PAPER • OPEN ACCESS
G aphene ex olia ion in cy ene o he sus ainable
p oduc ion o mic osupe capaci o s
To ci e his a icle: Ped o Mo ei a
e al
2025
J. Phys. Ene gy
7 035005
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PAPER
G aphene ex olia ion in cy ene o he sus ainable p oduc ion o
mic osupe capaci o s
Ped o Mo ei a1, Da id Ca alho1, Rod igo Ab eu1, Ma ia D Alba2, Joaquín Ramí ez-Rico2,3,
El i a Fo una o1, Rod igo Ma ins1, Joana Vaz Pin o1, Emanuel Ca los1,∗and Jo˜
ao Coelho1,2,3,∗
1CENIMAT|i3N, Depa men o Ma e ials Science, Facul y o Science and Technology, Uni e sidade NOVA de Lisboa and
CEMOP/UNINOVA, Campus da Capa ica, Capa ica, 2829-516, Po ugal
2Ins i u o de Ciencia de Ma e iales de Se illa, CSIC—Uni e sidad de Se illa, A da. Amé ico Vespucio 49, 41092 Se ille, Spain
3Dp o. Física de La Ma e ia Condensada, Uni e sidad de Se illa, A da. Reina Me cedes SN, 41012 Se ille, Spain
∗Au ho s o whom any co espondence should be add essed.
E-mail: [email p o ec ed] and [email p o ec ed]
Keywo ds: g aphene, cy ene, ene gy s o age, lexible elec onics, sus ainable ab ica ion
Supplemen a y ma e ial o his a icle is a ailable online
Abs ac
G aphene and i s composi es ha e a ac ed much a en ion o applica ions in ene gy s o age
sys ems. Howe e , he oxic sol en s equi ed o he ex olia ion p ocess ha e hampe ed he
exploi a ion o i s p ope ies. In his wo k, g aphene dispe sions a e ob ained ia liquid phase
ex olia ion (LPE) o g aphi e in cy ene, an en i onmen ally iendly sol en wi h solubili y
pa ame e s like hose o N-me hyl-2-pi olidone. The ob ained dispe sions wi h a concen a ion o
0.2 mg ml−1comp ised mul ilaye ed g aphene shee s wi h la e al sizes in he hund eds o
nanome e s, as con i med by scanning elec on mic oscopy, ansmission elec on mic oscopy, and
Raman spec oscopy. Mixing he ob ained dispe sions wi h e hanol made i possible o collec he
g aphene, which was edispe sed in 2-P opanol. This ac i e ma e ial was used o ab ica e
supe capaci o elec odes using a scalable sp ay deposi ion me hod on ca bon nano ube (CNT)
cu en collec o s wi h he aid o inyl masks. The de ice, es ed wi h a PVA/LiCl gel elec oly e,
achie ed a speci ic capaci ance o 3.4 mF cm−2(0.015 mA cm−2). In addi ion, he de ices show
excellen cycling s abili y (>10 000 cycles a 0.5 mA cm−2) and good mechanical p ope ies, losing
less han 10% o ini ial capaci ance a e 1000 bending cycles. This wo k demons a es he
adap abili y o liquid-phase ex olia ion o p oduce g aphene sus ainably, p o iding he
p oo -o -concep o u he 2D ma e ials p ocessing and g een mic osupe capaci o (MSC)
ab ica ion.
