In the capacitive
deionization (CDI) process, the degradation of desalting performance
is predominantly due to the co-ion expulsion effect and electrode
oxidation. To overcome these complications, carbon nanotubes grafted
with amine and sulfonic functional groups respectively were prepared
and used as the CDI electrodes. The structural characterizations and
performance tests confirmed that a uniform functional layer was formed
on the surface of the modified electrodes and it enhanced the ion
selectivity and wettability of the electrode surface. Moreover, the
effects of the functional layer on the electrode stability were investigated
by circulating CV tests and desalination tests. The positive shift
value of the potential of zero charge (PZC) for the as-prepared electrodes
was tested as a quantitative indication for their possible surface
oxidation during cyclic tests. Analysis of the PZC variation and desalting
performance demonstrated that the excellent desalting stability was
achieved by the Cell N–S assembled with the ammoniated CNTs
electrode as anode and sulfonated CNTs electrode as cathode. Because
the functional layer could preserve the pores system on the modified
electrodes and diminish the parasitic reactions that exacerbate the
electrode oxidation. This work provides an effective strategy for
promoting the electrode performance and prolonging the life of the
electrode.
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