S udy o he elec odeposi ion o conduc i e polypy ole doped saccha in
coa ings on 316L s ainless s eel pla e o PEMFC applica ion
S. Ben Jadi
a,b
, K. Bahend
a
, M. El Fazdoune
a
, A. I anzo
c,d,*
, F.J. Ga cía-Ga cía
e
,
M. Bazzaoui
a
a
Labo a o y o Ad anced Ma e ials and P ocess Enginee ing, Facul y o Sciences, Ibn To ail Uni e si y, 14000, Keni a, Mo occo
b
LME, Facul y o Sciences, Ibn Zoh Uni e si y, 80000, Agadi , Mo occo
c
The mal Enginee ing G oup, School o Enginee ing, Uni e sidad de Se illa, Camino de los Descub imien os, s/n, 41092, Se illa, Spain
d
ENGREEN Labo a o y o Enginee ing o Ene gy and En i onmen al Sus ainabili y, Uni e si y o Se ille, Spain
e
Depa amen o de Ingenie ía y Ciencia de los Ma e iales, Escuela Poli ´
ecnica Supe io , Uni e sidad de Se illa, Calle Vi gen de ´
A ica, 7, 41011, Se illa, Spain
ARTICLE INFO
Handling Edi o : D Meh an Rezaei
Keywo ds:
O ganic coa ing
Bipola pla e
Co osion
Sodium saccha in
Polypy ole
AISI 316L
PEMFC
ABSTRACT
The s udy in es iga es he elec osyn hesis o py ole doped wi h sodium saccha in as a p o ec i e coa ing o
AISI 316L bipola pla e. Elec opolyme iza ion du a ions a e sys ema ically a ied o op imize co osion inhi-
bi ion unde di e en concen a iona o he agg essi e en i onmen o ypical o PEMFC ope a ion. Weigh loss
measu emen s indica ed ha ilms syn he ized du ing 30 min pe iod exhibi supe io co osion esis ance
compa ed o hose p oduced unde sho e du a ions. Elec ochemical assessmen s, including po en iodynamic
pola isa ion and elec ochemical impedance spec oscopy (EIS), demons a e ha he sodium saccha in doped
PPy coa ing signi ican ly educes he pola isa ion densi y o 316L. de ailed s uc u al and mo phological analyses
we e conduc ed using X- ay pho oelec on spec oscopy (XPS) and scanning elec on mic oscopy (SEM). XPS
con i med he success ul inco po a ion o he saccha in dopan in he PPy ma ix wi h dopan a es inc easing
unde agg essi e acidic condi ion. While SEM e eals ha PPy coa ings o med h ough ex ended elec o-
polyme iza ion enhance co osion esis ance on AISI 316L h ough hei densely cauli lowe s uc u e. The
enhanced long- e m co osion p o ec ion obse ed can be a ibu ed o he obus physical ba ie and sou ce o
anodic p o ec ion compa ed o uncoa ed 316L.
1. In oduc ion
Du ing he las decades, he de elopmen o p o on exchange
memb ane uel cells has become inc easingly a ac i e due o hei high
ene gy densi y, low ope a ing empe a u e and weigh , and no emission
o pollu an s. Fu he mo e, PEMFC p esen s widesp ead ield applica-
ion o powe ing ehicles, ains, and ships, and dis ibu ed powe
gene a ion. In addi ion o ha , PEMFC is conside ed an en i onmen ally
iendly powe sou ce compa ed o con en ional ossil uels [1–3].
Bipola pla es (BPPs) a e used in PEMFC o conduc elec ici y be-
ween he anode and he ca hode, accele a e wa e managemen om
he cell, ensu e s uc u al suppo be ween cell componen s and sepa a e
uel and oxidan [4,5]. P ac ically, a BPP mus mee a se o e-
qui emen s such as high elec ical conduc i i y and co osion esis ance,
high mechanical s eng h, low-cos ma e ials, and low gas pe meabili y
[6]. So a , se e al ma e ials ha e been used as bipola pla es. G aphi e
BPP has shown good elec ical conduc i i y and high co osion e-
sis i i y. Al hough i s low mechanical s eng h makes i necessa y o use
a hea ie BPP and he e o e esul ing in highe cos s and a mo e
complica ed ab ica ion p ocedu e [7,8].
Me allic bipola pla es a e supposed o be an al e na i e o g aphi e
BPP as hey mee he majo equi emen s o a BPP [9]. Gene ally,
a ious me als and alloys a e used as BPPs, such as aluminum, i anium,
s ainless s eel (SS), coppe , and AISI 316L, among o he s. Howe e , he
majo incon enience o me allic BPP is hei co osion beha iou . In
ac , long con ac o he me al wi h he acidic and humid en i onmen o
PEMFC leads o he o ma ion o a passi a ion oxide laye due o he
elease o me al ions; he e o e, he elec oly e and memb ane elec ode
a e con amina ed causing an inc ease in con ac esis ance, lowe ing he
ionic conduc i i y, al e ing cell pe o mance, and sho ening cell li e
[9–12].
The e o e, se e al a emp s ha e been made by esea che s on he
* Co esponding au ho . The mal Enginee ing G oup, School o Enginee ing, Uni e sidad de Se illa, Camino de los Descub imien os, s/n, 41092, Se illa, Spain.
E-mail add ess: [email p o ec ed] (A. I anzo).
Con en s lis s a ailable a ScienceDi ec
In e na ional Jou nal o Hyd ogen Ene gy
jou nal homepage: www.else ie .com/loca e/he
h ps://doi.o g/10.1016/j.ijhydene.2025.05.122
Recei ed 18 June 2024; Recei ed in e ised o m 6 May 2025; Accep ed 8 May 2025
In e na ional Jou nal o Hyd ogen Ene gy 138 (2025) 1066–1076
A ailable online 22 May 2025
0360-3199/© 2025 The Au ho s. Published by Else ie L d on behal o Hyd ogen Ene gy Publica ions LLC. This is an open access a icle unde he CC BY-NC license
( h p://c ea i ecommons.o g/licenses/by-nc/4.0/ ).
basis o su ace modi ica ion echnologies using a o dable and inex-
pensi e ma e ials capable o enhancing me allic BBP pe o mance in
uel cell en i onmen s. Me allic coa ings ha e been s udied as Ti anium
Ni ide Oxide [13], Sil e [14], Ch oma e [15], Ch oma e ni ide [16],
e c. Howe e , he majo conce n o me allic coa ing is he cos o
deposi ion p ocess as hey equi e sophis ica ed equipmen such as
chemical/physical apou deposi ion, elec opho e ic deposi ion, pack
cemen a ion, e c., which a e less sui able o mass p oduc ion.
