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Understanding of the intensified effect of super
gravity on hydrogen evolution reaction
Mingyong Wanga,b,*, Zhi Wanga, Zhancheng Guoa,c
aNational Engineering Laboratory for Hydrometallurgical Cleaner Production Technologies, Institute of Process Engineering,
Chinese Academy of Sciences, Beijing 100190, PR ChinabGraduate University of Chinese Academy of Sciences, Beijing 100049, PR ChinacSchool of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, PR China
a r t i c l e i n f o
Article history:
Received 24 March 2009
Received in revised form
6 May 2009
Accepted 9 May 2009
Available online 7 June 2009
Keywords:
Super gravity
Hydrogen evolution reaction
Gravity coefficient
Hydrogen bubble
Buoyancy force
a b s t r a c t
Hydrogen evolution reaction (HER) under super gravity field was studied in 0.5 M H2SO4
aqueous solution by cyclic voltammetry (CV), linear sweep voltammetry (LSV), chro-
noamperometry and electrochemical impedance spectroscopy (EIS). Electrode surface
during HER was observed by electronic endoscope. The original understanding of the
intensified effect of super gravity on HER was discussed. The results indicated that HER
was enhanced by super gravity field. Little visible hydrogen bubbles were observed on
electrode surface under super gravity field. It was reasonable that the intensified effect of
super gravity on HER was ascribed to the smaller critical radii of forming bubble nucleus
and larger buoyancy force, which would promote the disengagement of gas bubbles and
decrease the gas coverage on electrode surface. As a result, more active sites remained and
HER rate increased.
ª 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights
reserved.
1. Introduction
Hydrogen evolution reaction (HER) is the basic reaction in
electrochemical industries such as water electrolysis and
chlor-alkali electrolysis. It is also significant for the production
of heavy water by electrolysis in atomic industry. However,
large overpotential and high ohmic resistance during HER
result in high energy consumption [1]. Therefore, it is benefi-
cial to seek effective solutions to reduce overpotential and
ohmic resistance.
During HER, gas bubble is the main root of high energy
consumption. Many efforts have been devoted to exploring
the effect of gas bubble on HER process [2–6]. These studies
indicated that gas bubbles led to significantly high ohmic
resistance and large overpotential from three aspects. The
first aspect is the dispersion of gas bubbles in the electrolyte.
Janssen [2] investigated the dispersion effect on ohmic resis-
tance and concluded that the effective ohmic resistance can
be well described by Bruggeman equation. The second aspect
is ascribed to adsorption of gas bubbles on membrane, which
would lead to high ohmic resistance [1]. The third aspect
relates to bubble coverage on electrode surface. Qian [4]
reported that the ohmic resistance was proportional to the
bubble surface coverage. Fukunaka [6] also measured the
ohmic resistance of bubble froth layer during water electrol-
ysis under microgravity. It has been demonstrated that even
for a well-designed cell such as the FM21 unit used in chlor-
alkali industry, the severe bubble coverage on electrode
surface would incur significant overpotential about 0.4 V at
a current density of 300 mA cm�2 [7].
* Corresponding author at: Graduate University of Chinese Academy of Sciences, Beijing 100049, PR China. Tel./fax: þ86 10 62558489.E-mail address: [email protected] (M. Wang).
Avai lab le a t www.sc iencedi rec t .com
journa l homepage : www.e lsev ier . com/ loca te /he
0360-3199/$ – see front matter ª 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.doi:10.1016/j.ijhydene.2009.05.043
i n t e r n a t i o n a l j o u rn a l o f h y d r o g e n en e r g y 3 4 ( 2 0 0 9 ) 5 3 1 1 – 5 3 1 7
In order to reduce the energy consumption of HER, the
overpotential can be lowered to a certain extent by using
higher active electrode and elevating reaction temperature
[8–10]. However, it may be more efficient to promote gas
bubble disengagement or spillover from electrode surface,
membrane and electrolyte. During multiphase separation,
the fluid dynamic behavior is controlled by the interphase
buoyancy term, Drg. In gas/liquid systems, heavy phase (i.e.
