Preparation Of Polypyrrole/activated Carbon Composite And Application In The Capacitive Deionization

Capacitive deionization （CDI） is a new, energy-efficient and environmental watertreatment technology. When the solution containing anions and cations flows throughthe CDI unit cell, the ions are electrosorbed by the electric field upon the surface ofpolarized electrodes and the electrodes will regenerate by removing the electric fieldwhen the ions go back into solution which likes capacitors charge-discharge. Thedeionization ability of CDI is influenced by the capacitive ability of electrodes,structure of CDI unit cell, desalination operation conditions and ion characters. As aresult, we have chemically synthesized polypyrrole/active carbon composite materialwith higher capacitance and good stbility.We have prepared composite electrode showed the highest capacitance whenpyrrole: KCl: Na₂SO₄=0.2:0.15:0.2mol·L-1, pyrrole: AC=0.4:1（wt%）, which was50%higher than that of activated carbon electrode. Besides we studied the infuluenceof material loading on the capacitive ability of electrodes and found that the iontransport path was lenthened rapidly with the increases of material loading whichleaded to bigger resistances because of the composite electrodes adsorbed ions with thecapacitors formed on the surfaces and inner parts. At last, the capacitance of bothelectrodes increased to580mF·cm-2at8.0mg·cm-2, at which level it had roughlyremained since then.The electrodes were constructed into CDI unit cells which were used indesalination experiments of solutions with different ions at different applied potentials.The results showed that the removal efficency of active carbon electrode decreasedwhen the applied potential was higher than1.2V, which didn’t happen to the compositeelectrode. This demonstrated the polypyrrole in composite material could supress the side reactions on the surface of electrodes. The prepared composite electrode mainlyshow adsorption ability to anions. And the adsorption ability of electrode wasinfuluenced by hydration radii and charge, so the adsorbed Cl-would be substituted bySO42-in the desalination experiments. However the bigger ions with higher chargewould decrease the stability of composite electrodes because the ions with biggerradius could’t be easily deadsorbed from polypyrrole.