In ecen yea s, mos BPs a e made up o me als. Speci ically,
Aus eni e s ainless s eel 316L is widely econgnised as a po en ial ma-
e ial o BPs. This is a ibu ed o i s high he mal and elec ical con-
duc i i y, high mechanical s eng h and low manu ac u ing cos [10].
Howe e , he supe io co osion esis ance o AISI 316L is due o he
ch omium con en , which o ms a hin ilm o C
2
O
3
. S udies ha e
shown ha highe ch omium and nickel con en ns he s eel esul in
hinne passi e ilm, which con ibu es in dec easing in e acial con ac
esis ance. Howe e , a majo conce n when using AISI 31L as bipola
pla e is he leaching o me al ions caused by co osion [11]. While AISI
316L is mo e expensi e han o he s eels. Howe e , i is s ill mo e
cos -e ec i e compa ed o p ecious me als such as pla inum and gold
[12].
In pa icula , he limi ed co osion esis ance o AISI 316L in highly
acidic en i onmen s is a ibu ed o he non-uni o mi y o i s passi e
oxide ilm, cha ac e ised by ch omium-deple ed a eas. This ac o con-
ibu es o i s poo pe o mance unde such condi ions, es ic ing i s
applica ions in PEMFCs [13].
In ecen yea s, conduc i e o ganic coa ings ha e ecei ed much
in e es as a p o ec ion ilm o BPP co osion. Typically, conduc i e
polyme s a e easy o syn hesise, p o ide good elec ical conduc i i y,
good s abili y, and good an i-co osion pe o mance [14–17]. In
pa icula , polyaniline has been elec ochemically deposi ed on 316L SS
by Le e al. [18]. The au ho s epo ed an imp o emen in co osion
esis ance. The polyaniline passi a ion ilm pe sis s a e se en days o
exposu e o he simula ed en i onmen o PEMFC (sul u ic acid) ye
316L SS was b oken a e h ee days. Polypy ole is widely s udied as a
conduc ing polyme due o i s excellen elec ical conduc i i y, ease o
syn hesis, and en i onmen al s abili y. PPy coa ing was also s udied by
se e al esea che s using di e en elec odeposi ion me hods (gal a-
nos a ic, po en ios a ic, cyclic ol amme y), and di e en bipola pla e
me als such as 304SS [19–21], aluminium [22], ca bon s eel, coppe
[26], and o he s. The p ope ies o PPy coa ings a e signi ican ly in lu-
enced by he choice o dopan s which a e p ima ily in eg a ed in he
polyme chain du ing py ole elec odeposi ion o imp o e he elec-
ical, chemical and mechanical cha ac e is ics o PPy coa ing. Sodium
saccha in, a well-known a i icial swee ening agen , is commonly used
in elec odeposi ion due o i s excellen adso p i e p ope ies [20].
Ac ing as an inhibi o o he hyd ogen e olu ion eac ion and wa e
educ ion a high po en ials, hus imp o ing he polyme ’s s uc u e.
When added in small amoun s o he py ole solu ion, saccha in in-
e ac s wi h py ole, leading o enhanced mechanical p ope ies o he
coa ing in e ms o esis ance o physical damage, du abili y, end
s eng h. Consequen ly, he pa h o co osi e subs ances becomes
slowe , mo e complex, and longe .
Fu he mo e, he addi ion o sodium saccha in du ing py ole elec-
odeposi ion enhances co osion esis ance by o ming a p o ec i e
laye ha e ec i ely inhibi s he co osion o he unde lying me al,
ollowing his ini ial adso p ion, he elec odeposi ion eac ion p o-
ceeds, leading o he o ma ion o PPy coa ing [21,22]. Sodium
saccha in and PPy exhibi enhanced s abili y unde a ious condi ions.
This s abili y is c ucial o bipola pla es, which a e subjec o luc u-
a ing empe a u es, humidi y le els, and chemical exposu es in uel cell
ope a ions [23,24]. The enhanced s abili y ensu es ha he p o ec i e
and conduc i e p ope ies o coa ing a e main ained o e p olonged
pe iods [25].
The co osion beha iou o polypy ole is in luenced by a ious
ac o s, such as i s s uc u e and elec onic p ope ies. These ac o s a e
closely ela ed o he p ocess and echniques o making he ilm, he
ype o ma e ial o which hey a e applied, he chemicals in ol ed and
he empe a u e. One o he signi ican ad an ages o using sodium
saccha in is i s abili y o p e en me al co osion [24]. Du ing he
elec odeposi ion o PPy, sodium saccha in adso bs on o he elec ode
subs a e o ming a p o ec i e laye which e ec i ely inhibi s he
co osion o he unde lying me al, ollowing his ini ial adso p ion, he
elec odeposi ion eac ion p oceeds, leading o he o ma ion o he
desi ed conduc ing polyme [25].
To he bes o ou knowledge, polypy ole coa ings ha e ne e been
s udied in s imula ed PEMFC en i onmen on an AISI 316L bipola pla e.
In his wo k, polypy ole ilms ha e been elec odeposi ed on AISI 316L
bipola pla e by cyclic ol amme y and gal anos a ic modes. The
co osion s udy was pe o med using open ci cui (OCP), Ta el me hod,
and elec ochemical impedance spec oscopy.
In ou s udy, we op o he elec osyn hesis o polypy ole wi h
sodium saccha in, which is a ela i ely la ge and immobile molecule
ha has a special abili y o a ac posi i e ions while epelling nega i e
ones. This esea ch ocusses p ima ily on conduc ing a compa a i e
analysis o he co osion esis ance exhibi ed by he PPy coa ing unde
a ious elec odeposi ion du a ions. The s udy aims a s udying he
impac o he mo phological s uc u e o he ilm on i s co osion
beha iou . This was especially use ul when we applied PPy doped wi h
saccha in as a p o ec i e coa ing on aus eni ic s ainless s eel 316l o
p o ec agains co osion, especially in he p esence o sul u ic acid and
hyd o luo ic acid.