electrolyte) moves along the direction of gravity acceleration,
while light phase (i.e. gas bubbles) moves along the counter
direction, i.e. the direction of buoyancy force. If HER process
can be carried out under super gravity field, high gravity
acceleration environment can increase interphase slip
velocity and intensify multiphase separation (i.e. gas–liquid
or gas–solid separation). Therefore, gas bubble coverage on
electrode surface will be weakened, which can lead to more
active sites for HER. Consequently, overpotential and ohmic
resistance may be reduced obviously. Simultaneously, gas
bubble disengagement or spillover from membrane or elec-
trolyte can be also facilitated greatly. Recently, several papers
have focused on gas evolution reaction in centrifugal field (i.e.
super gravity field) [1,11–14]. Their results demonstrated that
gas evolution reaction can be enhanced and electrolytic cell
voltages were reduced by super gravity field. In addition, it
must be emphasized that Cheng [12] has reported that
a 100 kA cell for chlor-alkali electrolysis operating with
a bubble overvoltage of 0.3 V has a potential energy saving of
approximately 30 kW, whereas the equipment rotor (1 m
long� 0.5 m diameter) will require about 2 kW to rotate at
around 700 rpm. The saving in energy consumption for HER
was significantly larger than the relatively small amount of
energy required obtaining super gravity field. Our previous
paper [14] also confirmed that chlor-alkali electrolysis can be
intensified by super gravity due to the efficient disengage-
ment or spillover of gas bubbles from electrode surface and
electrolyte.
However, the former papers were mainly related to apply
of super gravity in water electrolysis and chlor-alkali elec-
trolysis. It is unclear how super gravity affects the gas
evolution reaction. The present work focuses on the inten-
sified HER property and the understanding of the effect of
super gravity on HER. The primary comparisons of buoy-
ancy forces and radii of forming gas nucleus between
normal gravity condition and super gravity field are also
carried out.
2. Experimental
2.1. Experimental equipment
Super gravity field can be obtained by centrifuge with a cylin-
drical electrolytic cell of 100 ml volume (Fig. 1). The electro-
chemical signals, monitored by a computer-controlled CHI
604B electrochemical working station (CH Instrument, Inc.),
were transferred by the mercury slip ring (A3S, Shanghai Bige
M&E Co., Ltd.) which was fixed on the top of axis. The elec-
trolytic cell was horizontal under super gravity field (i.e.
rotating), while vertical under normal gravity condition (i.e.
not rotating). The gravity coefficient (G) value can be adjusted
by rotating the electrolytic cell with different speeds and it is
calculated as following equation:
G ¼u2r
g¼
N2p2L
900g(1)
Where N is the rotating speed (rpm), g the gravity acceleration
(9.8 m s�2) and L the distance between electrode center and
axis (0.11 m in this experiment). The G value is 1 under normal
gravity condition.
A standard three-electrode system was employed with
a large surface area platinum plate as counter electrode and
a solid state electrode (GD-IV, Beijing Research Institute of
Chemical Engineering and Metallurgy) as reference electrode.
All potentials in this work were measured against the solid
state electrode where its potential was 0.1852 V vs SHE.
A polycrystalline platinum electrode with the surface area of
0.03 cm2 was used as working electrode. Electrode surface
during HER was observed by electronic endoscope.
2.2. Electrochemical measurements
All electrochemical measurements were carried out using CHI
604B electrochemical working station (CH Instrument, Inc.).
Cyclic voltammetry (CV) with a potential range of �0.25 V to
1.2 V and linear sweep voltammetry (LSV) with a potential
range of �0.1 V to �1.2 V were employed in order to evaluate
the effect of super gravity on HER. The sweep rate of 50 mV s�1
was used for both CV and LSV. Chronoamperometry curves
for HER were measured at �0.7 V. The electrochemical
impedance spectroscopy (EIS) measurements were performed
under various gravity conditions in the frequencies range of
100 kHz to 0.1 Hz. The AC amplitude was set to 5 mV. The
3
1
2
610
8
9
4
57
13
12 11
14
Super gravity
direction
Fig. 1 – Experimental equipment for electrochemical
reaction under super gravity field. (1) Centrifuge; (2) lid of
the centrifuge; (3) mercury slip ring; (4) rotating axis; (5)
rotating bracket; (6) electrolytic cell; (7) working electrode;
(8) reference electrode; (9) counter electrode; (10) counter
part for balance; (11) control button; (12) revolution meter;
(13) computer; (14) electrochemical working station.
i n t e r n a t i on a l j o u r n a l o f h y d r o g e n en e r g y 3 4 ( 2 0 0 9 ) 5 3 1 1 – 5 3 1 75312
ZSimWin software was employed to approximate the EIS data
and the equivalent circuit of HER was obtained.
