Jou nal o The
Elec ochemical Socie y
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Elec ochemical Insigh s in o Coppe
Elec odeposi ion on Nd2Fe14B G ains: A P oo -o -
Concep S udy
To ci e his a icle: Č Saksida
e al
2025
J. Elec ochem. Soc.
172 022505
View he a icle online o upda es and enhancemen s.
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Elec ochemical Insigh s in o Coppe Elec odeposi ion on
Nd
2
Fe
14
B G ains: A P oo -o -Concep S udy
Č Saksida,
1,z
Mihaela Rebe nik,
1,2
TomažTomše,
1
László Pé e ,
3
Ca lo Bu kha d ,
4
Lau ence Schie en,
4
Zo an Sama džija,
1
and K is ina Žužek
1,2
1
Jože S e an Ins i u e, Depa men o Nanos uc u ed Ma e ials, SI-1000 Ljubljana, Slo enia
2
Jože S e an In e na ional Pos g adua ion School, SI-1000 Ljubljana, Slo enia
3
Ins i u e o Solid S a e Physics and Op ics, HUN-REN Wigne Resea ch Cen e o Physics, Budapes , 1525, Hunga y
4
Ins i u e o P ecious and Technology Me als, P o zheim Uni e si y, P o zheim 75175, Ge many
This s udy explo es Cu elec odeposi ion om a nea -neu al sulpha e ba h on o Nd-Fe-B bulk and powde elec odes. The o me
se ed o he p elimina y elec ochemical es s, while he la e was used o Cu coa ing o he co osion-sensi i e powde y aw
ma e ial. Cyclic ol amme y es ablished he po en ial in e als o Cu deposi ion (a leas −0.1 V and below) and he Nd-Fe-B
oxida ion (abo e −0.5 V). Cu elec odeposi ions we e pe o med on bo h elec odes in po en ios a ic mode o 30 s. Scanning
elec on mic oscopy/ene gy-dispe si e spec oscopy showed ha Cu deposi ed a high o e po en ials (−1.05 and −0.5 V) had a
dend i ic s uc u e mainly due o mass anspo limi a ions. A ch onoampe ome ic s udy on Nd
2
Fe
14
B powde elec odes a
−0.25 V esul ed in a posi i e cu en , indica ing he Nd-Fe-B oxida ion dominance. A −0.5 V, he cu en emained nega i e, bu
showed di usion limi a ions. The la e was imp o ed by using ul asonic agi a ion, which esul ed in a highe o al nega i e cha ge
and mo e uni o m Cu deposi s on Nd
2
Fe
14
B g ains. Cu-coa ed Nd₂Fe₁₄B g ains showed a mass magne iza ion dec ease om 137 o
127 emu g
−1
, co esponding o a ∼9% Cu mass inc ease de e mined ia g a ime y. The s udy demons a es success ul Cu
elec ochemical deposi ion wi h no magne iza ion loss beyond he pa amagne ic Cu phase, pa ing he way o g ain-bounda y
enginee ing o no el Nd-Fe-B magne s.
© 2025 The Au ho (s). Published on behal o The Elec ochemical Socie y by IOP Publishing Limi ed. This is an open access
a icle dis ibu ed unde he e ms o he C ea i e Commons A ibu ion 4.0 License (CC BY, h ps://c ea i ecommons.o g/
licenses/by/4.0/), which pe mi s un es ic ed euse o he wo k in any medium, p o ided he o iginal wo k is p ope ly ci ed. [DOI:
10.1149/1945-7111/adb339]
Manusc ip submi ed Oc obe 29, 2024; e ised manusc ip ecei ed Janua y 10, 2025. Published Feb ua y 19, 2025.
Supplemen a y ma e ial o his a icle is a ailable online
The ansi ion o a low-ca bon and ene gy-e ficien socie y by
2050, as en isioned by he EU’s G een Deal, equi es esou ce-
e ficien solu ions o achie e an 80% educ ion in g eenhouse-gas
emissions. Highly e ficien elec ic mo o s, essen ial o e-mobili y
and eco- iendly powe gene a ion, ely on a e-Ea h ansi ion-
me al pe manen magne s (PMs) like neodymium–i on–bo on
(Nd-Fe-B).
1
Nd-Fe-B PMs play a c ucial ole in echnological
ad ancemen s and ene gy conse a ion. These magne s a e widely
used in applica ions; howe e , hey s ill encoun e challenges ela ed
o low coe ci i y a ele a ed empe a u es, comp omising hei
he mal s abili y —especially in e-mobili y and high-e ficiency
mo o s.
1,2
To da e, he unde lying mechanism behind hei low
coe ci i y, ela i e o hei high aniso opy field, emains
un esol ed.
3
In addi ion, gi en he c i icali y o a e-Ea h elemen s,
as highligh ed by he EU’s lis o essen ial aw ma e ials,
4
he ocus
mus shi owa ds de eloping magne s ha maximize esou ce
e ficiency.
S udies o he coe ci i y o Nd-Fe-B magne s ha e conside ed a
demagne iza ion mechanism based on he nuclea ion o he e e se
domains.
5
Howe e , because o he expe imen al disco e ies ha
ha e poin ed o he e omagne ic na u e o he Nd- ich “subphase”
o “g ain-bounda y phase,”a mechanism o domain-wall pinning
has been p oposed.
2
The la e emphasizes he significance o
con olling he s uc u al and magne ic p ope ies a he in e aces
be ween he main ma ix Nd
2
Fe
14
B phase and he su ounding
subphase(s) o enhance he coe ci i y.
6–8
T ace amoun s o coppe
(a ound 0.1 a omic pe cen ) posi i ely influence he coe ci i y.
Se e al annealing p ocesses ha e success ully enhanced he coe -
ci i y, highligh ing he impo ance o coppe nea he in e ace.
9–12
In annealed Nd-Fe-B ma e ials, local-composi ion analyses e ealed
he o ma ion o a hin neodymium- ich (Nd- ich) amo phous laye
along he g ain bounda ies. Addi ionally, Cu seg ega es a hese
in e aces, en eloping he Nd₂Fe₁₄B g ains wi h a Cu-en iched
laye .
8
Op imal coe ci i y hus depends on he amoun o Cu and
how i seg ega es, ac o s which a e influenced by he coppe
concen a ion and he applied he mal ea men .
13
Based on hese findings, i is likely ha he p esence o Cu nea
he in e ace di ec ly imp o es he coe ci i y. A fi s -p inciples
s udy in es iga ed a Cu-doped Nd
2
Fe
14
B-NdO
x
sys em o explo e
Cu’s ole in enhancing he coe ci i y in annealed Nd-Fe-B magne s.
I was shown ha Cu eplaces he Fe a he in e ace, leading o a
40% imp o emen in he magne ic aniso opy o he Nd a oms.
14
In oducing Cu a ound he in e ace be ween he main ma ix
Nd
2
Fe
14
B phase g ains and he subphases is expec ed o p e en
he domain walls om pene a ing he main-phase g ains, hus
e ec i ely con ibu ing o an inc ease in he coe ci i y.
Theo e ically, he Nd
2
Fe
14
B phase con ains 26.7 w % o a e
Ea hs including Nd, P , Ce Tb and Dy and o he s,
15,16
whe e he Nd
con ibu es o a majo i y o a ound ∼23 w %.
17
The ∼72 w % o
ansi ion me als a e mainly p esen ed by i on (Fe), al hough small
amoun s o cobal (Co) a e up o 1 w %, a e usually added o
enhance he Cu ie empe a u e.
