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Y. Ren et al. / Electrochemistry Communications 13 (2011) 1317–1319
PAM/CMC BPM was allowed to be totally dried at room temperature for
around 2 days.
of the intermediate layer by \COO− in CMC layer and \NR2H+ in
PAM layer respectively. Accordingly, the recombination of H+ and
OH− was successfully restrained. Due to the dissociation equilibrium,
H+ and OH− removed from the system would continuously be
replenished. Consequently, the adequate water-dissociation resulted
in a low electrical resistance and a high permselectivity of PAM/CMC
BPM [10–12].
3. Results and discussion
3.1. Reversibility of MnO2/Mn2+
The cyclic voltammetry for nano-MnO2/Mn2+ was measured in Ar
atmosphere with H2SO4 electrolyte (0.5 mol L−1) in the cathode
3.3. Selective electro-oxidation of glycerol by nano-MnO2/Mn2+ in BPM
cell
chamber and
a ) and H2SO4
mixture of MnSO4 (0.5 mol L− 1
(0.1 mol L−1) in the anode chamber. Graphite electrodes (apparent
area=5.0 cm2) were used as both the working electrode and the
counter electrode while Ag/AgCl electrode as the reference electrode.
When the electrolysis began, Mn2+ was oxidized to nano-MnO2 on
the surface of the anode and highly dispersed in the anolyte under
ultrasonic [6–8], the size of which ranged from 10 nm to 50 nm. Nano-
MnO2/Mn2+ presented a good reversibility with the oxidation peak
and the reduction peak at 1.23 V and 1.05 V, respectively (Fig. 1).
During the indirect electrosynthesis of GAD, nano-MnO2/Mn2+
remained reproducible and active with negligible loss.
Fig. 3 shows the schematic depiction of indirect electrochemical
generation of GAD in PAM/CMC BPM-equipped cell using nano-
MnO2/Mn2+ as the cyclic intermediate under ultrasonic. The
electrolytic cell was divided into anode and cathode chambers by
PAM/CMC BPM (effective area=23.7 cm2). Graphite electrodes
(apparent area=5.0 cm2) were used as both cathode and anode
electrodes. A mixture of MnSO4 solution (0.5 mol·L−1) and glycerin
was filled in the anode chamber while H2SO4 solution (0.5 mol·L− 1
)
in the cathode chamber.
When the electrolysis began, Mn2+ was oxidized on the surface of
the anode to nano-MnO2 with a larger specific surface and higher
activity. Then nano-MnO2 was dispersed in the anolyte under
ultrasonic and selectively oxidized the primary hydroxyl groups of
glycerol to GAD, while nano-MnO2 itself was reversibly reduced to
Mn2+, and thus the cyclic oxidation–reduction reaction was carried
on throughout the entire electrochemical reaction.
3.2. SEM analysis of BPM
The morphology of PAM/CMC BPM was determined by scanning
electron microscope (SEM, NOVA NANO SEM 230) and shown in
Fig. 2. As expect, a laminate of a juxtaposed PAM layer (106 μm thick,
the anion-exchange layer, AEL) joining to CMC layer (154 μm thick,
the cation-exchange layer, CEL) with a clear interface was observed.
Both layers appeared dense morphology without pores. The interme-
diate layer of PAM/CMC BPM was nanometer-sized (less than
10−7 m), which meant that the electric field strength in the junction
of BPM was over 107 V m−1 and should lead to water splitting at 1.0 V
[9].
The main reactions of electrosynthesis of GAD were shown in
Eqs. (1) and (2).
Mn2þ þ 2H2O−2e−→MnO2 þ 4Hþ
ð1Þ
(2).
When a potential difference was established between two
electrodes, the cations migrated towards the cathode through CMC
layer while the anions through PAM layer in the opposite direction.
When all the salt ions initially contained were removed from the
intermediate layer of BPM, the transport of electrical charge through
BPM could only be accomplished by H+ and OH−, and thus the water
dissociation began.
Since PAM/CMC BPM possessed adequate charge densities and fine
The whole reaction in the anode chamber was as followed:(3.
ion-exchange capacity, H+ and OH− could be timely transferred out
According to Eq. (3), every 1 mol GAD generated would be
accompanied by the production of 2 mol H+. Obviously, the
accumulation of H+ in the anolyte was not conducive to the forward
reaction. Thus, PAM/CMC BPM was applied as the separator in the
electrolytic cell, which not only prevented GAD from diffusing into the
cathode chamber and reversing to glycerol on the cathode, but also
played an important role in the supply of OH− to neutralize H+
accumulated during the indirect electrosynthesis of GAD.
3.4. Electrosynthesis of GAD
After electrosynthesis, the anolyte was decompress-distilled until
no water was left, and then an equal volume of anhydrous ethanol
was added subsequently to speed up the crystallization of GAD. The
final product was decompress-filtrated and dried.
As shown in Fig. 4, the sharp vibration absorption at 2878 cm−1
,
Fig. 1. Cyclic voltammetry for nano-MnO2/Mn2+. (Inset: TEM image of nano-MnO2 in
anolyte).
1724 cm−1 and 1401 cm−1 belonged to the stretching vibration