All experiments were performed in 0.5 M H2SO4 aqueous
solution. Before each experiment, Pt electrode was cycled in
the range of�0.25 V to 1.2 V at a sweep rate of 50 mV s�1 by CV
until steady curves to be obtained. Fresh double-distilled
water was used throughout. All electrochemical studies were
carried out at ambient temperature andwere repeated at least
twice with fresh electrolyte solutions under the same condi-
tion to ensure reproducibility.
3. Results and discussion
3.1. Cyclic voltammetry
Cyclic voltammetry measurements were conducted and the
results were shown in Fig. 2. In the potential range of �0.20 V
to 1.3 V, typical CV curve of Pt electrode in H2SO4 aqueous
solution can be obtained (Fig. 2A, inset graph) [15]. However, in
order to observe more clearly the influence of super gravity
field, the potential range of CV curves were shifted negatively
to �0.25 V to 1.2 V to enhance HER. In this case, the peaks
representing hydrogen adsorption/desorption were covered
up by larger redox current of hydrogen (Fig. 2A). It can be seen
from Fig. 2A that the peaks for HER under various gravity
conditions were almost repetitive, but the peaks representing
hydrogen oxidation reaction (HOR) depressed with increase of
G value (Fig. 2B, inset graph). To show visually the effect of
super gravity on HER and HOR in CV, the integrated charge
quantities of HER (Qc) and HOR (Qa) were calculated according
to following equation:
Q ¼
Z t2
t1
idt ¼
Z E2
E1
i
vdE (2)
Where Q, E, i, and n represent the charge quantity (mC cm�2),
potential (V), current density (mA cm�2) and sweep rate
(mV s�1), respectively. The integrated regions of HER and HOR
in CV were based on the shadowy areas in Fig. 2B. That is, the
charge–discharge current densities for double-layer capaci-
tance of electrode/electrolyte interface have been deducted.
The values of integrated charge quantities under various
gravity conditions were listed in Table 1. It can be observed
that Qc value increased somewhat with increase of G value.
Due to the less overpotential for HER in these CV curves, HER
rate was relative low so that the effect of super gravity on
HER was almost invisible. The actual effect of super gravity on
HER would be shown in later linear sweep voltammetry
measurement. However, Qa value (i.e. the charge quantities of
HOR) decreased rapidly with increase of G value. When G
value was 256, Qa value (1.83 mC cm�2) was only about 46.8%
of that (3.91 mC cm�2) under normal gravity condition (i.e.
G¼ 1). In other words, the quantities of H2 oxidized under
super gravity field were much less than those under normal
gravity condition during CV sweep. Evidently, the large
interphase buoyancy term (6rg) under super gravity field
resulted in high interphase slip velocity [1]. As a result, the
disengagement of H2 bubbles evolved during cathodic sweep
and their subsequent movement out of three-phase boundary
of gas bubble, electrolyte and electrode was greatly facilitated
by super gravity; thereby the quantities of H2 oxidized during
anodic sweep were less.
3.2. Linear sweep voltammetry and chronoamperometry
Polarization curves were measured in potential range of
0.1 V to �1.2 V by linear sweep voltammetry (LSV) and the
results are shown in Fig. 3. At certain current density, the
potential of HER (E ) shifted positively with increase of G value
(Fig. 3). When current density was 1.40 A cm�2, the potentials
of HER were �1.18 V, �1.08 V, �1.05 V and �1.03 V under G
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2
-12
-10
-8
-6
-4
-2
0
2
4
i /
mA
cm
-2
E / V
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
-0.3 -0.2 -0.1 0.0 0.1 0.2
-14
-12
-10
-8
-6
-4
-2
0
2
4
i /
mA
cm
-2
E / V
2H++2e
-=H2
H2=2H++2e
-
-0.2 -0.1 0.0 0.1
0
1
2
3
4
G=1
G=25
G=101
G=256
A
B
Fig. 2 – (A) CV curves in 0.5 M H2SO4 aqueous solution
under various gravity conditions [G], sweep rate 0.05 V sL1.
Inset represents the typical CV curve of Pt electrode in
H2SO4 aqueous solution. (B) The integrated regions of HER
and HOR in CV. Inset represents the zoomed part of
negative potential region in (A).
Table 1 – The integrated charge quantity of HER (Qc) andHOR (Qa) in CV under various gravity conditions.