17
Fo simplici y, he e m Nd₂Fe₁₄B
is used as a gene al o mula o ep esen he ha d-magne ic
e agonal phase.
Howe e , comme cial Nd-Fe-B sin e ed magne s ha e composi-
ions ha a e much iche in a e Ea h, up o 32 w %, o ensu e he
liquid phase’s o ma ion o sin e ing
18
( he la e being Nd- ich).
Howe e , his Nd- ich phase is p one o oxida ion, jeopa dizing he
Nd-Fe-B magne ’s long- e m s abili y and equi ing addi ional cos s
o coa ing.
18,19
In his s udy we p esen an elec ochemical analysis
and p opose a new app oach o c ea ing a coppe -based g ain-
bounda y phase in Nd-Fe-B magne s. Since Cu is usually added o
he Nd-Fe-B- ype alloy in ace amoun s (a ound 0.1 a omic
pe cen ), his no el phase is designed o be mo e esou ce e ficien
and co osion esis an han he cu en Nd- ich g ain-bounda y
phase. Addi ionally, conside ing he s udies men ioned abo e,
inco po a ing a Cu-based g ain-bounda y phase could p o ide
con olled magne iza ion e e sal and he eby imp o e he coe -
ci i y. Fo his pu pose, Nd-Fe-B magne s we e ea ed wi h he
hyd ogen-assis ed p ocess o magne ic sc ap (HPMS) ha was
de eloped a he Uni e si y o Bi mingham, and in ol es placing
z
E-mail: [email p o ec ed]
Jou nal o The Elec ochemical Socie y, 2025 172 022505
end-o -li e Nd-Fe-B pe manen magne s in a eac o e acua ed and
filled wi h hyd ogen a con olled p essu es and ambien empe a-
u e. The Nd- ich g ain bounda ies eac wi h hyd ogen o o m
NdH
∼2.7
, while he Nd₂Fe₁₄B ma ix phase accommoda es dissol ed
(in e s i ial) hyd ogen a oms, causing a c ys al la ice olume
expansion up o 5%. This leads o emb i lemen and sepa a ion o
he Nd₂Fe₁₄B g ains and he Nd- ich phase in o coa se, iable
agg ega es. Once hyd ogen consump ion s abilizes, he ma e ial is
pa ially degassed and emo ed, yielding powde s anging om fine
pa icles (<10 μm) o agg ega es se e al mm in size consis ing o
he Nd₂Fe₁₄B g ains and he Nd- ich phase, which equi e u he
milling o b eak down he agglome a es.
20–22
Those we e la e
s ipped chemically o ou s udy o emo e he Nd- ich g ain-
bounda y phase.
17,23
The p ocess esul ed in a Nd₂Fe₁₄B main ma ix
phase on which he Cu was deposi ed.
Elec ochemical deposi ion is a me hod o choice in ou wo k due
o i s expe imen al and economic easibili y o coa ing powde
pa icles wi h me als and alloys. Howe e , se e al aspec s need o be
conside ed when deposi ing Cu on Nd-Fe-B. Neodymium is a
lan hanide; i possesses an excep ionally low s anda d edox
po en ial o −2.3 V s SHE (Nd
3+
/Nd). This cha ac e is ic makes
i highly sensi i e o common en i onmen al oxidan s like O
2
and
H
2
O, necessi a ing i s s o age and handling in an a gon a mosphe e.
The Fe
2+
/Fe sys em also has a nega i e s anda d edox po en ial o
−0.44 V s SHE. The elec oly ic ba h o Cu pla ing also con ains
ano he oxidizing agen , Cu
2
⁺. I is possible, hough undesi able, o
an elec on exchange o occu be ween he Nd-Fe-B and he coppe
ions, which ha e a posi i e s anda d po en ial o +0.34 V s SHE
(conce ning he Cu
2+
/Cu edox pai ). This could esul in he
elec oless deposi ion o coppe . The oxida ion, i.e., he co osion
beha iou o Nd-Fe-B sin e ed magne s, was s udied in.
24,25
The Nd-
ich phase in he Nd-Fe-B sys em is he mos suscep ible o
oxida ion due o i s high neodymium con en . This makes i mo e
eac i e and p one o ge oxidized compa ed o o he phases in he
sys em.
26
The la e was exploi ed o he selec i e leaching o he
Nd- ich phase and he sepa a ion o he ma ix Nd
2
Fe
14
B main
phase, ei he elec ochemically
27
o chemically,
22,23
and was used as
a p ecu so ma e ial o ou s udy.
The li e a u e on he elec odeposi ion o me als on o Nd-Fe-B
powde s is sca ce, and mainly conduc ed on nanoc ys alline sys ems
ha a e mo e co osion esis an . The li e a u e epo s he success ul
elec odeposi ion o Fe, Cu, Zn, Ni, and Sn on o mel -spun
nanoc ys alline Nd-Fe-B powde s o u he p ocessing o
bonded
28
o ho -p essed magne s.
28
Howe e , hey we e all ca ied
ou in a gal anos a ic mode wi hou assessing he comple e elec o-
chemical beha iou .
Gene ally, Cu elec odeposi ion on an indus ial scale is based on
es ablished elec oly ic ba hs, including ei he complexed alkaline
cyanide and py ophospha e sys ems o acid sul a e and fluobo a e
simple ion sys ems.
29
Among hese, he acid sul a e ba h is he mos
widely used in indus y due o i s abili y o p oduce b igh , smoo h
deposi s, i s low cos , and i s e ec i eness a high cu en densi ies.
I ypically uses a high concen a ion o H₂SO₄(1.8 M) o inc ease
he conduc i i y and emo e he oxide laye s on he elec ode
su ace. As Nd-Fe-B powde is no o iously suscep ible o oxida ion
(i.e., dissolu ion o su ace oxida ion in acids), Na₂SO₄was
employed in ou s udy as a subs i u e o sul u ic acid o p o ide a
nea -neu al en i onmen . Coppe elec odeposi ion om solu ions
o di alen non-complexed Cu
2+
ions is known o ake place ia he
o ma ion o he Cu
+
in e media e, i s o ma ion om he Cu
2+
ion
being he a e-de e mining s ep o he en i e p ocess.
30
I is also
known ha chlo ide ions can une he ace dis ibu ion o he
deposi ed Cu me al.
31
Chlo ide ions acili a e he o ma ion o he cup ous in e media e
om he cup ic ions.
32
E en i he Cl
−
concen a ion applied alls
in o he mM ange, no mass anspo limi a ion was ound by
Gab ielli e al. in ela ion o he impac o he chlo ide ions. Ra he ,
Cl
−
ions seem o eside a he Cu su ace pe manen ly as adso bed
species, hence o ming a monoa omic elec on ans e ca alys
laye .
32
The e o e, we applied NaCl in a low concen a ion o
make he eac ion as unhinde ed as possible.
He e, we p o ide a comple e s udy o he elec ochemical
eac ions du ing he elec odeposi ion o Cu on Nd₂Fe₁₄B main
ma ix phase, single c ys alline powde s. The main objec i es o he
s udy a e o p omo e Cu
2+
educ ion, o educe he a e o Nd-Fe-B
oxida ion, and o ob ain a uni o m mo phology o he Cu-based
deposi o se he guidelines o a possible no el, Cu-based, g ain-
bounda y phase in con en ional Nd-Fe-B pe manen magne s.
Expe imen al
Nd
2
Fe
14
B g ains (i.e., Nd-Fe-B powde ).—End-o -li e, wind-
u bine magne s se ed as he s a ing ma e ial. Be o e unde going
he HPMS ea men , he magne s we e he mally demagne ized and
sandblas ed o emo e hei coa ings. These magne s we e con e ed
in o a hyd ided powde using he HPMS p ocess acco ding o.
