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A1704
Towa ds high h oughpu PEMFC es ing: Dynamic and
P ecise Humidi ica ion o Reac ion Gases
Johanna Lü zenki chen*, Ka ha ina B aun, Lukas Weiß, Michael Wensing
F ied ich-Alexande -Uni e si ä E langen-Nü nbe g, P o esso ship o Fluid Sys ems
Technology, Caue s aße 4, 91058 E langen/Ge many;
*Con ac co esponding au ho s: www.EFCF.com/Con ac Reques
Abs ac
Fo he op imum ope a ion o p o on exchange memb ane uel cells (PEMFCs), con olled
humidi ica ion o he eac ion gases is essen ial and he e o e also i al in PEMFC es ing
and es con igu a ions. The abili y o apidly al e he humidi y o he eac ion gases is
aluable no only o dynamic ope a ion ials bu also o cos -e ec i e, high- h oughpu
es ing. In PEMFC es s, he ime equi ed o a ain s able ope a ing condi ions is ypically
domina ed by he humidi ica ion sys em. As ecen s udies show, con en ional ex e nal
humidi ica ion echniques like he bubble humidi ie exhibi a lack o lexibili y in adap ing o
changing condi ions [1]. To add ess hese limi a ions, his s udy expe imen ally in es iga es
he con olled addi ion o liquid wa e in o an e apo a o , whe eby he wa e is comple ely
apo ized and hen combined wi h a p ehea ed gas low in a mixing a ea. A comp ehensi e
wa e mass balance can be de i ed om he quan i y o wa e supplied by he mass low
con olle and he amoun collec ed by he condensa e sepa a o a he ou le o he uel cell.
The beha io o he e apo a o du ing al e ed humidi y is analyzed wi h espec o dynamic
and s a iona y cha ac e is ics. The e o e, he wa e mass supplied o he e apo a o is
changed a a s anda d uel cell ope a ion poin . The esul ing wa e con en measu ed wi h
a humidi y senso is in es iga ed ega ding eal- ime beha io and ep oducibili y. The
in es iga ed humidi ica ion sys em ep esen s an imp o emen on con en ional
humidi ica ion me hods, as he amoun o wa e in he sys em can be p ecisely con olled,
he eby enhancing he dynamic and accu acy o he humidi ica ion p ocess.
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In oduc ion
In PEMFCs, he anode and ca hode sides a e sepa a ed om each o he by a p o on
exchange memb ane. Due o hei chemical esis ance and high p o on conduc i i y,
pe luo ina ed sul onic acid (PFSA) memb anes a e used in a ious applica ions [2]. The
p o on conduc i i y o hese memb anes is dependen on he amoun o wa e p esen wi hin
hem. Highe conduc i i y esul s in a educ ion in ohmic losses, he e o e he pe o mance
o he PEMFC is dependen upon he memb ane’s humidi y. One wa e sou ce is he p oduc
wa e , which is p oduced du ing he chemical eac ion on he ca hode side. I is no possible
o se he amoun o p oduc wa e independen ly; a he , his is dependen on he uel cell's
load poin . To in luence he memb ane humidi y he eac ion gas s eams o ai and
hyd ogen a e ypically humidi ied ex e nal wi hin he balance o plan componen s. [3]
Humidi ica ion causes he isk o excessi e wa e looding he gas anspo channels in he
cell. Condensa ion c ea es wa e d ople s ha block he channels, which causes an
insu icien supply o eac ion gases [4]. In addi ion, luc ua ions in humidi y lead o cyclical
memb ane swelling and sh inking, esul ing in ele a ed mechanical s ess. This leads o a
loss o pe o mance and can cause memb ane deg ada ion, he eby educing he uel cell's
li espan [5]. Consequen ly, uni o m and con olled humidi ica ion is impo an in o de o
p e en memb ane deg ada ion and condensa ion wi hin he cell. This is ele an no only in
PEMFCs ield applica ion, bu also in he con ex o uel cell es ing. To op imise uel cell
ope a ion and li e ime, expe imen al es ing on uel cell es benches is done. Usually,
ma e ial changes a e made wi hin he memb ane elec ode assembly (MEA) and hen
di e en MEAs a e compa ed wi h each o he . To ge eliable esul s, he condi ions imposed
by he es bench ha e o be ep oducible and cons an . This app oach is manda o y o
ensu e he compa abili y o measu emen campaigns and he accu a e in e p e a ion o
measu emen esul s. In PEMFCs, he ela i e humidi y is equen ly used o desc ibe he
gas humidi y. Rela i e humidi y is de ined as he a io o wa e apou pa ial p essu e o
sa u a ion apou p essu e, and is co espondingly dependen on he empe a u e. To each
he same ela i e humidi y a highe empe a u es he absolu e amoun o wa e in he gas
inc eases. I is he e o e wo hwhile o examine he wa e con en x ins ead o ela i e
humidi y as a pa ame e o desc ibing humidi y in g ea e de ail. The wa e con en is
de ined as he mass o gaseous wa e con ained wi hin one kilog am o d y gas. As equa ion
(1) shows, he ideal gas law can be u ilised o demons a e a p essu e and empe a u e-
dependen ela ionship be ween he wa e con en and he ela i e humidi y [6].