2. Expe imen al de ails
2.1. Chemicals
Py ole (>98 %) was pu chased om Sigma-Ald ich and dis illed
p io o use. Sodium saccha in sal (C
7
H
4
NNaO
3
S.2H
2
O) was pu chased
om Tokyo chemical indus y. Sul u ic acid H
2
SO
4
(>99 %) and Hy-
d o luo ic acid (40 %) we e pu chased om PanReac AppliChem.
2.2. Elec ochemical appa a us
In his s udy, he 316L aus eni ic s ainless s eel shee used as a bi-
pola pla e was selec ed as he subs a e and i s chemical composi ion is
gi en in Table 1. The s eel shee wi h an exposed su ace a ea o 1 ×1
cm
2
is deg eased by ul asonic ib a ion wi h ace one and cleaned wi h
dis illed wa e o 15 min, and hen inally d ied. De-ionized wa e was
used o he solu ion p epa a ion. Polypy ole elec ochemical poly-
me iza ion was ca ied ou in a single compa men wi h AISI 316L as
he wo king elec ode (WE), g aphi e as he coun e elec ode (CE), and
Ag/AgCl as he e e ence elec ode. The elec odes we e connec ed o a
Gam y 3000 po en ios a /gal anos a moni o ed by he Gam y so wa e
amewo k. PPy elec opolyme iza ion was pe o med on AISI 316L a
oom empe a u e in an aqueous elec oly e medium con aining 0.5 M
py ole and 0.1 M sodium saccha in in gal anos a ic mode by applying
2 mA/cm
2
du ing 30 min. The p epa ed sample was labelled PPy/316L.
2.3. Co osion es
Co osion es s we e pe o med on uncoa ed AISI 316L and PPy/
316L elec odes in a simula ed co osi e medium o PEMFC. Acco ding
o he li e a u e, di e en acid concen a ions could be used as a simu-
la ed co osion medium such as 0.1 M H
2
SO
4
[26], 0.5 M H
2
SO
4
[27],
0.1 M H
2
SO
4
+2 ppm [30], and 0.5 M H
2
SO
4
+2 ppm [28].
Table 1
Chemical composi ion o AISI 316L used in his in es iga ion (weigh %).
Elemen C Si Mn C Ni Mo
%<0.03 0.50 1.50 17.80 12.70 2.60
S. Ben Jadi e al.
In e na ional Jou nal o Hyd ogen Ene gy 138 (2025) 1066–1076
1067
The co osion beha iou s o he uncoa ed AISI 316L and ilm coa ed
elec odes we e s udied by po en iodynamic pola isa ion and elec o-
chemical impedance spec oscopy. Elec ochemical measu emen s we e
pe o med wi h he Gam y 3000 Po en ios a /Gal anos a ins umen .
Po en iodynamic cu es we e eco ded s a ing om ±150 mV ela i e
o he equilib ium po en ial o he elec odes wi h a scan a e o 1 mV/s
a e 2 h o exposu e o co osi e media. AC impedance measu emen s
we e pe o med a an open ci cui po en ial measu ed be ween 100 kHz
and 0.01 Hz and a a cons an AC ampli ude o 5 mV o di e en im-
me sion imes (2, 96, and 192 h).
2.4. SEM, XPS, and con ocal analysis
The s uc u e o PPy coa ing was in es iga ed by scanning elec on
mic oscopy (SEM) using a FEO TENEO ins umen , wi h he dis ance
be ween he sample and he objec i e lenses was app oxima ely 15 mm.
X-Ray pho oelec on spec oscopy (XPS) was pe o med using a Shi-
madzu Co: AXIS ULTRA equipped wi h an Mg K
α
x- ay sou ce ope a ed
a 15 kV. The ope a ing p essu e in he analysis chambe is less han
10
−7
Pa, and he analysis a ea was 2 mm
2
. All spec a we e co ec ed
acco ding o he binding ene gy o ca bon C1s a 285 eV. Spec a ana-
lyses we e pe o med using CasaXPS so wa e. Thickness measu emen s
we e aken using con ocal mic oscopy wi h Senso a S-Neox.
3. Resul s and discussions
3.1. Polypy ole elec odeposi ion
PPy elec odeposi ion was pe o med di ec ly on an AISI 316L
elec ode in an aqueous solu ion using sodium saccha in as he dopan .
Fig. 1(a) depic s he cyclic ol amme y o PPy elec opolyme iza ion
du ing 10 cycles in he po en ial window o −1 o 1.5 V ( s Ag/AgCl).
Based on, he ol age scanning in he i s cycle, an inc ease in he
cu en densi y is obse ed a 0.75 V ( s Ag/AgCl) co esponding o he
py ole oxida ion po en ial and he o ma ion o PPy. Du ing successi e
scans, an inc ease in he cu en densi y is obse ed om he i s cycle
o he se en h, indica ing he o ma ion o hicke PPy. The ol ame ic
p o ile is simila o he ol ammog ams ob ained o PPy in aqueous
media [29,30]. Ch onopo en iome ic mode was in es iga ed o elec-
odeposi he PPy ilm on he AISI 316L. Fig. 1(b) p esen s he po en ial
e sus ime cu e o PPy elec odeposi ion a a cu en densi y o 2
mA/cm
2
. The elec opolyme iza ion o py ole in he p esence o sodium
saccha in is a complex p ocess in ol ing se e al s eps, as desc ibed in
he ollowing de ailed mechanisms.
In he ini ial s age o elec opolyme iza ion, i is obse ed in he
ini ial s age o elec opolyme iza ion ha he po en ial inc eases wi h
oxida ion o py ole monome s o oligome s.
In he second s age, an ins an aneous dec ease in po en ial is
obse ed due o he elec opolyme iza ion o py ole on AISI 316L. In
ac , he signi ican eac i i y o gene a ed py ole adical ca ions leads
o he o ma ion o dime and oligome s species by in e ac ing wi h one
ano he o wi h neu al py ole monome s, as ollow.