1. In oduc ion
Since i s disco e y, g aphene, a single laye o ca bon a oms a anged in a wo-dimensional (2D) honeycomb
la ice, has a ac ed immense scien i ic and echnological in e es . I s ex ao dina y p ope ies, including
high elec ical conduc i i y, mechanical s eng h, he mal conduc i i y, and a la ge speci ic su ace a ea, ha e
posi ioned i as a p omising ma e ial o a wide ange o applica ions, namely mic osupe capaci o s (MSCs)
[1–5]. Al hough ini ially isola ed by mic omechanical ex olia ion, he de elopmen o g aphene inks
compa ible wi h adi ional deposi ion me hods has led o he design o a a ie y o MSCs. G aphene based
MSCs ha e been al eady ab ica ed by sp ay coa ing [6–8], inkje p in ing [9–11], sc een-p in ing [12–14],
among o he s. Liquid-phase ex olia ion (LPE) has eme ged as a cos -e ec i e and scalable app oach o
p oducing g aphene inks [15–17]. LPE is a p ocess whe e bulk g aphi e is dispe sed in a sol en and
subjec ed o ul asonic ene gy o shea o ces o sepa a e he laye s in o single o ew-laye g aphene shee s
[18,19]. The choice o sol en is c i ical in his p ocess as i in luences he ex olia ion e iciency and he
quali y o he esul ing g aphene. T adi ionally, sol en s like N-me hyl-2-py olidone (NMP),
dime hyl o mamide ha e been used o LPE due o hei abili y o ma ch he su ace ene gy o g aphene,
© 2025 The Au ho (s). Published by IOP Publishing L d
J. Phys. Ene gy 7(2025) 035005 P Mo ei a e al
acili a ing he ex olia ion p ocess [20–22]. Howe e , hese sol en s a e oxic, ola ile, and pose signi ican
en i onmen al haza ds, leading o a g owing demand o g eene al e na i es. This has spu ed in e es in
sus ainable sol en s, wi h cy ene (dihyd ole oglucosenone) eme ging as a no able candida e due o i s g een
c eden ials and e ec i eness. Cy ene is a bio-based sol en de i ed om enewable cellulose. I has gained
a en ion as a sus ainable al e na i e due o i s low oxici y, biodeg adabili y, and excellen sol a ing
p ope ies [23–26]. Se e al s udies ha e demons a ed he e ec i eness o cy ene o g aphene ex olia ion as
i s solubili y pa ame e s (δD;δP;δH) o (18.7 MPa1/2; 10.8 MPa1/2; 6.9 MPa1/2) a e e y simila o hose o
NMP (18.0 MPa1/2; 12.3 MPa1/2; 7.2 MPa1/2) and g aphi e (18.0 MPa1/2; 9.3 MPa1/2; 7.7 MPa1/2) [20,27–31].
Fo ins ance, Sala agione e al compa ed he ex olia ion e iciency o cy ene wi h NMP and ound ha
cy ene p oduced a highe concen a ion o g aphene wi h ewe de ec s [31]. The s udy highligh ed cy ene’s
supe io abili y o s abilize g aphene, esul ing in a highe -quali y p oduc . O he s udies explo ed he
scalabili y o he p ocess, demons a ing ha la ge quan i ies o high-quali y g aphene could be p oduced
using cy ene in a scalable and en i onmen ally iendly manne [29,32]. Howe e , he e a e s ill some
challenges o conside ega ding p ocessing ma e ials in cy ene. I s high iscosi y (14.5 cP) and boiling poin
(227 ◦C) can p esen p ac ical challenges du ing he ex olia ion p ocess and subsequen s eps like
pu i ica ion and deposi ion, usually equi ing sol en exchange app oaches [33,34]. Ne e heless, cy ene’s
use in g aphene ex olia ion is a ela i ely new a ea o esea ch and mo e s udies a e needed o ully
unde s and i s long- e m iabili y and op imize p ocessing echniques.
In his wo k, we explo e he use o cy ene as sui able sol en o he ex olia ion o g aphene and
subsequen sol en exchange p ocess, so i can be used in scalable sp ay coa ing me hods. As a p oo o
concep , he ob ained dispe sions a e used o p epa e in e digi a ed MSCs composed o ca bon nano ube
(CNT) cu en collec o s and g aphene as he ac i e ma e ial. The p esen ed me hodology allows o a
g eene and sus ainable de ice ab ica ion.
2. Expe imen al me hods
2.1. G aphene ex olia ion and sol en exchange
In a no mal p ocedu e, 1.5 g o g aphi e lakes (Sigma-Ald ich-+200 mesh pa icle size) we e mixed wi h
30 ml o cy ene in cen i uge ubes wi h he aid o a o ex mixe . The dispe sions we e hen p ocessed in a
Fishe b and (11207) ul asonic ba h (60% powe , 37 kHz) o 8 h, ollowed by cen i uga ion in a So all
ST8 Cen i uge (4500 pm (RCF =3260)) o 90 min and collec ion o he supe na an ( op 90% olume).
Due o cy ene’s high iscosi y, he ob ained dispe sions we e u he cen i uged in a Sigma 3–18KS (10000
om (RCF =9300)) cen i uge o 30 min ollowed by he collec ion o supe na an (80%). The
concen a ion o he dispe sions was de e mined by il e ing 15 ml on a p e-weighed Wha man alumina
Anodisc il e discs (0.02 µm po e size). Then, 10 ml o he ob ained dispe sions we e mixed wi h 30 ml o
e hanol (1:3) and cen i uged in a Sigma 3–18KS (14600 pm (RCF =20018)) cen i uge o 45 min o
p ecipi a e he g aphene. The supe na an was disca ded, and 10 ml o 2-P opanol (Sigma-Ald ich) we e
added o he cen i uge ubes ollowed by igo ous s i ing in a Fishe b and (F202A0280FI) o ex mixe .