19,20
The condi ions used we e 3 ba o hyd ogen, he p essu e o which
was main ained un il i s abilized. The esul ing powde was coa se bu
iable. To educe he pa icle size, he powde was subjec ed o ball
milling. Fo each ba ch, 120 g ams o powde we e milled wi h 50 s eel
balls (10 mm in diame e ) a a equency o 35 Hz, wi h h ee milling
cycles o 10 min each, sepa a ed by a 10 min cooling pe iod.
The powde was u he degassed (hea ing a e =2°C min
−1
,
max empe a u e =450 °C, holding ime =20 min, unde acuum)
and s o ed in a glo e box unde a gon.
This powde was hen used as he base ma e ial o u he
expe imen s o selec i ely leaching he Nd- ich phase, pe o med in
0.5 mol l
−1
ci ic acid solu ion o 15 min. A e he se ime, he
acid solu ion was s ained o , and he powde was insed h ee imes
wi h deionized wa e , s ained wi h magne ic decan ing, and insed
3 imes wi h wa e and once wi h e hanol. The ICP-OES o he
a e age alues om he 4 ba ches a e lis ed in (Table S1 in
he Supplemen a y In o ma ion (SI)), showing he powde consis s
o 23.00 w % o Nd, 0.29 w % P , 4.20 w % Dy, 1.10 w % B,
71.90 w % Fe, 0.48 w % Al, 0.06 w % Cu, 0.02 w % Ga, 0.01 w %
Sn and 0.01 w % Si. The leaching expe imen s we e se o achie e
he s oichiome ic composi ion o he Nd
2
Fe
14
B wi h he a io
be ween he w % o Fe (72.30 w %) and o al w % o he a e
Ea h con en (26.70 w %) o be 2.71. The leaching p ocedu e
esul ed in a Fe and o al a e Ea h con en a io o 2.59, closely
app oxima ing he a ge s oichiome y, confi ming he p esence o
Nd₂Fe₁₄B phase g ains. The esul ing powde was examined wi h
SEM/EDS, which confi med ha he powde consis s o Nd
2
Fe
14
B
g ains wi h an a e age pa icle size o ∼10 μm as shown in (Fig. S1
in he SI), he ea e deno ed as Nd-Fe-B powde .
The elec ochemical cell.—The elec ochemical cell was a 50 ml
beake equipped wi h h ee elec odes: a ci cula P -mesh was used
as a coun e elec ode and Ag/AgCl om HANNA ins umen s as
he e e ence elec ode. The wo king elec ode was a ied o he
di e en expe imen s. All he po en ials in his wo k a e e e enced
s Ag/AgCl.
Wo king elec odes.—Cu-pla e.—A hin coppe pla e was po-
lished wi h sandpape , washed, and d ied. The pla e was hen used in
expe imen s o in es iga e i s in e ac ion wi h he elec oly e and Cu-
con aining elec oly e solu ion.
Bulk Nd-Fe-B elec ode.—A special elec ode was cons uc ed o
s udy he elec ochemical eac ions on he su ace o he Nd-Fe-B.
An image o such elec ode can be ound in Fig. S2b in he SI. The
Nd-Fe-B powde was p essed in o lumps and a ached o a coppe
ape. This was immobilized wi h epofix and hen polished. This
esul ed in a polished Nd-Fe-B g ains’c oss-sec ion and ensu ed
elec ical wi ing while keeping he magne and coppe ape sealed in
plas ic—sepa a ed om he solu ion. This elec ode was used o all
he ol amme ic expe imen s. I was s o ed in he a gon a mosphe e
and was polished be o e each expe imen wi h 5 μm sandpape .
Jou nal o The Elec ochemical Socie y, 2025 172 022505
Nd-Fe-B loose powde elec ode.—The wo king elec ode o he
elec odeposi ion consis ed o a coppe ape o which 20–30 mg o
Nd-Fe-B powde was a ached using an ex e nal pe manen magne
(see Figs. 1and S2a in he SI). Du ing he deposi ion, he ex e nal
magne was o a ed, which caused he magne ic powde o mo e
co espondingly, and ensu ed ha mos o he g ains we e exposed
o he solu ion. A ideo o his o a ion is p esen ed in he SI.
Ul asonic agi a ion was applied o aid he mass anspo using a
30-kHz ul asonic ba h. Du ing he b ie expe imen du a ion (30 s
o deposi ion and up o 5 min o handling), he sample was exposed
o ai and wa e . A e he Cu deposi ion, he powde was washed
ho oughly wi h deionized wa e and isop opanol, acuum d ied, and
s o ed in he glo e box.
Fo coa ing he powde used o measu ing he magne ic p ope -
ies he expe imen was scaled up o app oxima ely 1 g o powde
pe deposi ion (also using a la ge Cu- ape and a s onge ex e nal
magne ). Since he elec ode po en ial is he pa ame e p o iding he
d i ing o ce o a p ocess and is indica ing he s abili y egime o he
phases p oduced, he expe imen s pe o med wi h he same ca hode
po en ial bu wi h dissimila loadings can igh ully be assumed o be
quali a i ely alike.
Elec oly ic ba hs.—The solu ion used in his in es iga ion was a
“neu alized”sul a e ba h, wi h Na₂SO₄employed as a subs i u e o
H₂SO₄. The aqueous elec oly ic ba h included CuSO₄·5H₂O
(CARLO ERBA), anhyd ous Na₂SO₄(Sigma Ald ich and The mo
Scien ific), NaCl (Sigma Ald ich 99.99%) and FeSO₄·7H₂O (Sigma
Ald ich). All he eagen s we e o analy ical g ade and used wi hou
u he pu ifica ion. Table Ishows he ion concen a ions in he
di e en ba hs used in he ollowing expe imen s.
Cell no a ion.—To desc ibe he sys em being in es iga ed in a
pa icula expe imen , he ollowing cell no a ion is used: Wo king
elec ode | Solu ion composi ion | Coun e elec ode.
Fo example, Nd-Fe-B-bulk|Cu
2
⁺,Na
+
,SO
4
2−
,Cl
−
,H
2
O|P
means a bulk Nd-Fe-B elec ode imme sed in he coppe -con aining
solu ion, wi h a pla inum mesh se ing as he coun e elec ode.
Expe imen al condi ions.—The expe imen s we e always pe -
o med a 30 °C ± 2 °C. The pla inum mesh was soaked in ni ic
acid, washed and o ched in a bu ane flame o 30 s, each ime be o e
use. A Gam y Re e ence 600 po en ios a /gal anos a equipped wi h
PHE200 so wa e was used o all he measu emen s and deposi-
ions.
Cyclic ol ame ic (CV) s udies in es iga ed he po en ial egion
om −1.6 V o +0.7 V. The scan a e was 50 mV s
−1
in all he
expe imen s. The scan was ini ia ed immedia ely a e soaking he
wo king elec ode in solu ion wi hou a s abiliza ion ime o keep he
oxida ion a he lowes le el possible. To ensu e consis ency, a CV
s udy o he Nd-Fe-B-bulk|Cu
2
⁺,Na
+
,SO
4
2−
,Cl
−
,H
2
O|P sys em
was addi ionally pe o med in a de-ae a ed solu ion. As he e was no
significan di e ence in he ol ammog am shape, we concluded ha
dissol ed O
2
does no pa icipa e in he eac ions o an app eciable
ex en .
