of 12
Supporting Information
Outstanding
hydrogen
evolution
reaction
catalyzed
by
porous
nickel
diselenide
electrocatalysts**
Haiqing
Zhou,
Fang
Yu,
Yuanyue
Liu,
Jingying
Sun,
Zhuan
Zhu,
Ran
He,
Jiming
Bao,
William
A.
Goddard III,
Shuo Chen
*
, Zhifeng Ren
*
* Correspondence
and
requests
for
materials
should
be addressed
to
S.
C.
schen34@uh.edu
or
Z. F.
R.
zren@uh.edu.
1.
Methods
Material
synthesis.
The
commercially
purchased
Ni
foam
was
cut
into
small
pieces
with
an
area
of
1
cm
2
,
which
were
then
immersed
into
the
PVP/HAc
solution
(0.1
g PVP
in
5 ml
HAc)
for
several
seconds.
After
drying
it slowly,
they
were
placed
in
the
center
of a tube
furnace,
followed
by
direct
selenization
at
600
o
C
for
1h in Ar
atmosphere
with the Se powder
placed at the upstream as Se source.
Electrochemical
tests.
Electrochemical
tests
were
carried
out
in
a N
2
-saturated
three-electrode
system
(Gamry,
Reference
600),
1,2
where
a saturated
calomel
electrode
was
used
as
the
reference
electrode,
a Pt wire
as
the
counter
electrode
and
as-prepared
NiSe
2
foams
directly
as
the
working
electrode.
To
exclude
the
possible
contribution
of
any
Pt
contamination
to
the
catalytic
performance,
we
performed
similar
measurements
using
a graphite
foil
(Alfa
Aesar)
as
the
counter
electrode,
and
XPS
analysis
on
several
positions
of
the
catalyst
surface,
where
no
Pt
signals
are
found
on
post-HER
catalysts.
Electronic
Supplementary
Material
(ESI)
for
Energy
&
Environmental
Science.
This
journal
is
©
The
Royal
Society
of
Chemistry
2017
50-100
potential
sweeps
between
0.07
V to
-0.20
V vs.
reversible
hydrogen
electrode
(RHE)
at a scan
rate
of
50 mV/s
were
applied
to
electrochemically
activate
the
catalysts
prior
to the
HER
measurements
and
for
studying
the
electrochemical
stability.
The
electrochemical
impedance
spectroscopy
curves
were
collected
at a potential
of
-0.14
V vs.
RHE
in
the
same
device
configuration
by
tuning
the
frequency
from
10 mHz to 1 MHz with a
10 mV AC dither.
Computational
methods.
To
identify
the
active
site
for
HER,
we
performed
Density
Functional
Theory
(DFT)
calculations
using
the
Vienna
Ab-initio
Simulation
Package
(VASP)
3,4
with
projector
augmented
wave
(PAW)
pseudopotentials
5,6
and
the
Perdew-Burke-Ernzerhof
(PBE)
exchange-
correlation
functional.
7
We
used
400
eV
for
the
plane-wave
cutoff,
and
fully
relaxed
the
systems
until
the
final
force
on each
atom
is
less
than
0.01
eV/Å.
We
have
doubled
checked
the
free
energies
of
H
adsorption
on perfect
surface
and
vacancy-containing
surfaces
using
500
eV,
and
found
the
values
differ
by
< 10 meV.
We
used
a slab
of
2×2
surface
supercell,
with
a thickness
of
4 stoichiometric
layers,
and
5×5×1
Monkhorst-Pack
k-points
sampling.
8
Following
the
approach
of
Ref.
9 and
10,
the
free
energy
of
hydrogen
adsorption
G
H*
)
is calculated
as
Δ
G
H*
=
E
ad
E
ZP
+
TS
, where
E
ad
is the
adsorption
energy
of
H
onto
the
surface,
referenced
to
the
1/2
of
energy
of
the
H
2
moleccule
(see
below),
E
ZP
is the
difference
in
zero
point
energy
between
the
adsorbed
H and
the
H
2
molecule,
T is the
room
temperature,
and
S is the
1/2
entropy
of
H
2
molecule
at standard
conditions.
The
adsorption
energy
E
a
is calculated
as
E
a
=
E
(H+surface)
-
E
(surface)
-
E
(H
2
)/2,
where
E
(H+surface),
E
(surface)
and
E
(H
2
)
are
the
energies
of
H-adsorbed surface, pure surface,
and an
H
2
molecule, respectively.
2.
SEM
morphologies of porous
NiSe
2
catalyst from original Ni foam
Figure
S1.
Low
and
high-magnification
SEM
images
of
as-prepared
NiSe
2
foam
from
commercial
Ni
foam without any
treatment.
3.