This p ocess was conduc ed 3 imes o ensu e comple e cy ene emo al. The ob ained clean samples we e
e-dispe sed in 10 ml o 2-P opanol and s o ed o u he p ocessing. All chemicals we e used as pu chased
wi hou u he ea men .
2.2. Cha ac e iza ion Techniques
Scanning elec on mic oscopy (SEM) was used o e alua e he mo phology o he aw ma e ials and
deposi ed elec odes in a FEI Teneo, unde high acuum a an ope a ing ol age o 5 keV and a wo king
dis ance o 10.0 mm. A 10 nm pla inum coa ing was deposi ed on he samples o educe cha ge e ec s.
Fu he mo phological cha ac e iza ion was conduc ed by ansmission elec on mic oscopy (TEM) in a FEI
Talos S200 ope a ed a 200 keV in b igh ield con igu a ion. Raman and x- ay pho oelec on spec oscopy
(XPS) analysis was used o s udy he s uc u al composi ion o he p epa ed samples. Raman measu emen s
on bo h g aphene inks we e collec ed by a LabRAM Ho iba Jobin Y on con ocal Raman mic oscope using an
exci a ion line o 532 nm wi h a 100x objec i e lens, a 250 scans collec ion in he ange be ween 900 and
3000 cm−1. XPS analyzes we e pe o med using a SPECS Phoibos 150 ins umen wi h a
non-monoch oma ic Al Kαx- ay sou ce (15.4 mA, 13 kV). The ins umen ’s binding ene gy (BE) scale
(wo k unc ion) was calib a ed o gi e a BE o 84.0 eV o he Au4 7/2 signal om eshly ion-e ched me allic
gold (Au). The spec ome e dispe sion (ene gy ange) was adjus ed o gi e a BE o 932.62 eV o he Cu
2p3/2 line o eshly ion-e ched me allic coppe (Cu). A cha ge compensa ion sys em (neu alize ) was used
o all non-conduc i e samples. The su ace o each non-conduc i e sample was i adia ed wi h an
accele a ed elec on low a 2.0–5.0 eV o p oduce a nea ly neu al su ace cha ge. Scanning analyzes ( ange
0–1350 eV) we e pe o med using a s ep ene gy o 50 eV. High ene gy esolu ion analyzes o he chemical
2
J. Phys. Ene gy 7(2025) 035005 P Mo ei a e al
s a e ( ange 20–50 eV) we e pe o med using a s ep ene gy o 20 eV. Addi ionally, a scan ( ange o
0–1150 eV) was pe o med wi h a non-monoch oma ic Mg K alpha x- ay sou ce (15.4 mA, 13 kV) using a
pass ene gy o 50 eV. All samples ha e been deposi ed wi h gold (Aga spu e coa e equipmen ) so ha he
da a can be co ec ed ( e e enced) by loading using he Au4 7/2 signal. CasaXPS .2.3.26PR1.0 so wa e was
used o pe o m cu e i ing, a e pe o ming a Shi ley backg ound co ec ion, and o calcula e he a omic
concen a ions. Cu e i ing o Al2s and O1s spec a we e pe o med using a Gaussian–Lo en zian peak
shape. Fo he analysis o C1s spec a, s a ing i ing pa ame e s like he app oach aken o Biesinge we e
used [35]. These s a ing i ing pa ame e s include he main peak asymme y (de ined using an asymme ic
Lo en zian line shape) and π o π∗shake-up sa elli e ypical o g aphi e.
2.3. MSC elec ode ab ica ion
Fo deposi ing he MSC elec odes, in e digi a ed pa e ns wi h a inge wid h o 0.8 mm, leng h o 10 mm
and spacing o 0.8 mm we e p oduced by cu ing in e digi a ed elec ode (IDE) pa e ns in a 76 µm adhesi e
inyl using a Silhoue e Po ai plo e and ans e ed o polyimide subs a es. The IDE we e hen peeled
o om he subs a e c ea ing an adhesi e s encil ha wo ked as a physical mask du ing he deposi ion. The
sp ay coa ing was conduc ed wi h an ai b ush o e a ho pla e (∼10 cm) a 85 ◦C o p omo e as sol en
e apo a ion. Fi s , 50 ml o a 0.1 mg ml−1dispe sion o Ca bon Solu ions P3 single wall CNTs (SWCNTs) in
2-P opanol we e deposi ed by sp ay-coa ing o c ea e he cu en collec o s. The SWCNTs dispe sion
o mula ion can be ound elsewhe e [36]. The elec ode shee esis ance was measu ed in an Ossila
Fou -Poin P obe sys em. Then he p e iously p epa ed g aphene dispe sions we e sp ayed o e he inge s
in an a ea o ∼1 cm2. A he end, he inyl masks we e emo ed lea ing he deposi ed SC behind. The cu en
collec o s (0.5 cm ×0.5 cm) we e coa ed wi h sil e pas e and cu ed o 1 h a 60 ◦C. An aqueous PVA/LiCl
gel was used as a solid elec oly e. Typically, 4 g o PVA we e added o 40 ml o dis illed wa e a 90 ◦C wi h
con inuous s i ing. A e comple e solubiliza ion o he PVA, 8.5 mg o LiCl was added o he solu ion. The
mix u e was kep unde con inuous s i ing and hea ing un il i became a anspa en gel. P io o elec oly e
cas ing, he MSCs we e cu ed in an Ossila UV Ozone Cleane o 15 min a oom empe a u e o educe he
hyd ophobici y o g aphene. The elec oly e was hen d op-cas on o he g aphene laye . The assembled SCs
we e allowed o d y o e nigh a oom empe a u e be o e he elec ochemical es ing.
