1 5kw ht pefcstack with composite mea for chp application

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1.5 kWe HT-PEFC stack with composite MEA for

CHP application

G. Giacoppo*, O. Barbera, A. Carbone, I. Gatto, A. Sacca, R. Pedicini,E. Passalacqua

CNR-ITAE, via S. Lucia Sopra Contesse 5, 98126 Messina, Italy

a r t i c l e i n f o

Article history:

Received 31 October 2012

Received in revised form

25 February 2013

Accepted 2 April 2013

Available online 11 May 2013

Keywords:

Stack design and manufacturing

High temperature PEFC

Composite Nafion-YSZ MEAs

PEMFC stack

Flow field

a b s t r a c t

In this work, the performance of a High Temperature (HT) Polymer Electrolyte Fuel Cell

(PEFC) stack for co-generation application was investigated. A 3 kW power unit composed

of two 1.5 kW modules was designed, manufactured and tested. The module was

composed of 40 composite graphite cell with an active area of 150 cm2. Composite Mem-

brane Electrode Assemblies (MEAs) based on Nafion/Zirconia membranes were used to

explore the behavior of the stack at high temperature (120 C). Tests were performed in

both pure Hydrogen and H2 /CO2 /CO mixture at different humidification grad e, simulating

the exit gas from a methane fuel processor. The fuel cells stack has generated a maximum

power of 2400 W at 105 A with pure hydrogen and fully hydrated gases and 1700 W at 90 A

by operating at low humidity grade (95/49 RH% for H2 /Air). In case the stack was fed with

reformate simulated stream fully saturated, a maximum power of 2290 W at 105 A was

reached: only a power loss of 5% was recorded by using reformate stream instead of pure

hydrogen. The humidification grade of Nafion membrane was indicated as the main factor

affecting the proton conductivity of Nafion while the addition of the inert compound like

YSZ, did not affectthe electrochemical properties of the membrane but, rather has

enhanced mechanical resistance at high temperature.

Copyright ª 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights

reserved.

1. Introduction

The development of High temperature (HT) Polymer Electro-

lyte FuelCell (PEFC) could be an opportunity in Combined Heatand Power (CHP) systems to enhance the efficiency of a

decentralized power generation and heat supplying for

buildings. The main advantages with respect to other CHP

systems, consists in the high efficiency of the Fuel Cells (FCs)

under partial load condition, the modularity, the ability to

ensure substantial autonomy of the user and, last but not

least, the possible reduction of environmental pollution. In

the last decade, CHP system based on PEFC have been

intensively studied. Most of these are based on Nafion mem-

branes which generally operates at temperature below 100 C

(Low Temperature FC). Although many Low Temperature Fuel

Cell, based on the use of Nafion membranes, have been indi-cated to be reliably and highly efficient, in the view of a micro-

cogeneration distributed production, for domestic use [1], the

interest to develop high temperature PEFC has become more

relevant, due to undoubted advantages related to the use of

such technology. Indeed, the increasing of the operative

temperature of PEFC (>100 C) can also leads an improvement

of the kinetics of reaction occurring at cathode side, a better

tolerance of catalyst toward CO poisoning, an easier water

* Corresponding author. Tel.: þ39 (0) 90624294.E-mail address: [email protected] (G. Giacoppo).

Available online at www.sciencedirect.com

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i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 8 ( 2 0 1 3 ) 1 1 6 1 9 e1 1 6 2 7

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management due to the lowering of liquid water inside the

cell and finally, a more efficient use of the waste heat. How-

ever, the implications of increasing the operative temperature

are numerous and mainly related to the electrolytic polymer

behavior. At high temperature and low humidity operation,

conventional Perfluorosulfonic Acid (PFSA) membrane dras-

tically dehydrates with negative consequences in terms of

conductivity. For example, the protonic conductivity of Nafion117 at 100% RH increases from 0.1 to 0.2 S cmÀ1 when the

temperature is raised from 30 to 85 C [2]. Different ap-

proaches have been proposed [3] to develop polymeric mem-

branes capable of maintaining high proton conductivity in

anhydrous environments. These can be classified in three

groups [4]: (1) modified PFSA membranes, which incorporate

hydroscopic oxides and solid inorganic proton conductors; (2)

sulfonated polyaromatic polymers and composite mem-

branes, such as polyether-ether-ketone (PEEK), sulfonated

polyether-ether-ketone SPEEK, sulfonated polysulfone SPSf,

and polybenzimidazole PBI; (3) acidebase polymer mem-

branes, such as phosphoric acid-doped PBI. PFSA membranes

may be easily modified by incorporating inorganic com-pounds, such as SiO2 [2,5] and TiO2 [6,7] into the hydrophilic

domains in order to form nano-composite materials to

improve their mechanical strength, the thermal stability and

the water retention capacity at elevated temperatures.