A e wa ds, he PPy coa ing g ows un il he p ocess is comple ed,
esul ing in a slow po en ial dec ease. Du ing elec opolyme iza ion,
sodium saccha in ac s as a dopan by in eg a ing in o he polypy ole
ma ic o main ain cha ge neu ali y, acco ding o he eac ion bellow
[31,32].
In he elec opolyme iza ion o py ole, sodium saccha in can
s ongly adso b on o he me al elec ode su ace ia i s sul u a om,
which enhances he in e ac ion be ween py ole monome s and he
Fig. 1. (a) Vol amme ic p o ile o he po en iodynamic syn hesis o PPy; scan a e: 100 mV/s. (b) Ch onoampe og ams eco ded du ing PPy elec osyn hesis a 2
mA/cm
2
in aqueous medium (0.5 M Py ole +0.1 M C
7
H
4
NNaO
3
S) aqueous medium.
S. Ben Jadi e al.
In e na ional Jou nal o Hyd ogen Ene gy 138 (2025) 1066–1076
1068
elec ode. This adso p ion acili a es elec on ans e , p omo ing he
polyme iza ion p ocess. The induc i e e ec o saccha in u he s abi-
lizes he in e media e species, leading o enhanced elec ical and me-
chanical p ope ies o polypy ole ilm [33].
Based on he esul s o he ol ame ic p o ile, we can conclude ha
he op imal po en ial o py ole elec opolyme iza ion is 0.7, s Ag/
AgCl and he applied cu en densi y o 2 mA/cm
2
leads o he o ma ion
o an adhe en PPy coa ing as he cons an po en ial eached is high
enough o comple e polyme iza ion [34]. I is usually assumed ha he
ini ial high po en ial in cons an cu en pola isa ion is due o he
pola isa ion o cons an cu en s.
To calcula e he a adaic e iciency, we syn hesised PPy elec o-
chemically using he gal anos a ic me hod. We applied a cu en densi y
j =2mA/cm
2
du ing di e en imes
1
=5min,
2
=10 min and
3
=30
min o he AISI 316L wo king elec ode. Fo each ial, we weighed he
elec ode be o e and a e he deposi ion. Be o e measu emen , he
samples we e d ied o 1 h a 100 ◦C and hen cooled in a desicca o . We
de e mined he elec opolyme iza ion e iciency (γ) using he ollowing
equa ion:
γ=(2+y)(ΔmF +
τ
jMme /Z)
Q1(MM+yMA)(4)
Whe e Δm is he mass a ia ion, j is he cu en densi y, whe e j =Q/
τ
,
M
me
is he a omic mass o he subs a e, M
M
is he molecula mass o he
monome , M
A
is he mola mass o he doping anion,
τ
is he pola isa ion
ime, and Z is he ca ion me al cha ge.
The exp ession o he hickness o he PPy coa ing is de ined by he
ollowing equa ion:
θ=m h γ
A
ρ
(5)
And he m
h
is de ined by he ollowing equa ion:
m h =M1(MM+yMA) × 1
(2+y)F(6)
Whe e A is he su ace o he wo king elec ode and
ρ
is he polyme
densi y o PPy.
The combina ion o Eq. (1) and Eq. (2) yields he ollowing equa ion:
θ=Q1(MM+yMA)γ
(2+y)F A
ρ
(7)
Table 2 p esen s he esul s o he heo e ical hickness o PPy
calcula ed a di e en elec opolyme iza ion imes.
3.2. SEM analysis
The co e age o he subs a e su ace is one o he mos impo an
ac o s in p e en ing co osion. In his ega d, he co e age o PPy on
s ainless s eel was examined by SEM du ing di e en elec ocep ion
pe iods. Fig. 2(a–c) co esponds o saccha in doped samples du ing 5,
10, and 30 min ( he inse s a e low-magni ica ion mic og aphs o he
co esponding samples). The ypical globula mo phology is shown o
all samples wi h a el e y su ace simila o ha o cauli lowe . Se e al
s udies ha e epo ed he same mo phology o polypy ole syn hesised
in a ious elec oly ic media [29,35,36]. I has been epo ed ha
cauli lowe -like mo phology is ela ed o he di icul y o dopan
in e cala ion in he diso de ed polyme ic ma ix [37]. Mic o-sphe ical
g ains wi h diame e s anging om 0.5 o 15
μ
m we e obse ed.
These sphe es a e in e connec ed. The size o he o med sphe ical
s uc u es is no iceably a ec ed by he inc ease in he elec odeposi ion
ime. Thus, he inc ease in he elec opolyme iza ion ime esul ed in
hicke su ace and g ea e compac ion. The e o e, he 30 min coa ing
can p o ide long- e m co osion p e en ion due o he s onge physical
ba ie e ec .
Fig. 3 shows he su ace mo phologies o ba e s eel and o PPy coa ed
s eel a e po en iodynamic pola isa ion in di e en media. A e
pola isa ion, nume ous pi s could be seen in SEM images o he uncoa ed
su ace (Fig. 3(a)), while coa ed s eel does no unde go pi ing co osion
(Fig. 3(b-e)). The mo phology o PPy in 0.1 M H
2
SO
4
and 0.5 M H
2
SO
4
media, cha ac e ised by he o ma ion o sphe ical agg ega es, emains
almos in ac . A close iew e eals ha he diame e dec eases sligh ly
wi h inc easing concen a ion o sul u ic acid [38,39]. This esul shows
he e ec i eness o he PPy coa ing in inhibi ing he di usion o co -
osi e SO
4
2−
anions o he subs a e, p e en ing anodic dissolu ion and
ca hodic eac ion du ing co osion.
The co osion a e accele a es a e adding hyd o luo ic acid, and
only a ew small pa icles appea o ha e emained on he su ace (Fig. 3
(d)). The disappea ance o la ge polypy ole pa icles, such as
cauli lowe -like s uc u es, a e imme sion in a high-concen a ion acid
medium is p ima ily due o he b eakdown and dissolu ion o he la ge
PPy pa icles, esul ing in hei disappea ance om he solu ion. Less
damage is obse ed on he su ace o he AISI 316L wi h 0.1 M H
2
SO
4
han wi h 0.5 M H
2
SO
4
.