Energy dispersive X-ray
spectrum
(EDS) of as-grown
NiSe
2
catalyst
Figure
S2.
a
,
Elemental
EDS
mapping
of
Ni
(yellow)
and
Se
(purple)
elements
in the
same
image.
b
,
Original
EDS
analysis
on
the
chemical
composition
of
as-prepared
NiSe
2
foam
from
HAc
and
PVP
co-
treated Ni foam under TEM.
4.
XPS spectra of different as-prepared
NiSe
2
catalysts
Figure
S3.
XPS spectra
of
different
NiSe
2
foams.
5.
Comparison
of
the
catalytic
performance
of
HP-NiSe
2
catalysts
between
Pt and
graphite
foil
counter electrode
Figure
S4.
The
polarization
curves
of
the
HP-NiSe
2
catalysts
when
using
Pt or
graphite
foil
as
counter
electrode. No obvious
differences are detected during the measurements.
6.
The
summary of the
catalytic performance
for porous NiSe
2
catalysts
Table
S1.
The
main
performance
parameters
of
different
NiSe
2
foams
in
comparison
with
a Pt
wire
investigated
in
Figure
3.
Here
j
0
,
,
η
10
and
η
100
are
corresponding
to the
exchange
current
density,
the
potentials vs
RHE at
10 mA cm
-2
, and 100 mA cm
-2
, respectively.
Catalyst
Tafel slope
j
0
η
10
η
100
A-NiSe
2
46.0 mV dec
-1
8.6
μA
cm
-2
153 mV
200 mV
H-NiSe
2
42.6 mV dec
-1
64.6
μA
cm
-2
107 mV
153 mV
HP-NiSe
2
43.0 mV dec
-1
612.0
μA
cm
-2
57 mV
103 mV
Pt wire
31.0 mV dec
-1
1126.2
μA
cm
-2
32 mV
72 mV
7.
The
comparison of our catalystswith other
reported cheap electrocatalysts
Table
S2
.
The
comparison
on
the
HER
performance
of
our
catalysts
with
other
available
cheap
HER
electrocatalysts
in
the
literatures.
These
values
j
0
,
η
10
,
and
η
100
represent
the
exchange
current
density,
the
potentials vs
RHE at
10 mA/cm
2
and 100 mA/cm
2
, respectively.
Catalyst
Tafel slope
η
10
η
100
j
0
Source
NA:
not provided
in the data.
8.
Double-layer capacitance measurements
Benchmark Pt
31.0
mV
dec
-1
32 mV
72 mV
1126.2
μA
cm
-2
This work
HP-NiSe
2
foam
43.0
mVdec
-1
57 mV
103 mV
612.0
μA
cm
-2
This work
MoS
2(1-x)
Se
2x
/NiSe
2
42.0
mVdec
-1
69 mV
112 mV
299.4
μA
cm
-2
2
MoS
x
/N-CNT
40
mVdec
-1
110 mV
225 mV
33.1
μA
cm
-2
11
NiSe
2
nanosheets/CC
32
mVdec
-1
117 mV
NA
4.7
μA
cm
-2
12
CoS
2
/RGO-CNT
51
mVdec
-1
142 mV
178 mV
62.6
μA
cm
-2
13
FeS
2
nanosheets
46
mVdec
-1
108 mV
170 mV
5.5
μA
cm
-2
14
CoSe
2
/carbon fiber
42
mVdec
-1
139 mV
184 mV
6μA
cm
-2
15
WS
1.56
Se
0.44
nanoribbons
68
mVdec
-1
176 mV
NA
25
μA
cm
-2
16
Ni
5
P
4
-Ni
2
P
nanosheets
79
mVdec
-1
120 mV
200 mV
116
μA
cm
-2
17
Ni
2
P nanoparticles
46
mVdec
-1
105 mV
180 mV
33
μA
cm
-2
18
CoP nanowire array/CC
51
mVdec
-1
67 mV
204 mV
288
μA
cm
-2
19
Mo-W-P nanosheets/CC
52
mVdec
-1
100 mV
138 mV
288
μA
cm
-2
20
Metallic WO
2
/carbon
46
mVdec
-1
58 mV
NA
640
μA
cm
-2
21
MoO
2
/PC-RGO
41
mVdec
-1
64 mV
NA
480
μA
cm
-2
22
CoPS NPls/carbon
paper
56
mVdec
-1
48 mV
NA
984
μA
cm
-2
23
CoPS NWs/carbon paper
48
mVdec
-1
61 mV
NA
554
μA
cm
-2
23
MoS
2
/N-RGO
41.3
mVdec
-1
56 mV
NA
720
μA
cm
-2
24
Figure
S5.
