An Experimental Study On Polypyrrole Nanowire Modified Electrode Used In Capacitive Deionization

As one of late-model desalination technologies, capacitive deionization (CDI) accomplishes desalination using the Flow-Through Capacitor (FTC) structure and the charge/discharge principle. Compared with other desalination technologies, CDI has some advantages such as low energy consumption, without secondary contamination, a high recovery rate of water and so on. Those advantages make CDI develop rapidly recently.Polymerizing conditions, which include electrolyte solution concentration, monomer concentration, electrolyte acidity and polymerizing time, affect the capacitance and desalination rate of polypyrrole nanowire modified graphite (PPy/NG) electrode. The biggest capacitance of PPy/NG electrode can be obtained at conditions of 0.35 mol·L^-1 electrolyte concentration (LiClO4) among 0.10 mol·L^-1, 0.35 mol·L^-1 and 0.60 mol·L^-1 electrolyte concentration. When electrodes are polymerized at conditions of 0.10 mol·L^-1 and 0.35 mol·L^-1 electrolyte concentration, their desalination rates are the same. PPy/NG electrode which is polymerized at 0.19 mol·L^-1 monomer concentration has the highest capacitance and the biggest desalination rate among 0.14 mol·L^-1, 0.19 mol·L^-1 and 0.24 mol·L^-1 monomer concentration. The the polymerizing time is longer, the capacitance is higher and desalination rate is higher. Among pH4.50, pH5.91 and pH8.04, the capacitance of electrode is the biggest that polymerized at a condition of pH8.04, and the desalination rate is the biggest when electrode polymerized at a condition of pH5.91. When pH <6.0 or 7.5-1 electrolyte concentration, 0.19 mol·L^-1 monomer concentration and pH5.91 for 150 s.Additionally, testing conditions play an important role in CDI process as well, which include working voltage, solution concentration and the distance between the electrodes. From a comparision of working voltage ranging from 0.8 to 1.6 V, the desalination rate is biggest under 1.4 V. The bigger solution concentration is or the distance between the electrodes is shorter, the desalination rate is higher. The Cyclic voltammetric(CV)curves show that the capacitance of PPy/NG electrode only decreases 7.79% after 15 cycles. It means the capacitance stability of PPy/NG electrode is well. However, the mulit-desalination experiments denote that desalination rate decreases from 3.03% to 2.44% after 9 cycles. So it is necessary to improve the stability of mulit-desaliantion in future.