㓟⣲Ⓨ⏕཯ᛂࡢࡓࡵࡢ㔠ࢡࣛࢫࢱ࣮ᢸᣢ 1L)H/'+ ࢼࣀࢩ࣮ࢺ㟁ᴟ࡟࠾ࡅࡿゐ፹≉ᛶ໭㔝 ⩧ࠊᒣෆ⨾✑஑ᕞ኱Ꮫ ࣮࢝࣎ࣥࢽ࣮ࣗࢺ࣭࢚ࣛࣝࢿࣝࢠ࣮ᅜ㝿◊✲ᡤ෌⏕ྍ⬟࢚ࢿࣝࢠ࣮⏤᮶ࡢ㟁ຊࢆ⏝࠸ࡓỈ㟁ゎ࡟ࡼࡿࢢ࣮ࣜࣥ࡞Ỉ⣲⏕ᡂࡣࠊḟୡ௦ࡢ࢚ࢿࣝࢠ࣮㐠⏝࡟࠾࠸࡚ᚲせ୙ྍḞ࡞ᢏ⾡࡛࠶ࡿࠋỈࡢ 4 㟁Ꮚ㓟໬ࢆక࠺㓟⣲⏕ᡂ཯ᛂࡣᮍࡔ㐣㟁ᅽࡀ㧗ࡃࠊ㧗άᛶ࡞㟁ᴟゐ፹ࡢྜᡂࡀồࡵࡽࢀ࡚࠸ࡿࠋᒙ≧」Ỉ㓟໬≀㸦LDH㸧ࡣࠊ2 ౯࡜ 3 ౯ࡢ㔠ᒓ࢖࡛࢜ࣥᵓᡂࡉࢀࡿ㔠ᒓỈ㓟໬≀ࢼࣀࢩ࣮ࢺ࡜ࠊࢼࣀࢩ࣮ࢺ㛫࡟ᤄධࡉࢀࡿ࢔ࢽ࢜ࣥ࠾ࡼࡧỈศᏊ࡟ࡼࡗ࡚ᵓᡂࡉࢀࡿᒙ≧໬ྜ≀࡛࠶ࡿࠋ㏆ᖺࠊNi2+࡜ Fe3+ࢆྵࡴ LDH㸦NiFe-LDH㸧࠿ࡽ๤㞳ࡋࡓࢼࣀࢩ࣮ࢺࡀ㓟⣲Ⓨ⏕཯ᛂ࡟㧗࠸άᛶࢆ♧ࡍࡇ࡜ࡀሗ࿌ࡉࢀࡓࠋᮏ◊✲࡛ࡣࠊ
NiFe-LDH ࢼࣀࢩ࣮ࢺ㸦LDH-ns㸧࡟㔠ࢡࣛࢫࢱ࣮ࢆᢸᣢࡋࠊ㓟⣲Ⓨ⏕཯ᛂࡢࡓࡵࡢ㧗άᛶ࡞㟁ᴟゐ፹ࡢྜᡂࢆヨࡳࡓࠋSTEM ほᐹ࠾ࡼࡧ AFMᐃࡼࡾࠊ༢ᒙ࡟๤㞳ࡉࢀࡓ LDH-ns ୖ࡟ᖹᆒ⢏ᚄ 1.2 nm ⛬ᗘࡢ㔠ࢡࣛࢫࢱ࣮ࡀ㧗ศᩓ࡟ᢸᣢࡉࢀ࡚࠸ࡿࡇ࡜ࢆ☜ㄆࡋࡓࠋ1 M KOH Ỉ⁐ᾮ୰࡛㓟⣲Ⓨ⏕཯ᛂࢆ⾜ࡗࡓ࡜ࡇࢁࠊ㔠ࢡࣛࢫࢱ࣮ᢸᣢࢼࣀࢩ࣮ࢺࡣࢼࣀࢩ࣮ࢺࡢࡳ࡜ẚ㍑ࡋ࡚ᐃ࠿ࡽࠊࢼࣀࢩ࣮ࢺ࡜㔠ࢡࣛࢫࢱ࣮㛫࡛㟁Ⲵ⛣ືࡀ⏕