Fo he Cu po en ios a ic elec odeposi ion, expe imen s we e
conduc ed on bo h bulk and loose powde Nd-Fe-B elec odes. The
deposi ion po en ial was −0.25 V, −0.5 V o −1.05 V s Ag/AgCl,
wi h a deposi ion ime o 30 s in all expe imen s.
Elec og a ime y.—To analyse he coppe con en , he coa ed
powde was weighed, dissol ed in ni ic acid and he solu ion was
placed in an elec oly ic cell wi h a magne ic mixe , consis ing o a
pla inum wi e coun e , Ag/AgCl e e ence and pla inum-mesh
wo king elec ode. Coppe was deposi ed gal anos a ically, a a
cu en I=−600 mA un il he appea ance o a po en ial jump and
he occu ence o hyd ogen bubbles. A b igh coppe deposi was
ob ained, and i s mass was de e mined om he weigh di e ence o
he mesh.
SEM/EDS and VSM e alua ion.—Fo s udying he powde
mo phology using SEM, he powde pa icles we e moun ed on
conduc i e adhesi e ca bon ape, spu e ed wi h an 8-nm laye o
ca bon, and examined wi hou u he modifica ion. To analyse he
pa icle c oss-sec ions, he powde was embedded in o an epoxy
esin, allowed o cu e o e nigh , and hen g ound using SiC pape s
wi h g ain sizes down o 5 μm, ollowed by final polishing wi h
diamond pas e o 3 μm and 0.25 μm. Fo he SEM analysis o he
coppe deposi s on he bulk Nd-Fe-B elec ode, he en i e elec ode
was encapsula ed in epoxy and cu pe pendicula o he deposi ion
su ace. A e emo ing he coppe ape and he magne , he sample
was polished using he same p ocedu e as o he pa icle c oss-
sec ion analysis. Mic os uc u al cha ac e iza ion o he pa icle
mo phology and/o polished pa icles was pe o med using a field-
emission-gun scanning elec on mic oscope (FEGSEM) Ve ios G4
HP (The mo Fishe Scien ific Company, 5350 NE Dawson C eek
D i e, Hillsbo o, O egon 97124, USA) equipped wi h an ene gy-
dispe si e X- ay spec oscopy sys em (EDS) AZ ec wi h 65 mm
2
silicon-d i de ec o (SDD) Ul imMax (Ox o d Ins umen s
NanoAnalysis, Hali ax Road, High Wycombe HP12 3SE, UK).
Samples we e analysed a accele a ing ol ages o 18 kV and 7 kV
Figu e 1. Elec ochemical cell wi h P mesh as coun e elec ode (CE),
Ag/AgCl e e ence elec ode (RE) and coppe ape wi h Nd-Fe-B powde as
wo king elec ode (WE).
Table I. Elec oly ic ba h composi ion.
[Cu
2+
]/M [SO
4
2−
]/M [Cl
−
]/mM [Fe
2+
]/M
Coppe con aining solu ion 0.25 2.05 1.41 0
Coppe - ee solu ion 0 2.05 1.41 0
I on(II)-con aining solu ion 0 2.05 1.41 0.25
Jou nal o The Elec ochemical Socie y, 2025 172 022505
and a beam cu en o 0.2 nA. Elec on mic og aphs we e eco ded
using seconda y-elec on imaging (SE) o obse e he pa icle
opog aphy/mo phology and using backsca e ed elec on (BSE)
imaging o enhance he ma e ial con as , i.e., composi ional a omic
numbe Z-con as and phase composi ion. EDS spec a o he
composi ional analyses we e acqui ed o accumula e a la ge numbe
o X- ay coun s o he o de o magni ude 10
6
coun s pe spec um,
hus ensu ing eliable elemen al iden ifica ion and quan ifica ion
wi h high accu acy. Quan i a i e composi ional EDS analysis was
done using an AZ ec in e nal s anda ds da abase wi h he XPP-
PhiRoZ quan i a i e algo i hm, which is included in he so wa e
package. In he analysed EDS spec a we de ec ed only he elemen s
p esen in he Cu-coa ed Nd-Fe-B sys em, and no o he impu i ies
we e ound.
Composi ional analysis.—Fo p ecise quan i a i e analysis, ICP-
OES measu emen s we e pe o med. The g ound powde s we e
diges ed in aqua egia (HNO₃:HCl, 1:3) using a “Ma s 6”mic owa e
diges e (CEM GmbH) and analyzed wi h an “iCAP 7000 Se ies”
ICP spec ome e (The mo Fishe Scien ific Inc.).
Magne ic cha ac e iza ion.—The magne ic measu emen s o he
powde ed Nd-Fe-B samples coa ed wi h Cu a −0.5 V o 30 s we e
pe o med using a ib a ing-sample magne ome e (VSM LakeSho e
8600) wi h magne ic fields in he ange ±1000 kA m
−1
.
Resul s and Discussion
Cyclic ol amme y s udy.—ACVo heCupla eimme sedin
coppe -con aining solu ion deno ed as [Cu-pla e|Cu
2
⁺,Na
+
,SO
4
2−
,Cl
−
,
H
2
O|P sys em] was aken and is shown in Fig. 2a. The po en ial was
swep om 0 V o −1.6 V, hen o +0.5 V and finished a 0 V wi h a
scan a e o 50 mV s
−1
.
In Fig. 2a, an inc easing educ ion cu en was measu ed below
−0.1 V, and eached he fi s peak (C
Cu
2+
)a −0.36 V. We a ibu e
i o he p ocess o Cu
2+
educ ion o elemen a y coppe . Simila o
o he s udies wi h sufla e-based ba hs wi h mino Cl
–
concen a ion,
33
he peak immedia ely a e he s a o he Cu
deposi ion (he e, in he −0.2 o −0.5 V in e al) is ela i ely la ge
compa ed o he u he di usion-limi ed cu en densi y. Gi en he
low concen a ion o Cl
–
ela i e o Cu
2+
, he in e media e o ma ion
o [CuCl
2
]
–
does no appea as a dis inc s ep be o e he wo-elec on
educ ion o Cu
2+
ions, unlike in mo e concen a ed solu ions o
chlo ide sal s.
34
In he u he sec ion o he ca hodic sweep, Cu
deposi ion is con olled by he mass anspo . The cu en ise
(C
H2O
) a ound −1.4 V is due o hyd ogen e olu ion, and he
appea ance o bubbles is isually obse ed. The po en ial o wa e
decomposi ion occu s a a e y nega i e po en ial because Cu is no
a good elec oca alys (as compa ed o, e.g., pla inum), and he
solu ion is no acidic.
35
When he po en ial scan is e e sed, a highe
cu en is measu ed, because H
2
bubbles p o ide some agi a ion,
he eby aiding he mass anspo and enabling mo e coppe ions o
be educed. As he bubble e ec anished by e u ning he elec ode
po en ial o a alue whe e hyd ogen is no longe e ol ed (E >
∼−1.2 V), he Cu-deposi ion cu en e u ns o he alue seen in he
ca hodic-going scan jus p io o he onse o wa e decomposi ion.
A po en ials abo e ze o ol s, he inc easing anodic cu en (A
Cu
)is
measu ed o he whole in es iga ed po en ial ange up o 0.5 V. We
a ibu e i o he oxida ion o he deposi and he elec ode ma e ial
(bo h made o me allic coppe ). The posi i e-going and he nega i e-
going a ms nea ly coincide. The e is no di e ence in he eac an
supply, because a solid coppe ape is being oxidized.
To u he in es iga e his oxida ion, a coppe - ee solu ion was
p epa ed, and 2 CV cycles we e aken and a e p esen ed in Fig. 2b.