2.4. Elec ochemical cha ac e iza ion
The as-p epa ed MSCs we e cha ac e ized in a CS310X po en ios a (Co es Ins umen s) by means o
cyclic ol amme y (CV) (5–1000 mV s−1), gal anos a ic cha ge discha ge (GCD) (0.015–1 mA cm−2)
expe imen s and elec ochemical impedance spec oscopy (5 mV, 1 MHz o 10 mHz). The de ice speci ic
a eal capaci ance, C, was calcula ed om cha ge–discha ge cu es as ollows:
C=I∆
A∆V(1)
whe e Iis he applied cu en , ∆ is he discha ge ime, Ais he SC ac i e a ea, and ∆V=V2−V1 whe e V2
is he po en ial a he beginning o discha ge, a e he iR po en ial d op, and V1is he po en ial a he end o
discha ge. A eal ene gy (E) and powe (P) densi ies pe uni a ea we e calcula ed as ollows:
E=1
2
C∆V2
3600 (2)
P=E
∆ ×3600 (3)
whe e 3600 is a con e sion ac o om Ws o Wh. The de o ma ion es s we e conduc ed by acqui ing CVs a
10 mV s−1a e 10 essays o 100 bending cycles in a o al o 1000 bending es s.
3. Resul s and discussion
3.1. G aphene p ocessing and ink o mula ion
In his wo k, comme cial g aphi e lakes we e used as he s a ing ma e ial o he ex olia ion p ocess and
p ocessing o g aphene in cy ene (GC). Figu e 1(a) shows a SEM mic og aph o an unp ocessed lake
exhibi ing he cha ac e is ic laye ed s uc u e o g aphi e. A e sonica ion, a da k ink is ob ained, as shown
in igu e 1(b), composed o hin g aphene shee s wi h la e al sizes in he o de o hund eds o nanome e s
( igu e 1(c)). The concen a ion o hese inks was de e mined o be ∼0.2 mg ml−1, co esponding o an
ex olia ion yield (%E) o 0.4%.
3
J. Phys. Ene gy 7(2025) 035005 P Mo ei a e al
Figu e 1. Examples o (a) g aphi e lakes unde SEM; (b) g aphene dispe sion a e sonica ion; (c) TEM mic og aphs o he
ex olia ed g aphene in cy ene (GC) and (d) TEM mic og aphs o g aphene a e edispe sion in 2-P opanol (GP).
In he li e a u e i has been epo ed concen a ions o g aphene ex olia ed in cy ene as high as
3.70 mg ml−1(%E ∼7.4%) [29] sonica ed o 8 h. Howe e , in his speci ic wo k, a combina ion o
ex olia ion me hods ( ip sonica ion and shea mixing) was used o maximize he g aphene p oduc ion yield.