Electrochemical
cyclic
voltammetry
curves
of different
NiSe
2
foams
with
different
scan
rates.
a
,
A-NiSe
2
foam
with
scan
rates
ranging
from
20
mV/s
to
200
mV/s
with
a step
of 20
mV/s.
b
, H-NiSe
2
foam
with
scan
rates
from
5 mV/s
to
50
mV/s
with
a 5 mV/s
interval.
c
,
HP-NiSe
2
foam
with
scan
rates
ranging
from
2 mV/s
to
20
mV/s
with
an interval
point
of
2 mV/s.
The
potential
is scanned
from
0.1
to
0.2 V vs RHE where
no faradic current was
detected.
9.
Electrical conductivity
measurements of bulk NiSe
2
crystals
Figure
S6.
(a)
XRD
pattern
and
(b)
electrical
resistivity
measurements
of
a bulk
NiSe
2
sample
prepared
by
mechanical
alloying
of
high-purity
Ni
and
Se
powders
by
a high-energy
ball
mill
(SPEX
8000D)
for
20 h and hot pressing at
773
K for 2 min.
10.
Data
for
Fig. 4 and structure of the NiSe
2
slab (in VASP CONTCAR format)
perfect
V-Ni
V-Se
V-2Se
ad-Ni
ad-Se
ad-2Se
Free
energy(eV/H)
0.68
0.39
0.38
0.47
0.71
0.09
-0.01
NiSe
2
1.00000000000000
11.8719999999999999
0.0000000000000000
0.0000000000000000
0.0000000000000000
11.8719999999999999
0.0000000000000000
0.0000000000000000
0.0000000000000000
20.0000000000000000
Ni
Se
32
64
Selective dynamics
Direct
0.0066675993522886 -0.0004355373005453
0.2999600727090445
T
TT
-0.0001573366221758
0.9964795028284821
0.5978825527890403
T
TT
0.2499012177917495 -0.0031784384313857
0.4442511860497020
T
TT
0.2567799758378674
0.9986516520039094
0.7421057312696081
T
TT
0.2432973852295297
0.2495747208374209
0.2999697633520752
T
TT
0.2501173976560165
0.2464663422859265
0.5978950253180432
T
TT
0.0000848300246491
0.2468096293625826
0.4442550960502816
T
TT
0.9931873788988308
0.2486366513258388
0.7421053277570332
T
TT
0.0067043028102850
0.4995737853818545
0.2999353701053446
T
TT
-0.0001298464554059
0.4964721527274584
0.5978796696135562
T
TT
0.2498971985875931
0.4968145778524392
0.4442449734775105
T
TT
0.2568089549908256
0.4986335901639650
0.7420910833837595
T
TT
0.2433021255599140
0.7496188376144860
0.2999641487087098
T
TT
0.2501027529849907
0.7464764389217743
0.5978844609956306
T
TT
0.0000917638536297
0.7468215031264130
0.4442460897100310
T
TT
0.9931762041351612
0.7486665555319038
0.7420949265791846
T
TT
0.5067064339616435 -0.0004266420373065
0.2999536711075301
T
TT
0.4998460786650789
0.9964652581750038
0.5978864022950832
T
TT
0.7499102865149861 -0.0031877719648247
0.4442443633147298
T
TT
0.7567804537390733
0.9986501639412766
0.7421033000407599
T
TT
0.7432972336757780
0.2495646864052058
0.2999535705460435
T
TT
0.7501171792452987
0.2464816160993655
0.5978922480052052
T
TT
0.5000968095526603
0.2468125008092458
0.4442432347618467
T
TT
0.4931954618372723
0.2486353002224210
0.7421012516904474
T
TT
0.5066639486845046
0.4995791564660371
0.2999554306212046
T
TT
0.4998591017430232
0.4964796890511174
0.5978810304384220
T
TT
0.7499048370558340
0.4968222699209380
0.4442457222550898
T
TT
0.7567820392772402
0.4986481314187219
0.7420953472505711
T
TT
0.7433184301608693
0.7495736242801179
0.2999393646666617
T
TT
0.7501097081881132
0.7464520642833561
0.5978715305711257
T
TT
0.5001204646828332
0.7468298456148145
0.4442425102431442
T
TT
0.4931954578915905
0.7486381865746357
0.7421035469802468
T
TT
0.1907927969786359
0.1880541082591476
0.4117010696567121
T
TT
0.1901240492343139
0.1910094273591115
0.7214824237164089
T
TT
0.0654943068864851
0.3201315201670959
0.2563990355433776
T
TT
0.0616483255181409
0.3089730156614333
0.5607428114751568
T
TT
0.4382734752528953
0.0591782693844061
0.4813546495431387
T
TT
0.4345344224450297
0.0693235887129809
0.7857177870107539
T
TT
0.3098055216515955
0.4418072382557047
0.3206788003882028