𝒙 = 𝒎𝒘
𝒎𝒈,𝒅𝒓𝒚
=𝑴𝑾
𝑴𝒈,𝒅𝒓𝒚
∙𝒑𝒔(𝑻)∙ 𝝋
𝒑 − 𝒑𝒔(𝑻)∙ 𝝋
(1)
This app oach is applied in he in es iga ed humidi ica ion sys em by adjus ing he humidi y
ia he wa e con en .
1. Scien i ic App oach
Depending on he applica ion, di e en humidi ica ion sys ems a e used o he ex e nal
humidi ica ion o he uel cell’s eac ion gases. As al eady elabo a ed in a p e ious pape [1],
he ollowing equi emen s a e essen ial o humidi ica ion sys ems in a uel cell es bench:
Accu a e and ep oducible s a iona y beha io
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To apply a desi ed humidi ica ion s a e and ensu e ha he ac ual humidi y a he uel cell
inle co esponds o he expec ed humidi y, p ecise adjus abili y is essen ial. The applica ion
o equa ion (1) shows ha a 80°C, e en a small de ia ion o 3 g/h in he wa e load leads
o a change in he ela i e humidi y o 1%. In uel cell es s ands, i is some imes possible
o check he inle humidi y wi h app op ia e senso s. Howe e , con en ional humidi y
senso s ha e a limi ed accu acy, especially a high humidi y le els. The e o e, eliance on
his measu ed alue is limi ed. Condensa ion may occu a any poin wi hin he sys em i he
gas o wall empe a u e is lowe han he dew poin empe a u e. The gas becomes
sa u a ed and liquid wa e occu s, educing he wa e con en o he gas- apo mix u e. This
leads o a de ia ion in humidi y, which in u n could esul s in a lowe ela i e humidi y in he
PEMFC han expec ed [6].
Low ime delay/ine ia – high dynamics
To minimize he ime equi ed be ween di e en ope a ing poin s, a low ine ia in changing
he a ge humidi y is impo an . In he e en o he humidi ica ion sys em a aining he a ge
humidi y wi h high dynamics, i is possible o eac o he ope a ing s a us o he uel cell wi h
an inc eased esponse ime. Concu en ly, he du a ion o he es can be educed, sa ing
e o and cos s.
Rep esen a ion o he comple e ope a ing ange
Fu he mo e, he humidi ica ion sys em mus be capable o co e ing he en i e ope a ional
ange o a uel cell. Low- empe a u e PEMFCs a e ypically ope a ed wi hin a empe a u e
ange o 65°C o 85°C. In o de o achie e op imal cell pe o mance wi hin his empe a u e
ange, ela i e humidi y anging om 70% o 100% a e ypically es ablished. Pe o ming
accele a ed s ess es , empe a u es up o 90°C and low ela i e humidi y un il 30% mus
be easible.
