Graduate School of Engineering, Hokkaido University / Laboratory of Energy Conversion Systems

244th ECS MEETINGS
10A-1704

Performance Analysis of Non-Humidified High-Temperature PEFC
by Fuel Cell System Simulator

Ryosuke Ichikawa, Ryo Sakakibara, Suguru Uemura, Yutaka Tabe

Division of Mechanical and Aerospace Engineering

Graduate School of Engineering, Hokkaido University / Laboratory of Energy Conversion Systems
14/November/2004

Background

2/24■Polymer Electrolyte Fuel Cell (PEFC)
・Excellent start-ability and load followability
・FCEV is in practical use＊) https://toyota.jp/mirai/＊) https://www.toyota.co.jp/fuelcells/jp/applications.html

Huge development costs / Short of evaluation time

MBD※ by FC system simulator

Various applications※Model Based Development

Severe usage
PEFC

Heavy Duty Vehicles (HDVs)
are required high load operation
Cooling capacity：Qcool = A・K・ΔT

Insufficient cooling capacity

A：Radiator size
K：Overall heat transfer coefficient

Δ𝑻 = TFC – Tamb.
～100℃

about 30℃

Conventional PEFC：Small ΔTNafion© based membrane is widely used(over 100oC)

High-Temp. PEFC (HT-PEFC)
is expected： Large ΔT

HT-PEFC is needed for widespread use of Fuel Cell

Basic principle of HT-PEFC

3/24

Conventional-PEFCe.g. Nafion©

HT-PEFC
e.g. PBI

Operating condition～100℃
Humidification is required.
Dry-out occurs above 100℃.

～200℃
H+ conduction is possible under
non-humidified condition.

H+ conducting path

Sulfonic acid + Water

doped Phosphoric acid

Structure of MEA

H+ is conducted under non-humidified condition→ High temp. operation is possible

Objective

4/24＊) https://www.toyota.co.jp/fuelcells/jp/applications.html

Objective
Evaluating the HT-PEFC’s utility for HDV byFC system simulator, especially its cooling performance_Appling in this study
HT-PEFC

FC-DynaMo(1,2,3)・Based on data obtained fromTOYOTA Gen.2 MIRAI*)https://www.toyota.co.jp/fuelcells/jp/

FC stack, hydrogen system, air system,
and cooling system are modeled➡ Possible to simulate unsteady vehicle driving(1) S. Hasegawa et al., ECS Transactions, 104, 3-26 (2021).
(2) S. Hasegawa et al., ECS Transactions, 109, 15-70 (2022).
(3) S. Hasegawa et al., Comput. Aided Chem. Eng, 49, 1123-1128 (2022).
Developed by NEDO(※)’s project※New Energy and Industry Technology Development Organization, Japan

Evaluating HT-PEFC system for HDV by FC-DynaMo

Outline(1) Simulation results of conventional system☞ Necessity of HT-PEFC(2) Construction of oil cooling system(3) HT-PEFC’s IV performance and simulation resultsConv.
systemOilcoolingHT
PEFC

5/24

Outline(1) Simulation results of conventional system☞ Necessity of HT-PEFC(2) Construction of oil cooling system(3) HT-PEFC’s IV performance and simulation resultsConv.
systemOilcoolingHTPEFC

6/24

Target：Vehicle class and driving pattern■Using driving data of engine vehicle in the U.S.(4)7/24

HTPEFC← uphill →severe30-3Engine power[kW]＊) https://www.volvotrucks.us/trucks/vnl/

severe6360

Vehicle speed[km/h]

Target vehicle classClass 8 (HDV)

Oilcooling

Target driving pattern
Long-haul dairy trip including uphill roads

Road gradient[%](4) C. Zhang, et al，Transportation Research Part D 95, (2021), 102843.