Sul u ic acid, a s ong acid and oxidizing agen c ea es a highly
acidic en i onmen by dona ing p o ons (H
+
), which a acks he me al
and accele a e me al ion dissolu ion [40,41]. On he o he hand, HF
enhances me al dissolu ion by o ming soluble complexes wi h me al
ions ia luo ide ions (F
⎯
) [42,43]. When bo h H
2
SO
4
and HF a e p esen ,
hei syne ge ic e ec accele a es he co osion p ocess, leading o a
con inuous and agg essi e a ack on he me al su ace and esul ing in a
highe co osion a e [44].
3.3. Co osion p o ec ion
3.3.1. G a ime ic s udy
The s udy ocused on in es iga ing how he co osion o PPy elec-
osyn he ised on AISI 316L a di e en imes (5, 10, and 30 min) in 0.1
M H
2
SO
4
solu ion was a ec ed. Thus, he weigh loss me hod was used
a e imme sing he samples o 4 days a oom empe a u e. The
esul ing co osion a e (CR) and inhibi ion e iciency
η
W(%)we e
calcula ed using he ollowing equa ions [45,46]:
CR=wb−wa
A (8)
η
W(%) = (1−wi
w0)×100 (9)
Whe e wband wa ep esen he weigh o he specimen be o e and a e
imme sion in he co osi e solu ion, and w0and wi p esen he alues o
co osion weigh losses in coa ed and uncoa ed specimen. A e e s o he
o al a ea o he specimen (cm
2
), while ep esen s he exposu e ime in
hou s (h).
The alues ob ained a e summa ized in Table 3. I is clea ly obse ed
ha elec osyn he ized coa ings a 30 min demons a e supe io co o-
sion esis ance, as e idenced by weigh loss measu emen s and inhibi-
ion e iciency. Con e sely, co osion p e en ion elies on impeding
di usion, and a educ ion in coa ing hickness, as well as he appea ance
o po es, laws, and c acks, esul s in an inc eased co osion a e [47].
Thus, he ollowing s udy will ocus on PPy/316L (
3
). The esul s o ou
s udy indica e ha he e was no no iceable imp o emen in co osion
esis ance wi h he coa ing imes beyond 30 min o
elec opolyme iza ion.
Table 2
The heo e ical hickness o PPy calcula ed a di e en elec opolyme iza ion
imes
1
=5 min,
2
=10 min, and
3
=30 min.
Label Theo e ical hickness (
μ
m) Expe imen al hickness (
μ
m)
PPy/316L (
1
)5.5 5
PPy/316L (
2
)8 7.5
PPy/316L (
3
)19.6 20
S. Ben Jadi e al.
In e na ional Jou nal o Hyd ogen Ene gy 138 (2025) 1066–1076
1069
3.4. XPS analysis
XPS was u ilised o cha ac e ise he su ace chemis y o he PPy, o
e i y he o ma ion o he coa ing, examining he le el o oxida ion, and
iden i y he chemical bonding o he polyme . The high- esolu ion C1s
spec um o he PPy ilm a e elec opolyme iza ion o 30 min in so-
dium saccha in elec oly e could be di ided in o ou componen s
(Fig. 4). One o he componen s wi h a binding ene gy alue o 284 eV
co esponds o he β - ca bons in he py ole ing. The o he componen s
a e assigned o peaks a 248.92 eV (C
α
), 285.9 eV (C–N), 287.02 eV
(C
–
–
N, C–O), 288.23 eV (C–N
+
, C
–
–
N
+
), and 289.4 (
π
-
π
in e ac ion)
[48–50], which a e he esul o he g oupings ha a ise du ing he
polyme ilm o ma ion p ocess. I is possible ha du ing elec o-
polyme iza ion o he PPy, he ca bon unde goes oxida ion, leading o
Fig. 2. Top iew SEM mic og aphs o he PPy ilm on AISI 316L ob ained a a cu en densi y o 2 mA/cm
−2
s. Ag/AgCl in a 0.5 M py ole and 0.1 sodium saccha in
aqueous solu ion o (a) 5min, (b) 10min and (c) 30 min.
Fig. 3. SEM images o ba e AISI 316L a e pola isa ion in (a) 0.5 M H
2
SO
4
and PPy/316L coa ing a e pola isa ion in di e en media: (b) 0.1 M H
2
SO
4
, (c) 0.5 M
H
2
SO
4
, (d) 0.1 M H
2
SO
4
+2 ppm HF, (e) 0.5 M H
2
SO
4
+2 ppm HF solu ions a oom empe a u e.
S. Ben Jadi e al.
In e na ional Jou nal o Hyd ogen Ene gy 138 (2025) 1066–1076
1070

he o ma ion o C–OH g oups in he i s s ep, ollowed by he o ma ion
o C
–
–
O in he subsequen s ep. The N1s peak obse ed in he PPy ilm is
a mul icomponen peak, co esponding o h ee di e en ni ogen spe-
cies (Fig. 4) [51]. Speci ically, he peak can be decon olu ed in o h ee
componen s a 398.1, 399.4, 400.9, and 401.9 eV, which co espond o
C
–
–
N, –NH, C–N
+
-, and C
–
–
N
+
-, espec i ely [52]. The high binding
ene gy componen a , 400.9 and 401.9 which is assigned o posi i ely
cha ged ni ogen in he polyme ma ix, equi es a nega i ely cha ged
coun e ion, in ou case (C
7
H
4
NSO
3
)
-
, o main ain cha ge neu ali y in
he polyme . Hence, he peaks a e associa ed wi h he doping le el o he
PPy coa ing and a e di ec ly ela ed o hei elec ical conduc i i y. A
highe doping le el ypically leads o a highe elec ical conduc i i y
due o he inc eased numbe o cha ge ca ie s in he polyme ma ix,
and i is exp essed as he a io o he posi i ely cha ged ni ogen a ea
(N
+
) o he o al a ea o he N1s peak (N
+
/N a io). Typical doping
alues o PPy ange om 0.1 o 0.33. In ou s udy, we ound a doping
le el o 0.2 which means ha 20 % o PPy epea uni s we e doped wi h
sodium saccha in.
