat ﬂux sensors.25,35 When the heat of a com-

plete cell is measured, differences between cathodic and an-

odic heat production cannot be distinguished. This limitation

disappears when the heat of individual electrodes is measured.

However, when the cell has only two electrodes, even though

it is clear that the charge that exits one electrode enters the

other electrode, it is more difﬁcult to clarify differences be-

tween cathodic and anodic behavior, because the potentials

applied to each electrode are not determined against a constant

reference. In the setup presented here, a reference electrode is

introduced as the third electrode. The current still ﬂows from

the working electrode to a counter electrode, but the poten-

tial on the working electrode is applied and measured with

respect to an invariant reference electrode. A three-electrode

cell is commonly used in electrochemistry,36 but not for mea-

surements on commercial batteries or supercapacitors. In Sec-

tion II, the design and operation of the setup are presented, and

typical measurements are shown in Section III.

arXiv:2210.00980v1 [physics.ins-det] 3 Oct 2022

Three-Electrode Cell Calorimeter for Electrical Double Layer Capacitors 2

II. DESIGN AND OPERATION

A. Electrochemical setup

The electrochemical cell developed to measure heat effects

of capacitive porous electrodes in a 3-electrode conﬁguration

is shown in Fig. 1. The cell has three glass parts. The cen-

tral part consists of a horizontal cylinder (6.4 cm in length,

2.5 cm in external diameter) whose extremities are glued into

the central hole (2.5 cm diameter) of square blocks (5 cm by

5 cm, 5 mm thick). These glued square blocks of the central

part are connected to two outer square parts of the cell via

plastic screws inserted into four holes at the corners of the

squares, see Fig. 1(a). One of the outer square parts contains

the counter electrode (CE), and the other contains the working

electrode (WE) and the heat ﬂux sensor (HFS). The WE and

CE are mounted vertically, allowing gas to escape from the

electrode surface. The separation of 6.4 cm between the elec-

trodes ensures that no measurable heat of the CE reaches the

heat ﬂux sensor mounted behind the WE. The volume of the

cylinder (30 mL) is sufﬁciently large that the salt concentra-

tion remains approximately constant. The reference electrode

(RE) senses the potential of the solution near the WE via a

Luggin tube. Typically, a Radiometer Analytical REF201 Red

Rod Ag/AgCl/saturated KCl is used as RE.

The WE and the CE each consist of a disk of porous car-

bon with a diameter of 22 mm and a thickness of typically

0.4 mm. Compared to a Pt CE, a porous carbon CE has the

advantage that it does not produce hydrogen or oxygen gas

under our measurement conditions, gases which can be oxi-

dized or reduced at the WE, leading to faradaic currents which

complicate the interpretation. At the center, these electrodes

are glued to a nonporous carbon disk of 25 mm in diameter

using a minimal amount of nonconductive Bison Kombi Snel

epoxy glue. Mechanical contact between the WE and the cur-

rent collector (a nonporous carbon disk of the same dimen-

sions) is realized by pushing them together at their outer rims

with a ﬂat 50 µm thick Teﬂon ring itself pushed by a 2 mm

thick rubber O-ring with a diameter of 21 mm. The central

part of the electrode exposed to the solution has a diameter

of 18.5 mm. An electrically insulated copper wire is glued to

the back side of the current collector using silver epoxy glue

(Chemtronics®CW2400 conductive epoxy), ensuring electri-

cal contact. This is topped off with nonconductive epoxy glue

to insulate electrically the outer portion of the silver epoxy

glue. The HFS (greenTEG gSKIN®XP 26 9C, earlier used to

measure heat from supercapacitor electrodes by Munteshari

et al.35), is placed behind the WE in a separate glass compart-

ment with walls of 0.15 mm in thickness. This compartment is

an additional protection of the sensor (which must remain dry)

against salt solution leaking around the outer rim of the cur-

rent collector. The 1 cm ×1 cm surface of the HFS faces the

electrode and current collector and is centered with respect to

them. In contrast, the ohmic contact between current collector

and copper wire is more to the side, see Fig. 1(c).

The HFS voltage is sampled twice per second using a Keith-

ley 2182A Nanovoltmeter, connected to a personal computer

via a GPIB interface. The electric potential is applied between

FIG. 1. (a) Technical drawing of the electrochemical cell used for

heat measurements on a porous electrode, connected in a 3-electrode

conﬁguration. A 3D pdf of this ﬁgure is provided in the Supporting

Information; A = outer square part containing the working electrode,

with the HFS in purple behind it; the HFS is thermally stabilized

by a copper block at the back; B = reference electrode; C & D =

electrolyte solution in- and outlets; E = outer square part containing

the counter electrode. (b) Schematic overview of the cell and its

connections to the potentiostat. The yellow circles are cross-sections

of the O-rings seen in part (a) of the ﬁgure. (c) Position of the HFS

with respect to the electrode, the current collector, and the ohmic

contact.

the WE and the CE using a channel of an AMETEK PAR-

STAT MC-1000 multichannel potentiostat, with a feedback

loop to keep the electrical potential of the WE stable with re-

spect to the RE. The same instrument measures the resulting

current between the WE and the CE.

B. Temperature stabilization

The electrochemical cell is in a controlled thermostatic en-

vironment to ensure a stable background level of the heat ﬂux

signal. The HFS is in thermal contact with a copper heat sink

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Three-ElectrodeCellCalorimeterforElectricalDoubleLayerCapacitorsThree-ElectrodeCellCalorimeterforElectricalDoubleLayerCapacitorsJorenE.Vos,1HendrikP.Rodenburg,1DannyInderMaur,1TiesJ.W.Bakker,1HenkjanSiekman,2andBenH.Erné11)Van'tHoffLaboratoryforPhysicalandColloidChemistry,DebyeInstituteforNanomateri...

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Three-Electrode Cell Calorimeter for Electrical Double Layer Capacitors Three-Electrode Cell Calorimeter for Electrical Double Layer Capacitors Joren E. Vos1Hendrik P. Rodenburg1Danny Inder Maur1Ties J. W. Bakker1Henkjan Siekman2and Ben H.

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