Conv.
system120← max330kW →240120080← Speed down →40

Cooling disadvantage

0051015

Time [min]Analyzing the most severe usage for HDV

202530FC system for HDVConv.
systemOilcooling■HDVS. Hasegawa et al., ECS Transactions, 109, 15-70 (2022).
■Using FC-DynaMo(1,2,3) (2)(3) S. Hasegawa et al., Comput. Aided Chem. Eng, 49, 1123-1128 (2022).
・Based on data obtained fromTOYOTA Gen.2 MIRAI(1) S. Hasegawa et al., ECS Transactions, 104, 3-26 (2021).

(FC system×4)
FC system＊) https://www.volvotrucks.us/trucks/vnl/*) https://www.toyota.co.jp/fuelcells/jp/

FC system
Multiplicationof FC systems

Request：max 330kW

w/ Battery400

Gross power

100

Net power

50

Net power [kW]FC stack power [W]Heat generation rate [W]Battery
Request_Required330kW

FC system■FC stack’s net power and heat generation
Waste heat

280kW

FC systemmax 100kW

150

8/24

HTPEFC50kW

FC-output
FCstack net power
Request power exceeds 280kW→ Battery assist：max 50kW

300
200
100

00.0
0.8
1.6
2.4
Current density [A/cm2]

Request power falls below 80kW
→ Battery is charged by FC power generation

0010Time [min]2030

Introducing 4-FC systems and battery assist for HDV

HDV driving simulation results by FC-DynaMoConv.
systemOilcoolingHTPEFC

9/24■Using MIRAI-MEA (Conventional MEA)
Radiatorsize

FC stack net power
poer

Current density

Cell voltage

Cell temp.

H2 consumption[Ref.]MIRAI×42
1.28m 2
(A=1.28m )(Ref.)＊) https://toyota.jp/mirai/

Possible to drive below 100oC[m2][W] A：Radiator size
OverOutput Cooling capacityOutput
Output
K：Overall heat transfer coefficient [W/(m2・K)]
100℃
limitation Qcool = A・K・ΔT
limitation
limitation
ΔT：TFC – Tamb. [K]20.83m(FCsystem×4)(Target)(0.32m2×4)(5) A. Hosoi and K. Inui,
Transactions of Society ofAutomotive Engineers of Japan,
52, 142-147 (2021).

(6) D.T. Hountalas, et al.,Energy Conversion and Management,
53, 19-32 (2012)

Overheated while climbing a hill → Unpossible to drive

Engine HDV

Ref. size = 1.28m2

Target size = 0.83m2＊) https://www.volvotrucks.us/trucks/vnl/

HDV w/conventional PEFC is possible to drive below 100℃

HDV driving simulation results by FC-DynaMoConv.
systemOilcoolingHTPEFC

10/24■Using MIRAI-MEA (Conventional MEA)
Radiatorsize

FC stack net power
poer

Current density

Cell voltage

Cell temp.

H2 consumption[Ref.]MIRAI×42
1.28m 2
(A=1.28m )(Ref.)

Possible to drive below 100oC[Target]20.83mEngine
HDV(A=0.83m(Target)2)

Outputlimitation

Outputlimitation

Over100℃

Outputlimitation

Shutdown

Overheating
hill → Unpossible to drive
Overheated when
while climbing a hill
Conventional PEFC w/target radiator size results in insufficient cooling
Conventional FC coolant boils
👉 Applying HT-PEFC：Large ΔT👉 Considering oil cooling：Non-boiling coolant

Considering competitive HT-PEFC w/target radiator size, oil coolingOutline(1) Simulation results of conventional system☞ Necessity of HT-PEFC(2) Construction of oil cooling system(3) HT-PEFC’s IV performance and simulation resultsConv.
systemOilcooling

HT
PEFC

11/24

Overview of cooling systemConv.
systemOilcooling

HT
PEFC

12/24

Cooling capacity [W] Qcool = A・K・ΔT
A：Radiator size [m2]
K：Overall heat transfer coefficient [W/(m2・K)]
ΔT：TFC – Tamb. [K]■Effect of applying heat transfer oil on cooling system