Another approach to stabilize the high temperature mem-

branes relies on the sulfonation of thermally resistant poly-

mers such as SPEEK [8], polyimides (PI) [9], and polysulfones

(PSF) [10]. A further approach to achieve high proton conduc-

tivity in membranes at high temperature, is to replace water

with proton transport assisting solvent possessing higher

boiling point, e.g., phosphoric acid orimidazoles. Poly(2,5-

benizimidazole) (ABPBI) membranes prepared by simulta-

neous doping and casting from a solution of poly(2,5- benz-imidazole)/phosphoric acid/methanesulfonic acid (MSA)

containing up to 3.0 H3PO4 molecules per ABPBI repeating unit,

has given a maximum conductivity of 1.5 Â 10À2 S cmÀ1 at

temperatures as high as 180 C under dry conditions [11].

Although several papers [12e16] are focused to the develop-

ment of high temperature stack, mainly regards to the use of

PBI membranes, only few works relate to the use of modified

PSFA membranes operating at 120 C.

In this paper a PEFC power unit, with a modular architec-

ture (two stacks of 1.5 kW each), is designed manufactured

and tested. All design steps are described considering the

stack sizing, the definition of active area and plate layout, the

design of both flow field and cooling path, the choice of gas-kets and the electrochemical components. Electrochemical

tests using a Nafion-YSZ membrane are reported by operating

both with H2 and simulated CH4 reformate stream.

2. Experimental

2.1. Membrane preparation

According to the preparation procedure elsewhere reported

[11,17], Nafion dry residue was obtained from a 5%wt/wt Ion

PowerÒ alcoholic Nafion solution, then it was dissolved in

dimethylacetamide (DMAc), to obtain a 20%wt/wt Nafion

solution, maintaining a constant temperature of 50 C in a

thermostatic bath.Successively, a 10% wt/wt of commercial

Yttria stabilized (8% molar ratio) Zirconia powder (ZSZ-Aldrich

Submicron 99.9% Purity) was added and uniformly dispersed

using an ultrasonic bath. Through a slow re-concentration at

80 C, under a magnetic stirring, a solution with suitable vis-

cosity was obtained and stratified on a glass sheet with the

Doctor Blade method. By this process, the slurrywas placed ona glass plane beyond a knife (doctor blade)whose distance

from substrate is controlled by a micrometric screw. Whena

constant relative movement was established between the

doctor blade and the substrate, the slurry was spread on the

substrate forming a thin film having a calibrated thickness.

The obtained film was dried for 3 h on a hot plate at 80 C until

the solvent was completely evaporated. At this point, the film

was detached from the glass using distilled water, then it was

dried between two sheets of blotting paper. Once well dried,

the membrane was thermally treated at 155 C to improve the

mechanical proprieties. The size of membrane was of

20 Â 25 cm with a nominal thickness of 50 mm. Finally, after a

chemical treatment in a 7 M HNO3 and in a 1 M H2SO4 solu-tions, the membrane was cropped to fit the bipolar plate

shape.

2.2. Electrodes and MEA preparation

Electrodes were prepared using the spray technique else-

where described [18]. A catalytic ink was obtained mixing a

50%wt/wtPt/C (Johnson Mattey) as an electro-catalyst with a

33%wt/wt Nafion alcoholic solution (Aldrich, 5%wt/wt), a 20%

wt/wt of ammonium carbonate (Carlo Erba) as a pore-former

and a 8%wt/wt of the same YSZ powder used for the mem-

branes casting. Then it was sprayed on a polytetrafluoro-

ethylene (PTFE) support and dried up to 125 C to obtain thecatalytic layer. The Catalyst Coated Membranes (CCMs) were

then assembled by transferring the so obtained catalytic layer

from the PTFE support to the previously cast composite

membranes, through a decal technique. The final Pt loading

was of0.5 mgcmÀ2 both for anode and cathode respectively. A

25 mm thick adhesive polyester sheet was used as a pre-gasket.

