Orderly Proton Conductor Based On Polyelectrolyte Brushes

With the rapid development of mobile electronic devices, such as smartphones, tablets, etc., traditional lithium-ion batteries will not meet the needs of high energy consumption. Due to the competitive characteristics like high energy conversion efficiency, zero emission, the potential to remove the moving parts and high-energy density, which exceeds that of batteries by an order of magnitude, Micro fuel cell may be one of the favorable candidates. However, new problems would arise when fuel cell came to miniaturization, such as manufacturing technology, reliability, cost and properties, among which the properties of proton conductor is one of the core problems. Developing a new proton conductor that have relatively high conductivity at low humidity and that can avoid volumetric size change with humidity may be an effective solution. Among traditional proton conductors, Nafion® as one typical perfluorosulfonic acid(PFSA) polymer membrane has been the most widely applied in the fuel cell because of its high selectivity of proton conduction ability、stable chemical properties and excellent physical and mechanical properties. However, the conductivity of Nafion® would heavily depend on the moisture content of proton conductors. When operating temperature increases, the moisture of membrane will volatilize, which will result in rapid decrease of conductivity. In order to improve this disadvantage, we prepared a new kind of organic-inorganic conductor based on polyelectrolyte brushes, in which the polyelectrolyte was formed through in situ the free-radical polymerization on the internal surface of anodic titanium oxide nanotubes array. Some conclusions has been shown as follows:1) When prepare the through-hole titanium dioxide nano-tube array, we found that there exist optimum parameters for the electrolyte, in which the optimum water content is 8vol% and 0.2wt% for NH4F; and the optimum anodic oxidation voltage should exceed 40V; operating around low-temperature environment would benefit to decreasing the nanowires on the top surface of array.2) To obtain through-hole titanium dioxide nano-tube array, we provide an abrupt increase in thevoltage at the end of anodic oxidation(from 60 V to 120-180V) for 2.5-5 minutes, which also induce large amount of nanowires. In order to remove the nanowires, we add about 0.3vol%-1vol% to the electrolyte with stirring for 5-10 hours.3) With the increase of monomer concentration, the inner state of nanotube present as partial-fill~full-fill~partial-fill, which caused by viscosity change of solution.4) Polymerization time and monomer concentration would affect the proton conductivity. With monomer concentration of 15% and polymerization time of 3.5h, the proton conductor show the best conductivity. At 100% RH, the conductivity increase from 0.037Scm-1 to 0.125 Scm-1 when change the temperature from 40℃ to 140℃.