Heat exchange in radiator
Decrease inK value

TubeCoolant

AirRadiator

HotFanCool

Increase inpressure loss

FCstackFinAir

Coolantpump
Decrease infrow rate

Quantifying the effect of applying oil on cooling capacity is neededEffect on coolant flow rate
A：Radiator size [m2]
K：Overall heat transfer coefficient [W/(m2・K)]
ΔT：TFC – Tamb. [K]■Effect of applying heat transfer oil on cooling system■Viscosity of coolant
100

Viscosity μ [mPa・s]

Cooling capacity [W] Qcool = A・K・ΔT

OilcoolingConv.
systemHTPEFC(2) S. Hasegawa et al., ECS Transactions, 109, 15-70 (2022).
(7) https://www.fragol.de/en/heat-transfer-fluids/heat-transferfluids/products/fragolthermr-s-15-a.html

Heat transfer oil (7)Oil’s viscosity is high101

FC coolant(2)improving at high temp.

0.1
2575

100 125 150
Temperature [℃]175200■Flow rate by coolant pump

FanCoolCoolantpump

FCstack・ Considering the influence of coolant viscosity→ Improved MIRAI’s empirical model (2) is used
→ Considering the influence of coolant viscosity
250

Ref. flowrate [L/min]

AirRadiatorHot50at 5500rpm

20073mPa・s34mPa・s13mPa・s9.2mPa・s
4.1mPa・s
1.3mPa・s
0.9mPa・s

150
100
50090110130150170190Ref. pressure drop at coolant pump [kPa]

Coolant frow rate model is improved considering viscosity

13/24

Effect on K valueConv.
systemCooling capacity [W] Qcool = A・K・ΔT
A：Radiator size [m2]
K：Overall heat transfer coefficient [W/(m2・K)]
ΔT：TFC – Tamb. [K]HTPEFC

14/24■Formula of K value

1=𝐴・𝐾 𝜶1𝑡𝑡
1++𝐴𝑐𝐴𝑐
𝜶𝑎 𝜂𝑎𝜆𝒄𝐴 +𝐴𝑡𝐴 +𝐴𝑡𝑓𝑡𝑓■Effect of applying heat transfer oil on cooling system

AirCoolant
Metal thermalheat transfer conductivity heat transfer
ac ：Coolant’s heat transfer coefficient (FCC→Oil)

Decrease inK value

aa ：Air’s heat transfer coefficientha ：Fin efficiency.
A：Radiator size
Af ：Fin’s total contact area at air side
At ：Tube’s total contact area at air side
Ac：Tube’s total contact area at coolant side
λt ：Tube’s thermal conductivity
tt ：Tube’s thickness

Radiator

HotAirOilcoolingFanCoolFCstackTubeCoolantpumpCoolant

FinAirTemp.：60～200℃
Flow rate：0～240L/min➡ Calculating αc (FCC→ Oil)

Temp.：30℃
Velocity：2～12m/s➡ Calculating αa

Calculating α value is essential for K valueEffect on K value■Formula of K value

Boundarycondition

1𝑡𝑡
1++𝐴𝑐
𝐴𝑐
𝜶𝑎 𝜂𝑎𝜆𝑡 𝐴 + 𝐴𝒄𝐴 +𝐴𝑡
𝑓𝑡𝑓

Air
Coolant
Metal thermalheat transfer conductivity heat transfer

Coolant

2000 ≤ Re < 4000=

𝑁𝑢 ∙ 𝜆𝑐𝛼𝑐 =𝐿ac ：Coolant’s heat transfer coefficient
Nu ：Nusselt number
λ：Thermal conductivity
L：Effective length

15/24

Friction coefficient：f(Haaland Eqs.)

1=+1+ 1++
1==

Re ≥ 4000

1++0.5(2) S. Hasegawa et al., ECS Transactions, 109, 15-70 (2022).
(7) https://www.fragol.de/en/heat-transfer-fluids/heattransfer-fluids/products/fragolthermr-s-15-a.html

FC coolant(2)0.4

λc is 0.4 times smaller

0.3
0.2

Heat transfer oil (7)0.1251250

Air

HT
PEFC

==5075 100 125 150
Temperature [℃]… FC coolant
ー Heat transfer oil

1000

αc [W/m2K]

FinTemp.：60～200℃
Flow rate：0～240L/min➡ Calculating αc (FCC→ Oil)

Nusselt number：Nu(Gnielinski Eqs.)