In he applica ion o comme cial uel cell es s ands he humidi ica ion sys em o a bubble
humidi ie is o en used. In hese, wa e is hea ed in a column and he d y gas is led h ough
he ho wa e om below. This humidi ica ion me hod is based on he assump ion ha he
gas is ully sa u a ed upon exi ing he wa e column. I he wa e is hea ed homogeneously,
i can be hypo hesized ha he gas dew poin empe a u e co esponds o he wa e
empe a u e. Fo humidi y changes, i is he e o e necessa y o adjus he dew poin
empe a u e o he gas ia he wa e empe a u e. As demons a ed in p e ious
in es iga ions [1], he dynamic o bubble humidi ica ion is limi ed because a la ge mass o
wa e mus be hea ed. As he gas exi s he bubble in a s a e o comple e sa u a ion, he e
is also an ele a ed isk o condensa ion, which can lead o de ia ions om accu acy. To
o e come hese limi a ions, we in eg a ed a di e en humidi ica ion sys em in o he design
o ou sel -buil uel cell es bench. The ollowing sec ion will p o ide a de ailed desc ip ion
o he op imized humidi ica ion sys em.
2. Expe imen s
The expe imen al se up u ilized a sel -buil uel cell es bench capable o accommoda ing
s acks wi h a powe class o up o 1.5 kW. In o de o measu e no only indi idual cells bu
en i e uel cell s acks in his powe class, i is necessa y o use media low a es o up o 100
no m li e s pe minu e. Consequen ly, he amoun o wa e necessa y o achie e he equi ed
humidi y le els also inc eases. Fo ins ance, i he eac ion gas low o 100 Nl/min is o be
condi ioned o 90% a 80°C and 2.4 ba (a), a wa e mass low o app oxima ely 1000 g/h is
equi ed. To ul il hese equi emen s o he humidi ica ion sys em we used an e apo a o
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manu ac u ed by aD op. Compa ed o he bubble humidi ie , his e apo a o has a mo e
p ecise humidi y con ol and enhanced esponse ime which we wan o show in he ollowing
sec ion. Figu e 1 shows a schema ic ep esen a ion o he gas condi ioning p io o i s en y
in o he uel cell.
Fig. 1 Schema ics ep esen a ion o he humidi ica ion sys em o condi iona e he PEMFC gas inle
The key aspec o his humidi ica ion sys em lies in he con olled addi ion o wa e , which is
in oduced o he e apo a o in liquid o m and egula ed by a mass low con olle (MFC 1).
This mass low con olle u ilizes he Co iolis p inciple and he eby acili a ing p ecise
egula ion o he wa e supply. The wa e is apo ized wi hin he e apo a o ’s co e (e ap.
co e) and which is hea ed o an ele a ed empe a u e (𝑻𝒆𝒗𝒂𝒑𝑪𝑶𝑹𝑬) o 200 °C. The capaci y
o he hea e is egula ed in acco dance wi h he quan i y o wa e supplied, he eby ensu ing
comple e apo iza ion. In addi ion o he liquid wa e , d y gas is ed o he e apo a o ia a
second mass low con olle (MFC 2). The gas is hea ed in he p e-hea chambe so ha i
can ully abso b he wa e apo in he mixing uni . The empe a u e o he humid gas
esul ing om he hea ing/e apo a ion p ocess can be se ia he empe a u e measu ing
poin a he apo ize ou le (𝑻𝒆𝒗𝒂𝒑𝑶𝑼𝑻). Due o he spa ial condi ions, he dis ance be ween
he ou le o he e apo a o and he inle o he uel cell is 50 cm. T ace hea ing is he e o e
used o p e en condensa ion. To acili a e p ecise analysis o he gas eed a he uel cell
inle , we ins alled a senso pla e. I includes h ee senso s o enable he simul aneous
measu emen o empe a u e (𝑻𝒊𝒏), p essu e (𝑷𝒊𝒏) and he dew poin empe a u e (𝑫𝒆𝒘𝑻𝒊𝒏).
To p e en condensa ion in he senso pla e, he la e is also hea ed ia a he mos a so
ha he senso pla e empe a u e (𝑻𝒑𝒍𝒂𝒕𝒆) is abo e he dew poin empe a u e. The senso
pla e is composed o aluminum, a ma e ial ha is well-known o i s abili y o acili a e e en
hea dis ibu ion. We use humidi y senso s manu ac u ed by Vaisala, ea u ing a hea ed
senso head, which can be ope a ed a high humidi y le els wi hou he isk o condensa ion.