G 1 25 101 256
Qc (mC cm�2) 10.15 10.02 10.46 11.26
Qa (mC cm�2) 3.91 3.20 2.07 1.83
i n t e r n a t i o n a l j o u rn a l o f h y d r o g e n en e r g y 3 4 ( 2 0 0 9 ) 5 3 1 1 – 5 3 1 7 5313
values of 1, 25, 101 and 256, respectively. The potential
reduction of HER was up to 0.15 V under G value of 256.
Obviously, HER was intensified by super gravity. From Fig. 3B,
at all current densities, the linear relationships between E and
log(G) were observed, which was accordant with Cheng’s
results [13]. It was reasonable that the formula between E and
G was written as:
E ¼ b�logðGÞ þ E1 (3)
where b was the change rate of E with gravity coefficient,
a constant at certain current density, E1 was the potential of
HER under normal gravity condition. According to the exper-
imental data in Fig. 3A, the correlations between E and G at
various current densities can be expressed as following:
1:0 A cm�2 E ¼ 0:042�logðGÞ � 0:978 (4)
1:2 A cm�2 E ¼ 0:053�logðGÞ � 1:078 (5)
1:4 A cm�2 E ¼ 0:063�logðGÞ � 1:176 (6)
It can be found from Eq. (4) to Eq. (6) that b value increased
with increase of the current densities. In other words, with
increase of HER rate, the effect degree of super gravity on E
became larger.
Chronoamperometry was also measured and the results
are shown in Fig. 4. More obviously, current densities of HER
under super gravity field were much larger than that under
normal gravity condition, which was accordant with the
results in Fig. 3. Both the results in Figs. 3 and 4 indicated that
the HER rate was enhanced by super gravity field.
During HER process, the formation energies (6G) of
bubbles under various gravity conditions can be represented
according to the formula [11]:
DG ¼ 4pr2sþ43pr3DG�
V ¼ 4pr2sþ43pr3
P0 þ rGgh
P0DGV (7)
where r is the radii of bubbles, s surface tension, DGV the
energy variation forming one unit normal volume hydrogen
gas, DG�V the standard energy variation, P0 the atmospheric
pressure, r the liquid density and h the distance from elec-
trode center to solution surface. In critical condition, the
bubbles began to form, vDG=vr ¼ 0. The critical radii r* for
forming a gas bubble can be obtained by derivation of Eq. (7):
r� ¼�2sDGV
�P0
P0 þ rGgh(8)
Under normal gravity condition, the critical radii r�1 can be
expressed as:
r�1z�2sDGV
(9)
Under super gravity field, the critical radii r�G was charac-
terized as:
r�Gz�2sDGV
�1
1þ 0:1Gh¼
r�11þ 0:1Gh
(10)
From Eq. (10), it can be concluded that the larger G value was,
the smaller r�G was. The h value was 0.06 m in our experiment.
Therefore, when G value was 200, the critical radii r�200 were:
r�200z511
r�1 (11)
V�200 ¼
43p�
r�200�3¼
43p
�
511
r�1
�3
z0:094�43p�
r�1�3¼ 0:094V�
1 (12)
-1.2 -1.0 -0.8 -0.6 -0.4 -0.2
-2.0
-1.8
-1.6
-1.4
-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
i /
A c
m-2
E / V
G=1
G=25
G=101
G=256
0.1 1 10 100 1000
-1.30
-1.25
-1.20
-1.15
-1.10
-1.05
-1.00
-0.95
-0.90
-0.85
E /
V
G
1.0 A cm-2
1.2 A cm-2
1.4 A cm-2
A
B
Fig. 3 – (A) Polarization curves of HER and (B) the
relationship of E and G at various current densities.
0 200 400 600 800 1000
-0.070
-0.065
-0.060
-0.055
-0.050
-0.045
-0.040
i /
A c
m-2
t / s
G=1
G=25
G=101
G=256
Fig. 4 – Chronoamperometry curves for HER under various
gravity conditions. Potential: L0.7 V.