Figu e 2. CV o he Cu-pla e in coppe -con aining solu ion (a) and coppe -
ee solu ion (b).
Figu e 3. CVs o he Nd-Fe-B-bulk elec ode (a) in coppe - ee (ligh g ey)
and coppe -con aining solu ion (black), s a ed a 0 V, and (b) in i on(II)-
con aining (da k g ey), coppe - ee (ligh g ey) and coppe -con aining
solu ion (black), s a ed a −0.6 V.
Jou nal o The Elec ochemical Socie y, 2025 172 022505
The po en ial was swep om 0 V o −1.6 V, hen o +0.7 V and
finished a −1.6 V.
When he po en ial is fi s swep in he nega i e di ec ion (black
solid line), s a ing a 0 V, no educ ion cu en is measu ed excep
o hyd ogen e olu ion (C
H2O
) a po en ials lowe han −1.2 V.
Then, a po en ials abo e ze o ol , oxida ion (A
Cu
) occu s, bu we
canno desc ibe i wi h a single chemical eac ion. In his egion he
p e iously anspa en solu ion akes on a pale-blue colou indica ing
he o ma ion o disol ed Cu
2+
and also he me al elec ode begins
o change i s colou . I becomes da ke (black) bu also con ains
o ange-b own colou s sugges ing he o ma ion o solid coppe
oxides/hyd oxides. Then, when he po en ial is again swep in he
nega i e di ec ion (g ey dashed line) wo educ ion peaks occu . The
fi s one (C
Cu
2+
)a −0.3 V indica es he educ ion o hyd a ed,
dissol ed Cu
2+
ions o elemen a y coppe and is ound a he same
po en ial as in a coppe -con aining solu ion (Fig. 2). We a ibu e he
peak (C
CuO
)a −1.05 V o he educ ion o he adhe en solid laye
composed o coup ous/coup ic oxides o hyd oxides since i does no
appea i he coppe is no p e iously oxidized. This is in good
ag eemen wi h,
36
who s udied coppe edox beha iou in NaOH
solu ion and a ibu ed he peak a app oxima ely he same po en ial
o he educ ion o coppe (I) oxide and coppe (II) oxide o me alic
Cu. Publica ions dealing wi h he elec ochemical oxida ion o Cu in
neu al o alkaline media con aining chlo ide ions epo he
o ma ion o a ious oxides, hyd oxides and laye s con aining
chlo ide sal s,
37,38
some imes in a a ying a io as a unc ion o
ipening ime.
39
I is ag eed ha he in ense elec ochemical
oxida ion o Cu migh lead o a slowly dissol ing CuCl laye ha
can decele a e he elec ochemical p ocesses.
Figu e 3a shows wo CVs o he bulk Nd-Fe-B elec ode scanned
in bo h coppe -con aining solu ion (black) and coppe - ee solu ion
(ligh g ey). The po en ial was swep fi s in he nega i e di ec ion
om 0 V o −1.6 V, hen in he posi i e di ec ion ill +0.7 V and
ended a 0 V.
In Fig. 3b h ee CVs o he bulk Nd-Fe-B elec ode scanned in
coppe -con aining, coppe - ee and i on(II)-con aining solu ions a e
shown. The po en ial was swep fi s in he nega i e di ec ion om
−0.6 V o −1.6 V, hen in he posi i e di ec ion ill +0.7 V and
ended a −0.6 V. He e, only he fi s ca hodic pa o he scan is
p esen ed, bu ull CVs can be ound in Fig. S3 in he SI.
As he po en ial in Fig. 3a is swep down om 0 V, a high
posi i e cu en is measu ed in bo h solu ions, esul ing om he
oxida ion o he Nd-Fe-B elec ode. F om p e ious CVs (see Fig. 2),
we know ha Cu
2
⁺ions begin o be educed a po en ials as high as
−0.1 V in he Cu-pla e|Cu
2
⁺,Na
+
,SO
4
2−
,Cl
−
,H
2
O|P sys em. This
implies ha hey unde go educ ion a all po en ials lowe han
−0.1 V. In coppe -con aining solu ion, a po en ials abo e −0.5 V, a
posi i e cu en is measu ed ha is app oxima ely 0.01 A lowe han
in coppe - ee solu ion. This occu s because he educ ion o coppe
ions, which con ibu es a nega i e cu en , akes place simul a-
neously wi h he oxida ion o he Nd-Fe-B elec ode. Below −0.6 V,
Nd-Fe-B oxida ion is supp essed, and he cu en in coppe - ee
solu ion d ops o ze o. In he coppe -con aining solu ion, a pla eau o
nega i e cu en is eached, as he Cu
2+
educ ion is con olled by
di usion.
A −1.05 V a ca hodic peak (C
Fe
2+
) appea s in bo h solu ions,
which we a ibu e o he educ ion o Fe
2+
ions, o med du ing he
oxida ion o he Nd-Fe-B elec ode a po en ials highe han −0.5 V.
Al hough he peak occu s a he same po en ial as in he second
cycle (Fig. 2b) o Cu-pla e|Na
+
,SO
4
2−
,Cl
−
,H
2
O|P sys em, i
ep esen s a di e en eac ion which was s udied mo e in de ail in
Fig. 3b. He e, as he po en ial is swep down om −0.6 V, in
coppe - ee solu ion no ca hodic cu en is measu ed un il −1.2 V,
because Fe
2+
ions canno be p esen i he elec ode is no p e iously
oxidized. When Fe
2+
a e in oduced o he solu ion (i on(II)-
con aining solu ion, da k g ey line), an in ense C
Fe
2+
peak appea s,
hus assigning i o educ ion o Fe
2+
o elemen a y i on. The
po en ial o his peak is in acco dance wi h he he modynamics, as i
is below he Fe
2+
/Fe equilib ium po en ial (−0.65 V s Ag/AgCl
40
).
In coppe -con aining solu ion he o e all cu en is app oxima ely
0.01 A g ea e han in he coppe - ee solu ion because o a cons an ,
di usion limi ed Cu
2+
educ ion. Appea ance o C
Fe
2+
indica es he
p esence o Fe
2+
, e en hough he po en ial below −0.6 V ( oo
nega i e o Nd-Fe-B elec ochemical oxida ion) has been kep om
he s a . This means ha Fe
2+
is o med when Nd-Fe-B is imme sed
in o a coppe -con aining solu ion as a esul o elec oless Cu
2+
deposi ion (Fe +Cu
2+
→Fe
2+
+Cu). Nd
3+
is also likely o be
eleased du ing his spon aneous eac ion, bu do no esul in a
ca hodic peak, because hei educ ion po en ial is much oo
nega i e.
When he po en ial in Fig. 3a becomes mo e nega i e han
−1.2 V, an inc easing ca hodic cu en is measu ed due o hyd ogen
e olu ion (C
H2O
). In he posi i e scan an anodic cu en is obse ed
a po en ials highe han −0.5 V, again indica ing he oxida ion o
Nd-Fe-B. In a coppe - ee solu ion, he oxida ion cu en (A
Nd-Fe-B
)
con inues o inc ease un il +0.4 V, whe e i eaches a peak and s a s
dec easing, indica ing some deg ee o passi a ion. In coppe -con-
aining solu ion, his peak (A
Nd-Fe-B
) is al eady eached a +0.1 V,
possibly due o deposi ed Cu co e ing he Nd-Fe-B g ains and hus
p e en ing he Nd-Fe-B om u he oxida ion, bu a e +0.2 V a
ise in cu en is again obse ed due o oxida ion o he deposi ed
coppe (A
Cu
) which is ound a a simila po en ial as in Fig. 2. As he
p e iously deposi ed coppe is anodically s ipped o , he ee
su ace o he Nd-Fe-B g ains is ge ing oxidized, which addi ionally
inc eases he cu en du ing A
Cu
.