The ela i e humidi y o he gas is calcula ed om he dew poin empe a u e measu ed by
he humidi y senso and he measu ed gas empe a u e. The wa e con en is calcula ed
om he dew poin empe a u e using he measu ed p essu e and equa ion (1). This alue
will be e e ed o as he senso ’s wa e con en . This is in con as o he e apo a o ’s
wa e con en which is de i ed om he a io o he d y gas low and he amoun o wa e
supplied o he e apo a o . The con olled addi ion o liquid wa e ensu es p ecise
knowledge o he wa e con en . P o ided ha he sys em is adequa ely hea ed and
insula ed, he eby ensu ing ha he gas empe a u e emains abo e he dew poin
empe a u e a all imes, he wa e con en emains uni o m h oughou he lines. A e he
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uel cell, he gas low is cooled down and he esul ing condensa e is collec ed. This p ocess
enables he de e mina ion o a wa e mass balance o he uel cell.
3. Resul s
The objec i e o he measu emen s was o analyses he de eloped humidi ica ion sys em
wi h ega ds o he equi emen s p esen ed in Chap e 2. The e o e, he e apo a o was
used o se a ying wa e con en le els unde di e en condi ions. These we e hen
compa ed wi h he esul ing measu ed humidi y. Gene ally, he wa e con en o he
humidi ied gas can be adjus ed ei he by changing he supplied mass o wa e o by
changing he d y gas low. When es ing uel cells, he gas low a e is de e mined by he
uel cell's load. The e o e, he gas wa e con en is al e ed ia he supplied wa e mass. We
in es iga ed he beha io o he e apo a o a a ypical uel cell ope a ing poin (gas
empe a u e = 80°C, p essu e = 2.4 ba , gas low a e = 25 Nl/min). The e o e, we inc eased
he wa e mass low in 50 g/h s eps om 50 o 300 g/h (Se poin ), hus co e ing a ange o
20-95 % ela i e humidi y. Figu e 2 shows he wa e con en measu ed by he humidi y
senso compa ed wi h he wa e con en se by he MFC’s.
Fig. 2: Inc ease o he wa e con en acco dingly o he mass low supplied o he
e apo a o in 50 g/h s eps
A e changing he wa e low he se poin inc eases di ec ly. The e apo a o ’s wa e con en
inc eases also di ec ly as he MFC con ols he desi ed wa e mass low o ma ch he
se poin . In compa ison o he e apo a o wa e con en he senso ’s wa e con en s a s o
inc eases wi h a delay o 15 seconds. The senso ’s wa e con en shows he beha io o an
e- unc ion and app oaches he se poin asymp o ically. This beha io is ypical o he s ep
esponse o he PT1 elemen and can be explained by he hea ing con ol o he e apo a o .
When wa e is added, he capaci y o he hea e adjus s acco dingly o enable comple e
e apo a ion o he wa e . A compa ison o he s eps e eals ha he h ee middle s eps (150,
du a ion min
wa e con en
e poin
wa e con en e apo a o
wa e con en senso
as low l min
. a (a
T C
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200, 250 g/h) exhibi he smalles ime delay. He e, he senso alue app oaches he se poin
and emains cons an a e app oxima ely ou minu es. Wi hin he low and high humidi y
anges, he ime equi ed o each a cons an s a e is double he du a ion obse ed in he
middle humidi y ange (8 minu es). This indica es, ha i is challenging o ope a e he sys em
a i s bounda y condi ions. The emaining de ia ion be ween he se poin and he senso ’s
wa e con en lies wi hin he measu emen inaccu acy o he used senso s. Howe e , i has
been demons a ed ha he humidi ica ion sys em can success ully achie e he a ge
humidi y wi hin a sho e ime ame when compa ed o he bubble humidi ie . Wi h a bubble
humidi ie a ime o mo e han 80 minu es is equi ed o inc ease he dew poin empe a u e
om 45°C o 65°C [1]. This disc epancy can be a ibu ed o he ac ha , in he bubble
humidi ie , he wa e con en canno be modi ied di ec ly; a he , he dew poin empe a u e
can only be inc eased indi ec ly by inc easing he empe a u e o he en i e wa e column.
To asce ain whe he he ime delay is solely in luenced by he hea ing con ol o he
e apo a o , we also in es iga e how he wa e con en is in luenced by changing he gas
low. This es measu emen s showed ha an inc ease in he gas low caused a sudden
educ ion in he senso ’s wa e con en . As seen in Figu e 3 he senso ’s wa e con en
ini ially d ops o a alue below he se poin , bu hen quickly ises again and displays
cons an beha io a e a pe iod o one minu e. This demons a es ha he obse ed PT1
beha io is p edominan ly in luenced by he e apo a o ’s hea ing and he wa e con ol by
he MFC. Despi e he ac ha his app oach a ained a s eady s a e mo e quickly, his ype
o humidi y change is no used in he con ex o uel cell ope a ion, as he gas low a e is
de e mined by he uel cell's load.