80 mV ప࠸㐣㟁ᅽࢆ♧ࡋࡓࠋXAFS3+ࡌࠊάᛶⅬ࡛࠶ࡿࢼࣀࢩ࣮ࢺࡢ Fe ࡢ㟁Ꮚ≧ែࡀኚ໬ࡋࡓࡓࡵάᛶࡀྥୖࡋࡓࡇ࡜ࡀ᫂ࡽ࠿࡜࡞ࡗࡓࠋ㓟⣲Ⓨ⏕཯ᛂࡢࡓࡵࡢ㔠ࢡࣛࢫࢱ࣮ᢸᣢNiFe-LDHࢼࣀࢩ࣮ࢺ㟁ᴟ࡟࠾ࡅࡿゐ፹≉ᛶ䕿 ໭㔝 ⩧䚸ᒣෆ ⨾✑ (஑ᕞ኱Ꮫ 䜹䞊䝪䞁䝙䝳䞊䝖䝷䝹䞉䜶䝛䝹䜼䞊ᅜ㝿◊✲ᡤ)
Introduction
Renewable energyderived electricity

Layered Double Hydroxide:
LDH4OH- ↔ OHydroxidenanosheett2 + 2H2O + 4e

1.23 V vs RHE
䕺 4-electron transfer step䕺 High overpotential
Slow kinetics

O2e-e-

H2O

Enhancement of catalytic activity
Au

Combination withChgold clusters

Exfoliation
ELDH

Monolayer

LDH

Nat. Chem., 2014, 5, 4477

Improvementof conductivity

LDH nanosheetsn(LDH-ns)

Carbon nanotube (CNT) /NiFe-LDH

A /L
Au/LDH-ns
electrocatalyst

Au cluster

Hydroxide nanosheet
M2+
M3+

M3+: Al3+, Ga3+
In3+, Fe3+
M2+: Mg2+, Zn2+
Mn2+, Ni2+

Highly active
electrocatalysts

H2O

Water electrolysis

NiFe-LDH nanosheet

WaterAnion(in alkaline solution)
H2

Objective

Oxygen Evolution Reaction(OER)

䕺 Low conductivity

䞉Electron pathway
through Au clusters

䞉Stability
䞉High conductivity
J. Am. Chem. Soc. 2013, 135, 8452

e-Synthesis of a highly active LDH-based
electrocatalyst by loading of Au clusters‫ ی‬Improvement of conductivity‫ ی‬Instability of carbon materials

Results and discussion
Synthesis of NiFe-LDH nanosheet

d = 0.921 nm
NiFe-LDH ClO4-Stirring with Ar flow : 1h
Washing : methanol
Drying, 24 h

1 !mSynthesis of gold nanoclusters
DMF : 5 ml

HAuCl4 in DMF: 100 mM, 37.5 !lHeating with stirring: 150oC, 4 hHeating with stirring: 150oC, 8 hHeating with stirring: 150oC, 2 h

Au cluster : S

Au cluster : M

Au cluster : LS

M

4000

3000
2000
1000
-1
Wavenumber (cm )1.4Fe

1.50.011905 11910 11915 11920 11925
Energy (eV)

Ni

0.10
X (!m)

0.15

0.20

Catalytic performances

0.8
0.6

Reduction

0.4

NiFe-ns
Au/NiFe-ns
Fe foil

0.20.07115

71207125
7130
Energy (eV)

7135

-2

1.0

e2+ Ni2+

LSV (iR-corrected)

20

Au foil

1.0

0.0
8330

Au(OH)3

No change

0.5

Ni foilNiFe-ns
Au/NiFe-ns
8335

8340
8345
Energy (eV)Au clusters (S)8350

Charge transfer from
Au clusters to nanosheet

Fe3+Ni

0.4

Cluster size : S < M < L

Au/NiFe-ns
on rotating disk electrode

Current density (mA cm )Au foilAu clusers
Au/NiFe-ns

Intensity (a.u.)