To allow compa ison, XPS spec a we e collec ed om he PPy ilm
syn he ized in saccha in sodium, and he su ace o he PPy ilm
imme sed in a solu ion con aining 0.1 M H
2
SO
4
, 0.5 M H
2
SO
4
, 0.1 M
H
2
SO
4
+2 ppm HF, and 0.5 M H
2
SO
4
+2 ppm HF espec i ely, as shown
in.Fig. 5. As expec ed, he absence o any addi ional peaks co espond-
ing o he AISI 316L o aces om o he impu i ies demons a es he
high co osion esis ance o he PPy coa ings o he agg essi e medium
o he uel cell.
XPS was employed in his s udy o e alua e he doping a e o PPy
be o e and a e exposu e o co osi e medium. In ac , he doping a e
o PPy is c i ical as i is signi ican ly in luencing he chemical and
elec ical p ope ies o he coa ing. Speci ically, PPy doping ans o m
he coa ing om a neu al s a e o a conduc i e ilm by in oducing
cha ge ca ie s, he eby enhancing i s conduc i i y. The N
+
/N a ion is a
key indica o o assessing he doping s abili y o he ilm. Pa icula ly,
PPy p o ec s AISI 316L h ough anodic passi a ion. Whe e doped PPy
main ain a passi e oxide laye . A dec ease in he doping a e would
indica e coa ing ailu e [53–55] (see Fig. 6).
Table 4 p esen s he XPS decon olu ion o ni ogen peaks in PPy
a e imme sion in a ious acidic media. The s udy demons a es how
di e en concen a ions o sul u ic acid and he addi ion o HF impac
he binding ene gies o ni ogen species and he doping a e o PPy. Fo
each acid ea men , sligh shi s o highe binding ene gies a e
obse ed, indica ing modi ica ions in he ni ogen en i onmen a ib-
u ed o he oxidizing e ec s o H
2
SO
4
and HF. The esul s show ha
inc easing he concen a ions o H
2
SO
4
om 0.1 M o 0.5 M leads o a
sligh inc ease in doping a e om 29.88 % o 32.52 %. Howe e , he
addi ion o HF a 0.1 M H
2
SO
4
esul s in a subs an ial inc ease in doping
47.30 %, and he combina ion o 0.5 M H
2
SO
4
wi h HF yields he highes
doping a e (69,5 %). This enhanced doping and binding ene gy shi a e
a ibu ed o he in ensi ied oxidizing en i onmen p o ided by bo h
acids, which ex ensi ely modi ies he ni ogen en i onmen o he PPy
ma ix. Pa icula ly, when sodium saccha in doped PPy is exposed o
H
2
SO
4
en i onmen , The coa ing inco po a es he anions om he co -
osi e medium, hus highe doping le el is obse ed. This p ocess a-
cili a es he s abiliza ion o he oxidized PPy
+
by p o iding
supplemen a y coun e ions. These obse a ions co ela e wi h SEM
images, which e ealed s uc u al change in PPy.
Pa icula ly, When PPy is exposed o H
2
SO
4
medium, PPy inco po-
a e anions om he co osi e medium, hus highe doping le el is
obse ed, supplying addi ional coun e ions o s abilize PPy
+
. These
indings co ela e wi h SEM images whe e PPy exhibi s swelling due o
Table 3
The co osion pa ame e s o polypy ole-coa ed and uncoa ed AISI 316L in 0.5
M H
2
SO
4
acqui ed by weigh loss measu emen s.
CR (mg cm
−2
h
−1
)
η
W(%)
Blank 3.4 -
PPy/316L (
1
) 1.7 49.9
PPy/316L (
2
) 1.35 60.41
PPy/316L (
3
) 0.26 92.30
Fig. 4. C1s and N1s decon olu ion o PPy ilm syn hesised using he gal anos a ic me hod (2 mA/cm
2
o 30 min) on he AISI 316L elec ode in 0.5 M py ole and
0.1 sodium saccha in.
Fig. 5. XPS su ey o polypy ole coa ed on AISI 31L a e 4 days o imme sion
in a)0.1 M H
2
SO
4
, b) 0.5 M H
2
SO
4
, c) 0.1 M H
2
SO
4
+2 ppm HF and d) H
2
SO
4
+
2 ppm HF solu ion.
S. Ben Jadi e al.
In e na ional Jou nal o Hyd ogen Ene gy 138 (2025) 1066–1076
1071
excessi e anions up ake.
XPS analysis was also used o e alua e he e ec o adding HF o
H
2
SO
4
on he elemen al composi ion o he AISI 316L su ace a e im-
me sion in highly co osi e medium. Fig. 5 displays he co esponding
XPS spec a o he AISI 316L a e imme sion in 0.1 M H
2
SO
4
and 0.1 M
H
2
SO
4
+2 ppm HF espec i ely, and Table 5 p o ides he a omic
concen a ions o he elemen s a he espec i e su aces. As p esen ed in
he able, oxygen is he dominan elemen on all he AISI 316L imme sed
in co osi e medium due o he o ma ion o a passi e oxide ilm. I is
also obse ed ha he e is an inc ease in he a omic pe cen age o
ch omium wi h he addi ion o HF o he co osi e medium.
Fig. 7 Also indica es he p esence o nickel wi h he addi ion o HF,
which may be ela ed o possible oxida ion o nickel. This obse a ion
sugges s ha he nickel, which is a componen o he AISI 316L, may
ha e unde gone oxida ion due o i s exposu e o he agg essi e en i-
onmen c ea ed by HF. The oxida ion p ocess could cause nickel a oms
wi hin he alloy o mig a e o he su ace and o m nickel oxides o o he
nickel compounds, which no only al e s he su ace composi ion bu
also in luence he o e all co osion esis ance o he ma e ial, po en-
ially impac ing i s pe o mance in highly acidic and luo ide con aining
Fig. 6. N1s decon olu ion o PPy elec osyn hesised on he AISI 316L elec ode in 0.1 M H
2
SO
4
, 0.5 M H
2
SO
4
, 0.1 M H
2
SO
4
+2 ppm HF and H
2
SO
4
+2 ppm
HF solu ion.