Finally, Gas Diffusion Layers (GDLs) with a micro porous layer

sprayed onto, were hot-pressed onto the CCM in order to

obtain the complete NZr-MEA. Then the MEA was shaped by a

CO2 laser device (Gravograph LS 100) to fit the bipolar plate

profile.

2.3. Fuel cell stack preliminary design

The 3.0 kW HT fuel cell power unit was designed as a scale up

of a 500 W fuel cell stack [19]. Stack design started from

electrochemical data obtained using a 25 cm2 single cell,

tested at 1.5bara, 120 C and RH with a stoichiometric ratio of

3/4 for H2 /Air. A current density of 500 mA cmÀ2 was selected

as design point which corresponds to 0.570 V. Considering the

above cited electrochemical data, a loss factor of 0.95 was

considered to take in to account the ohmic losses due to the

“stacking” effect. Following this criterion, a value of single cell

voltage of 0.543 V was determined. As consequence, starting

from the design parameter of the power unit (3.0 kW of design

power, 43.4 V of nominal voltage), the total current, the single








cell active area and the number of stack cells were algebrai-

cally calculated (Table 1).

The preliminary design phase was supported by a specif-

ically developed worksheet.

2.4. Stack architecture

2.4.1. Stack architecture definition

Generally, each system that is composed by n-base unit, can

be considered as a ‘modular system’. Here,two base unit of

1.5 kW (two stacks) were connected to achieve the requested

nominal power of 3.0 kW, while three base unit of 50 cm2

(three active area) were considered to obtain the calculatedactive area of 150 cm2. Conventional structure of a FC stack is

equivalent to a connection in series of several voltage sources,

each one with its own internal impedance, then the output

power of the stack is limited by the state of the weakest cell

[20]. The state of a cell can be determined from the voltage

across its terminals, which is affected by parameters such as

fuel, airpressure, and membrane water content.Furthermore,

if a stack is affected by malfunctioning or defective cells, the

whole system has to be taken out of service. In order to

mitigate such problems, the modular architecture was adop-

ted. Moreover concerning the application on the base of the

fuel cell stack was conceived, the modular device here pro-

posed can be more flexible with respect to thermal or elec-trical load requirements. As regard the internal distribution of

fluids, the gas and coolant distribution systems are formed by

two different subsystems, the first distributes the gases and

the water to each single cell (inlet and outlet gas and water

manifolds) while the second distributes the gases on the

active surface area (gases flow field) and the coolant on the

backside of the active area (coolant flow field). For a more

homogenous distribution of fluids, a Z-shape manifold was

used for the reactants and coolant distribution. The di-

mensions of its chosen rectangular crossesection was calcu-

lated by mean a semi-empirical method. This one takes into

account that manifold pressure drop has to be 2.5 times lower

than the flow field one (D pMan < D pFF /2.5) [21]. Counter currentflow arrangement for fuel and oxidant was used to maintain

as constants as possible the reactants concentration ratio

across the membrane. With this arrangement a more uniform

current density distribution together with a better perfor-

mance are assured [22].

2.4.2. Clamping system

The clamping system for fastening MEA, gaskets and bipolar

plates, has a primary importance in a fuel cell stack to ensure

the correct pressure distribution over the active area surface

and, consequently, a lower ohmic resistance in the current

transmission. All the cells were stacked together with steel tie

rods (10 Â M8) through two anodized aluminum clamping

plates. Tieerods were designed to guarantee a minimum

clamping pressure of about 20 kg/cm2 on the electrode sur-

face, with a torque of 4.2 Nm. This value of clamping pressure

was adoptedto limit the compression stress of graphite at 20%

of material compressive strength (100 kg/cm2).

2.4.3. Sealing system

Sealing system was realized by using conductive and non-conductive gaskets to assure internal fluid separation and

absence of external gas leakage. The non-conductive gaskets

were assembled between the MEA and the graphite plate (on

the flow field side) while the conductive gaskets were sand-

wiched betweentwo graphite plates on the cooling side. At the

interface between end plates of graphite and current collec-

tors the same conductive frame was interposed. Two insu-

lation plates were assembled between the current collectors

and the aluminum plates; these components ensure the

thermal and electrical insulation of the clamping plates.