Cu elec odeposi ion s udy.—To ob ain a me allic coppe deposi
wi h he maximum supp ession o Nd-Fe-B oxida ion and p e en ion
o spon aneous elec on exchange be ween Nd-Fe-B and Cu
2+
,an
ex emely nega i e po en ial o −1.05 V, co esponding o he
educ ion peak in Fig. 3, was chosen o he fi s elec odeposi ion.
The deposi ion was pe o med po en ios a ically o 30 s om a
coppe -con aining solu ion on he bulk Nd-Fe-B elec ode (cu en
ansien p esen ed in Fig. S4 in he SI). The SEM BSE image o his
deposi in c oss-sec ion is shown in Fig. 4a. The b igh e g ains a e
he bulk Nd-Fe-B elec ode and he sligh ly da ke ee-like
s uc u es on he le -hand side o bo h images a e he coppe
deposi . As seen om he SEM image, he deposi ed Cu exhibi s a
nonuni o m dend i ic s uc u e. The la e can be explained by he
la ge o e po en ial, di usion-limi ed g ow h, and he onse o he
hyd ogen e olu ion, as e iden om he CV p esen ed in Fig. 3.A
mo e posi i e po en ial o −0.5 V o 30 s was la e used o he Cu
po en ios a ic deposi ion. The co esponding mic os uc u e is p e-
sen ed in Fig. 4b, which e eals a mo e homogenous Cu deposi wi h
only an onse o he dend i ic Cu g ow h.
Based on hose esul s, he Cu deposi ion was pe o med a
−0.5 V om a coppe -con aining solu ion o 30 s; howe e , now
using a loose Nd-Fe-B powde elec ode. Figu e 4c p esen s a SEM
SE and Fig. 4d BSE image o Nd-Fe-B powde pa icles a e
pe o ming he Cu deposi ion. The numbe o coa ed pa icles was
high, bu he deposi , despi e enhanced powde mo emen s and
educed di usion-limi ed g ow h, exhibi ed dend i ic mo phology.
A c oss-sec ion o he Cu-coa ed Nd-Fe-B powde pa icle is
p esen ed in Fig. 4. Quali a i e EDS analysis o he deposi /coa ing
de ec ed Cu as he main elemen in he deposi (i.e., in he in e acial
zone) wi h a low oxygen con en . EDS quan i a i e analysis o hese
iny submic ome e-sized phases was no accu a e enough because
o hei small size.
To make he mo phology o he Cu coa ing mo e homogenous,
he po en ial was se o an e en less nega i e alue. Figu e 4e shows
he SEM SE images o he su ace o he Nd-Fe-B powde pa icles
coa ed wi h Cu and Fig. 4 shows he SEM BSE he c oss-sec ion o
he polished pa icles, o a deposi ion a −0.25 V o 30 s on a loose
Nd-Fe-B powde elec ode. Unde hese condi ions, app oxima ely
50% o he pa icles a e coa ed (see Fig. S5 in he SI), bu he coppe
coa ings exhibi ed subs an ial a ia ions in deposi hickness. While
some pa icles we e co e ed wi h hin deposi s, wi h hickness o
∼300 nm (Fig. 4 , he igh -hand g ain), o he s we e conside ably
Jou nal o The Elec ochemical Socie y, 2025 172 022505
hicke , eaching up o 2.5 μm (Fig. 4 , he le -hand g ain). A
quan i a i e EDS analysis pe o med on he hicke coa ing e ealed
a composi ion ich in Cu (i.e., 94.6% Cu, 0.7% O, 3.8% Fe, 1.0% Nd
in w %). Addi ionally, i has been p o en wi h a low- ol age EDS
se up a 7 kV (see Fig. S6), ha only Cu and O a e p esen in he
coa ing, which means ha he Nd and Fe signals o igina e om
neighbou ing Nd-Fe-B pa icles. This confi ms ha he deposi is
me allic coppe wi h a negligible deg ee o oxida ion.
In o de o in es iga e and op imize he elec odeposi ion o Cu
on o loose Nd-Fe-B powde s, he empo al e olu ion o cu en
p ofiles o di e en Cu deposi ion condi ions, a E=−0.25 V and
E=−0.5 V, wi h and wi hou ul asonic agi a ion, a e p esen ed in
Fig. 5 o a ime in e al o 30 s. Le us fi s conside he deposi ions
wi hou ul asonic agi a ion, which a e p esen ed by he black lines.
Fo bo h in es iga ed po en ials, he cu en s a e nega i e a he
beginning o he eac ion. Howe e , when he po en ial was se o E
=−0.25 V (Fig. 5a), he cu en shi ed o posi i e alues a e 8 s o
deposi ion, indica ing a p e ailing oxida ion o e educ ion, as
al eady expec ed om he cyclic ol ammog am in Fig. 3. When
he applied po en ial was se o E=−0.5 V (Fig. 5b), he cu en
was seen o app oach ze o wi h ime; howe e , i emained nega i e
o he whole deposi ion ime in e al o 30 s.
When he bulk Nd-Fe-B elec ode is oxidized in a coppe - ee
solu ion a E=−0.25 V (see Fig. S7) he cu en ini ially inc eases
du ing he fi s 4 s and hen g adually dec eases o he es o he
deposi ion p ocess. Since he oxida ion a e is no expec ed o
change significan ly du ing his ime (excep o he impac in he
educed ee su ace a ea due o he Cu deposi ion), he inc easingly
posi i e (o less nega i e) cu en obse ed in all he expe imen s
shown in Fig. 5likely eflec s a dec ease in he educ ion cu en ,
meaning a slowe deposi ion a e. This pa e n is ypical o
p ocesses wi h insu ficien mass anspo . I is impo an o
emphasize ha hese expe imen s we e conduc ed using a mo ing
elec ode, bu he agi a ion p o ided by he ex e nal magne p o ed
inadequa e o o ally elimina e he mass- anspo limi a ions.
Consequen ly, he addi ional agi a ion o he elec oly e solu ion is
equi ed, which in his case in ol es he use o ul asonica ion.
In Fig. 5, ch onoampe ome ic da a o wo new expe imen s
conduc ed in a coppe -con aining solu ion a E =−0.25 V (a) and E
=−0.5 V (b) unde ul asonic agi a ion a e p esen ed wi h g ey
lines. Ul asonic agi a ion du ing he Cu deposi ion no ably impac ed
he ch onoampe ome ic beha iou . Wi hou agi a ion, he cu en
becomes mo e posi i e (o less nega i e) o e ime, indica ing a
dec ease in educ ion cu en . When ul asonic agi a ion is applied,
his end pe sis s, bu he a e a which he cu en becomes mo e
posi i e is less p onounced. Also, he ini ial cu en is mo e nega i e
i ul asonic agi a ion is applied. The US agi a ion was ound o
inc ease he o al nega i e cha ge passed wi hin he 30 s deposi ion
pe iod, changing om +0.61 C o −0.42 C a −0.25 V and om
−2.21 C o −4.10 C a −0.5 V, as gi en in he igh bo om o bo h
g aphs p esen ed in Fig. 5. Since agi a ion has no e ec on he
he modynamics o deposi ion, he obse ed inc ease in he ca hodic
cu en mus be due o he imp o ed mass anspo .