Table 4
XPS decon olu ion o ni ogen peaks in PPy a e imme sion in a ious acidic
media.
Acid medium Binding ene gy (eV) Assignmen Doping a e (%)
0.1 M H
2
SO
4
399.14 C
–
–
N 29.88
399.85 C–N
400.84 C–N
+
401.96 C
–
–
N
+
0.5 M H
2
SO
4
399.00 C
–
–
N 32.52
399.69 C–N
400.51 C–N
+
401.64 C
–
–
N
+
0.1 M H
2
SO
4
+HF 399.18 C
–
–
N 47.30
400.08 C–N
401.18 C–N
+
402.05 C
–
–
N
+
0.5 M H
2
SO
4
+HF 398.92 C
–
–
N 69.5
400.31 C–N
401.19 C–N
+
402.28 C
–
–
N
+
Table 5
A omic pe cen age o uncoa ed AISI 316L in sul u ic acid.
316L 0.1 M H
2
SO
4
316L 0.1 M H
2
SO
4
+2 ppm HF
C 1s 38.36 9.65
O 1s 28.26 48.00
Cl 2p –6.86
S 2p –1.63
Mo 3d 3.40 0.14
C 2p 9.95 28.06
Ni 2p –5.67 Fig. 7. AISI 316L XPS su ey a e 4 days o imme sion in a)0.1 M H
2
SO
4
and
b) 0.1 M H
2
SO
4
+2 ppm HF.
S. Ben Jadi e al.
In e na ional Jou nal o Hyd ogen Ene gy 138 (2025) 1066–1076
1072
en i onmen s [56].
3.4.1. Ta el Pola isa ion
Ta el Pola isa ion measu emen s a e used o es he co osion pe -
o mance o coa ed and uncoa ed AISI 316L in 0.1 M and 0.5 M H
2
SO
4
.
The co osion po en ial (E
co
) and co osion cu en (J
co
) we e e al-
ua ed by he in e sec ion o he co esponding anodic and ca hodic
pola isa ion (see Fig. 8). Elec ochemical pa ame e s calcula ed by
i ing he po en iodynamic pola isa ion cu es a e summa ized in
Table 6. Lowe J
co
, and a mo e posi i e E
co
indica e ha he coa ing is
mo e di icul o co ode by acidic media [14]. The co osion o AISI
316L in sul u ic acid in ol es he des uc ion o he passi e ilm o
ch omium oxide by he eac ion:
C 2O3+3H2SO4→2C 3++3SO42−(10)
The ca hodic eac ion in ol es he educ ion o hyd ogen ions om
he sul u ic acid wi h elec ons om he me al as ollow:
2H++2e−→H2(11)
I is obse ed ha he E
co
o uncoa ed AISI 316L in 0.1 M H
2
SO
4
exhibi s s sligh ly posi i e co osion po en ial indica ing ha he un-
coa ed subs a e exhibi s mode a e esis ance o co osion in a less
concen a ed en i onmen . Howe e , when imme sed in s highly acidic
en i onmen (0.5 M H
2
SO
4
) a highly nega i e alue was obse ed
indica ing a high suscep ibili y o co osion in a mo e concen a ed
acidic en i onmen hus dec easing he co osion esis ance. O he wise,
he coa ed me al has a high posi i e co osion po en ial in 0.1 M H
2
SO
4.
This signi ican ly posi i e alue sugges s excellen co osion esis ance
in a less concen a ed acidic medium. In ega ds o a mo e highly acidic
en i onmen , he co osion po en ial is nega i e bu i is less nega i e
compa ed o he uncoa ed AISI 316L in he same en i onmen (0.5 M
H
2
SO
4
).
I
co
is ano he c i ical indica o in Ta el analysis, ep esen ing he
a e o co osion. Lowe I
co
alues gene ally indica e be e co osion
esis ance. In summa y, we ind ha he I
co
e ol es in a noble di ec-
ion, which means ha he polypy ole coa ing p esen s excellen
co osion esis ance in a less concen a ed acidic medium and e ains a
conside able le el o p o ec ion in a mo e concen a ed acid, hough he
e ec i eness diminishes as he acid concen a ion inc eases.
Wang e al. and Gha bi e al. also ob ained simila esul s o 316
s ainless s eel in 0.1 M sul u ic acid solu ion [57] and 0.5H
2
SO
4
[44].
The PPy coa ing in he a icle shi s Eco posi i ely by abou 251 mV
compa ed o ba e coppe , which is consis en wi h imp o ed co osion
esis ance. Ou s udy demons a es ha he PPy coa ing signi ican ly
enhance he co osion esis ance o AISI 316L in acidic en i onmen s,
achie ing an imp essi e educ ion in Ico o 4.59 ×10
−4
μ
A. cm/cm
2
in
0.1 M H
2
SO
4
. This pe o mance is supe io o some PPy based coa ings
on di e en subs a es, such as he PPy dopped wi h ch omium ni ide
[58] PPy doped wi h oxalic acid [59], TnNB and TiNBN coa ings on
316L s ainless s eel [60].
3.4.2. Elec ochemical impedance spec oscopy (EIS)
Elec ochemical impedance spec oscopy measu emen s allow he
cha ac e isa ion o he in e ace esis ance beha iou o he elec oly e
and he me al exposed o a co osi e medium wi h oxides and adso bed
species. Fig. 9 shows he ypical Nyquis plo o he AISI 316L elec ode
o e ime in he 0.1 M H
2
SO
4
and 0.5 M solu ions a oom empe a u e.
The dep essed semici cle shown in he Nyquis plo is gene ally a ib-
u ed o he high oughness, po osi y, o inhomogenei y o he elec ode
su ace [61]. A he beginning o imme sion, i is obse ed ha he
high- equency semici cle expanded as he imme sion ime inc eased
om 2 h o imme sion o 96 h which can be a ibu ed o he spon a-
neous g ow h o he passi e ilm o he AISI 316L elec ode. A e 192 h
o imme sion in sul u ic acid, he low equency semici cle becomes e y
la ened o bo h concen a ions, which is ela ed o he weakness o he
passi e ilm and he appea ance o di usion p ocess h ough a po ous
laye [62]. When compa ing he EIS plo s ob ained o bo h concen-
a ions, i is seen ha in he 0.1 M H
2
SO
4
solu ion he e is a highe
impedance, indica ing ha he AISI 316L is less co oded han he one
imme sed in 0.5 M H
2
SO
4
. These esul s a e consis en wi h hose ound
by Li e al. [63].