2.4.4. Flow field design

The design of flow fieldhas a fundamental impact on the stackperformance since it affects i) the distribution of the reactants

on active surface area; ii) the mechanisms of liquid water

removal from the MEA; iii) the pressure drop of the stack. To

accomplish all these design issues, as first step a serpentine

flow path was chosen for reactants distribution. The geomet-

rical parameters of this flow path were calculated using an

own developed worksheet. This is able to determine the ribs

width, the channels width, the channels height, the number

of the parallel serpentines and the number of the serpentine

turn-backs. The serpentine flow filed parameters were calcu-

lated by considering two set of physical and geometrical

constraints. Indeed, the shape and the size of active area have

to be respected in accordance with the pressure drop and theratio between the electrical contact area and the total active

area [23]. The pressure drop considered as target for the

calculation was 100 mbar because, as pointed out in [24], this

value was found to be a good compromise between parasitic

losses and electrochemical performances. By respecting all

the constraints, two kinds of serpentines were found; this

result was possible by considering a different orientation of

the active area, as schematically reported in Fig. 1.

Table 2 reports the geometrical parameters for the two

possible solutions.

Table 1 e 3.0 kW fuel cell stack preedesign parameters.

Number of cells e 80

Single cell active area cm2 150

Power W 3250

Stack voltage V 43.4

Total current A 75

Fig. 1 e Possible serpentine flow field arrangements

depending on the active area orientation.

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 8 ( 2 0 1 3 ) 1 1 6 1 9 e1 1 6 2 7 11621







Considering that, the uniformity of reactants distribution

over the entire electrode surface is an essential requirement

for the flow field, the choice between the two solutions was

addressed by mean of computational fluid dynamics study.

Two different flow field configurations, were implemented as

computational domain as showed in Fig. 2 and solved using

Star CD eversion 4.12 with an expert module in PEFC (ESe

PEMFC version 2.4). The modeling and simulation calculations

were performed by a 4 core 3 GHz Opteron 64bit compute

node. It takes approximately 30 s to complete an iteration step

for the 3.5 million element grid used. The total time for

reaching a converging solution was about 15 h.

In general, the simulated PEFC consisted of two flow field

patterns (cathode at the top and anode at the bottom) sepa-

rated by GDLs and MEA. The properties and parameters used

in the simulation are reported in Table 3.

Operating conditions considered for this study were:dew

point of 120 C/120 C and stoichiometric of 2.0/2.0 for H2 and

air respectively, pressure of 3 bara, cell temperature of 120 C,

average current density (Iavg ) of 1 A cmÀ2. The electrochemical

model adopted and equations detail can be found in the

software manual [25].

Fig. 3a shows the calculated current density distributions

referred to the MEA surface. For the two examined flow paths,

the current density distribution decreases from inlet toward

outlet due to the consumption of the reactants. For the case 1

the maximum and minimum current density were 1.24 and

0.76 A cmÀ2 respectively with a voltage of 0.424 V; for the case

2 the maximum and minimum current density were 1.29 and

0.74 A cmÀ2 respectively, with a voltage of 0.418 V. For both

cases, the obtained current density range and voltage were

similar, thus this information was not sufficient to establish

which flow field solution (case 1 or case 2) had the most uni-

formity in current density distribution.

Therefore, a statistical representation was used to

discriminate the best flow field. Fig. 3b presents the area dis-

tribution of current density values drawn from Fig. 3a. For the

distribution that has the best uniformity, the profile of area

distribution should show as narrow as possible with per-

centage of MEA surface area close to 100%. Indeed, Fig. 3b

shows that case 1 displays the most uniform distribution

because the percentage of MEA surface with a local current

density of 1 A cmÀ2 is about 38% instead of 33% for the case 2.

2.4.5. Bipolar plate layout

The bipolar plate layout was defined by adopting the following

criteria:

Active area was shared in three sub-flow fields.

An offset of 10 mm was set to house the gasket for the flow

field sealing.

Area of each manifold was calculated on the basis of

manifold pressure drop.

A second offset of 10 mm was set to seal the reactants and

cooling manifolds from the outside.

A serpentine cooling path was placed on the plates to

distribute the liquid coolant behind the active area. The

coolant flow field was designed to have a maximum pressure

drop of 10 mbar at 107 ml minÀ1 per cell, corresponding to an

Table 2 e Serpentine flow fields geometrical parameters.

Name Case 1 Case 2 Description

Lcos (mm) 0.90 1.00 Rib width

Lcan (mm) 0.90 1.3 Channel width

Ndiv 4 4 Number of parallel

serpentine

Hcan 0.90 0.60 Channel heightAmea (cm2) 50.0 50.0 Active area size

(rectangular shape)

Lmea (mm) 50 50 Active area length

Shape factor (b) 0.5 2 MEA width (b)/height

(h) ratio

Dp (mbar) 102.30 100.38 Calculated pressure

drop

Fig. 2e

Computational domains of the two analyzed solutions.

