Control of the Ni non-stoichiometry in Ni_1-xO nanoparticles : "Core-shell"-like model

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Submitted on 12 Jul 2017

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Control of the Ni non-stoichiometry in Ni1-xO

nanoparticles : ”Core-shell”-like model

Baptiste Polteau, Franck Tessier, François Cheviré, Laurent Cario, Stéphane

Jobic

To cite this version:

Baptiste Polteau, Franck Tessier, François Cheviré, Laurent Cario, Stéphane Jobic. Control of the Ni

non-stoichiometry in Ni1-xO nanoparticles : ”Core-shell”-like model. ”Solid State Chemistry” Gordon

Research Conference (GRC), Jul 2016, New London, NH, United States. �hal-01560944�

a

_{Institut des Sciences Chimiques de Rennes &UMR CNRS .gg.z- Université de Rennes w- France}

b

_{Institut des Matériaux Jean Rouxel- &UMR CNRS .=Agz- Université de Nantes- France}

To improve the performances of pb>ye Sensitized Solar <ell 4pb>SS<. [X]° the synthesis of modi�ied pbtype nickel oxide semiconductor° commonly used as

a photocathode in such devices° was initiated using a mixed valent nickel oxyhydroxide Ni

E

O

R

4O9.

M

5 The decomposition of this precursor in air at

temperatures lower than …AA°< leads to nonbstoichiometric Ni

Xbx

O nanoparticles 4from R to EA nm. with tunable nickel vacancies concentration 4up to

RBO for RbEnm particle sizes. [R]5 Iccording to our chemical characterizations 4XR>° T=M° density° chemical analysis° V=T measurement….° the nickel

vacancies segregate at the surface of the Ni

Xbx

O nanoparticles to create a gcorebshellgblike edi�ice 4similarly to our previous work on Znbde�icient Zn

Xbx

O

nanoparticles [E].5 This gcorebshellg is constituted by a dense stoichiometric NiO coated 4or terminated. by an oxygen 4hydroxide or carbonate groups.

surface layer free from nickel atom5 The Nibfree surface layer in�luences drastically the density of the smaller nanoparticles by decreasing it5 When the

nanoparticles size increases° the density evolves until reaching the theoretical density of stoichiometric nickel oxide for the bigger particles 4≥ BA nm.5

Thus° with the control of the particles size° we can also control the Ni nonbstoichiometry in Ni

Xbx

O following our gcorebshellgblike model5

<ontrol of the Ni nonbstoichiometry in Ni

_Xbx

O

nanoparticles : g<orebshellgblike model

Vaptiste Polteau

a

_{° 8ranck Tessier}

a

_{° 8rançois <heviré}

a

_°

Laurent <ario

b

_{° Stéphane Jobic}

b

Nickel precursor synthesis p characterizations

Thermal decomposition in air

NiO synthesis

Muf�le Furnace Time Tamb XA°<5minbX >well Rh Iir T /vD°L ≤ T ≤ ?DD°L Nickel precursor NiEOBDOHy.powder

=xperimental procedure : NiO materials prepared at X °L are labeled as NiOBX

NiwXxO NiO / Theta g°x +D ,D vD &D 6D >nt ensit y gak ukx g+++x g/DDx g//Dx g,++x_g///x RAA°< &DD°L

Irea I A Surface dehydration Irea III A Thermal stability range of Ni+BxO

Area IhII Area III Area IV Ni,O/gOWxw In situ XRD vs temperature Area I Area II

Area III Area IV

exo

Irea II A Phase transformation from Ni,O/gOWxwinto Ni+BxO

Irea IV A Thermal stability range of NiO

TGA DTA

Precipitation

Route

NiDNO

E

y

B

= *H

B

O

NaOHmNaClO

Ni

E

O

B

DOHy

. Flack color Nickel oxyhydroxide gXRYx Nanoparticles ≈ / gnmx Speci�ic surface area ≈ /vD m/_kgB+ Ni,4_RNi/4_{ratio ≈ / gXPSP magnetismx}

Ni/4_+Ni,4_{/O/gOWxwformula} 5 nm F>é ç R°XR nm Yiameter >nt ensit y

NiO nanoparticles with high speci�ic surface areas

Evidence of Ni

wXx

O nanoparticles at low decomposition temperatures

NiOhBÅ" NiOhE"" NiOhEÅ" NiOh."" NiOh.Å" NiOhÅ"" NiOh*"" NiOhv"" NiOhM""