Fig. 3: Dec ease o he wa e con en acco dingly o he gas low supplied o he
e apo a o in 5 Nl/min s eps
The accu acy o he humidi y supplied by he e apo a o was e i ied by he epea ed
measu emen o he same a iable on mul iple occasions. The e o e, h ee wa e mass lows
ime hh mm p
wa e con en
e poin wa e con en
Measu ed wa e con en
wa e low h
. a (a
T C
du a ion min
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(50, 200, 300 g/h) a e added in he e apo a o , whils all o he ope a ional condi ions
main ained cons an . Once he measu ed humidi y has eached a s eady s a e, we
de e mined o each wa e mass low he esul ing a e age dew poin empe a u e. We
di ec ly used he measu ed alue om he humidi y senso in o de o a oid in luences om
he calcula ion wi h o he measu ed a iables. This measu emen was epea ed
independen ly on wo u he days. The esul s show as ha he dew poin empe a u es
measu ed on he a ious days di e om each o he only sligh ly (see able 1).
Table 1: epea ed dew poin empe a u e measu emen s in dependence on wa e mass
In addi ion o he compa ison o he s a iona y s a es o he inal alue, he cou se o he dew
poin empe a u e is also compa ed. Figu e 4 illus a e he inc ease in dew poin empe a u e
o a wa e mass o 300g/h. The measu emen s we e conduc ed independen ly and o e a
pe iod o h ee days. Howe e , he changes in dew poin empe a u e we e ound o be
almos iden ical. This beha io is indica i e o he ep oducibili y and p ecision o he
humidi ica ion sys em.
Figu e 3: epea ed measu emen s o wa e mass low inc eased o 300g/h
To summa ize, we in es iga ed a humidi ica ion sys em ha added a con olled wa e mass
low in an e apo a o . The wa e is comple ely apo ized, esul ing in he o ma ion o a
wa e con en wi hin he humid gas, in conjunc ion wi h he d y gas low. We ha e analyzed
he humidi ica ion sys em in e ms o i s accu acy and dynamics. I has been demons a ed
h ough measu emen s ha he a ge humidi y can be a ained wi hin a b ie ime ame a
da a poin
.
.
.
.
dew poin empe a u e C
dew poin emp day
dew poin emp day
dew poin emp day
as low l min
T C
p . a (a
50 g/h
200 g/h
300 g/h
Day 1
45,46 °C
71,91 °C
80,08 °C
Day 2
45,48 °C
70,85 °C
79,99 °C
Day 3
45,94 °C
71,25 °C
80,07 °C
EFCF 2025: Low-Temp. Fuel Cells, Elec olyse s & H2 P ocessing 1 – 4 July 2025, Luce ne Swi ze land
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he s anda d uel cell ope a ing poin . Repe i ions o he measu ing poin ha e con i med he
epea abili y.
Acknowledgemen s
The wo k was ca ied ou as pa o he p ojec H2Season which was unded by he Ba a ian
Minis y o Economic A ai s, Regional De elopmen and Ene gy.
Re e ences
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Ohio, Uni ed S a es, 2024
[2] Sa ono a, E. Yu.; Lyso a, A. A. Pe luo osul onic Acid Polyme Memb anes:
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2023
[3] Dicks, And ew L.; Rand, Da id A. J. Fuel Cell Sys ems Explained: Wiley, 2018
[4] Li, Hui; Tang, Yanghua; e al. A e iew o wa e looding issues in he p o on exchange
memb ane uel cell. In: Jou nal o Powe Sou ces 178 (1), S. 103–117, 2008
[5] Madha , Dha mjee ; Wang, Jun u; e al. A Re iew o P o on Exchange Memb ane
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Keywo ds: EFCF2025, H2, LowTemp. Fuel Cells & Elec olyse s, Gas Humidi ica ion
Rema k: This wo k is licensed unde C ea i e Commons A ibu ion 4.0 In e na ional