Table 3 e Simulation properties and parameters.

Name Value

Current collector

Thermal conductivity (W mÀ1 KÀ1) 40

GDL

Thickness after compressed (mm) 250

Permeability (m2

) 1.e-12Porosity after compressed (%) 70

Thermal conductivity (W mÀ1 KÀ1) 0.25

Membrane Electrode Assembly

Thickness (including catalyst layer) (mm) 50

Thermal conductivity (W mÀ1 KÀ1) 0.15

Dry membrane density (g cmÀ3) 2.0

Equivalent weight of dry membrane (g molÀ1) 1100

Cathode exchange current density (A cmÀ2) 0.02

Cathode transfer coefficient 0.6

Anode exchange current density (A cmÀ2) 0.2

Anode transfer coefficient 1.2








overall flow rate of 4.3 l/min, which was sufficient to maintain

a temperature difference of 5 C between the stack coolant

inlet and outlet. Bipolar plates were obtained by coupling

anodic and cathodic plates with a conductive sheet of

expanded graphite. This component allows both the external

sealing of fluids and the cells serial connection. Anodic and

cathodic plates were made by 3 mm thick composite graphite

sheet (Shanghai Hong Feng-SHF) and manufactured by Com-

puter Numerical Controlled (CNC) milling machine.

2.4.6. Modular stack concept

Digital prototyping can be used to visualize and simulate a

product to reduce the necessity of building expensive physical

prototypes. The modular stack concept is shown in Fig. 4 was

attained using this technique. Both the gas and coolant inlets

were connected in parallel allocating the common inlet

junction on the frontal panel of the box.

A similar kind of connection was designed for the gases

and coolant outlet. The electrical connection of the stacks was

conceived as a rigid connection, adopting copper stick of

rectangular cross-section. Also in this case, power output

connections were placed on the front panel of the box.

Main characteristics of each module are reported in

Table 4.

2.4.7. 1.5 kW module setup

The 40 cells stack was manually assembled. Firstly, the tie

rods were screwed in the clamping plate, insulated with a

shrinkable sleeves and then the insulation plate and current

collector were stacked together (see Fig. 5a).

Using the tie rods as alignment guide, the first graphite

plate was placed; subsequently the non-conductive gasket,

the MEA and the non-conductive gasket again were progres-

sively positioned. Following this procedure the whole stack

was assembled and clamped with a torque of 7 Nm (see

Fig. 5b); this value was set as the best compromise to reach a

good electrical contact and an efficient sealing.

Once the assembling procedure was completed, fuel cell

stack was checked with respect to electrical insulation and

fluids leakage, then, the device was mounted on the test

bench (Fig. 6). It consists of a test station (Lynnthec Ltd) and a

digital data acquisition unit. The test station was used to

regulate the flow rates, humidity, pressure and temperatures

of reactants. The FC Powerä software provides the graphical

interface for the test station control. An electronic load (Agi-

lent N3303A) was used to drain the current from the stack and

to monitor the overall voltage. The fuel cell stack was equip-

ped with three thermocouples, two were placed on the

external cell plates (cathode/anode) and one on the central

Fig. 4e

Digital representation of modular stack.

Table 4 e 1.5 kW stack electrical data.

Name Value

Nominal power 1.5 kW

Cells number 40

Active area 150 cm2

Stack potential (OCV) 43 V

Stack current 75 A

Cooling type Pressurized DI water

Operative temperature 120 C

Operative pressure 3baraStoichiometry 2/2

Reactants H2 /Air; H2ref /Air

Fig. 3 e Current density distribution at Iavg [ 1 A cmL2 a) on the MEA active surface, b) statistical distribution.








cell plate. Voltage probes were inserted in the cell external

side for measuring each cell potential. Reactant and coolant

stainless steel pipes were provided with thermocouples to

monitor inlet and outlet temperatures. A data acquisition unit

(National Instruments “Compact DAQ”) was connected to a

computer to collect all the acquired data (stack overall voltage

and current, single cell voltage and stack temperatures).

3. Results and discussion

The electrochemical characterization results of the developed

HT stack are mainly IeV curves, carried out at different

operative conditions. Indeed IeV curves offer an immediate

overview of the device performance, in terms of: a) maximum

power, b) activation losses, c)ohmic losses and d) concentra-

tion losses. Particularly, the effect of relative humidity, (100/

100, 95/49 RH% for fuel and air respectively) and the fuel

composition on fuel cell stack performance,was investigated.