Intensity (a.u.)

Intensity (a.u.)

Oxidation

0.20.3X (!m)C

Au ratio :0.4-6.8 wt%

L

1.2

0.2

0.3

Mixing, stirring

Change in electronic stateof Fe active site

Au/NiFe-ns (S) 2wt%

0123
Distance (Å)

4

Au clusters bonded to oxygenof NiFe-ns.

15
10

Au/NiFe-ns(S, 2wt%)
NiFe-ns
IrO25

Au (S)
01.40

1.45 1.50 1.55 1.60
Potential (V vs RHE)

Effects of Au ratio
Overpotential at 10 mA/cm2 (V)

Au-O

1.0

0.4

0.05

0.2
X (!m)

TEM 䠃 STEMXAFS measurement (Au(S)/NiFe-ns, 2wt%)

0.6

0.1

3.0
2.5
2.0
1.5
1.0
0.5
0.00

0.1

B

12 !l
Drying at 125oC

1.6

0.8

200 nm

3.0
2.5
2.0
1.5
1.0
0.5
0.0

A

Au/NiFe-ns"Au108

NiFe-LDH ClO4-

3.0
2.5
2.0
1.5
1.0
0.5
0.0

NiFe-ns: 150 !lColloidal solution (10 ppm)

1.2

NiFe-LDH nanosheet

㽢4150oCDMF

200 nmColloidal Au : 30 !l

HAuCl4 in DMF: 100 mM, 150 !l

Au cluster

50$(COO32-) $(ClO$(C 4-)

Synthesis of Au/LDH-ns

DMF : 5 ml

HAuCl4 in DMF: 100 mM, 150 !l

HAuCl43040
2 # (degree)

CB

Height (nm)NiFe-LDH nanosheet(NiFe-ns)

20

NiFe-LDH CO32Transmittance (a.u.)

Formamide
Stirring with Ar flow
: 24 hG. Abellan, et.al., J. Mater. Chem., 2010, 20, 7451
Iyi, et.al., Appl. Clay Sci., 2011, 54, 132

DMF : 5 ml

10Enlargement

AHeight (nm)

5 !m101
102
105

Ni0.75Fe0.25(CO3)0.125(OH)2䞉0.38H2O

Height (nm)

Washing, drying

NiFe-LDH nanosheet

NiFe-LDH CO32-d = 0.780 nm
NiFe-LDH CO32-

NiFe-LDH ClO4-

NiFe-LDH CO32Ni : Fe = 3 : 1003 : layers distance

NiFe-LDH CO32-006

Hydrothermal
treatment
150oC, 36 hCharacterization of NiFe-LDH nanosheet

NiFe-LDH CO32ClO4- exchange solution
Methanol + aq. HClO4:50 ml (ClO4- /CO32-= 2.5)003

Ni(NO3)2䞉6H2O : 60 mM
Fe(NO3)3䞉9H2O : 20 mM
Urea : 140 mM
Distilled water : 40 ml
Triethanolamine : 50 mM

Au/NiFe-ns (S)Au/NiFe-ns (M)Au/NiFe-ns (L)

0.34

0.32

0.3

0.28

0.26

0.262 V01

23
45
Au ratio (wt%)

67

Au/LDH-ns showed high activities for OER.

Conclusions
䕺 The Au/NiFe-ns showed much higher activity than that of NiFe-ns, indicating that application of Au clusters to NiFe-ns significantly
improved catalytic activities.
䕺 Performances of the Au/NiFe-ns electrocatalyst depended on size and amount of gold clusters, and smaller Au clusters were preferable
for higher performances of the Au/NiFe-ns.