Re < 2000

λc [W/mK]

1=𝐴・𝐾 𝜶Tube

OilcoolingConv.
system

750

175

200

100℃
80℃
60℃

500180℃
↑60℃

250
0050
100
150200
Coolant flow rate [L/min]Compared to FCC,oil‘s αc is reduced
to 0.2 times

250

By using oil, αc is reduced to 1/5 → Estimating K value

Estimating result of K value from formula
Cooling capacity [W] Qcool = A・K・ΔT
60oC

FCcoolant

A*K [W/K]

4Decrease inK value

Air velocity
12m/s

31086421Compared to FC coolant,
Oil’s K value is～0.7 times smaller

2m/s

0A=0.32m2

50 100 150 200 250
Coolant flow rate [L/min]

4CoolCoolantpumpFCstackHeattransferoil4

Oil’s K value ispoor at low temp.

32
10

A=0.32m2

A*K [W/K]Fan

A*K [W/K]

Radiator

Air

16/24

180oC

0Hot

HTPEFC

Coolant temp.

A：Radiator size [m2]
K：Overall heat transfer coefficient [W/(m2・K)]
ΔT：TFC – Tamb. [K]■Effect of applying heat transfer oilon cooling system

OilcoolingConv.
system3Improving at high temp.

210050 100 150 200 250
Coolant flow rate [L/min]

050 100 150 200 250
Coolant flow rate [L/min]

K value is improved at high temp.→ Oil cooling could be used for HT-PEFC

Outline(1) Simulation results of conventional system☞ Necessity of HT-PEFC(2) Construction of oil cooling system(3) HT-PEFC’s IV performance and simulation resultsConv.
systemOilcooling

HT
PEFC

17/24

IV characteristics of MIRAI-MEA ＆ PBI-MEA
Cell voltage [V]1.2

OilcoolingConv.
system

18/24

HTPEFC(1) S. Hasegawa et al., ECS Transactions, 104, 3-26 (2021).
(2) S. Hasegawa et al., ECS Transactions, 109, 15-70 (2022).
(3) S. Hasegawa et al., Comput. Aided Chem. Eng, 49, 1123-1128 (2022).

@100kPa

80℃, MIRAI-MEA
calculated by FC-DynaMo(1,2,3)

0.8

0.4

160℃
140℃ PBI-MEA

obtained by experiments

0.0
0.0

0.5
1.0
1.5
2.0
2
Current density [A/cm ]Compared to MIRAI-MEA,
PBI-MEA’s overpotential is very large.

Single cell is used.
(Active area is 25cm2)■Separation of overpotential
MIRAI-MEA@80℃, 100kPa

0.80.40.01.2
Large Activation

0.8

Resistance

0.4

Large Concentration

0.0
0.0

0.5
1.0
1.5
2.0
Current density [A/cm2]

Limit to reduce
0.8
Material improvement
is also required

0.0

0.5
1.0
1.5
2.02
Current density [A/cm ]Cell voltage [V]Activation※ ※Calculated by Tafel eq.
Resistance (= iR)
Concentration

PBI-MEA@160℃, 250kPa

1.2

OCV
Cell voltage [V]Cell voltage [V]1.2

PBI-MEA@160℃, 100kPa

0.4

Large Activation

Resistance
Small Concentration

0.0
0.00.51.0
1.5
Current density [A/cm2]

2.0

PBI has large activation overpotential → Proposing required performanceHDV driving simulation results by FC-DynaMo
MEA

Coolant

Radiatorsize

MIRAI

Conv.
FC
coolant

1.28m(Ref.)

power
FC stack net poer

Current density

Cell voltage

Conv.
systemCell temp.