Temperature and pressure were held constant during tests at

120 Cand3bara with fixed stoichiometric factor of 2/2 for fuel

and air respectively. Fuels used for the tests were: pure

hydrogen (99.9999%) and a CH4 reformate simulating mixture

(H2ref ) H2 /CO270%e30% containing about 100 ppm of CO.

3.1. Tests with pure hydrogen

Preliminary tests, with pure hydrogen differently saturated H2

stream, were performed to obtain a reference result. The po-

larization curves with pure hydrogen at high and low hu-

midity are shown in Fig. 7. The results show that the

performances of the HT fuel cell stack is strongly influenced

by the relative humidity of the reactants (H2 and air). With full

hydrated gases, a maximumpower (Pmax) ofabout2400 W was

reached at 105 A. Considering the nominal current density

value used to design the fuel cell stack (0.5 A cmÀ2 corre-

sponding to a total current of 75 A), a nominal power (Pnom) of

2100 W was obtained at 28 V. By decreasing of the humidifi-

cation level from 100/100 of RH% to 95/49 of RH% for H 2 /air

respectively, a decreasing of the maximum power to

1696 Wwas observed, in correspondence of 90 A instead of

Fig. 5e

Stack assembling procedure: a) intermediate step; b)final setup.

Fig. 6 e The assembled fuel cell stack mounted on the test

bench.

Fig. 7 e Effect of relative humidity on IeV curve for FC stack

fed with pure hydrogen.








105 A. At the nominal current of 75 A, a power of 1650 W was

recorded. Therefore, the Pmax and Pnom decreased by 29.2 and

21.4% respectively. Furthermore, as can be observed from

Fig. 7, the ohmic losses in the linear region of IeV curve in-

creases. This effect causes a decreasing of difference between

Pmax and Pnom values.

To better highlight how the overall stack performance is

affected by the humidification, a theoretical concise indicator(power decay) was defined to compare results obtained at high

and low humidity by feeding the stack with pure hydrogen.

It is defined as:

Pdh ¼ÂPHuðIÞ À PLuðIÞ=PHuðIÞ

ÃÂ 100

where:

PHu(I) represents the power recorded as function of current

with fully hydrated gases and PLu(I) represents the power

recorded with low RH. As shown in Fig. 8, the power decay

increases as the current increases. Such behavior can be

explained considering that, the decreasing of water content in

the inlet stream provokesa loss of proton conductivity due to

the dehydration of membrane. Moreover, by lowering the

water content in the inlet gas stream, the total mass flow rate

diminishes and consequently the total pressure drop. As

already reported [26], there is a strong dependence between

the pressure drop along the flow path andthe convective mass

flow towards the electrode. Thus, the reduction of the total

pressure drop causes the reduction of reactant flux through

the gas diffusion layer.

3.2. Tests with reformate simulating stream

The employment of a fuel cell stack in CHP system often

impose that the stack be fed by hydrogen rich streams,

generally coming from a reformer. To investigate the behavior

of stack using a reformate fuel, as previously stated, a gas

mixture (H2ref ) H2 /CO270%e30% containing about 100 ppm of

CO, to simulate a gas stream coming from a reformer was

used.

Fig. 9 shows the IeV curves obtained in the following

operative conditions: 120 C,3bara, H2ref /air stoichiometry 2.0/

2.0, at two RH% 100/100, 95/49 for H2ref and air respectively.

Also in this case, the performance of the HT fuel cell stack

was strongly influenced by the relative humidity of the inlet

stream. As stated before, the effect of membrane dehydrationled to the lowering of voltage and power for a given current,

especially in the ohmic and diffusion controlled regions. In

this case, a maximum power of about 2300 W was achieved at

105 A, and a nominal power of 1980 W was obtained at 75 A

(nominal current). In the case of low humidification, the Pmax

decreases by 31.8% (1560 W), overlaps Pnom and the limiting

current dramatically decreases. In Fig. 10, a comparison be-

tween the power decay, calculated in the case of pure

hydrogen and reformate mixture feeding, is shown. It can be

noticed that, power decay linearly increases in the range

0e75 A for both pure hydrogen and reformate stream. At

current higher than 75 A, the loss of power became signifi-

cantly higher in case of reformate stream.The power decay was also calculated both at high and low

humidification levels as follows:

Pdf ¼ÂÀ

PH2ðIÞ À PH2ref ðIÞÁ

PH2ðIÞÃ

Â 100

where:

PH2(I) represents the power recorded as function of current

by feeding the stack with pure hydrogen and PH2ref (I) repre-

sents the power recorded with H2ref stream. By this equation,

the evaluation of the influence of fuel composition on power

Fig. 8 e Effect of humidity on power decay (humidified pure

hydrogen feeding).