In Fig. 4g we p esen an SEM SE image o he mo phology and
in Fig. 4h a BSE image o he c oss-sec ion o he pa icles a e
coppe deposi ion om a coppe -con aining solu ion a −0.5 V wi h
ul asonic agi a ion. A compa ison o SEM images in Figs. 4g–4h
wi h Figs. 4c–4d, whe e he Cu deposi ion was pe o med wi hou
he US agi a ion, confi ms ha Cu coa ings on Nd-Fe-B powde s
Figu e 5. Ch onoampe ome ic da a o Cu deposi ion a E =−0.25 V o
30 s (a) wi hou agi a ion (black line) and wi h US agi a ion (g ey line). In
he bo om igh he o al nega i e cha ge passed wi hin he 30 s deposi ion
pe iod is p esen ed o bo h cases (a). Cu en – ime cu es o Cu deposi ion
a E =−0.5 V o 30 s (b) wi hou agi a ion (black line) and wi h agi a ion
(g ey line). In he bo om igh he o al nega i e cha ge passed wi hin he
30 s deposi ion pe iod is p esen ed o bo h cases (b).
Figu e 4. SEM images o Cu deposi s on Nd-Fe-B elec odes a e 30 s o
deposi ion unde a ious applied po en ial condi ions: (a) BSE image, bulk
Nd-Fe-B elec ode, −1.05 V; (b) BSE image, bulk Nd-Fe-B elec ode,
−0.5 V; (c) SE image, powde ed Nd-Fe-B elec ode (Nd₂Fe₁₄B g ains),
−0.5 V; (d) BSE image, Nd₂Fe₁₄B g ains in c oss-sec ion, −0.5 V; (e) SE
image, powde ed Nd-Fe-B elec ode (Nd₂Fe₁₄B g ains), −0.25 V; ( ) BSE
image, Nd₂Fe₁₄B g ains in c oss-sec ion, −0.25 V; (g) SE image, powde ed
Nd-Fe-B elec ode (Nd₂Fe₁₄B g ains), −0.5 V ul asonic agi a ion; (h) BSE
image, Nd₂Fe₁₄B g ains in c oss-sec ion, −0.5 V, ul asonic agi a ion.
Jou nal o The Elec ochemical Socie y, 2025 172 022505
wi h ul asonic agi a ion exhibi a significan ly less dend i ic su ace,
sugges ing a deposi ion no , o only pa ly, limi ed by di usion
(mixed ac i a ion and mass- anspo con ol).
41
A −0.25 V, ul a-
sonica ion supplies an addi ional −1.03 C, and −1.88 C a −0.5 V,
as calcula ed by sub ac ing he cu en in eg als in Fig. 5, showing
ha he educ ion a e is inc eased. Ul asonica ion, he e o e,
posi i ely a ec s he mass anspo , which leads o an inc ease in
he a e age ca hodic cu en and enhances he mo phology and he
numbe o coa ed pa icles du ing he 30 s o deposi ion.
Analysis o he magne ic p ope ies.—Based on ou expe i-
men al findings, he op imal condi ions o Cu deposi ion we e
achie ed using he po en ios a ic mode a −0.5 V o 30 s by
applying he US agi a ion. Unde hese condi ions, we success ully
p oduced 5 g ams o Cu-coa ed Nd-Fe-B powde . The magne ic
p ope ies o he coa ed ma e ial we e subsequen ly measu ed wi h
he VSM. The magne ic hys e esis loops o bo h he Cu-coa ed Nd-
Fe-B powde and he o iginal powde samples a e shown in Fig. 6a,
indica ing mass magne iza ion alues and coe ci i y. Bo h samples
we e magne ically so wi h a coe ci i y o 0.24 kA m
−1
o he Cu-
coa ed Nd-Fe-B powde and 0.34 kA m
−1
o he o iginal Nd-Fe-B
powde . The mass magne iza ion sa u a es a ≈127 emu g
−1
o he
Cu-coa ed Nd-Fe-B sample and a 137 emu g
−1
o he uncoa ed Nd-
Fe-B sample, which is in acco dance wi h ou p e ious findings on a
simila sys em.
23
This educ ion in mass magne iza ion is a ibu ed
o he dilu ion wi h a non- e omagne ic phase, i.e., he deposi ed
coppe , which does no con ibu e o he magne ic momen bu
inc eases he o e all sample mass. This end is ob ious om a
compa ison o he no malized hys e esis loops. By mul iplying he
cu e o he o iginal uncoa ed Nd-Fe-B pa icles by a ac o o 0.92,
a pe ec o e lap wi h he hys e esis loop o he Cu-coa ed Nd-Fe-B
powde is ound (Fig. 6b). The coppe con en , de e mined by
elec og a ime y, was 9 mass % (see expe imen al sec ion), which
aligns well wi h he VSM no maliza ion ac o , indica ing ha he
sample con ains 8 mass % Cu.
Conclusions
By employing Na
2
SO
4
o he suppo ing elec oly e ins ead o
he commonly used H
2
SO
4
, we we e able o elec odeposi coppe on
easily oxidizable subs a es based on Nd
2
Fe
14
B g ains. A CV s udy
indica ed ha pa o he po en ial egion o Cu
2
⁺ educ ion o e laps
wi h he egion o Nd-Fe-B oxida ion (abo e −0.5 V), esul ing in a
spon aneous eac ion be ween Nd-Fe-B and Cu
2+
. As a esul Cu
elec oless deposi ion occu s and Fe
2+
ions a e eleased in o solu ion
leading o loss o e omagne ic ma e ial. Du ing he po en ios a ic
deposi ion o Cu on bulk Nd-Fe-B-based elec odes a such highly
nega i e po en ials (−1.05 V), he coppe deposi s exhibi a nonuni-
o m dend i ic s uc u e due o di usion-limi ed g ow h and he
onse o hyd ogen e olu ion. Less-nega i e po en ials, such as
−0.5 V, s ill esul ed in a nega i e cu en h oughou he whole
deposi ion expe imen indica ing p e ailing Cu educ ion o e he
Nd-Fe-B oxida ion. The achie ed Cu deposi s we e mo e uni o m
bo h on bulk and powde Nd-Fe-B-based elec odes; howe e , hey
s ill had mino dend i ic g ow h and he co e ing equency o he
powde Nd-Fe-B-based elec ode was low. The applica ion o
ul asonic agi a ion enhances he mass anspo , leading o im-
p o ed coppe -deposi uni o mi y on he Nd-Fe-B powde s and an
inc eased Cu deposi ion a e, as e idenced by measu ing a mo e
educ i e cu en . Choosing mo e posi i e po en ials like −0.25 V
would imp o e he Cu deposi ’s mo phology bu cause a significan
Nd-Fe-B oxida ion, as e idenced by a significan anodic cu en .
This s udy demons a es he success ul elec ochemical deposi ion o
Cu on o Nd₂Fe₁₄B g ains, wi h no magne iza ion educ ion aside
om he in oduc ion o he pa amagne ic Cu phase. These findings
lay he g oundwo k o u u e esea ch in o sin e ing and mic o-
s uc u al op imiza ion o explo e Cu’s ole as a no el g ain
bounda y phase in enhancing coe ci i y and magne ic pe o mance.
In es iga ing a sys em o Nd₂Fe₁₄B/Cu, combined wi h densifica ion
and sin e ing app oaches, will be essen ial o ully unde s and
coppe ’s impac on key magne ic p ope ies such as emanen
magne iza ion and coe ci i y in bulk Nd-Fe-B magne s. Coppe
elec odeposi s hus ep esen a c i ical fi s s ep in ad ancing g ain-
bounda y enginee ing, in oducing new phases ha enhance co o-
sion esis ance and p omo e cos and esou ce e ficiency.