i n t e r n a t i on a l j o u r n a l o f h y d r o g e n en e r g y 3 4 ( 2 0 0 9 ) 5 3 1 1 – 5 3 1 75314
Where V�200 and V�
1 were the critical volumes of bubble forming
under super gravity field (G¼ 200) and normal gravity condi-
tion, respectively. On the other hand, during HER, the disen-
gagement of gas bubbles from electrolyte and electrode
surface was driven mainly by buoyancy force. Under normal
gravity condition, the buoyancy force (F1) was defined by:
F1 ¼ rgV�1 (13)
While under super gravity field, for example, G¼ 200, the
buoyancy force (F200) can be written as:
F200¼r�200gV�200¼r�200g�0:094V�
1¼18:8�rgV�1¼18:8F1 (14)
According to Eqs. (12) and (14), under super gravity field
(G¼ 200), the buoyancy force (F200) was 18.8 times of the
buoyancy force (F1) under normal gravity condition, while the
critical volume (V�200) of gas bubbles was only 0.094 times of
that under normal gravity condition. Although the compar-
ison about buoyancy force and gas volume between normal
gravity condition and super gravity condition was based on
the bubble nucleus, the results can be extrapolated to grown
bubbles.
In addition, under normal gravity condition, hydrogen
bubbles evolved moved upwards along electrode surface
(Fig. 5A) and disengagement of bubbles from electrode surface
went through line-contact between bubbles and electrode
surface. However, under super gravity field, hydrogen bubbles
moved upwards with an arc due to the inertia [11] and
disengagement of bubbles went through point-contact
(Fig. 5B). That is, during disengagement process of bubbles, the
contact time between bubbles and electrode surface was
shorter under super gravity field.
Considering buoyancy force, critical volume and disen-
gagement type of bubbles from electrode surface, when
hydrogen were evolved, it was easier for bubbles to form and
disengage rapidly from electrode surface due to much smaller
critical volume, larger buoyancy force and shorter contact
time under super gravity field. From the photographs of
electrode surface during HER (Fig. 6), it can be also observed
that under normal gravity condition (G¼ 1), lots of hydrogen
bubbles with a diameter of about 200 mmadhered on electrode
surface (Fig. 6A) and bubbles moving upwards along electrode
surface formed a bubble froth layer, which would result in
large ohmic resistance. Under super gravity field (G¼ 101),
electrode
bubbles
electrode surface
Moving track
Rotary direction
A
B
Fig. 5 – Moving track of bubbles on electrode surface under
normal gravity condition (A) and super gravity field (B).
Fig. 6 – The photograph of electrode surface during hydrogen bubble evolution process at 0.05 A cmL2 under (A) normal
gravity condition (G[ 1) and (B) super gravity field (G[ 101) in 0.5 M H2SO4 aqueous solution. The working electrode was
1 cm2 Pt foil.
i n t e r n a t i o n a l j o u rn a l o f h y d r o g e n en e r g y 3 4 ( 2 0 0 9 ) 5 3 1 1 – 5 3 1 7 5315
little bubbles can be found visually on electrode surface
(Fig. 6B). The movement of hydrogen bubbles was almost
invisible owing to smaller diameter and larger moving rate.
Electrode surface can be renewed in time and more active
sites remained. Therefore, the ohmic resistance due to bubble
coverage can be reduced under super gravity field during HER.
In the light of above discussion, efficient gas bubbles
disengagement would bring about high HER rate. Thus,
potential reduction of HER was achieved, which had been
confirmed by the experimental data in Fig. 3.
3.3. Electrochemical impedance spectroscopy
The electrochemical impedance spectroscopy (EIS) is
a powerful tool to study the electrode/electrolyte interface and
many researchers have used this technology to investigate
HER process [10,16–18]. In this paper, EIS measurements were
carried out over six frequency decades (100 KHz–0.1 Hz) under
an overpotential value (h) of �0.1 V. Two semicircles were
observed in Nyquist plots under all gravity conditions (Fig. 7).
The similar two-semicircle Nyquist plots were reported in
former papers under normal gravity condition [17–20]. In two-
semicircle Nyquist plots, the semicircle at high frequencies
was related to the HER kinetics, i.e. the charge transfer
process, while the semicircle at low frequencies represented
the response of hydrogen adsorption on electrode surface [20].
To better understand the electrode/electrolyte interface of
HER, the EIS experimental data were modeled using ZSimWin
software and the electrical equivalent circuits (EEC) is also
shown in Fig. 7 (inset graph). During fitting procedure, the
capacitances representing hydrogen adsorption and charge
transfer processwere replaced by the constant phase element,
CPE (S sn cm�2). The EECparameters are presented in Table 2. It
can be seen that both charge transfer resistance (Rct) and
hydrogen adsorption resistance (Rp) decreased with increase
ofG value. Under normal gravity condition, plentiful hydrogen
bubbles adsorbed on electrode surface (Fig. 6A) formed a froth
layer with large ohmic resistance, which would lead to high
charge transfer resistance. Meanwhile, bubbles layer would
separate electrode from electrolyte and obstruct the path that
Hþ transported to electrode surface. However, under super
gravity field, hydrogenbubbles can bedisengagedquickly from
electrode surface and no visible bubble layer was formed,
which has been demonstrated by the photographs in Fig. 6B.