Fig. 9 e Effect of relative humidity on IeV curve for FC stack

fed with reformate stream.

Fig. 10 e Comparison of Power decay as a function of the

fuel type.








loss was possible, at same humidification level. As shown in

Fig. 11, when the stack works with low humidification level

streams, the Pdf slightly rises from 0 to 5% about, in the rangeof 0e75 A and rapidly increases (up to 50%) at higher currents.

On the contrary, as the current changes, if the inlet reactant

contain high level of humidity, the trend of power decay re-

mains quite constant and always below 10%.

These results clearly show that the membrane is able to

operate with reformate stream without significant power loss

in case of high humidity. On the contrary, the power losses

became more evident when the stack was fed with low hu-

midification stream. This implies that the humidification level

has a higher impact on the FC power performance rather than

the type of fuel, due to the fact that the conductivity of Nafion

based membrane is strongly affected by its hydration level.

4. Conclusions

In this paper a 3 kW power unit composed by two 1.5 kW

modules was designed and testedwiththe aim to evaluate the

feasibility of an integrated HT-PEFC system for co-generation

application.

By computational fluid dynamic study the best flow field

geometry, ensuring the higher current density, was selected.

The 1.5 kW stack has generated a power close to 2400 W at

105 A by operating at 3 bara and 120 C with fully hydrated

pure hydrogen. The power lowered to 1696 kW at 90 A by using a low humidified H2 stream. In case reformate stream was fed

instead of pure hydrogen, only a slight difference in terms of

power generation was observed (2300 against 2400 kW) at high

humidification level. It confirms that the as produced reformate

stream contains sufficient water to maintain a high grade of

membrane hydration which is essential to ensure high proton

conductivity. The addition of YSZ inert material to the Nafion

membrane allowed enhancing its mechanical resistance

without affecting the electrochemical properties of mem-

brane, even operating at high temperature (120 C).

In conclusion, in this study the feasibility of a fuel cell stack

working at high temperature (120 C) and based on a modified

Nafion membrane, for CHP purposes, is demonstrated.

Acknowledgments

The presented research work was financially supported by the

2006e2009 Program Agreement between the Italian Economic

Development Minister (MSE) and National Research Council

(CNR) in the framework of Italian Research Found for the

Electric System (Research line-Development of Materials andComponents, Design, Demonstration and Optimization of FC

Systems for Co-Generative Applications).

r e f e r e n c e s

[1] Briguglio N, Ferraro M, Brunaccini G, Antonucci V. Evaluationof a low temperature fuel cell system for residential CHP.International Journal of Hydrogen Energy 2011;36:8023e9.

[2] Ma C, Zhang L, Mukerjee S, Ofer D, Nair B. An investigation of proton conduction in select PEM’s and reaction layerinterfaces-designed for elevated temperature operation.

Journal of Membrane Science 2003;219:123e36.[3] Alberti G, Casciola M, Palombari R. Inorgano-organic proton

conducting membranes for fuel cells and sensors at mediumtemperatures. Journal of Membrane Science 2000;172:233e9.

[4] Li Q, He R, Jensen J, Bjerrum N. Approaches and recentdevelopment of polymer electrolyte membranes for fuel cellsoperating above 100C. Chemistry of Materials2003;15:4896e915.

[5] Senthil Velan V, Velayutham G, Hebalkar N,Dhathathreyan K. Effect of SiO2 additives on the PEM fuel cellelectrode performance. International Journal of HydrogenEnergy 2011;36:14815e22.

[6] Shao Z, Xu H, Li M, Hsing I. Hybrid Nafioneinorganic oxidesmembrane doped with heteropolyacids for high temperatureoperation of proton exchange membrane fuel cell. Solid State

Ionics 2006;177:779e85.[7] Sacca A, Carbone A, Passalacqua E, D’Epifanio A, Licoccia S,

Traversa E, et al. NafioneTiO2 hybrid membranes formedium temperature polymer electrolyte fuel cells (PEFCs).