νOWB δW/OνLO,/B νNiBO

Tr

ansmit

tance

8TIR : Llear correlation between the intensity of the absorption bands of hydroxide and carbonate groups vs particles size

Surface OWB_{c LO} ,/Bgroups

NiObulk

Oxygen analysis : Wigh oxygen nonBstoichiometry at low decomposition temperatures in comparison with NiO

NiO+4xor Ni+BxO formulation =

Yensi

ty

/P/ /P& wP/ &PD +/Pz +6Pz /?Pv v+Pw +DD

NiObulk

Tailles des cristallites gnmx

Lrystallites size gnmx

x

in

Ni

+B

x

O

Area III Area IV

Ni

wXx

O

NiO

NiwXxO nanoparticules with tunable Ni vacancies concentration vs synthesis temperature and particles size

>ensity : ]t low densitiesP Ni+BxO

formation with nickel vacancies up to /vf at T < zDD °L g]rea >>>x Yensity of stoichiometric NiO at T ≥ zDD °L g]rea >Vx

Lon�irmation of the two areas gTq]x Density of NighxO nanoparticle R = particle radius r = shell thickness

NiO

Rw r

NiO

Rg r NiO Stoichiometric CCoreC Oxygen CShellC Dor hydroxide= carbonate groupsy

Nanoparticle

CBulkC particle

g<orebshellg structure : Yense stoichiometric NiO sphere coated by an oxygen surface layer gfree from nickel atomx

NaClhtype d 7 .D4w

NaClhtype Dwithout Niy

d 7 wDEw

Speci�ic surface area of NighxO nanoparticle

NiObulk gD= Å wDA Å A Å hhh CorehShell model Experimental data Yensi ty x in Ni+B xO

Speci�ic surface area r = "= gS"= BSÅ Å NiObulk A Å AD= Å wDf Å hhh CorehShell model Experimental data Yensi ty x in Ni+B x O Particles size gnmx r = "= "SÅ= gSE Å

>ensity vs SV=T: Fest �it with r V /kv ]�

>ensity vs particles size : Fest �it with r V +k, ]�

Average shell thickness 7 wDÅ Å close to dNiXOin NiO at gDw Å The oxygen surface layer is a monoXlayer

lCoreXshelllXlike model

References

[+]k Jk OdobelP Lk Le PleuxP Yk PellegrinP Ek FlartP ]cck Lhemk ReskP MEP +Dz,P g/D+Dxk [/]k Fk PolteauP Jk TessierP Jk LheviréP Lk LarioP Jk OdobelP Sk JobicP Solid State ScikP BMP ,& g/D+zxk

[,]k ]k RenaudP Lk LarioP Xk RocquefelteP Pk YeniardP Lk PayenP Ek qautronP Ek JaulquesP Jk LheviréP Jk TessierP Sk JobicP Scik RepkP BP +/6+w g/D+vxk

Lry stalli tes size gnmx f

T=M : Well crystallized NiO nanoparticles with a narrow particles size distribution B <YG the average particles size qradual increase of the NiO crystallites size with temperature Wigh SFETP up to /wD m/kgB+at low temperatures

Lontrol of the NiO particles size vs the decomposition Excellent agreement

between the crystallites and the

particles sizes for temperatures ≤ 8AA °C

temperature

f By Rietveld re�inement

NiOhBÅ" NiOhE"" NiOhEÅ" NiOh.""

NiOh.Å" NiOhÅ"" NiOh*"" NiOhv""

5 nm 20 nm 5 nm F>é ç R°RZ nm Yiameter >nt ensit y 5 nm F>é ç R°Z… nm Yiameter >nt ensit y 5 nm Yiameter >nt ensit y F>é ç M°ZA nm 200 nm F>é ç B…°" nm Yiameter >nt ensity 50 nm F>é ç XW°B nm Yiameter >nt ensity F>é ç "°EZ nm Yiameter >nt ensity F>é ç XR°… nm Yiameter >nt ensity 50 nm F>é ç EA°" nm Yiameter >nt ensit y