Sala agione e al ob ained a %E o 47% o g aphi e sonica ed in cy ene o 2 h wi h he aid o a sonic ip
[31]. I is e iden ha he p ocessing condi ions o g aphene exe a subs an ial in luence on he ex olia ion
yield. As illus a ed in able S1, he g aphi e s a ing concen a ions and sonica ion me hodologies
demons a e a conside able impac on he p oduc ion o g aphene, e en in ins ances whe e he same sol en s
a e employed. Addi ional ex olia ion pa ame e s, such as sonica ion powe and du a ion, and cen i uga ion
speed, also exhibi a subs an ial e ec on he ex olia ion yield [37]. Mo eo e , i canno be dis ega ded he
s uc u e and lake size o he g aphi e used. Ng e al ha e ecen ly shown ha besides ini ial concen a ion,
hese g aphi e p ope ies ha e a signi ican impac on he ex olia ion e iciency o g aphene in a wide ange
o sol en s [38]. Addi ionally, i is also shown ha ex olia ion e iciency and dispe sibili y can be analyzed as
independen p ope ies. Fo ins ance, he mass o g aphene pe su ace a ea o g aphi e (pa icles size
∼150 µm) ex olia ed in 2-P opanol was 29 imes highe han he alues measu ed o NMP. Fo a pa icle
size o ∼50 µm, his alue ose up o 48. Howe e , his ex olia ion e iciency is hinde ed by he 2-P opanol
lowe g aphene dispe sibili y, which is also dependen on he g aphi e p ope ies (g aphi e mo phology,
la e al size, de ec densi y, edge de ec s, d-spacing, among o he s) [38]. As such he epo ed alues o
g aphene ex olia ed in cy ene may in ac a y ac oss di e en wo ks epo ed in he li e a u e. Fo ou s udy,
we p e e ed o use a lowe powe sonic ba h as i causes less damage o he samples and p oduces la ge
lakes, al hough usually a a lowe concen a ion. I was also used longe cen i uga ion cycles, which
p obably con ibu ed o u he emo al o ma e ial in suspension. As such, in his wo k i is shown ha i is
possible o ex olia e GC and use i o ene gy s o age applica ions.
As wi h NMP, he high boiling poin o cy ene poses some challenges o i s use on a la ge scale.
The e o e, i is no mal o ca y ou a sol en exchange p ocess. In his wo k, he ob ained dispe sions we e
i s mixed wi h e hanol in a a io cy ene: e hanol (1:3). The poo dispe sibili y o hese sol en s
combina ion g ea ly acili a es g aphene deposi ion, as a clea anspa en supe na an is ob ained upon
cen i uga ion. A e eco e ing and cleaning he samples, he g aphene was e-dispe sed in 2-P opanol
(GP—G aphene in P opanol), which has been conside ed a g een sol en , while exhibi ing a ela i ely low
boiling-poin (82.3 ◦C). A TEM mic og aph o he g aphene e-dispe sed in 2-P opanol ( igu e 1(d)) is qui e
like he o iginal samples p ocessed in cy ene. To in es iga e i he e a e s uc u al o chemical changes o he
g aphene du ing he sol en exchange p ocess, he samples we e examined by means o Raman Spec oscopy
and XPS ( igu e 2).
Figu e 2(a) shows he Raman spec a o bo h GC and GP whe e he cha ac e is ic peaks o g aphene can
be iden i ied. The D band (∼1350 cm−1) is asc ibed o he A1gmode o ib a ion and i is usually associa ed
wi h he deg ee o de ec s and s uc u al diso de o he ca bon ma ix. The G band (∼1580 cm−1)
4
J. Phys. Ene gy 7(2025) 035005 P Mo ei a e al
Figu e 2. (a) Raman spec a o he g aphene samples in cy ene (GC) and 2-P opanol (GP); (b) close-up o he Raman peak o he
g aphene samples compa ing he ull wid h hal medium (FWHM) o bo h samples and (c), (d) XPS spec a o C1s o bi als o
GC and GP, espec i ely.
co esponds o he in-plane E2g ib a ion mode o C–C bond s e ching. Finally, he 2D band (∼2700 cm−1),
a D-band o e one, esul s o double esonance be ween he K-poin s in he B illouin zone [39,40]. I has
been e i ied ha o monolaye g aphene I2D >IG. In ou samples, he weake and symme ical 2D peak is
indica i e o a ew-laye s g aphene [41–43]. Fo he example gi en in igu e 2(a), a mo e in ense 2D peak is
obse ed o GP. In he case o solu ion p ocessed g aphene, ex eme ca e should be aken when analyzing
Raman da a as andom es acking o he lakes and de ec s can signi ican ly change he spec a [42]. The ull
wid h-hal medium (FWHM) o 2D peak is also indica i e o numbe o laye s in a sample. In his wo k, he
FWHM o GC and GP was measu ed as ∼81 cm−1( igu e 2(b)), which may be indica i e o he same
numbe o laye s o bo h samples. Ne e heless, no signi ican changes a e obse ed o ei he GC o GP
spec a. As such, based on p e ious li e a u e, i is sa e o assume ha he Raman spec um co obo a es he
obse a ions made o he TEM mic og aphs. Figu es 2(c) and (d) show he C1s spec a o bo h g aphene
samples exhibi ing he cha ac e is ic C–C sp2signal g aphi ic ca bon a 284.4 eV. The π-π∗ ansi ion loss
peak is de ec ed a 291.5 eV [44]. O he chemical shi s a e de ec ed a 286.4 eV, 287.9 eV and 289.9 eV which
a e ypically assigned o C–OH/C–O–C, C =O and O-C =O unc ional g oup espec i ely [35,44]. I is
common o obse e oxygena ed species in ex olia ed g aphene due o esidual sol en molecules. In addi ion,
as he measu emen s we e pe o med in il e ed ilms, i is possible ha a la ge amoun o sol en is apped
in he laye s o he il a e. Mo eo e , shown by Skal sas e al sonica ion induces de ec s and oxygena ed
species on g aphene which con ibu e o he sp3signal [45,46]. This obse a ion is in good ag eemen wi h
he D peak obse ed in he Raman spec a. The ac ha he D and G bands a e no b oad (as obse ed o
g aphene oxide and educed g aphene oxide) sugges s ha he de ec s p esen a e no basal plane de ec s bu
a he edge de ec s [46]. Finally, he sp3signal loca ed a 285.3 eV can also be a ibu ed o he p esence o
ad en i ious ca bon on he sample. Fu he XPS analysis con i ming he p esence o g aphene can be ound
in he p o ided supplemen a y in o ma ion (sec ion S2). The XPS da a co obo a es he Raman esul s,
showing ha no damage o sample de e io a ion occu ed du ing he sol en exchange p ocess. As such, GP
will be es ed as supe capaci o elec ode ac i e ma e ial in he ollowing sec ions.