Acknowledgmen s
This esea ch was unded by he Slo enian Resea ch and
Inno a ion Agency ( esea ch co e unding no. P2–0084) and he
Eu opean Union’s Ho izon Eu ope Resea ch and Inno a ion
P og am REESILIENCE (g an ag eemen no. 101058598) and
GREENE (g an ag eemen no. 101129888). All figu es c ea ed
wi h BioRende .com.
ORCID
Č Saksida h ps://o cid.o g/0009-0002-4648-1578
László Pé e h ps://o cid.o g/0000-0001-5604-0982
K is ina Žužek h ps://o cid.o g/0000-0003-2652-1966
Re e ences
1. B. Podmiljšak, B. Saje, P. Jenuš, T. Tomše, S. Kobe, K. Žužek, and S. Š u m,
Ma e ials,17, 848 (2024).
2. J. W. Heim II and R. L. Vande Wal, Mine als,13, 1274 (2023).
3. J. Li, H. Sepeh i-Amin, T. Sasaki, T. Ohkubo, and K. Hono, Sci. Technol. Ad .
Ma e .,22, 386 (2021).
4. M. G ohol and C. Veeh, Eu opean Commission: Di ec o a e-Gene al o In e nal
Ma ke , Indus y, En ep eneu ship and SMEs, S udy on he c i ical aw ma e ials
o he EU 2023, Publica ions O fice o he Eu opean Union, 2023, (2024), h ps://
da a.eu opa.eu/doi/10.2873/725585.
5. O. Gu fleisch, J. Phys. D,33, R157 (2000).
Figu e 6. As-measu ed magne ic hys e esis loops o Nd-Fe-B powde
be o e and Cu a e deposi ion a −0.5 V o 30 s wi h US agi a ion (a)
and he no malized hys e esis loop o Cu-coa ed Nd-Fe-B powde a
−0.5 V o 30 s wi h US agi a ion o e lapping he loop o uncoa ed
Nd-Fe-B powde (b).
Jou nal o The Elec ochemical Socie y, 2025 172 022505
6. T. Sch efl, J. Fidle , and H. K onmülle , Physical Re iew B,49, 6100 (1994).
7. K. Hono and H. Sepeh i-Amin, Sc . Ma e .,67, 530 (2012).
8. H. Sepeh i-Amin, T. Ohkubo, T. Shima, and K. Hono, Ac a Ma e .,60, 819 (2012).
9. J. Fidle and J. Be na di, J. Appl. Phys.,70, 6456 (1991).
10. S. Pandian, V. Chand aseka an, M. Ga imella, K. Iye , and K. Rao, J. Appl. Phys.,
92, 6082 (2002).
11. A. Yan, X. Song, Z. Chen, and X. Wang, J. Magn. Magn. Ma e .,185, 369 (1998).
12. W. Li, T. Ohkubo, and K. Hono, Ac a Ma e .,57, 1337 (2009).
13. H. J. Engelmann, A. S. Kim, and G. Thomas, Sc . Ma e .,36, 55 (1997).
14. Y. Ta e su, S. Tsuneyuki, and Y. Gohda, Phys. Re . Appl.,6, 064029 (2016).
15. J. Dai, Z. Yang, and Q. Liu, Ma e ials,13, 4360 (2020).
16. S. Pandian, V. Chand aseka an, M. Ga imella, K. Iye , and K. Rao, J. Alloys
Compd.,364, 295 (2004).
17. A. Mish a, S. Khoshsima, T. Tomše, B. Podmiljšak, S. Š u m, C. Bu kha d , and
K. Žužek, Ma e ials,16, 6565 (2023).
18. W. Li, T. Ohkubo, K. Hono, and M. Sagawa, J. Magn. Magn. Ma e .,321, 1100
(2009).
19. L. Schul z, A. M. El-Aziz, G. Ba klei , and K. Mumme , Ma e . Sci. Eng. A,267,
307 (1999).
20. A. Wal on, Y. Han, N. A. Rowson, J. D. Speigh , V. S. J. Mann, R. S. She idan,
A. B adshaw, I. R. Ha is, and A. J. Williams, J. Clean. P od.,104, 236 (2015).
21. A. Wal on, A. J. Williams, J. D. Speigh , and I. R. Ha is, U.S. Pa en , 8,734,714 B2
(2014).
22. C. Bu kha d *, S. an Nielen, M. Awais, F. Ba olozzi, J. Blomg en, P. O iz, M.
B. Xico enca l, M. Deg i, S. Nayebossad i, and A. Wal on, J. Magn. Magn. Ma e .,
588, 171475 (2023).
23. S. Khoshsima, J. Vidma , Z. Sama džija, T. Tomše, M. Kuš e , A. Mish a, S. Š u m,
and K. Žužek, Ma e ials,16, 5181 (2023).
24. H. Bala, S. Szymu a, and J. J. Wysłocki, J. Ma e . Sci.,25, 571 (1990).
25. G. W. Wa en, G. Gao, and Q. Li, J. Appl. Phys.,70, 6609 (1991).
26. P. Venka esan, T. Hooge s ae e, T. Hennebel, K. Binnemans, J. Sie sma, and
Y. Yang, G een Chem.,20, 1065 (2018).
27. X. Xu, S. Š u m, Z. Sama džija, J. Vidma , J. Ščanča , and K. Rožman,
ChemSusChem,12, 4754 (2019).
28. J. Zheng, X. Cheng, H. Chen, L. Qiao, M. Lin, L. Jiang, and S. Che, J. Adhes. Sci.
Technol.,30, 275 (2016).
29. M. S. Pauno ic and M. Schlesinge , Mode n Elec opla ing 5 h ed. ed.736 (New
Yo k), (Wiley, Hoboken, NJ) (2010).
30. G. G. Láng, M. Uj á i, and G. Ho ányi, J. Elec oanal. Chem.,522, 179 (2002).
31. Q. Wu and D. Ba key, J. Elec ochem. Soc.,147, 1038 (2000).
32. C. Gab ielli, P. Moço éguy, H. Pe o , and R. Wia , J. Elec oanal. Chem.,572,
367 (2004).
33. W. Shao, G. Pa anaik, and G. Zanga i, J. Elec ochem. Soc.,154, D201 (2007).
34. , Low, , Ponce, de León, , and Walsh, T ansac ions o he IMF,93, 74 (2015).
35. P. Venka esan, Z. H. Sun, J. Sie sma, and Y. Yang, P oceedings o he
1s Eu opean Ra e Ea h Resou ces Con e ence163 Milos, G eece (2014).
36. J. B. Raoo , R. Ojani, A. Kiani, and S. Rashid-Nadimi, In . J. Hyd ogen Ene gy,35,
452 (2010).
37. S. M. Abd El Haleem and B. G. A eya, J. Elec oanal. Chem. In e acial
Elec ochem.,117, 309 (1981).
38. J. Kunze, V. Mau ice, L. H. Klein, H-H. S ehblow, and P. Ma cus, Elec ochim.
Ac a,48, 1157 (2003).
39. S. Kologo, M. Ey aud, L. Bonou, F. Vacandio, and Y. Massiani, Elec ochim. Ac a,
52, 3105 (2007).
40. S. Sa hiyana ayanan, M. Sah e, and W. Kau ek, Co os. Sci.,41, 1899 (1999).
41. C. Lupó and D. Schle wein, J. Elec ochem. Soc.,166, D3182 (2018).
Jou nal o The Elec ochemical Socie y, 2025 172 022505