Oilcooling

19/24

HTPEFCH2 consumption

2Possible to drive below 100oC

PBI

Thermaltransferoil(S15A)

Outputlimitation
0.83m2(Target)

Outputlimitation

Outputlimitation

Outputlimitation

Poor output

Large overpotential → Poor output and large waste heat

VirtualHT-MEA↑↑

required_IV performance → Possible to drive at high-temp.
Given necessary

Virtual HT-MEA x oil cooling : Possible to operate w/small radiatorHDV driving simulation results by FC-DynaMo
MEA

Coolant

Radiator
size

MIRAI

Conv.
FC
coolant

1.28m(Ref.)

power
FC stack net poer

Current density

Cell voltage

Conv.
systemCell temp.

Oilcooling

20/24

HTPEFCH2 consumption

2Possible to drive below 100oC

Thermaltransferoil(S15A)

PBI

Outputlimitation
0.83m2(Target)

Outputlimitation

Outputlimitation

Outputlimitation

Poor output

Large overpotential → Poor output and large waste heat

VirtualHT-MEA↑↑

Given necessary IV performance → Possible to drive at high-temp.

Impossible to operate w/PBI-MEA’s because of large overpotential

HDV driving simulation results by FC-DynaMo
MEA

Coolant

Radiator
size

MIRAI

Conv.
FC
coolant

1.28m(Ref.)power
FC stack net poer

Current density

Cell voltage

Conv.
systemCell temp.

Oilcooling

21/24

HTPEFCH2 consumption

2Possible to drive below 100oCThermaltransferoil(S15A)

PBI

Outputlimitation
0.83m2(Target)Given required
IV performance
VirtualHT-MEA↑

Outputlimitation

Outputlimitation

Outputlimitation

Poor output

Large overpotential → Poor output and large waste heat↑required_IV performance → Possible to drive at high-temp.
Given necessary

Oil cooling’s disadvantage ≪ Large ΔT

Virtual HT-MEA x oil cooling : Possible to operate w/small radiatorRequired IV performance for competitive HT-PEFC

Conv.
systemOilcooling

22/24

HTPEFC

Cell voltage [V]1.2

MIRAI-MEA, 80℃, 100kPa
0.8

Virtual HT-MEA, 160℃, 250kPa👈
0.4

PBI-MEA, 160℃, 250kPa
PBI-MEA, 160℃, 100kPa・Required performance for HT-PEFC
・Target for material improvement

Possible to reduce concentration overpotential

0.0
0.0

0.5
1.0
1.5
Current density [A/cm2]

2.0■Separation of overpotential
MIRAI-MEA@80℃, 100kPa

PBI-MEA@160℃, 250kPa
1.2

0.8

ResistanceConcentration

0.4
0.0
0.0

0.5
1.0
1.5
2.02
Current density [A/cm ]1.2
Large Activation

0.8

Improving

Resistance0.4Concentration

0.0
0.0

0.5
1.0
1.5
2.0
Current density [A/cm2]

Cell Voltage [V]Activation

Cell voltage [V]Cell voltage [V]1.2

Virtual HT-MEA@160℃, 250kPa
Small Activation

0.8

ResistanceConcentration

0.4
0.0
0.0

0.5
1.0
1.5
2.02
Current density [A/cm ]Improving activation overpotential to the same level as MIRAI is required

Conclusion■We evaluated HT-PEFC’s utility for HDV by FC system simulator.
・By applying oil cooling, the cooling capacity is very poor at low temp.
However, the cooling capacity is improved at high temp.
Oil cooling is effective for HT-PEFC.
・HT-PEFC has large concentration overpotential because the oxygen molar
concentration decreases at high temp., but this can be improved byincreasing the gas pressure.
・Current HT-PEFC (e.g. PBI) has large activation overpotential, resulting ininsufficient output and large waste heat.
・By improving the activation overpotential to the same level as MIRAI,
HDV is possible to drive with oil cooling system and small radiator size.

23/24

Acknowledgment

24/24・We would like to thank Prof. Hasegawa and Prof. Kawase of Kyoto University
and the development staff for their great support in using FC-DynaMo.

・This study was supported by the SUZUKI FOUNDATION, Japan.