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J. Phys. Ene gy 7(2025) 035005 P Mo ei a e al
Figu e 3. (a) inyl mask on polyimide subs a e; (b) sp ay-coa ed MSC; (c) 5x magni ica ion o he in e inge s spacing and (d)
SEM mic og aph o he deposi ed g aphene ilm.
3.2. Elec ode ab ica ion and cha ac e iza ion
In his wo k, he MSC elec odes we e ab ica ed by sp ay coa ing he GP in o a polyimide subs a e
(Kap on) wi h he aid o adhesi e inyl masks as shown in igu e 3(a). Fi s , a conduc i e SWCNT laye was
sp ay coa ed o e he whole mask o deposi he cu en collec o s (∼20 Ωsq−1). In his wo k, SWCNTS
wi h 1–3 a omic % ca boxylic acid g oups we e used due o hei dispe sabili y in 2-P opanol. Then, 10 ml o
he GP dispe sions we e deposi ed o e he inge s a ea o achie e a mass loading o ∼1 mg cm−2. A e
pain ing he sil e elec ical con ac pads, he mask is li ed, a gel elec oly e is applied o he GP coa ed
inge s and a comple e de ice is ob ained ( igu e 3(b)). This de ice has (2 cm ×2 cm) composed o inge s
wi h ∼0.09 mm sepa a ed by a 0.06 mm gap ( igu e 3(c)). The magni ica ion o he sp ayed GP ( igu e 3(d))
shows ha i is composed o shee -like g aphene lakes. Rega ding dimensions, hey seem o be in good
ag eemen wi h he TEM mic og aphs ( igu e 1(d)). La ge g aphene lakes could be expec ed o sonic ba h
p ocessing cy ene’s high iscosi y may also con ibu e owa ds he s abiliza ion o la ge lakes. The ull
p ocess o he p epa a ion o he masks and MSC ab ica ion is desc ibed in he p o ided supplemen a y
in o ma ion (sec ion S3).
The elec ochemical and ene gy s o age p ope ies o hese GP-based MSC we e ex ensi ely analyzed
h ough CV and GCD es s. PVA/LiCl was employed as he elec oly e, while he GP and CNT laye s se ed
as he MSC ac i e ma e ial and cu en collec o s, espec i ely. These esul s a e shown in igu e 4. The CV
cu es ( igu e 4(a)) display a quasi- ec angula shape (5–100 mV s−1), ypical o ca bon-based elec ic
double-laye capaci o s, sugges ing good elec ochemical s abili y. CV cu es up o 1 V s−1a e depic ed in
igu e S7(a). These esul s a e u he co obo a ed by he GCD cu es p esen ed in igu e 4(b), whe e he
nea ly ideal symme ic iangula shapes and minimal ol age d op indica es a s ong capaci i e beha io . By
applying equa ion (1) o he discha ge cu es, he a eal capaci ance, C, was calcula ed o he di e en
cu en s applied du ing he GCD es s ( igu e 4(c)).
A maximum capaci ance o 3.34 mF cm−2was measu ed o a cu en densi y o 0.015 mA cm−2. A a
highe cu en densi y o 0.5 mA cm−2, he GP MSC s ill demons a es a Co 1.34 mF cm−2( igu e 4(c)).