Therefore, Rct and (Rp) decreased with increase of G value.
On the other hand, solution resistance (Rs) betweenworking
electrode and reference electrode can be also obtained accord-
ing to the meeting point of real axis and semicircle at high
frequencies from Nyquist plots [21]. Profitably, Rs decreased
with increase of G value (Table 2). The reduction of solution
resistance may be attributed to two factors: (1) the bubbles
dispersed in solution were easier to spillover under super
gravity field [14]; (2) the velocity of convection anddiffusionwas
enhanced by super gravity [22] and high migration rate of
conductive ion can be achieved.
It must be emphasized that HER rate was determined by
the total resistance related to the combination of Rs, Rct and Rp.
So, impedance–time curveswere alsomeasured under various
gravity conditions and the results are shown in Fig. 8. The total
resistance (Z ) reduced obviously with increase of G value.
Furthermore, Z would increase gradually with time under all
gravity conditions, but the trend of increase (i.e. the slop of
impedance–time curves) was lower under super gravity field
than that under normal gravity condition. As discussed above,
bubbles disengagement would be greatly facilitated by super
gravity field and gas coverage on electrode surface would be
reduced markedly. The accumulation of hydrogen bubbles on
Table 2 – Equivalent circuit parameters obtained by fittingEIS experimental data.
G 1 25 101 256
Rs (Ucm2) 6.14 5.28 3.96 3.83
R1 (Ucm2) 49.66 17.49 5.896 5.183
CPE1 (S sn cm�2) 8.18E�03 6.248E�03 14.6E�03 7.15E�03
n1 (0< n< 1) 0.6864 0.4846 0.4529 0.5215
R2 (Ucm2) 45.53 17.44 10.93 9.559
CPE2 (S sn cm�2) 6.76E�03 1.36E�03 2.64E�03 2.34E�03
n2 (0< n< 1) 0.4807 0.6873 0.836 0.7108
0 20 40 60 80 100
0
2
4
6
8
10
12
14
16
18
20
22
24
-Z''
/ Ω
cm
-2
Z' / Ω cm-2
G=1
G=25
G=101
G=256
CPE1
RS
Rct
CPE2
Rp
Fig. 7 – Nyquist plots of Pt electrode at h[L0.1 V. Insets
were equivalent circuits used to describe HER.
0 100 200 300 400 500 600
0
10
20
30
40
50
60
Z /
Ω c
m2
t / s
G=1
G=25
G=101
G=256
Fig. 8 – Impedance–time curves at h[L0.14 V, frequency:
1 Hz.
i n t e r n a t i on a l j o u r n a l o f h y d r o g e n en e r g y 3 4 ( 2 0 0 9 ) 5 3 1 1 – 5 3 1 75316
electrode surface was less with time under super gravity field
and more active sites remained. Therefore, the reduction of
total resistance for HER was achieved.
4. Conclusions
It had been demonstrated in this paper that hydrogen evolu-
tion reaction (HER) can be intensified by super gravity field. At
certain current density, the linear relationships between HER
potential (E ) and log(G) can be observed. HER resistances
decreased with increase of G value. Under super gravity field,
the critical radii for forming bubble nucleus were much
smaller, while the buoyancy forcewas larger than those under
normal gravity condition. It was easier for hydrogen bubbles
to form and disengage rapidly from electrode surface, and
then gas coverage on electrode surfacewas reducedmarkedly.
Therefore, more active sites remained and HER would be
intensified by super gravity field. Especially, at higher current
densities, the enhanced effect of super gravity field on HER
was more distinct. Based on these achievements, the benefi-
cial effect of super gravity field on HER can be understood. It is
promising that the energy consumption of water electrolysis,
chlor-alkali electrolysis or production of heavy water is
reduced substantially by the application of super gravity field.
Acknowledgments
This work is supported by the Natural Science Foundation of
China under a grant 50804043, 50674011 and Major Programs
on Equipment Development of the Chinese Academy of
Sciences under a grant YZ0618.
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