The AISI 316L elec ode exposed o sul u ic acid a di e en con-
cen a ions can be simula ed by he equi alen ci cui p esen ed in
Fig. 10. The simula ed heo e ical impedance pa ame e s a e summa-
ized in Table 7. R
s
ep esen s he elec oly e esis ance; R
and CPE
ep esen he esis ance and capaci ance o he po ous co osion p oduc
laye ; R
c
ep esen s he ans e esis ance; CPE
dl
p esen s double-laye
capaci ance. As a esul o a nonideal capaci i e beha iou , he CPE
in e ace was used ins ead o pu e capaci ance.
I can be seen ha he R
alues inc eased wi h ime be o e 96 h o
imme sion, which is due o he passi a ion o AISI 316L in an acidic
en i onmen . Howe e , his passi e ilm g adually de e io a es due o
he pene a ion o co osi e p oduc s, leading o a dec easing end o R
alues a e 96 h o imme sion. Fu he mo e, he dec ease in R
c
a e 96
h o imme sion indica es ha AISI 316L is a acked by he co osi e
species. The inc ease in R
c
alues du ing his pe iod is a ibu ed o he
accumula ed co osion p oduc s on he su ace o he AISI 316L.
The i ed esul s o PPy/316L co espond o he equi alen ci cui
p esen ed in Fig. 10(b). These ci cui s a e consis en wi h hose known
in la ge pa in he li e a u e o his ype o coa ing. In his sys em, Rc is
he esis ance o he polypy ole coa ing po es, CPE
C
is he cons an
phase elemen o he polyme ic coa ing, and Zd is he Wa bu g imped-
ance. I should be no ed ha hese models ake in o accoun he exis-
ence o po es in polyme ic coa ings. Fig. 9(c and d) show o he
imme sion ime o 2 h ha he Nyquis plo p esen s wo di e en be-
ha io s: a single capaci i e loop a high equencies and an inclined line
a ibu ed o semi-in ini e di usion p ocess associa ed in he low e-
quencies. Fo he o he imme sion imes (96 and 192 h) he impedance
Fig. 8. Po en iodynamic pola isa ion cu es o ba e AISI 316L and PPy/AISI in
0.1 M H
2
SO
4
and 0.5 M H
2
SO
4
solu ions a oom empe a u e wi h a scan a e o
1 mV/s.
Table 6
Pola isa ion pa ame e s o he AISI 316L and PPy/316L coa ing in 0.1 M H
2
SO
4
and 0.5 M H
2
SO
4
solu ions a oom empe a u e.
E
co
(mV) I
co
(
μ
A)
AISI 316L In 0.1 M H
2
SO
4
37 713 4.273
In 0.5 M H
2
SO
4
−304,284 76.133
PPy/316L In 0.1 M H
2
SO
4
187 335 4.59 ×10
−4
In 0.5 M H
2
SO
4
−192 967 8.894
S. Ben Jadi e al.
In e na ional Jou nal o Hyd ogen Ene gy 138 (2025) 1066–1076
1073
beha iou is simila o ha obse ed in he case o ba e AISI 316L, wi h
capaci i e beha iou a high equency. The i ed R
c
alues p esen ed in
Table 8 indica e ha he coa ing exhibi s a low ini ial R
c
alue compa ed
o he uncoa ed AISI 316L. The low R
c
alue polyme ic ilm is mainly
due o i s conduc i e p ope ies. The inc ease in R
c
indica es ha he PPy
coa ing is educed and he dec eased coa ing conduc i i y dec eases he
conduc i i y du ing imme sion, aking he sca e ing beha iou a low
equencies o indica e ha he mo emen o coun e ions h ough he
polypy ole backbone. Du ing dedoping ( he educ ion p ocess),
saccha in ions emain apped in he polyme laye due o hei low
Fig. 9. Nyquis plo o he ba e AISI 316L in (a) 0.1 M H
2
SO
4
, (b) 0.5 M H
2
SO
4
and PPy/316L in (c) 0.1 M H
2
SO
4
, (d) 0.5 M H
2
SO
4
.
Fig. 10. Equi alen ci cui o he EIS plo s o uncoa ed AISI 316L/sul u ic acid
(a) and PPy/AISI 316L (b), Rs, elec oly e esis ance; CPE
and R
a e a ibu ed
o he capaci ance and esis ance o he oxide ilm, espec i ely; CPEdl and Rc
a e a ibu ed o he capaci ance o he double laye and he cha ge ans e
esis ance, espec i ely, and Z
d
, di usion impedance.
Table 7
Elec ochemical pa ame e s alues ob ained by EIS simula ion o uncoa ed
AISI316L a e a ious exposu e imes in solu ion wi h 0.1 M H
2
SO
4
and 0.5 M
H
2
SO
4
.
0.1 M H
2
SO
4
0.5 M H
2
SO
4
2 h 96 h 192 h 2 h 96 h 192 h
Rs (Ω) 5906 5825 4883 1358 1389 1281
CPE
dl
(F.
s
n−1
)
54,72e-
6
41,15e-
6
0,178
7e-3
78,69e-6 96,44e-6 0,145
3e-3
n
dl
0,910 5 1 0,823 3 0,886 4 1 0,856 7
Rc (Ω) 806 278 1,52e6 42 798 449 834 176 403 70 675
CPE
(F.
s
n−1
)
0,613
9e-3
0,174
1e-3
0,202
9e-3
7,621e-6 98,7e-6 0,245
8e-3
n
0,701 7 0,826 0,894 6 0,8874e-
3
0,869 0,843 8
R (Ω) 1027 12 585 126 0,085 84 2,905E19 7370
S. Ben Jadi e al.
In e na ional Jou nal o Hyd ogen Ene gy 138 (2025) 1066–1076
1074