These esul s a e in line wi h o he g aphene and ca bon based MSC. Shi e al epo ed a Co 4.9 mF cm−2
(a 2 mV s−1) o sp ay coa ed G aphene/PEDOT: PSS composi es [47]. Coelho e al p epa ed lase -induced
g aphene (LIG)—MSC on pape deli e ing 4.6 mF cm−2(0.015 mA cm−2). Finally, Mendonza-Sanchez e al
measu ed a speci ic capaci ance o 0.543 mF cm−2 o ul a- hin elec odes o g aphene ex olia ed in liquid
phase [46]. Simila commen s can be made ega ding ene gy and powe densi ies ( igu e S7(b)). The GP
sp ay coa ed MSC deli e ed a maximum o 0.23 µWh cm−2(a 0.45 µW cm−2). I is also impo an o
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J. Phys. Ene gy 7(2025) 035005 P Mo ei a e al
Figu e 4. Summa y o he elec ochemical cha ac e iza ion es s conduc ed on he GP sp ay coa ed supe capaci o s: (a) cyclic
ol ammog ams (CV) on he ange 5 mV s−1–100 mV s−1; (b) gal anos a ic cha ge discha ge cu es a cu en densi ies anging
om 0.015 mA cm−2 o 1 mA cm−2and (c) espec i e a eal capaci ance, C; (d) capaci ance e en ion and coulombic e iciency a
0.5 mA cm−2and (e) de ices Nyquis plo . Fo simplici y pu poses C will used h oughou he ex as he symbol o a eal
capaci ance.
men ion he ac ha he e is a capaci ance e en ion o 42% a a cu en densi y o 0.5 mA cm−2
( igu e 4(c)). This capaci ance d op is less han ideal, bu he GP MSCs we e p epa ed wi hou any
conduc i e addi i e. PEDOT:PSS is equen ly used o lowe he shee esis ance o g aphene ilms [29].
Howe e , his polyme can also be used as MSC elec ode ac i e ma e ial. In ac , g aphene and me al oxide
pa icles ha e been es ed as addi i es o PEDOT:PSS hyb id elec odes [48–50]. To ully s udy he cha ge
s o age capabili ies o GP, no conduc i e ma e ials we e added, and hin ilms we e p e e ed. In e ms o
cyclabili y, a 14% capaci ance loss is obse ed a e 10 000 cycles (0.5 mA cm−2). Howe e , his p ocess is
mo e e iden in he i s 1000–2000 cycles, upon which he alues o C end o s abilize ( igu e 4(d)). The e
a e se e al ac o s ha a ec supe capaci o ac i i y, leading o de ice deg ada ion and e en ual loss o
capaci ance. Elec oly e decomposi ion and wa e e apo a ion, as well as e en ual delamina ion o ac i e
ma e ials and he p esence o esidual con aminan s, a e known e ec s ha con ibu e o capaci ance ading
in supe capaci o s [51,52]. Fo he GP-based mic osupe capaci o s, capaci ance deg ada ion is mo e
p onounced in he i s cycles, sugges ing ha i is mo e likely based on he s abiliza ion o he elec oly e
wa e con en and he possible p esence o species ha con ibu e o non- e e sible eac ions. A e 2000
cycles, he speci ic capaci ance s abilizes and he loss o pe o mance (<2%) is a ibu ed o he aging
mechanisms o he supe capaci o , namely elec oly e deg ada ion and loss o su ace a ea [52]. The
Coulombic e iciency ( igu e 4(d)) emains a 97.86% a e 10 000 cycles ep esen ing a small capaci ance
loss upon each cha ge/discha ge cycle. The EIS spec um ( igu e 4(e)) is cha ac e is ic o po ous elec odes
exhibi ing double laye capaci ance wi h equency dispe sion esul ing in de ia ion om e icali y o he
capaci i e (low equency) b anch, wi h no app eciable pseudocapaci ance. The spec um was i ed using an
elemen (Zpo es) implemen ing he de Le ie model o ideally pola izable po ous elec odes inco po a ing a
cons an phase elemen , wi h an addi ional capaci o (C la ) in pa allel o accoun o he la ge ex e nal a ea
o he elec odes due o he high aspec a io o g aphene pla ele s (χ2=3 10−5) [53–55]. The i e eals an
equi alen se ies esis o (ESR) o ∼160 Ωwhich is common o his ype o de ice wi h pain ed sil e
con ac s [56]. A i o he impedance spec a using he simpli ied Randle’s model was also pe o med, bu i
esul ed in a signi ican ly wo se i (χ2=80 10−5) and a cha ge- ans e esis ance o ∼108kΩ, con i ming
ha he GP sp ay-coa ed MSCs s o es cha ge exclusi ely h ough he o ma ion o double laye wi h no
cha ge- ans e due o a adaic eac ions. A mo e in-dep h discussion ega ding EIS can be ound in
supplemen a y in o ma ion (sec ion S4).