T
TT
0.3091934879496128
0.4375878979398209
0.6304944851914969
T
TT
0.3117391337281156
0.3091985459275519
0.4813517223413623
T
TT
0.3154304176215944
0.3193094517882245
0.7857234113765283
T
TT
0.4401632965040815
0.1918024362855373
0.3206766445655260
T
TT
0.4408151279048972
0.1875763918870014
0.6304884411473085
T
TT
0.0591931825569547
0.4380453468232652
0.4116952597259013
T
TT
0.0598582551509802
0.4410091579621155
0.7214731202646336
T
TT
0.1845089154489411
0.0701504821939064
0.2564412920472130
T
TT
0.1883227815738421
0.0589622981282898
0.5607504511263314
T
TT
0.1907845473173868
0.6880422699905895
0.4116918424394442
T
TT
0.1901017132084825
0.6909583376680670
0.7214708668304328
T
TT
0.0655054031783750
0.8201360171669303
0.2564570429851847
T
TT
0.0616281092922571
0.8089659038567116
0.5607537832990638
T
TT
0.4382679532654134
0.5591487870953404
0.4813592356828884
T
TT
0.4345601618797899
0.5693021905892026
0.7857130462359814
T
TT
0.3098389000428427
0.9418020752203080
0.3206971924977297
T
TT
0.3091606441510620
0.9376046176444035
0.6304731045066628
T
TT
0.3117338346394587
0.8091688834998868
0.4813540871290615
T
TT
0.3154175588899016
0.8193016184854949
0.7857164804727512
T
TT
0.4401799252041339
0.6918290029186221
0.3206988409518404
T
TT
0.4407904428212158
0.6875988957005982
0.6304696779245298
T
TT
0.0591888657781381
0.9380713428028414
0.4116970084732689
T
TT
0.0598580685411532
0.9410167134243548
0.7214723815480248
T
TT
0.1845386031740807
0.5701442117764831
0.2564067193881803
T
TT
0.1883295214683958
0.5589669181277239
0.5607573572598141
T
TT
0.6907903039682503
0.1880586417204357
0.4116867631148922
T
TT
0.6901334886223732
0.1909827088446823
0.7214841925142834
T
TT
0.5654844178423125
0.3201250622804722
0.2564049463806853
T
TT
0.5616447910445674
0.3089588160885678
0.5607510506675475
T
TT
0.9382614956887729
0.0591600588299648
0.4813632082713937
T
TT
0.9345704151888586
0.0693059465126342
0.7857099229220765
T
TT
0.8098323496788763
0.4417948675768673
0.3206749013780870
T
TT
0.8092131232492673
0.4375884051035964
0.6304774596008289
T
TT
0.8117227373637743
0.3091650971237694
0.4813512999135273
T
TT
0.8154390960495758
0.3193053949275121
0.7857191884930221
T
TT
0.9401735469030668
0.1918165242740675
0.3206803107843350
T
TT
0.9407802795686209
0.1875980880700108
0.6304705262947893
T
TT
0.5591895258608022
0.4380254619596619
0.4116906921646882
T
TT
0.5598749638151488
0.4409617888717802
0.7214651306412450
T
TT
0.6845155943607977
0.0701521541125364
0.2563890928069552
T
TT
0.6883245108402770
0.0589609389730473
0.5607606985175621
T
TT
0.6907928027439331
0.6880434905669380
0.4116849724032006
T
TT
0.6901220056106002
0.6909645776734742
0.7214729440377659
T
TT
0.5655001000555500
0.8201455096499601
0.2564192727345181
T
TT
0.5616450033776776
0.8089754943179465
0.5607444708306982
T
TT
0.9382712819849818
0.5591628963709566
0.4813532242279144
T
TT
0.9345439569257222
0.5693333761092404
0.7857059193933913
T
TT
0.8098414292983948
0.9417958949554656
0.3206489539350427
T
TT
0.8091619346508335
0.9375940438711092
0.6304768472966098
T
TT
0.8117526509632023
0.8091401843513990
0.4813513926163112
T
TT
0.8154230525620177
0.8193016496835899
0.7857164528301454
T
TT
0.9401905271530422
0.6917975698632581
0.3206757459046545
T
TT
0.9407868164150627
0.6875933064051533
0.6304707395936480
T
TT
0.5592080123492229
0.9380657619104064
0.4116782894191566
T
TT
0.5598618224287812
0.9410138190517696
0.7214843827920081
T
TT
0.6844921077911069
0.5701213795585953
0.2564245044986694
T
TT
0.6883318078720868
0.5589735181576025
0.5607544276187836
T
TT
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