Journal of Power Sources 2005;152:16e21.[8] Carbone A, Pedicini R, Portale G, Longo A, D’Ilario L,

Passalacqua E. Sulphonated poly(ether ether ketone)membranes for fuel cell application: thermal and structuralcharacterization. Journal of Power Sources 2006;163:18e26.

[9] Guo X, Fang J, Watari T, Tanaka K, Kita H, Okamoto K. Novelsulfonated polyimides as polyelectrolytes for fuel cellapplication 2 synthesis and proton conductivity of polyimides from 9,9-bis(4-aminophenyl)fluorene-2,7-disulfonic acid. Macromolecules 2002;35:6707e13.

[10] Pedicini R, Carbone A, Sacca A, Gatto I, Di Marco G,

Passalacqua E. Sulphonated polysulphone membranes formedium temperature in polymer electrolyte fuel cells (PEFC).Polymer Testing 2008;27:248e59.

[11] Asensio J. Proton-conducting membranes based on poly(2,5-benzimidazole) (ABPBI) and phosphoric acid prepared by directacid casting. Journal of Membrane Science 2004;241:89e93.

[12] Siegel C, Bandlamudi G, Heinzel A. Systematiccharacterization of a PBI/H3PO4 solegelmembranedmodeling and simulation. Journal of PowerSources 2011;196:2735e49.

[13] Javier Pinar F, Canizares P, Rodrigo M, Ubeda D, Lobato J.Scale-up of a high temperature polymer electrolytemembrane fuel cell based on polybenzimidazole. Journal of Power Sources 2011;196:4306e13.

[14] Lee H, Kim B, Lee D, Park S, Kim Y, Lee J, et al. Demonstration

of a 20 W class high-temperature polymer electrolyte fuel

Fig. 11 e Comparison of power decay as function of the

humidity.








cell stack with novel fabrication of a membrane electrodeassembly. International Journal of Hydrogen Energy2011;36:5521e6.

[15] Li Q, Hel R, Jensenl J, Bjerruml N. PBI-based polymermembranes for high temperature fuel cellsepreparation,characterization and fuel cell demonstration. Fuel Cells2004;4:147e59.

[16] Radu R, Zuliani N, Taccani R. Design and experimental

characterization of a high-temperature proton exchangemembrane fuel cell stack. Journal of Fuel Cell Science andTechnology 2011;8:0510071e5.

[17] Sacca A, Gatto I, Carbone A, Pedicini R, Passalacqua E.ZrO2eNafion composite membranes for polymer electrolytefuel cells (PEFCs) at intermediate temperature. Journal of Power Sources 2006;163:47e51.

[18] Lufrano F, Passalacqua E, Squadrito G, Patti A, Giorgi L.Improvement in the diffusion characteristics of low Pt-loaded electrodes for PEFCs. Journal of AppliedElectrochemistry 1999;29:445e8.

[19] Giacoppo G, Carbone A, Gatto I, Sacca A, Pedicini R,Barbera O, et al. Stack operation using compositemembrane-electrodes assemblies at 120C. Journal of FuelCell Science and Technology 2012;9:0310051e8.

[20] PalmaL,EnjetiP.Amodularfuelcell,modularDCeDCconverterconcept for high performance and enhanced reliability. IEEETransactions on Power Electronics 2009;24:1437e43.

[21] Barbir F. PEM fuel cells theory and practice. 1st ed. AcademicPress; 2005.

[22] Alaefour I, Karimi G, Jiao K, Li X. Measurement of currentdistribution in a proton exchange membrane fuel cell withvarious flow arrangementsea parametric study. Applied

Energy 2012;93:80e9.[23] Squadrito G, Barbera O, Giacoppo G, Urbani F, Passalacqua E.

Polymer electrolyte fuel cell stack research anddevelopment. International Journal of Hydrogen Energy2008;33:1941e6.

[24] Squadrito G, Giacoppo G, Barbera O, Urbani F,Passalacqua E, Borello L, et al. Design and development of a7kW polymer electrolyte membrane fuel cell stack for UPSapplication. International Journal of Hydrogen Energy2010;35:9983e9.

[25] ES pemfc version 2.40 user guide. CD-Adapco; 2010.[26] Squadrito G, Barbera O, Giacoppo G, Urbani F, Passalacqua E.

Computer aided fuel cell design and scale-up, comparisonbetween model and experimental results. Journal of AppliedElectrochemistry 2006;37:87e93.






1 5kw ht pefcstack with composite mea for chp application

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