Effects of Electrodeposition Time on Ni/rGO Composite Electrode as an Efficient Catalyst for Hydrogen Evolution Reaction in Alkaline Media
Authors: Wang Lixin , Zhang Peipei , Bai Lei , Cao Lei , Du Jing , Wang Yazhou , Qin Xiujuan 
Published: April 2018

Background:

Ni/rGO composite electrode has been fabricated by facile supergravity electrodeposition
as a low-cost catalyst for efficient hydrogen evolution in alkaline media. In this paper,
the electrodeposition time is the main research variable. When the electrodeposition time is 100 minutes,
the Ni/rGO-100 catalyst manifests the highest electrocatalytic activity toward the hydrogen
evolution reaction (HER). In 1.0 M NaOH solution, the overpotential at a current density of 100 mA
cm-2, Tafel slope and charge transfer resistance of Ni/rGO-100 catalyst is 184 mV, 77 mV dec-1 and
4.173 Ω, respectively. In addition, Ni/rGO-100 catalyst shows a long-term durability at a constant
current density of 100 mA cm-2 for 10 h. The outstanding HER electrocatalytic performance of the
Ni/rGO-100 is mainly related to the synergetic combination of Ni and rGO, as well as the enlarged
exposure of catalytically active sites and improved transport of electrons arising from the good conductivity
of graphene.

Method:

In a classic experiment, GO was prepared by modified Hummers method. The Ni/rGO
composite electrodes were prepared by supergravity electrodeposition, which has been reported in
detail in our published paper. Firstly, a ø10 cm × 2 cm Ni foam circle was cleaned sequentially in
HCl solution (15%), acetone and DI water for 5 min with ultrasonication to be used as a cathode.
And a pure nickel pipe was used as anode. The Ni/rGO composite cathodes were electrodeposited in
a blackish green plating bath which contained 350 g L-1 Ni(NH2SO3)2·6H2O, 10g L-1 NiCl2·6H2O, 30
g L-1 NH4Cl , 1.0 g L-1 GO colloidal solution with different electrodeposition time, 10min, 30min,
60min, 80min, 100min, respectively. The pH value of the plating bath is 3.5-3.8. The above five
electrodes were respectively denominated as Ni/rGO-10, Ni/rGO-30, Ni/rGO-60, Ni/rGO-80,
Ni/rGO-100. All composite electrodes were performed under the strength of the supergravity with
G=350 g at a current density of 3 A dm-2 at 318 K. Afterwards the Ni foam coated with Ni/rGO hybrid
was taken out of the reaction vessel, followed by washing with deionized water to remove
physical adsorption residua, and then dried at 80°C.

Results:

In this paper, the electrodeposition time is the main research variable. When the electrodeposition
time is 100 minutes, the Ni/rGO-100 catalyst manifests the highest electrocatalytic activity
toward the hydrogen evolution reaction (HER). In 1.0 M NaOH solution, the overpotential at a current
density of 100 mA cm-2, Tafel slope and charge transfer resistance of Ni/rGO-100 catalyst is 184
mV, 77 mV dec-1 and 4.173 Ω, respectively.

Conclusion:

In summary, we have synthesized a class of composite electrodes (Ni/rGO) for HER in
alkaline solution by electrodeposition under supergravity field. We studied the effect of electrodeposition
time on electrode performance in detail. With the increase of electrodeposition time, the
number of active sites is enlarged provided by the electrode. When the electrodeposition time is 100
min, we fabricate the best electrode (Ni/rGO-100). The η100, Tafel slope and charge transfer resistance
of Ni/rGO-100 is 184 mV, 77 mV dec-1 and 4.173 Ω, respectively. The introduction of graphene
and supergravity field plays a key role in improving the performance of the electrodes. This
work is a pivotal part of the development of Ni/rGO as a non-precious HER catalyst for green energy
field.