In ela ion o applica ions, in-plane in e digi a ed MSC on polyme ic subs a es ha e been p oposed as
powe sou ces o wea able echnologies and o he lexible echnologies. Consequen ly, he MSC mus
wi hs and conside able mechanical de o ma ion, such as bending and olding, wi hou comp omising he
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J. Phys. Ene gy 7(2025) 035005 P Mo ei a e al
Figu e 5. GP MSC capaci ance e en ion as unc ion o 1000 bending cycles. The p esen ed da a was acqui ed om cyclic
ol amme y expe imen s conduc ed a a scan a e o 10 mV s−1. Bo om le inse :examples o he mechanical de o ma ion
applied o he samples and bo om igh inse : CVs acqui ed a each consecu i e 100 bending cycles.
o e all elec ochemical pe o mance. To e alua e he mechanical p ope ies o he GP sp ay-coa ed MSC, he
p epa ed samples we e subjec ed o 1000 consecu i e cycles o bending, wi h he speci ic capaci ance
measu ed a e e y 100 h cycle. The esul s a e shown in igu e 5.
A capaci ance d op o only 8% is obse ed a e 1000 manual bending cycles, sugges ing ha GP-MSC
can be implemen ed as lexible ene gy s o age de ices. Howe e , wi h adequa e encapsula ion he MSC may
be mo e s able and e ain i s capaci ance o longe pe iods o de o ma ion. I is impo an o poin ou ha
a pe o mance upli (abou 10%) can be obse ed in igu e 5. This inc ease in capaci ance has been obse ed
in o he lexible de ices and is likely o esul om an imp o emen in he elec ode/elec oly e in e ace due
o he mechanical de o ma ion, as he elec oly e can pene a e u he in o he elec ode s uc u e and
p omo e he o ma ion o he elec ical double laye [57]. I can also be ound elsewhe e ha hese de ices
can easily be a anged in se ies and pa allel o illus a e he scalabili y and in eg a ion capabili ies o such
sys ems. As such i is possible o adap he ene gy powe uni s o he desi ed ol ages and cu en s, hus
inc easing he possible numbe o applica ions.
I has been shown in his s udy ha g aphene p ocessed in cy ene and hen ans e ed o 2-P opanol
(GP) has he po en ial o be used in sp ay coa ed MSC elabo a ion unde low empe a u es p ocessing.
GP-MSC exhibi s igu es o me i like o he g aphene inks bu being p ocessed in a much sa e and
en i onmen ally iendly way being compa ible wi h low-cos lexible subs a es such as bio-based polyme s
and pape [58,59]. Howe e , due o i s po ous na u e, pape could abso b he inks and lead o de ice
sho -ci cui ing. In his case he p oposed elec odes could be used in a sandwich con igu a ion [58]. Be e
elec ochemical pe o mance and highe capaci ances can also be ob ained by inc easing he ilm hickness
and/o using me allic subs a es [7,60,61]. In hese cases, conduc i e polyme s o ca bon addi i es and
binde s may be equi ed, hus impac ing he o e all g a ime ic capaci ance and de ice lexibili y. Fo
ins ance, Ga akani e al de eloped high-powe g aphene-based supe capaci o s ope a ing a a wide ange o
empe a u es [6]. In his s udy, MSC g aphene elec odes we e p epa ed by sp ay coa ing on o aluminium
cu en collec o s a mix u e o g aphene, ac i a ed ca bon and cellulose. In ac , he mix u e o g aphene
wi h ca bon species o dopan s (such as ni ogen) has also shown p omising esul s o high pe o mance
supe capaci o de elopmen [62,63]. As such, he e a e a lo o oppo uni ies o GP g aphene o u he
MSC de elopmen . In ac , i can be highly ele an o simple, low cos , as pa e ning, lexible sys ems ha
do no need o adhe e o highly con olled en i onmen s and sophis ica ed manu ac u ing p o ocols, being
poised o occupy a niche in lexible/wea able de ices manu ac u ing and may play a ole in igh ing he
e e -inc easing amoun o elec onic was e (e-was e).
4. Conclusions
This wo k has demons a ed a sus ainable me hod o he g een ex olia ion o GC and i s subsequen sol en
exchange and deposi ion as an ac i e ma e ial o mic osupe capaci o elec odes. The sol en exchange
p ocess om cy ene o e hanol was ound o be e y e ec i e wi hou causing any damage o s uc u al
changes o he g aphene. In addi ion, he sol en exchange me hod does no esul in any loss o possible
con amina ion compa ed o g aphene isola ion by il a ion. The use o inyl masks acili a ed he deposi ion
8
