Supplementary Information
Ultrahigh capacitive performance from both Co(OH)2/graphene electrode and K3Fe(CN)6
electrolyte
Cuimei Zhao, Weitao Zheng*, Xin Wang, Hengbin Zhang, Xiaoqiang Cui & Haoxiang Wang
Department of Materials Science, Key Laboratory of Mobile Materials, MOE, and State Key
Laboratory of Superhard Materials, Jilin University, Changchun 130012, PR China
Corresponding author: W.Z., wtzheng@jlu.edu.cn (W.T. Zheng).
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Supporting material 1: X-ray diffraction patterns for original Co(OH)2/GNS (a) and
Co(OH)2/GNS after 2000 galvanostatic charge-discharge cycles in mixed KOH/K3Fe(CN)6
electrolyte (b).
Supporting material 2: SEM images for original Co(OH)2/GNS (a) and Co(OH)2/GNS after
2000 charge-discharge cycles in mixed KOH/K3Fe(CN)6 electrolyte (b).
Supporting materials 3: In the practical application, high coulomb efficiency can be recovered
by charging electrolyte to enhance the concentration of K3Fe(CN)6.
In system 3 (Co(OH)2/GNS electrode in mixed 1 M KOH and 0.04 M K3Fe(CN)6 aqueous
solution), capacitive properties were test by the continuous charge-discharge experiments at a
current density of 40 Ag−1. When coulombic efficiency is close to 100%, a high constant potential
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of 0.4V is set up, Fe(CN)64− will be oxidized until the electrolytic current close to zero, finishing
the transformation process from K4Fe(CN)6 to K3Fe(CN)6, therefore high coulomb efficiency can
be recovered. The coulomb efficiency is listed in the following table with the increasing of cyclic
times.
Table 1. Coulomb efficiency for the system of Co(OH)2/GNS electrode in mixed 1 M KOH and
0.04 M K3Fe(CN)6 solution calculated by charge-discharge curves at a current density of 40 Ag−1.
cyclic times
1
600
recover
1200
recover
2000
recover
coulomb
efficiency
120.1%
101.3%
117.0%
101.4%
114.2%
103.6%
121.5%
Supporting materials 4: Peak current (at a scan rate of 25 mVs−1) vs. different K3Fe(CN)6
concentrations for the system of Co(OH)2/GNS electrode in 1 M KOH containing different
concentrations of K3Fe(CN)6 mixed solution.
Supporting materials 5: A cation exchange membrane is used to demonstrate whether the redox
reaction occurs at the counter electrode.
It is worth noting that the redox reaction of Fe(CN)63−/Fe(CN)64− exists at the working electrode,
the reverse reaction occurs simultaneously at the counter electrode, i.e so-called ‘‘electron shuttle
effect’’. We have added a cation exchange membrane between working electrode and counter
electrode to prevent Fe(CN)63−/Fe(CN)64− from passing, so that only K+ can be used as the
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exchange ion, and the reaction of Fe(CN)63−/Fe(CN)64− cannot occur on the counter electrode. For
system 3 (Co(OH)2/GNS electrode in mixed 1 M KOH and 0.04 M K3Fe(CN)6 aqueous solution)
with cation membrane, the specific capacitance is 2638.5 and 1460.4 Fg−1, coulombic efficiency is
196.3% and 136.4% at current densities of 16 and 32 Ag−1, respectively, slightly more than that
without cation membrane. The little change of specific capacitance and coulombic efficiency
means that redox reactions of Fe(CN)63−/Fe(CN)64− occur at the counter electrode, electron shuttle
effect’’ occurs that lead to relatively low electrochemical performance. In practical application, a
cation exchange membrane is necessary.
Supporting materials 6: Fe(CN)63−/Fe(CN)64− plays a key important role in redox reaction for the
system.
For system 3 the initial redox material is K4Fe(CN)6 instead of K3Fe(CN)6, the specific
capacitance is 2228.4 and 1309.1 Fg−1, coulombic efficiency is 192.9% and 133.9% at current
densities of 16 and 32 Ag−1, respectively. Because the open circuit potential for our mixed 1 M
KOH and 0.04 M K4Fe(CN)6 aqueous solution is 0.334 V, the potential is just in the range of the
oxidation of Fe(CN)64− to Fe(CN)63− and stable existence of Fe(CN)63−. Therefore, the stability for
K3Fe(CN)6 is much better than that for K4Fe(CN)6 in an alkaline solution, which will result in a
large amount of K3Fe(CN)6 in the initial state solution for the reduction of Fe(CN)63− to Fe(CN)64−.
The enhanced specific capacitance and coulombic efficiency still result from the K3Fe(CN)6 with
a high concentration.
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